Buying a Revox A77 or B77: Versions, Heads and What to Check

Revox built the A77 from 1967 and the B77 from 1977, and both stayed in production long enough to accumulate a great many running changes. Two machines wearing the same model name on the front panel can differ in head block, electronics, speed pair and track format. When you are buying, the badge tells you very little. The details tell you everything.

This page collects what is worth knowing before money changes hands: which versions exist, how to tell them apart, what the head material means for a machine that has already run for decades, and which sockets on the back panel do what.

If you are looking at a machine that needs work rather than one that is ready to play, the two companion guides cover what that work involves: the tape transport guide for the mechanism and the electronics guide for the boards. Part numbers for both are in the parts reference.

Revox A77: which version to buy

Before the B77, there was a 'god'

In the previous article, we discussed the completed masterpiece, the Revox B77.

However, when talking about the history of Revox, there is one model that absolutely cannot be avoided.
That is the Revox A77.

Since its introduction in 1967, it shocked the world by 'achieving studio quality in a consumer machine' and became a bestseller with cumulative production in the hundreds of thousands.
The basic design of the B77 was already completed in this A77.

However, because it was a long-selling model for about ten years, the A77 exists in four versions, from MK I to MK IV.

These are mixed together on the used market, and many people must be wondering, 'The appearance is different, but what about the insides?' or 'Which one should I buy?'
This time, we will thoroughly explain how to distinguish the four generations of the A77 and the characteristics of each.

1. MK I & MK II: The Shining Silver Era (1967-1971)

The early A77 is characterized by an overall bright color scheme.
Since the MK I and MK II are very similar in appearance, we will explain them together.

Exterior Features: The Aesthetics of Silver and Aluminum

• Bottom panel (lower control surface): A beautiful silver (aluminum color) panel is used. This is the biggest difference from the MK III and later.
• Top case (chassis): Wooden cabinet is standard, but many models also exist with a portable plastic case (gray).
• Knobs: Simple, glossy design that makes use of a metallic texture.

Distinguishing MK I and MK II (an extremely difficult challenge)

To be honest, even for professionals (super enthusiasts), distinguishing MK I from MK II by appearance alone is difficult.

• MK I (1967-1969): The very earliest model. Reliability is somewhat problematic; specifications such as the capstan bearing differ from later models.
• MK II (1969-1971): A minor change version that corrected the faults of the MK I. The brake mechanism that stops the reels and the reliability of the electronic circuits are improved.

Points for identification:
It is necessary to check the serial number and the internal boards, but many of the "silver panel" units on the market have often been updated to MK II equivalent in the course of maintenance.

2. MK III: A turning point in design (1971-1974)

In 1971, the A77 underwent a major image change.
It took on a more professional, sharp-looking appearance.

External features: The arrival of dark gray (anthracite)

• Bottom panel: Changed from silver to dark gray (anthracite color). This instantly gives a modern and subdued impression.
• Knobs: The design was completely renewed, becoming a type with "gray plastic and an aluminum plate in the center." The finger grip is improved.

Functional and internal evolution

3. MK IV: The Completed Final Form (1974-1977)

Produced right up to the debut of the B77, this is the ultimate evolution of the A77. This model passes the baton to the later B77.

Exterior Features: Blue Logo and a Hint of the B77

• Revox logo: The logo on the left side of the panel changed from the previous black/silver to a vivid blue. This is the definitive mark of the MK IV.
• Bottom panel: Same dark grey as the MK III, but with a slightly different texture.
• Knobs: Serrated knobs in the same style as the B77 were adopted, further improving operability.

Functional and Internal Evolution

• Improved input amplifier: The microphone input and other circuits were revised, increasing overload (clipping) tolerance.
• Introduction of Dolby models: Models equipped with the Dolby B noise reduction system (A77 Dolby) became widely available (Dolby-equipped units are marked below the logo).
• Refined tape transport: The material and shape of the tension arms and guides were improved to reduce tape damage.

MK IV and the B77

By the time of the MK IV, the specifications are almost identical to the B77 MK I. Which one to choose is a matter of preference, but the A77 is actually smaller and more compact, making it more convenient to carry.

While portability may be irrelevant for most people, at Kuon R&D, we sometimes take open-reel tape machines into the field like a field recorder when requested, so this size difference is significant.

Of course, being smaller, the A77 feels denser and heavier.

Also, the slight difference in tape threading feel between the A77 and B77 is a very interesting point. It is true that the A77 is harder to thread; the B77 is overwhelmingly easier to thread (though it is larger, sacrificing compactness).

Naturally, with other tape recorders, such as those from Studer, some have heads that protrude beyond the front panel, making tape threading considerably easier.

About Modifications

We have highlighted the overwhelming difference in size between the A77 and B77. So, what are the advantages besides size and portability? Yes, ease of modification.

Kuon R&D currently owns a total of three B77s and one A77. Two of the B77s have been modified as dedicated recording machines using the Kaneda-style analog balanced current transmission DC recording method, with all audio boards removed.

Because the A77 is more compact, its boards and parts are packed tightly, making modifications more difficult. For example, if you wanted to modify it for remote control using a Raspberry Pi, the B77 has ample space to house a Raspberry Pi or M5Stack, whereas the A77 would honestly be a tight fit.

It might be fun to choose from that perspective as well!

Ultra-enthusiast edition: The phantom models not found in catalogs

So far, we have explained the "official history" from MK I to MK IV.
However, the story of the Revox A77 has a "hidden side" that never appears prominently in catalogs.

These are the models custom-built for industrial and broadcast use, commonly known as "STTA" (Special Tape Transport Application).

These are not for listening to music at home; they are special-forces machines ordered by police, airports, broadcasters, and research institutes to carry out specific missions.

If you come across an A77 at an auction that somehow feels different, it might be one of these special specifications.

① The astonishing long-duration recording "SLS" (Super Low Speed)

It looks like a regular A77, but when the tape moves, it is abnormally slow.
This is a specification for surveillance and logging.

