Restoration Tips & Notes » reels

Studer A80 RC modifications for 1/2-inch two track and other modifications

Richard L. Hess — Fri, 20 Jan 2012 13:16:37 +0000

In a discussion on 2012-01-20 in the New Studer list, Todor Dimitrov posted the differences between the record and repro boards between a 1/4-inch and a 1/2-inch two-track A80RC repro cards. Here are the changed components for the 1/2-inch version. There are five different oscillator versions in the manual, including one for 1/2-inch.

RECORD: C34=68pF
REPRO: R1=100K; R21=330

CBC A80RC Repro capacitor mod

I had previously posted in the original (and now reconstituted) Studer List on 2008-04-24 that there were other extant and possible modifications. Here is a slightly edited and reformatted version of that post:

The Canadian Broadcasting Corp mod to the A80RC repro board involves the addition of two capacitors on the foil side of the repro board. Every ex-CBC repro board I’ve seen has that mod on it and it makes a world of difference in how the machine sets up with standard Studer NAB heads and NAB EQ daughter cards.

The new capacitors are paralleled with C21 (fast) and C25 (slow) which are under the alignment pots mounted on the front extrusion.

C21 and C25 are both 1n2 capacitors (tubular). All the boards I’ve obtained with ex-CBC machines (and the one I obtained elsewhere I modified for this) have C21 (fast) paralleled with a 1n0 making the fast capacitor 2n2 total.

Likewise, C25 (slow) is paralleled with 6n8 making the total capacitance for C25 8n0.

I tried a board without this and it didn’t equalize as well at all for NAB. I have not evaluated this for IEC 1 (CCIR).

Try it before going any farther — also replace the three big electrolytics on the repro board if they haven’t been already.

A80RC Repro mod for no VU meter bridge

The other mod I do relates to not using the meter bridge. I put in R48 and R49 on the repro board. I actually make R49 out of two paralleled 6k8 resistors making it 3k4 rather than 3k3 and I disconnect the shielded cable conductor at point (5). In this way, I’ve reduced the capacitive loading on this point of relatively high impedance (when the knob is at -6 dB on the meter bridge, all that cable is being driven by a 2500 ohm source impedance which results in slight, but measurable HF rolloff which varies with the level setting of the pot. With the fixed 10 dB attenuator, the source impedance drops to 2267 ohms — still high. There are also potential headroom issues if you turn down the front panel control more than 10 dB (which is normal).

Electrical reasons to not use VU meters

I don’t use the VU meters (obviously if the meter bridge is not there…). In the Ampex AG440 which has a similar output topology (but higher source impedance) the distortion caused by the meter is clearly measurable. Since the A80 source impedance is lower, the VU meter-induced distortion would be lower, but it would still add some.

I would suspect that the distortion level would be about 12-15 dB lower in the A80 than the AG-440 based on the spec’d source impedance ratio, but I suspect it’s still there — just another reason in my book for no meter bridge. The concept was initially started by not owning any stereo meter bridges, but even with a stereo meter bridge available, I chose not to install it…or rather I de-installed it.

I’ve never been a fan of VU meters across program audio. In my early days of designing, we’d have two resistive buildouts, one for the line and one for the VU meter. Later, VU meters always had buffer amp boards.

Conversion of A80 transport from 7.5/15 to 15/30 in/s

One of these years, I will create a 15/30 A80RC as I bought an NOS high speed capstan motor, but, for now, my Sony APR-5003V machines are doing well at that speed.

One minor drawback is that the magnet in the slower-speed unit’s Eddy Current Drag apparatus on the left roller going into the head assembly needs to be reduced in size to decrease the drag. This is outlined in Studer A80 (All Versions) Service Information Bulletin SI)064081_D-E_Mod.pdf available at the Studer ftp site in this folder.