• Speed: Ultra-low speed of 2.38 cm/s (15/16 ips).
• Application: For continuous recording of 12 to 24 hours on a single tape, used for recording communications with airport control towers or intercepting police communications.
• Identification: The capstan shaft is extremely thin (about 3 mm).
• Note: If you record music with this, the high frequencies will be completely absent, making it unusable as hi-fi audio. It is often mistaken for being broken, but it is a normal specification.

② Professional field specification "HS" (High Speed) 2-track

This, on the other hand, is a specification specialized for creating master tapes.

• Speed: Two speeds, 19 cm/s and 38 cm/s (15 ips).
• Application: Master recording at broadcast stations and recording studios.
• Identification: The capstan shaft is very thick (about 9 mm), so removing the head cover reveals it immediately.
• Value: The sound quality is the best among A77s. Even today, it is the most highly traded "hit" specification.

③ Variations such as the broadcast-station-only "ORF"

Models made for institutions like the Austrian Broadcasting Corporation (ORF) have their input/output terminals changed from consumer RCA pins to professional XLR (Cannon) connectors.

The internal reference level is also changed to broadcast specifications, making them ideal for connection with modern studio equipment.

The Revox swamp has no visible bottom.

"STTA" and special-specification A77s are often not clearly marked on the panel; their true identity is often only revealed by the sticker on the back, the thickness of the capstan shaft, and "the moment you hear the sound."

If the A77 you accidentally acquired looks like an MK IV but spins at ultra-high speed, or has XLR connectors growing out of it... congratulations.
You have stepped into the deepest part of Revox, where only the "chosen ones" can reach.
It is an ultra-ultra-ultra rare item that is also traded as an investment property overseas.

The differences between MK I and MK IV are merely the entrance.
Now, let us spend a lifetime turning tapes in this deep and comfortable swamp.

above

Comparison summary list: Which one is recommended for you?

1. Head wear: The A77 heads have a "Revox-specific shape." If they are worn flat, high frequencies will not be reproduced. Even if it is an MK IV, if the heads are dead, it cannot beat a well-maintained MK I.
2. Rifa capacitors: A common chronic disease of the A77/B77, the old RIFA capacitors used in the power supply section etc. can smoke or burst due to aging (commonly known as firecrackers). Even if it is advertised as "fully restored," be sure to check whether these have been replaced.

Also, replacement, restoration, and repair of such capacitors are handled by Kuon R&D.

The A77 STTA and what makes it different

Recently, during a conversation with a specialist studio in Germany that restores and services Revox machines, the topic of repairing an STTA model came up.

I had never heard of the STTA model before, so I decided to research it thoroughly this time.

In this article, I will explain in detail why the STTA-spec A77 is special, the differences from the standard model, how to identify it, and its future investment value, in a way that is easy to understand even for beginners.

At the end of the article, I have also compiled information on the STTA gathered from around the world using GPT research, so audio enthusiasts and Studer/Revox fans should enjoy reading to the end.

What is the Revox A77 STTA Specification?

"STTA" stands for "Staatliche Technische Testanstalt," which means the German National Technical Testing Institute.

This specification is a special model manufactured for broadcasting stations and research institutions, and it is proof that it has passed strict quality certification by a national institution.

It is said to account for only about 1% of the total production of the A77, making it an extremely rare model.

Differences from the Standard Model

• Fixed speed, providing more stable performance
• Special input/output and sound quality specifications, such as DIN connectors and broadcast-standard EQ
• Equipped with a DIN-scale peak meter, optimized for professional use
• Some chassis structures allow rack mounting, with robustness as professional equipment being a key appeal

The speed is fixed at 38 cm/s, and the lack of an option to use 19 cm/s is typical of a model intended for national broadcasting.

The most distinctive feature is a sensitivity switch near the VU meter.

Also, regarding the audio signal, it has a function that automatically turns on the power when a signal is input, and automatically enters standby mode when the signal is interrupted for 5 seconds.

This is indeed a unit designed for broadcasting stations, programmed to prevent mistakes.

Additionally, due to the design (Revox motor control board), fast forward/rewind is only possible manually, and there is no locking mechanism.

How to Identify the STTA Specification and Its Rarity in the Market

Three Points for Identification

1. There is a label or engraving on the back saying "STTA" or "Bauart geprüft"
2. There is no speed selector switch; it is a single-speed specification
3. The meter scale is not VU but DIN specifications such as "nWb/m"

DIN audio connectors (DIN connectors) were mainly used in European audio equipment from the 1960s to the 1980s.

Typical examples are 5-pin or 3-pin round connectors, which allow stereo input/output with a single connector, an efficient design.

While ensuring stability and reliability according to DIN standards is an advantage, disadvantages include incompatibility with modern audio equipment (RCA is mainstream, so conversion is necessary) and difficulty in obtaining parts.

Why is the STTA Rare?

The production number of the STTA-spec A77 is very small, estimated to be less than 1-2% of the total.

Since it was mainly delivered to public institutions within Germany, opportunities for it to appear on the international market are limited, and its value is expected to rise in the future.

A German friend also said that it hardly ever appears on the market, making it extremely rare.

Why the Revox A77 STTA is an Excellent Investment Target

Five Strengths as an Investment

1. The absolute number is small, so if the supply-demand balance collapses, the value will rise rapidly
2. Brand power backed by national quality assurance
3. Continued popularity of analog audio
4. Appeal as a practical item (an asset that can produce sound)
5. Reliability and cultural value of being made in Germany

The brand value of Revox alone provides sufficient investment value, and it is natural to think that, like Hasselblad in the camera world, its value will only increase in the future.

In addition, being a national quality assurance model and its rarity suggest that its value will be higher than the standard model.

Above all, (for some reason) the sound is said to be incredibly good...

I have never actually heard it myself, but they say the sound is outstanding.

Points to Note and Risks

• Modifications or parts replacement will cause loss of originality
• Playback environment depends on DIN connectors, etc., so practical use may be difficult
• Appraisal varies greatly depending on the condition of the exterior and accessories

Considering Future Sale? Recommendations for Preservation and Recording

• Carefully keep maintenance history, STTA labels, and other information
• Regular power-on and operation are recommended to maintain it as a working unit
• Keep maintenance records and screenshots of auction prices
• Pay attention to physical storage conditions, such as humidity control and dust protection

Summary: The Revox A77 STTA is a "Usable Asset"!

I think this as someone who uses an A77 every day.

For audio lovers, it is the ultimate sound.

Every morning, before even drinking a glass of water, I turn on the A77.
And enjoy that sound.

That is truly the ultimate joy.

Buying gold bullion may also have investment value.

However, I feel every day that vintage equipment like the A77 or Hasselblad is like an income gain that you receive each time you actually use it.

The Revox A77 STTA specification is not just an open-reel deck.

It is an industrial heritage packed with the essence of German broadcasting culture and technology, and an investment target that allows you to actually enjoy the sound.

By owning it, you can enjoy both musical pleasure and asset value at the same time: that is the greatest appeal of the A77 STTA specification.

Bonus: Information Organized by GPT Research

1. Historical background: Origin of the STTA certification and its relationship with the A77

The birth of the "STTA specification": The STTA model of the Revox A77 is a special version that appeared in the 1970s, enhancing the automatic recording function of the tape recorder.

STTA stands for "Startautomatik" (automatic start recording). It detects an input signal such as audio, automatically starts recording, and stops automatically after a set time when the signal ceases.

Because of this feature, contemporary technical literature described it as a tape recorder for "surveillance tasks (Überwachungsaufgaben)."

According to some sources, STTA is derived from "selbsttätige Tonbandaufzeichnung" (automatic tape recording), but it is also often explained as an abbreviation for "Staatliche Technische Testanstalt" (State Technical Testing Institute).

This suggests that the model may have been designed and certified to meet the requirements of government agencies and technical testing laboratories.

In fact, at that time in Germany and neighboring countries, national bodies such as public broadcasters and postal/telecommunications authorities sometimes set their own certification standards for equipment procurement. It is believed that the A77 STTA specification was developed with such standards in mind.

The Revox A77, whose first model was released in 1967, became a huge hit, widely used from audio enthusiasts to professional applications, with an estimated total production of over 290,000 units over about ten years.

The STTA specification is presumed to have appeared mainly in the early to mid-1970s. During the Cold War, there was a growing demand for communication interception and broadcast monitoring. Equipment capable of recording for long periods without human intervention was needed for tasks such as telephone wiretapping, monitoring of aviation and maritime radio, and automatic recording of noise measurements.

To meet these needs, Studer-Revox developed the STTA model as a special version of the A77.

It added automatic recording and stop functions, and it is believed that it was introduced after undergoing technical tests by public institutions.

The STTA specification is a derivative version that incorporates additional circuits for special purposes, while basing its basic design on the MkII to MkIV models of the A77 (a two-dimensional tape recorder).

In other words, it is a model that adds functions for surveillance and log recording to the robust mechanism and high-quality sound design of the A77.

Within Studer, it was positioned as one of the "special versions" alongside the Dolby-equipped version, monaural version, and broadcast station specification version (the ORF specification described later).

With the STTA model on the market, the A77 expanded its field of activity not only to home and business use but also to professional applications in the public security and communications sectors.

2. Production numbers: Production volume of the STTA-certified A77 2-track machine

The total production of all Revox A77 models amounts to several hundred thousand units, but among them, the STTA specification machine is a special model manufactured in extremely small numbers.

There is no official record of the exact production numbers, but among experts and collectors, it is regarded as a rare model that is "hardly ever seen on the market."

For example, auction listings emphasize it as "extrem selten" (extremely rare).

Based on information gathered from multiple enthusiast forums, it is estimated that probably only a few dozen to at most a few hundred STTA-spec A77s were manufactured.

On a German bulletin board, it is mentioned that "this special model does not come up for sale that often," pointing out the scarcity of units in circulation.

In fact, there are voices from enthusiasts who have dealt with Revox machines for many years saying that they were unaware of the existence of the STTA model until recently, which also indicates the extremely small production and circulation numbers.

The STTA specification may have been close to a build-to-order product for government offices and special applications.

In other words, it is thought that it was not sold to the general public, but manufactured only in limited batches in response to requests from specific corporate customers.

Therefore, rather than being mass-produced at once, it was made in small lots as needed, resulting in a very small total number.

Surviving units are also extremely rare today, with only a few confirmed in specialized second-hand markets and auctions.

3. Use cases: Examples of adoption by broadcasters, research institutions, and government agencies

Austrian Broadcasting Corporation (ORF): A known example closely related to the STTA specification is the Austrian public broadcaster ORF.

Studer-Revox manufactured a dedicated A77 derivative model for ORF, and a broadcast station specification machine called "A77-ORF" was delivered.

The ORF specification machine is a high-speed 2-track machine at 19/38 cm/s, equipped with balanced inputs/outputs (XLR/LEMO connectors with transformers) and enhanced tape tension function, and was used for recording/playback and archiving in broadcast studios.

This ORF model itself does not have the STTA (automatic recording) function, but it was also "a recorder considered suitable for archiving and eavesdropping purposes," with surveillance use in mind.

Therefore, ORF is one of the broadcasters that actively introduced special specifications of the A77 series, and it is possible that they also tested and adopted the STTA specification machine in some form.

In West Germany, the Ministry of Posts and Telecommunications, communications regulatory authorities (so-called PTT), and public broadcasters (ARD stations) adopted the Revox A77 as a voice recording device.

In particular, it is believed that automatic recording machines like the STTA specification were valued by communications supervisory agencies and police radio interception departments.

In fact, examples of STTA model applications in the literature include keywords such as "telephone (wiretapping)," "aviation radio," "maritime radio," and "noise," suggesting that it may have been used in Germany for police telephone wiretapping records, log recording of air traffic control and maritime communications, and environmental noise monitoring. For instance, monitoring of aviation and maritime radio was the task of the Ministry of Posts' radio regulatory agency at the time, and the STTA function had the advantage of recording only necessary communications, saving tape consumption while capturing important communications.