End of tape sensor modification

The A80RC transport normally requires both tension sensors to drop out in order to stop the tape. It is safer to use the model found in the A810 where either tension sensor dropping out will stop the tape. This simple modification—done only to a single plug-in board—makes the end-of-tape sensing on the A80RC (and possibly all A80 transports) work when EITHER tension sensor drops out.

Capturing both directions of a half-track mono tape

Richard L. Hess — Fri, 06 Jan 2012 20:39:50 +0000

It is possible to capture both directions of a two-sided half-track mono tape in one pass.

The critical factors are:

Azimuth
Direction
Polarity

The azimuth of both sides needs to be the same. If the two sides were recorded at different sessions and/or on different machines, then there is no guarantee that azimuth will be the same on both sides. In a large-volume project, this can be addressed by installing two repro heads, one for each direction, and adjusting azimuth separately. This does not work well for stereo tapes with different azimuths because any temporal perturbations in either the recording or reproduce passes will result in severe stereo image shift. If a record head had azimuth scatter between the two channels, it is best to split the difference, if possible without severe high-frequency attenuation.

Obviously, the direction of the playback needs to be reversed in the DAW (Digital Audio Workstation) software, but that happens pretty quickly on a current computer.

Not-so-obviously, the polarity of the signal is also reversed when played backwards. That, too, can be addressed, possibly in the same pass or, worst case, a separate pass in the DAW software.

This is not recommended for any tapes using noise reduction such as Dolby or dbx, nor for the highest quality of music. However, most two-track tapes recorded on both sides are not of this quality.

Playing full-track mono tapes

Richard L. Hess — Fri, 06 Jan 2012 20:28:58 +0000

About ten years ago, when I transferred the oldest tapes in the United States as part of the Mullin-Palmer collection, my good friend Don Ososke pressured me to use a full-track head for the project. I had started transferring these full-track tapes with a Woelke NAB stereo (two 80 mil (2 mm) tracks) head and recording both channels. When I obtained a Nortronics full-track head, the difference was night-and-day. The full-track reproduction sounded fuller, smoother, and quieter. There were no tracking problems to speak of that would cause azimuth wander large enough to create a “flanging” or “phasing” effect of in-and-out high-frequency loss.

About 2004-2005, I had some full-track 7.5 in/s tapes to transfer that had been badly warped and found that there was enough azimuth wander that the tapes sounded better using one channel of an NAB stereo head. If I used the full track head, while the results were quieter, the azimuth phasing was unacceptable. At that point, I was using a Studer A810 for this type of transfer.

A few years after that, I was asked to recover audio from a 7.5 in/s full-track tape that was part of the Monterrey Jazz Festival. The client was very impressed at my efforts. I was able to use the full-track head, but one of the major differences was that this time it was on a Studer A80RC rather than a Studer A810 and the difference in tape guiding seems to have been the “magic” in that transfer.

The rule is use the most stable transport available and the widest head available to capture as much of the sound as possible without annoying azimuth-wander-based high-frequency combing/phasing effects.

If you use a head narrower than the full-track width, there may be objectionable low-frequency fringing that would need to be compensated.

Updates posted for “winding tapes for long-term storage”

Richard L. Hess — Thu, 17 Feb 2011 14:49:43 +0000

There was yet another discussion about winding tapes for long term storage. This time it was on the Society of American Archivists list. While it was focused on VHS tapes, where it was decided that it was more important not to leave the tape in the middle with active content exposed, some discussions of the mechanics arose and I have added them as comments to the original post, which is available here.

Track Configuration page updated

Richard L. Hess — Fri, 04 Feb 2011 19:59:02 +0000

I added a Track Configuration page to the resources hierarchy in the sidebar at the right. This points to other resources on the web to provide further insight into the various analog audio track configurations. There is also a brief note there about the variation in the two-track, half-inch format. These differences are minor, but they could be a source of some problems under some extraordinary circumstances.

This page was updated 2012-01-05 to provide track widths on higher-density audio multi-track formats.

A link to the Studer track dimensions page was added 2012-01-06.

IASA TC04 Guidelines on the Production and Preservation of Digital Audio Objects available online.