Also, for telephone recording, it could skip silent parts, so it is speculated that public security authorities used it for evidence collection.

In countries such as Switzerland and the Netherlands, which had their own PTT (Postal, Telegraph and Telephone) at the time, it is possible that the A77 special model was adopted for long-duration automatic recording.

For example, the Swiss PTT conducted call recording and radio monitoring in its laboratories, and there are testimonies that they used Revox alongside Nagra and others.

On the other hand, in East Germany (DDR), it was rare for state agencies to officially adopt Western-made equipment, but there is a theory that they secretly obtained A77s and used them for communication interception.

Furthermore, in academic research fields, there may have been cases where the STTA machine was experimentally used to automatically collect animal calls and environmental sounds.

Although records of specific institution names have not been preserved, it is certain that the STTA specification A77 was active at least in broadcasters, communications monitoring departments, and law enforcement agencies in Germany and abroad.

4. Technical Specifications: Differences Between the STTA Version and the Standard Model

The defining feature of the STTA version is a dedicated circuit that detects the presence of an audio signal and automatically controls recording.

When an audio or signal input exceeds a preset threshold, recording begins within approximately 0.2 seconds. Once the signal ceases, the machine automatically stops after about 5 seconds (adjustable up to a maximum of roughly 7 seconds).

This "start automatic" circuit is implemented as an additional electronic board and operates independently of the conventional manual recording switch.

On the front panel of the STTA machine, there are two extra buttons not found on a standard A77.

These are "auto-record switches" for enabling or disabling the automatic recording function on each channel (track) individually.

For example, it was possible to set automatic recording only on track 1 while track 2 remained in constant recording (manual mode). Each button is labeled with the corresponding channel number and an AUTO/MANUAL indicator, toggling the automatic function on and off when pressed.

With the addition of these buttons, the position and function of the "reel motor OFF (rewind motor stop)" button found on earlier models have been replaced (the service manual mentions this modification).

Internally, an electronic circuit board for automatic start/stop control is added separately from the main recording amplifier board.

This circuit works in conjunction with a sensitivity adjustment potentiometer (located on the front panel or internally) that monitors the input signal. When the signal exceeds the threshold, a relay is activated to switch the machine into recording mode.

The service manual (STTA supplement) includes detailed schematics of this circuit. For instance, the "STUDER REVOX A77 STTA" schematic PDF is available on the Elektrotanya website.

According to this documentation, the standard machine's take-up motor stop button and related circuitry were modified to incorporate a relay circuit that switches between VOX control and manual control.

As described above, the Revox A77 STTA version incorporated numerous improvements over the standard model, making it a tape deck optimized for specialized applications.

Its design philosophy, "record only when necessary and save tape when not," was advanced for its time and can be considered a forerunner of modern voice-operated recording (VOX).

As stated in official documentation, it was "particularly suited for surveillance tasks," and both technically and operationally, it can be regarded as an important piece of equipment that supported national projects and broadcasting/communication infrastructure of the era.

Revodur heads and why they matter

Revodur is the name given to the wear-resistant metal heads that Studer-Revox adopted from the late A77 (Mk IV) through the B77 generation.

The technical core consists of three points.

1. Base material: A permalloy-type alloy with high permeability and low coercivity, suitable for record and playback heads. Earlier machines also used this family of materials.
2. Surface “wear-resistant treatment”: The tape-contact surface (face) is hardened or a treatment layer is formed to suppress wear. This results in longer life and stable azimuth and track positioning.
3. Upper and lower shield (guard) layers: Strip-shaped metal layers are added above and below the head face. They help slow edge wear and control leakage flux, a feature confirmed in field reports by service technicians.

Important: The name is a product name or series name, not a generic material name. It is not a third-party standard material name like ferrite or sendust.

Who, when, and why: History and development background

• Background: During the open-reel boom of the 1960s and 70s, high-speed, high-tension operation was standard in studio use. Conventional permalloy heads suffered from wear, leading to alignment drift and degradation of S/N and high-frequency response.
• Developer: Studer-Revox (Switzerland). They pursued a “high-durability, high-stability” head as a common concept for professional (Studer) and consumer (Revox) machines.
• Models equipped: Revox A77: Revodur from Mk IV onward (earlier Mk I-III used standard permalloy). Revox B77: Basically Revodur as standard (exceptions exist due to production lots or replacement history).

Incidentally, the A77 Mk IV is easy to identify: the front panel has blue lettering.

Comparison of Revodur, permalloy, ferrite, and sendust

How to identify in the field

1. Bands above and below the face: When viewing the head front with a loupe, many units show thin metal bands (shields) above and below.
2. Part numbers: B77 head block part numbers (e.g., playback 1.116.0x7.00 / record 1.116.0x2.00 series) belong to the Revodur generation.
3. Wear pattern: The shoulders tend not to collapse, and wear is often uniform and shallow.
4. Service records: Past servicing may include “Revodur” notation.

Sound quality and operation: Myths and reality

• “Revodur sounds better” is a myth: Sound impression is far more influenced by amplifier/EQ, head height, azimuth, and tape contribution.
• The real value is “maintainability”: Slower wear and higher alignment stability mean the same sound can be maintained longer.
• B77 vs A77: Differences in playback logic, servo, power supply, and board component generations have a greater effect than head material. Playback logic can be retrofitted to the A77, but cost may diminish the B77’s advantage.

What the rear MIC IN sockets are for

The Revox A77 is known as a masterpiece among open-reel tape decks.
On its rear panel, there is an input terminal labeled "MIC IN (RCA)" that seems puzzling at first glance.

"Is this where I connect a microphone?"
"How is it different from AUX IN?"

Many people have these questions.

The short answer is that the "MIC IN (RCA)" terminal on the back of the Revox A77, despite its name, is actually a "high-sensitivity line input."

This circuit was designed to connect devices with low output levels, such as home radio tuners or portable players.