Richard L. Hess — Fri, 08 Oct 2010 22:26:25 +0000

The International Association of Sound and Audiovisual Archives (IASA) has released their landmark Guidelines on the Production and Preservation of Digital Audio Objects as a free web (HTML) edition, available here.

I provided some information for the listing of tape equalizations, and I find the compiled table (here) most useful.

Thanks to Kevin Bradley and the IASA team for their work in making this available. If you want a PDF copy, join IASA and it’s available.

Long-term stability of different batches of Ampex 456 – a guest article by Gary Galo

Gary Galo — Wed, 21 Oct 2009 20:14:59 +0000

Here’s some info that might be useful concerning which batches of Ampex 456 are good and which have sticky shed problems.

I recently unearthed 26 brand new 10 1/2-inch reels of 456 from 8 different batches. I checked one reel from each batch by playing them back and forth at 15ips (I only played the bad reels in one direction – that was enough!). The following batches were bad:

90297, 91049, 91055, 91079 and 91149

The following were fine:

94132, 94133, 94298 and 96190

The reels that were bad did not squeal during playback, but left debris on the heads and guides that was just barely sticky, so these are obviously in the beginning stages of deterioration.

All of these were Ampex (pre-Quantegy) tapes purchased in the early 1990s. Batch 96190 have lighter grey boxes as opposed to the textured, darker grey background found on the earlier batches, and the reel labels appear to be silk screened, rather than having sticker labels. None of these reels have the old rainbow-style logo.

I would guess that the good batches will probably remain OK – they’ve had a good 17 years to go bad and would probably have done so by now if there was a problem.

For whatever it’s worth…

Gary Galo
Audio Engineer
SUNY Potsdam
…speaking for himself

Dangers of old tape recorders for playback; using the elevator head

Richard L. Hess — Wed, 02 Sep 2009 20:01:02 +0000

We are currently working on some un-published tapes for a major Canadian folk artist. We have a 7.5 in/s 2-track stereo recording that was one of (if not the) first studio recording of this artist from circa 1972.

At some point, this tape was played on a 1/4-track machine that injected hum onto the left channel. Here’s what the magnetic viewer showed:

At the very top we can see a remnant of the left channel material, then the 120-Hz bars (62.5 mil spacing), then the remainder of the left channel material. In the middle is the guard band and at the bottom, the right channel.

Using a specially manufactured (by JRF Magnetics) assembly that contains a 4-channel 8-track head with a continuously variable height adjustment, we were able to lower the track one head to the middle of the good portion of the left channel. With that height positioning, track five’s head was well into the right channel, so we got a good transfer without the hum.

We believe this hum was written by the record head due to a malfunction in the recorder rather than an intentional erasure. If there had been an erasure, more of the left channel would have been erased and there would be a guard band between hum bars and the left channel audio as almost all erase heads were wider than the audio heads.

This type of damage is all too common using old consumer tape machines for playing tapes. I had an old junker machine in the 1960s that did this once to a tape. Unfortunately, it was also a quarter-track recording, so it was gone.

The magnetic record is fragile.

Sony APR-5000 head assembly problem

Richard L. Hess — Tue, 14 Jul 2009 21:34:32 +0000

I was having slightly intermittent connections on one head assembly on a Sony APR-5000 and was concerned as to the cause because the 78-pin head connectors are essentially unobtanium and a headache to change.

As I installed and de-installed the head, I got to thinking that the connector might not be positioned correctly (i.e. perhaps the wrong hardware had somehow found its way into the connector mounting system.

When I measured the bottom (oriented as if the head were mounted in the machine) face of the connector mounting flange referenced to the bottom of the mounting posts (using a straight-edge across two of them), I discovered that, indeed, this connector was recessed about 25 mils (0.025″) further into the head assembly than several other ones. Adding a 25-mil thick washer should solve the problem.