In this article, we will clearly explain the true nature and correct usage of the Revox A77 rear "MIC IN (RCA)," including how it differs from a microphone amplifier.

What is the Revox A77 rear "MIC IN (RCA)"?

It is not a microphone input

To get straight to the point, the rear "MIC IN (RCA)" is not a terminal for inputting microphone-level signals (a few mV).

This terminal is actually classified as a "high-sensitivity line input."
The design concept was to provide an input terminal for connecting audio devices with relatively low output levels, such as radio tuners or portable equipment.

The front MIC IN on the Revox A77 has a completely dedicated microphone amplifier circuit.

It is designed to directly accept a standard dynamic microphone, with input impedance optimized for microphones.

Difference from AUX IN

Difference from the front MIC IN (important)

The Revox A77 also has a "MIC IN" on the front panel.
This is a completely separate circuit with a built-in microphone amplifier.

Connecting an external condenser microphone amplifier

So, is it possible to use an external condenser microphone preamp and connect it to the rear MIC IN via RCA?

If you are using an external condenser microphone amplifier (with phantom power) and its output is at line level, you can "basically use it" by connecting to the Revox A77 rear MIC IN (RCA).
However, there are conditions and precautions.

The Revox A77 rear MIC IN (RCA) is designed for high-sensitivity line level, not microphone level.
Therefore, a line-level signal that has passed through a microphone preamplifier can be input circuit-wise.

✅ Suitable cases

• High-quality microphone preamps such as Neve or Millennia → with RCA output or via adapter
• Microphone preamp with phantom power → use with output volume reduced
• Vintage vacuum tube microphone amp → ideal if output is a few hundred mV

❌ Cases to avoid

• Direct condenser microphone → rear MIC IN (RCA) → ✕ (no power supply and sensitivity mismatch)
• Professional equipment with output over 1V → may cause distortion

Revox B77 MK1 and MK2 compared

The eternal classic, Revox B77

In the world of vintage audio, the Revox B77 open-reel tape deck continues to be loved for its design and durability.
When you come across one on the used market or at an auction, or when you glance at the classic machine in your own home, have you ever wondered:
"Is this an MK1 (early) or an MK2 (late)?"
"What exactly is different inside?"

These two machines look almost identical, but in terms of functionality and internal design, there are clear differences that reflect the engineers' dedication.
For those considering maintenance or repair, knowing these differences is especially important.

Here, we will thoroughly explain the differences between the Revox B77 MK I and MK II, from visual identification to the detailed circuit board variations.

1. Release period and historical background

First, let's review the basic data.
The Revox B77 is a long-selling model that was manufactured for a very long period.

• MK I (Original): 1977 to around 1980. The early model. It appeared as the successor to the A77 and swept the world with its refined design.
• MK II: 1980 to around 1998. An improved model based on feedback from the MK I. Features were added in response to requests from professionals and advanced amateurs.

Because it was manufactured for about 20 years, there are many units on the market, and both versions coexist.

2. [Beginner] Identify at a glance! External differences

The area above this line is displayed for free.

At first glance they look the same, but you can tell immediately by looking at the front panel.

① Logo and markings

• MK I: Often has only the simple "REVOX" logo.
• MK II: Many units have "MK II" clearly written below the logo or on part of the panel.

② Control panel (the biggest difference)
The decisive factor is the group of switches at the bottom right of the panel.

• MK I: There are switches such as the speed selector, but there is no "variable pitch knob".
• MK II: Here, there is a small knob labeled "Variable Speed", or an adjustment hole.

If your B77 has a small knob at the bottom right that allows you to subtly change the playback speed, it is definitely an MK II.

3. [Functional] Practical evolution

Why was the MK II introduced? Because it reflected "feedback from the field".

The decisive difference: Variable speed (pitch control)
The MK II is equipped with a standard ±10% pitch control function.

• Advantage: When playing old tapes where the recording speed is slightly off, you can correct to the correct pitch. You can also change the playback speed to match the tuning of an instrument.
• To do this on the MK I, you needed an optional external controller.

Improved operability for editing (cueing)
When performing tasks like "scrubbing" to find edit points by turning the tape by hand, the MK II has improved operability with the head cover open.
Editing can be done more intuitively.

4. [Advanced / Repair] Differences in internal boards (capstan motor)

From here, we will talk about the "internals" for those aiming for repair or overhaul, or for those who love mechanics.
More than the exterior, the internal PCBs have undergone major changes.

The capstan motor control board, which can be called the heart of the B77.
This is completely different between the MK I and MK II.

• MK I (Standard Speed Control): Part number: 1.177.320.xx etc. A very simple constant-speed control circuit. It is highly stable, but the function to change speed is not built into the board itself.
• MK II (Vari-Speed Control): Part number: 1.177.325.xx etc. To achieve variable speed, a dedicated IC and more complex circuitry have been added.

[Caution]
When obtaining boards as "spare parts" at auctions, etc., there is often no compatibility between MK I and MK II boards, so you must always check the part number.

https://note.com/embed/notes/n664745598152

Other circuit changes

• Audio circuit: In the MK II, the values of capacitors and transistors in the recording and playback amplifiers have been revised to improve noise characteristics.
• Input selector: Crosstalk (signal leakage) countermeasures may have been strengthened.

Conclusion: Which should you choose?

Advice for those considering getting a Revox B77.

• Recommended for MK II: You have many old tapes and want to correct pitch deviations. You want to use it with musical instrument performance. You feel safer with a slightly newer manufacturing year (though it is still over 30 years old).
• MK I is sufficient if: You simply want to enjoy music as audio (constant speed playback is fine). You think that a simpler internal structure has a lower risk of future failure (it is simpler because there is no pitch control circuit).

Both are wonderful decks packed with Swiss precision technology.
Choose your destined machine according to your needs.

More detailed explanation in the video!

For the "capstan motor speed adjustment method" that is hard to convey with text alone, we also explain it on YouTube.

Where to touch on the board? How to use the measuring instruments?
If you are interested in repair, please check out this video.

https://www.youtube.com/embed/pFRMuHpi9Ik?rel=0

If you found this article helpful, please give it a "like" and follow!

Bonus: Revox B77 MK III (Mark 3)

Here is the latest news that made every Revox fan do a double-take, then celebrate.

About a quarter of a century after the B77 was discontinued.
In late 2023 to 2024, Revox (Revox Audio AG) officially announced and released the "Revox B77 MK III".

This is not merely a refurbished second-hand unit.
It is a brand-new product that Revox has brought to market as a "redefinition of a legend".

In recent years, as vinyl records and cassette tapes have been re-evaluated, demand for the ultimate analogue audio, the ultimate high-resolution format that is open-reel tape, has been growing, particularly among the high-end crowd.

However, the only machines available on the market were vintage units over 40 years old. There was a dilemma: "I want to listen with the best sound quality, but I'm worried about the risk of breakdowns and maintenance."

So Revox made a decision.
"Let's bring the B77 back to life with today's technology."

• Complete redesign: While inheriting the design philosophy of the original B77, the audio circuitry and control systems have been renewed with modern technology.
• Optimised for modern tape: Perfectly calibrated at the factory to match the characteristics of currently available new tape (LPR35/SM900 etc.) from "Recording The Masters (RTM)".
• Specifications: 2-track, high speed (19/38 cm/s), and equipped with XLR (balanced) connectors to match modern high-end equipment.

This is not about consuming the legacy of the past, but a strong statement of intent from the manufacturer to "preserve analogue tape sound for the future".

What about the price? (Guide to global and domestic prices)

Now, this dream-like MK III comes with a price tag that is equally dream-like, set at the high end.

• Global price (reference): Around 15,950 euros (approximately 17,000 to 18,000 US dollars)
• Domestic price in Japan (estimate): Even a simple calculation at the current exchange rate (1 euro = approx. 160-165 yen) comes to about 2.6 million yen. Adding customs duties, shipping costs, and importer margins, it is expected to be around 2.8 to 3.3 million yen.

It is a price that could buy a car, but orders are already coming in from wealthy individuals and studio professionals around the world.
That is how much value the "B77" brand holds.

MK I, MK II, and the miraculously revived MK III.
Despite differences in generation and internals, what they all share is the irreplaceable experience of "watching the reels spin while immersing yourself in a rich, lifelike sound".

Buying a brand-new 3-million-yen MK III is one kind of romance, but you could say that the true joy of an audiophile lies in carefully maintaining and using a vintage MK I or MK II that you picked up for tens of thousands to a few hundred thousand yen.

The B77 MK3 and buying one today

The legendary models that defined the golden age of reel-to-reel decks, Revox's A77 and B77, are reborn with modern technology.

Its name is the B77 MKIII.

Kuon R&D has archived restoration information on the A77 and B77, and now the MKIII will finally be available in Japan starting December 20, 2025.

The price is a staggering 3,575,000 yen.

This stereo tape recorder is the ultimate machine for experiencing the full richness of analog recording. It is the latest model in the lineage of the A77, which appeared in the late 1960s and captivated audiophiles with its sound quality and design, and its improved successor, the B77. The beloved classic machine, supported by many fans, has finally returned after the digital age.

It features in-house developed high-precision motors and highly durable tape heads, with balanced circuits and XLR terminals for input and output to minimize loss, incorporating full-fledged specifications throughout.

Furthermore, against the backdrop of renewed interest in analog media such as records and cassette tapes, for audio enthusiasts seeking "something beyond digital," the B77 MKIII could be considered the pinnacle of ultimate analog sound.

Who is it recommended for?

The B77 MKIII is an ultimate-oriented analog device in both price and scale, but its appeal reaches a wide range of users.

From the perspective of "Who is it recommended for?", here is a summary of user profiles that fit this machine.

• For fans seeking the peak of pure audio: For those who want to realize a vivid music experience at home that cannot be tasted with digital. It provides the ultimate analog playback, allowing you to enjoy studio-quality sound right in your living room analogplanet.com.
• For young audio enthusiasts who don't know the analog generation: Even for the generation that became interested in analog through the record and cassette boom, this machine offers a fresh experience. Through the hands-on enjoyment of reel rotation and tape editing, you can savor the joy of "owning and manipulating" music. Precisely because it's the digital generation, you may find the romance of the machine itself refreshingly new.
• For professional/semi-professional engineers and musicians: It is also ideal for creators who want to record and play back master tape quality in their home or private studio. With specifications comparable to professional equipment, such as XLR balanced inputs/outputs and NAB/CCIR compatible equalizers, it is immediately useful for archiving recorded works and analog mastering applications analogplanet.comanalogplanet.com.

As described above, the B77 MKIII is widely recommended, from audiophiles who refuse to compromise on sound quality, to the younger generation seeking an analog experience, and even professionals. Of course, to draw out the high performance commensurate with the price, knowledge of tape handling and maintenance is required, but that hurdle is also part of the appeal of handling the "real thing." For those who can even enjoy the effort, it will provide unparalleled satisfaction.

Learn about the brand

Revox is a consumer audio brand established in the 1950s by Willi Studer, the founder of professional audio equipment manufacturer Studer.

In 1951, he founded the company under the name "Revox" (a coined word combining "Re" for "again" and "Vox" for "sound", meaning to reproduce sound), and since then has released many products that bring studio quality into the home.

Among them, the A77, released in 1967, became a landmark home reel-to-reel machine, and together with its successor, the B77, which appeared in 1977, it is renowned as a famous machine that remains in recording history.

The tape recorders of the parent company Studer brand were loved in top studios around the world, and there are famous anecdotes about captivating artists such as the Beatles and Pink Floyd.

The Revox brand products were created with the creed of "allowing everyone to enjoy studio sound," incorporating the development know-how of such professional machines.

The B77 MKIII is no exception, strongly embodying the brand philosophy of "reproducing music as it was recorded in the studio at home."

It is equipped with high-precision in-house motors and tape heads, and from the chassis to the circuit design, it is uncompromisingly crafted, inheriting from professional machines.