This is posted in case you’re scratching your head with a similar problem. This is something I wouldn’t have immediately thought of. I don’t know if this was caused by aftermarket work or if it perhaps represents a manufacturing error.

Kodak Durol triacetate tape with bad vinegar syndrome

Richard L. Hess — Tue, 07 Apr 2009 20:40:53 +0000

I recently received two 7-inch reels of Kodak Type 31A Triacetate tape (1250 feet, Durol Base) that smelled of vinegar even before I got the envelope open.

These tapes were badly warped due, most likely, to the vinegar-syndrome induced differential shrinkage. Other factors may have been poor winding during long-term storage (I had received them after several attempts to play them on another machine).

Not only was the tape cupping about its centre axis (with the basefilm shrinking so the edges were pulling back from the tape plane (away from the heads), it also had extremely wavy edges. In addition, the tapes would not lie flat on the reel due to the dimensional changes that were strongly embedded in the tapes.
We were able to play this tape on our stereo (NAB) A80, but discovered it was a 1/4 track tape (the original source had said it was half-track mono). We elected to stay with the A80 because:

The A80 has the stabilizer roller which tends to “break the back” of cupping
We had already adjusted the machine to have substantially higher tension to help flatten the tape–this was clearly a case of wanting the knobs to go to 11 or 12, but we had to settle for 10 on the play tensions.
We do not have a four-track head for this machine AND the machines for which we have compatible heads do not have as easily adjustable tensions or the ability to safely set the tensions as high as we did on the A80
The original recording was off-air AM radio after a trip of 1,000 miles through landline telco audio networks from 1964

So while the reproduction was only fair, we maintained good tape-to-head contact despite the inability to play this tape on other machines. If the content had been better fidelity and the client had been willing to pay for mounting a four-track head on the A80, we might have achieved some improved noise performance, but the original recording was quite low level (even correcting for the 1/4 track mismatch). Depending on segment, VU meter zero for the quarter track recording was somewhere around 15 nWb/m! We could hear recorded hiss, however, over the tape noise even in this configuration!

We were able to improve listenability by using a filter that matched the playback bandwidth to the recorded bandwidth (it appeared to be about 200-3500 Hz, we filtered for 200-4000 Hz) and it sounded about as good as we would have expected hearing over a transistor radio in 1964. Further processing with Algorithmix Noise Free Pro reduced background noise (including random crowd noise, but not loud cheers–it was a football game) and made the announcers pop out more, so if someone is intent on listening to the details of what the announcers said, this would be easier to listen to, but less authentic to the sound of the original broadcast.

These tapes were transferred somewhere near their effective end-of-life. It would have been better if these tapes had been transferred 10-20 years ago. Based on other experience with Kodak tapes, I am not surprised with this. Interestingly, the Durol basefilm in its present state of decay was not translucent as most magnetic tapes are, so translucency of basefilm is not a 100% accurate test for acetate basefilm.

Images of Scotch (3M) tape boxes available

Richard L. Hess — Thu, 05 Feb 2009 04:24:03 +0000

I was interested in the progression of the Scotch/3M tape boxes over the years, especially after someone contacted me because his father was in the picture on some of the 1960s tape boxes.

Use your browser back button to return to this page.
Here are the ones with the picture of the chamber orchestra
http://www.richardhess.net/restoration_notes/111.jpg (red 7″)
http://www.richardhess.net/restoration_notes/120.jpg (orangy-brown 7″)
http://www.richardhess.net/restoration_notes/200.jpg (blue 7″)
http://www.richardhess.net/restoration_notes/311.jpg (grey-green 5″)

The moirÃ© pattern you may see is the screening of the printing beating with your monitor.

These are earlier boxes for two if the above
http://www.richardhess.net/restoration_notes/111(A)_early.jpg
http://www.richardhess.net/restoration_notes/120(A)_early.jpg

And then it all became standardized in the 1970-era box
http://www.richardhess.net/restoration_notes/200_1970.jpg

When I get a chance, I’ll scan the box between the musicians one and the 1970s one.

Studer A807 digital noise improvement

Richard L. Hess — Tue, 03 Feb 2009 22:48:29 +0000

I received an email from Andrew Pearson of the British Library providing some hints in reducing noise during playback on the Studer A807 tape machine. He would be interested in hearing from people who had other ideas and people who had either successes or failures attempting his techniques.

Please remember that these modifications are provided “as is” and neither Andrew Pearson nor Richard L. Hess (owner of this site) can or will accept any responsibility for any damage, loss-of-use, or any other incident relating to this information. You may contact Andrew at Andrew(dot)Pearson(at)bl(dot)uk

RE: Clock and other digital noise on the Studer A807

I managed to reduce the 9.6kHz contribution by moving a wiring loom from the capstan servo board away from the audio boards. I discovered that sliding the audio board assembley out past the capstan board caused the interference to pass from mainly channel 2 to channel 1, as that board became closer, and discovered the source of noise in the J1 connector – ‘M3-9600′ signal. I redirected the loom up towards the spooling motors and made about 9dB improvement, although in some cases the 28.798kHz became slightly worse. However, that’s much less objectionable than the audible whistle from the 9.6kHz.

Another way to identify a tape with Sticky Shed Syndrome (SSS)

Richard L. Hess — Fri, 22 Aug 2008 05:18:15 +0000

For a current list of degrading analog tapes, click here.

Teaching people how to identify tapes that are suffering from sticky shed syndrome is often difficult.

I would like to propose that a careful inspection of how the tape comes off the pack may be a good way. Please provide comments as to how it’s working for you.

The tape should come off the tape pack at a precise tangent to the tape. If the tape starts to adhere and not pull off straight, that is a sure sign that the tape needs baking.

Of course, don’t bake acetate tapes even if they show this indicator, but on the last batch of questionable SSS tapes, I’ve been looking at this and it’s a fair indicator, and it seems to show at the outer edge of the pack.

More than one “test” or “factor” is needed to be sure, but this one is looking good.

Another almost sure sign of SSS is brown oxide and black back-coat.

Five historic standards now linked from the history page

Richard L. Hess — Thu, 21 Aug 2008 23:14:30 +0000

About two years ago, I asked the EBU to make available a copy of their historic document, Review of existing systems for the synchronisation between film cameras and audio tape-recorders and they complied, making it available on their website.

I asked the National Association of Broadcasters about their Cartridge, Cassette, and Reel tape standards as well as their Disc standard and they gave me permission to post these standards at my website.

These five standards plus some other articles of historic interest are available here in the history portion of this website. I hope that you find these of use in unraveling some of the challenges that old media present.

Studer A80RC mod for either tension sensor stop

Richard L. Hess — Tue, 03 Jun 2008 04:04:36 +0000

The Studer A80RC as designed stops only when both tension sensors lose tension. When using fragile archival tapes, especially at slower speeds, this creates some difficulties as the tape end weaves through the head block. Here is a modification which makes the A80RC operate like an A810, stopping the tape when either tension sensor looses tension. The mod is completely done on the 1.081.393 Command Receiver board and involves adding two parts and removing one.

Here is the circuit diagram for the modification:

Use this at your own risk. If it doesn’t work, breaks a tape, or blows up the machine, I am not responsible. Please be careful, the +24V trace is under the likely area to add the parts.

A solution to reduce spoking in old acetate tapes

Richard L. Hess — Tue, 15 Apr 2008 15:48:13 +0000

It appears that many old acetate tapes when played on high-quality audio recorders will suffer spoking when left in a play wind condition. I have discussed this problem here. Since posting that, I have taken one of my Racal Store 4DS recorders and removed the heads to save them from wear and now use that to re-spool any tape that shows spoking when played on a Studer A80, Sony APR-5000, or Studer A810.