On the other hand, it also has connectivity and safety considerations for easy home use, and its robust structure that can be used for a long time is also appealing.

In fact, the original B77 was often diverted for professional and broadcast use due to its solid design and durability, and it is still highly regarded as a "lifetime" reel-to-reel machine.

Revox/Studer has gone through various transitions in its corporate history since then, but it continues product development, albeit in small quantities, at its headquarters factory in Villingen, Germany.

The B77 MKIII can truly be called a flagship model that fuses the brand's tradition with cutting-edge technology.

Specifications Overview

Release date and price: The B77 MKIII was released on December 20, 2025, with a standard price of 3,575,000 yen (tax included).

This price tag is fitting for a high-end machine, reflecting the technology and labor invested in this limited-production model (maximum 20 units per month).

The main specifications and features are summarized below.

• Format: Open-reel, 2-track, stereo recording and playback (3-head system). Equipped with separate erase, record, and playback heads, enabling real-time monitoring while recording. Tape width: 1/4 inch.
• Tape transport: 3-motor direct-drive configuration (1 capstan motor + 2 reel motors). The capstan motor is a direct-drive unit with precise servo control, maintaining highly accurate tape speed. The reel motors are also powerful, capable of quickly starting and stopping even heavy metal reels. Electronic braking ensures smooth and safe tape handling during rewind and fast-forward.
• Supported speeds and performance: Standard two-speed operation at 19 cm/s (7.5 ips) and 38 cm/s (15 ips). Wow and flutter (pitch variation) is extremely low: 0.08% or less at 19 cm/s, 0.04% or less at 38 cm/s. Distortion is also kept to 0.3% or less at 19 cm/s and 0.24% or less at 38 cm/s. Although the official playback frequency response is not published, further improvements have been made compared to the previous MKII model, achieving flat studio-quality response up to high frequencies.
• Equalization/bias: NAB/CCIR equalization switching is available via a switch on the unit. At 38 cm/s, the studio-standard CCIR (IEC) curve and the US-standard NAB curve can be selected with one touch; at 19 cm/s, the NAB curve is fixed (50/3180 µs). Additionally, the reference recording level can be switched, supporting both 320 nWb/m and 510 nWb/m at 38 cm/s, allowing full playback of professional tapes.
• Input/output terminals: Line inputs and outputs are equipped with XLR balanced connectors (two systems each for left and right), and RCA conversion adapters are included for consumer unbalanced equipment. A line level switch allows selection between studio reference (+4 dBu) and consumer reference (-10 dBV), ensuring optimal connection in any audio environment. Microphone inputs (standard 6.3 mm phone jacks × 2) are also provided, enabling direct recording with dynamic microphones. Headphone outputs feature two standard 6.3 mm jacks. A high-quality headphone amplifier circuit compatible with both high and low impedance drives studio monitors and commercial headphones optimally.
• Controls and other features: The front panel includes large analog VU meters and a newly added digital counter (tape time display). Various switches follow the design of the original B77 but are redesigned with new parts for long-term reliability. A built-in tape splicer and cutter for editing is still included, allowing free cut editing unique to analog tape. Power supply is 100 V AC for Japan, external dimensions are 414 mm (H) × 452 mm (W) × 207 mm (D), and weight is a substantial 18 kg. A 2-year manufacturer's warranty is included.

In this way, the B77 MKIII can be described as a "re-creation of a classic," inheriting the basic design of the original B77 while incorporating modern performance and features.

While retaining the operational feel unique to open-reel tape, updates have been made in connectivity, stability, and usability, and the maintenance concerns typical of vintage machines are irrelevant with a new unit.

It is a highly attractive model for pursuing the ultimate analog sound with peace of mind over the long term.

Comparison with Other Models

To better understand the positioning and characteristics of the B77 MKIII, let's review the differences from past models.

Here, we will look back at the history of evolution, focusing on comparisons with its predecessors, the A77 and the original B77 (MK I/MK II).

From A77 to B77: The lineage of a masterpiece and points of evolution

The Revox A77, introduced in 1967, was a groundbreaking model that achieved all-transistor design and compact, lightweight construction at a time when vacuum-tube open-reel machines were mainstream, enabling studio-quality recording and playback in the home.

Combined with its beautiful aluminum front panel and wood cabinet design, it became a worldwide hit and underwent continuous improvements over a decade.

The A77 was updated up to the Mk IV version, and later models incorporated technological refinements such as the long-life "Revodur" head described later.

Its successor, the Revox B77, appeared in 1977.

While the basic configuration followed the A77, the control system was revamped with more precise electronic logic, improving tape transport control accuracy and operability.

For example, smooth operations like transitioning from fast-forward/rewind to playback with a single button were refined in the B77 generation.

Additionally, a tape editing block (splicer) was built into the lower part of the front panel, making physical tape editing with scissors easy.

On the other hand, the audio circuitry and basic performance did not deviate significantly from the A77, and initially it was positioned as a "matured version of the A77."

In fact, since the later A77 models had already reached a high level of completion, there was no dramatic difference in sound quality, and the B77 can be said to be a model that mainly improved operability and durability.

Technically, the adoption of the aforementioned Revodur head was a major topic.

This wear-resistant metal head developed by Studer-Revox was adopted from the final A77 Mk IV (earlier Mk I-III used conventional permalloy heads), and in the B77 it was basically standard equipment on all models.

The Revodur head is based on a permalloy alloy with excellent magnetic properties, with a specially treated surface to significantly reduce wear, and a unique structure with metal guard layers above and below the head gap to maintain stable characteristics over the long term.

This was based on Studer's philosophy of creating a head that would not shift even under heavy professional use, and as a result, the B77 is less prone to alignment drift and high-frequency degradation, offering the advantage of being able to use it with the "same sound" reliably for a long time.

Regarding sound quality itself, it is said that "circuit design and adjustment have a greater impact than head material," so the Revodur head does not necessarily mean specially good sound.

However, in terms of reducing the hassle of frequent head replacement and adjustment and allowing use in always-optimal condition, the B77 can be said to have been practically more advantageous than the A77.