I have just completed about 25 seven-inch reels of circa 1960-1965 acetate tapes (Scotch 111A, Audiotape, Soundcraft, Ampex 511, etc.) and about 20% of the tapes showed evidence of spoking after being played on the A80. These were rewound (approx 120 in/s under capstan control) on the Racal Store 4DS and then played at 15 in/s back onto their original spool.

With the heads removed, there are no fixed guides that contact the tape, just the two rolling tension guides and the capstan.

For photos of the Racal Store 4DS, please look here where I discuss its use (with head/guide assembly) for playing squealing tapes.

Please also read this post for a “do not try this at home” note.

TAPE Project Audio Tape Digitisation Workflow

Richard L. Hess — Fri, 07 Mar 2008 00:12:38 +0000

The Training for Audiovisual Preservation in Europe (TAPE) Project has just published an excellent Audio Tape Digitisation Workflow document here. It is authored by Juha Henriksson of the Finnish Jazz & Pop Archive and Nadja Wallaszkovits of Phonogrammarchiv, Austrian Academy of Sciences. It is aimed at the newcomer but still addresses all of the major points without being overwhelming.

I had the pleasure of speaking with Nadja at length about her work and I was very impressed by her approach and knowledge — as well as her practicality in getting the job done.

This document is a must-read for anyone planning a digitization project. While it is not as detailed or comprehensive as the Sound Directions publication, it cuts to the heart of what we’re trying to do in digitization. Starting with as good a playback as possible is the key to obtaining a good digital representation of the original. It also provides excellent photographs of various failure modes — and some are truly spectacular.

I must provide a disclaimer here that this website graciously links back here as well.

Slow speed 4-channel cassette digitization

Richard L. Hess — Sun, 24 Feb 2008 00:38:37 +0000

There has been some discussion recently about the 4-channel cassette recorders that were used for court reporting and other logging- or court-reporter-type applications. It seems that the players only have one output and can select any combination of one or more playback channels into that one output.

This monitoring topology is actually identical to two 1-inch 40-channel reel-to-reel logging machines I have where one can listen to any combination of one through forty tracks on a single output.

The solution for the reel machine is that I have about half figured out how to create 40 different outputs–and then I have to figure how to digitize 40 channels simultaneously. All can be overcome, but the cost to do it generally terminates the inquiry.

Fortunately, there is a solution for the 4-track cassette machines: use the higher-quality 4-track machines designed for music recording. I have a Tascam 234 (as well as a 238 8-track unit). Yes, I know these operate at 3-3/4 in/s while the logging recorders are running at 15/16 in/s (normal cassettes are in the middle at 1-7/8 in/s).

What I do is record the four tracks playing at 3-3/4 in/s into the computer at 88,200 samples/second (s/s). In samplitude, after the recording is made, I make a new virtual project that has a project sample rate of 44,100 s/s. I load the tracks into that. I then adjust all four tracks to -50% speed in the object properties panel. I use resampling for highest quality. This provides a 1/4-speed playback of the original files while maintaining a 44,100 s/s output file.

The digital data, of course, is actually at some point being processed at 22,050 s/s, placing the Nyquist frequency at 11,025 kHz, for an effective bandwidth of perhaps 10 kHz.

But, that isn’t a problem as only a very few Nakamichi cassette recorders ever made better than 10 kHz at 15/16 in/s — this wasn’t even officially in the Philips standard.

So, there you have a way to migrate these recordings into 44,100 ks/s WAV files while doing the bulk of the work in 4x real time.

You may add equalization and other filtering to improve the usually poor sound after the output is at the correct speed.

I actually had to put the recordings back on this infernal format after repair of the defect (very poor recording speed due to a broken machine), so I reversed the process with the Tascam 234 without adding any equalization and the client was apparently happy (I received payment and no feedback).
As an alternate to the speed/pitch adjustment in the virtual project, one could bounce the 88,200 s/s track played at 44,100 s/s to a second 88,200 s/s track and then repeat the process of loading that as a 44,100 s/s file and it will be in time. I prefer the single-pass approach that I can do in Samplitude.