Differences between the B77 Mk I/Mk II and the new B77 Mk III

The original B77 evolved from the early 1977 model (referred to as Mk I for convenience) to the Mk II around 1980, incorporating minor circuit changes and feature additions.

Specifically, incremental improvements were made, such as strengthening the output driver stage, enhancing tape transport stability, and refining the VU meter needle. Additionally, the professional PR99 model was released based on the B77, a derivative that met broadcast needs with XLR inputs/outputs, a digital counter, and remote control terminals (its appearance closely resembles the late B77 Mk II).

The B77 Mk II itself had several versions depending on the production period, but no major design changes were made, and due to its robustness, it is said to have been manufactured for a long time from the 1980s to the late 1990s.

Then, the B77 Mk III appeared as a new model after about 40 years, and while its appearance follows the original, the internals have been significantly updated with modern technology.

The key enhancements over the old Mk II are summarized below.

• Refreshed electronic circuits: While based on the original analog circuits, optimization was carried out by replacing components with currently available high-performance parts and utilizing simulation technology. As a result, further improvements in frequency response and lower noise (enhanced immunity to external noise and power supply voltage fluctuations) have been achieved. However, there is a thorough commitment to keeping it "analog as analog," with all software elements such as microcomputer control completely excluded.
• Enhanced input/output interface: The line inputs/outputs, which were mainly unbalanced RCA on the Mk II, have been changed to XLR balanced as standard on the Mk III. In addition, as mentioned earlier, flexible adjustments such as NAB/CCIR equalization switching and level switching are now possible, providing connectivity that is immediately usable in both home and professional settings. The headphone jack and microphone input have also been newly designed for high sound quality.
• Digital counter: While the Mk II and earlier had a mechanical counter (three-digit numbers), the Mk III is newly equipped with a digital tape time counter. Practicality has improved, with the ability to display remaining time in minutes and seconds.
• Refined chassis and design: At first glance, the Mk III strongly retains the appearance of the past, but the details have been redesigned with modern technology. While maintaining chassis rigidity, the aluminum die-cast frame has been lightened, and stable operation and quietness have been improved with new parts, resulting in significant evolution in usability and reliability. On the other hand, the reel size, switch layout, VU meters, and other characteristic features are retained, so there are actually not many parts where a B77 user can tell the difference between old and new at a glance. If one were to point out external distinguishing features, the presence or absence of the digital counter display and the rear terminal configuration (presence of XLR) would be key points.

Through these improvements, the Mk III maintains the analog warmth and operational feel of the original B77 while achieving "reliability and specifications that are relevant today."

The manufacturer also cites improved frequency response and enhanced external noise immunity as "clearly superior points over the Mk II," and one can expect that the actual sound quality has been further polished.

For fans familiar with past models, it is both nostalgic and fresh, and for first-time users, it is an attractive refined model that allows them to experience the essence of a legendary classic machine in its latest form.

Review from a professional engineer's perspective

The Mk III has been a topic of discussion in Europe since around 2024.

It is said that they developed their own heads and motors, and that is likely reflected in the price.

However, in the case of the B77, the Mk I was priced in the high 500,000 yen range at the time. My mentor, Akihiko Goto, said that when he was a university student, while everyone around him was buying cars, he had a senior arrange a loan for him to purchase a B77, so in terms of price perception, it probably feels like around 2 million yen.

As for the evolution of the audio section, it is likely of corresponding quality.

However, regarding the motors and transport system, I think the essential parts are the same, so it comes down to whether one can spend 3 million yen on that.

It might be easier to understand if you think of it in terms of cameras.

A vintage Leica and a Leica incorporating the latest technology.

You can say they are completely different things.

Even if you try to imitate the color and rendering of a red Elmar, you cannot achieve it by buying a modern Leica lens.

In that sense, the same goes for audio. Analog machines like the B77 naturally create the sound of their era; it's a feeling that the atmosphere, consciousness, and trends of the time are reflected unconsciously, almost like a subconscious mind.

I sometimes use an A77 Mk II as a preamp by changing audio parts, and even when listening to digital audio, I can still obtain a somewhat smoky analog sound.

Also, at Kuon R&D, we restore B77s, but basically, the audio section uses Kaneda-style balanced current transmission DC recording, so the recording and playback sections are all directly connected externally.

The original internal audio boards of the B77 are removed.

For high-end amateurs, I think one option is to purchase a used B77 Mk I or II, restore and repair it, and enjoy the vintage sound.
After all, it is an extraordinary recorder where the latest model appears nearly half a century after the release of the first A77.

There is no doubt that it will reign as a legendary analog recorder for another half century and beyond.

For professional and commercial use, the question arises: what about ADC? Considering that if you are going to invest in equipment here, the orthodox path is undoubtedly to invest in ADCs, mic preamps, and microphones, it is probably a tough sell, so it will inevitably be positioned as an item for high-end amateurs.

Overall, it is a tape recorder with an extremely high level of perfection as a "tool."

Although it belongs to the world of hobby, its capability is not merely for show; it is a genuine product that can withstand professional demands.

It fully provides the warmth unique to analog and the joy of directly touching the machine and conversing with music.

Kuon R&D also offers B77 restoration services (details in preparation).

What to look at before you pay

Almost every fault on these machines can be repaired, which is a real statement rather than an optimistic one: they were designed to be serviced, the documentation exists, and most parts are either available or substitutable. That changes what you should be worried about when inspecting one.

Consumables and electronics are not the problem. Hardened pinch rollers, dead capacitors, glazed brakes and perished belts all look alarming and are all routine. What you cannot easily fix is a worn head block, a damaged head gap, a bent or scored capstan shaft, or a chassis that has been drilled and rewired by a previous owner who did not document what they did.

So look past the cosmetics. Check the heads under a light for wear grooves. Turn the capstan by hand and feel for roughness. Look underneath for non-original wiring. A dusty machine with good heads and untouched wiring is a better purchase than a polished one with a worn head block.