One of the things that affects my procedure is that my audio interface (RME Multiface) does not work below 44,100 s/s.

Good 4-track recorders like the 234 have not been made for a while. Find them while you can.

UPDATE 2011-11-12: I sold my broken Tascam 234 a few months ago as I have not received requests for this format in years and I have obtained two DataTape CMS-1000 professional voice logging systems. The first one I tried worked and they are modular. I didn’t even try the second one. These run from 15/32 to 7.5 in/s and have four parallel outputs. Also recommended and perhaps better at longevity as I believe the Tascams run on belts which failed.

Tape recorder bias frequencies

Richard L. Hess — Sat, 02 Feb 2008 20:44:02 +0000

The discussion of what bias frequencies were used over time keeps recurring. Special thanks to Jay McKnight of Magnetic Reference Lab, Tom Fine, and Brian Roth for input to this list. I posted this to the ARSC list, but wanted to include it here as well. This knowlege is useful for those who wish to archive the bias along with the audio for future application of time-base-error correction tools such as the Plangent Processes.

Bias frequences started low, apparently with 60 kHz for early consumer recorders, but Ampex started with 100 kHz. Other later machines used different bias and erase frequencies. We can see with a few exceptions, the top bias frequencies were commonly limited to 250 kHz for audio, with the Sony APR series and the Ampex ATR series in the 400 kHz region. For cassettes, a practical maximum appears to be about 150 kHz. Much higher frequencies (up to at least 8 MHz) were used in instrumentation recorders. An enumeration of several machines follows.

Wire and Reel Tape Audio Recorders

In the early days, apparently wire recorders used bias as low as 30-40 kc, but Jay McKnight recalled in the pre-Ampex days, 60 kHz was common.

Ampex

The Ampex 200A used a bias frequency of 60 kHz [Jay McKnight 2012-03-25 post to Studer List] He indicated that this was probably the lowest for any professional recorder.

The Ampex Standard was 100 kc up to the MR-70.

With the MR-70, Ampex switched to 150 kHz bias frequency (and adopted the Hz) [Larry Miller, ex Ampex]

Ampex AG-440 (A) stayed with 150 kHz [manual]

Ampex ATR-100 144 kHz erase, 432 kHz bias (1:3) [manual]

MCI-Sony

MCI JH-24 Multitrack 210 kHz bias, 105 kHz erase [manual via Brian Roth]

Sony APR-5000, APR-24 100 kHz erase, 400 kHz bias (1:4) [manual]

Otari

Otari MTR-10/12 II Bias 250 kHz (erase not spec’d) [manual]
Otari MTR-90 (original) 246 kHz bias, 123 kHz erase [manual via Brian Roth]

Studer

Studer A80VU (All versions) 80 kHz erase, 240 kHz bias (1:3) [manual]
Studer A80 RC 150 kHz [manual]
Studer A810, A807, A820 2CH, A820 MCH, A827 153.6 kHz [manual]
Studer B67 150 kHz [manual]
ReVox A77 120 kHz [manual]
ReVox B77 150 kHz [manual]
ReVox PR99 150 kHz [manual]

Tascam

Tascam 32/44-OB — 150kHz [manual via Tom Fine]

Technics

Technics 1500/1506/1520 — 120kHz [manual via Tom Fine]

Cassette Audio Recorders

Here is a quick sampling of published bias frequencies for two top-of-the line cassette recorders, a better-than-average portable, and an early compact portable.

Nakamichi Dragon (Along with the Nakamichi CR-7A, perhaps the finest machines ever made for overall audio quality) 105kHz [Service manual dated 1985 (scan) 1990 (copy)]
Nakamichi MR-1 — 105kHz [manual via Tom Fine]

Studer A710 (a high-end cassette recorder, without the auto-azimuth that makes the Dragon superior) 150kHz [no date, scan on Studer ftp site]

Sony TC-D5M (a workhorse, good quality stereo portable) 85 kHz [Svc Manual dated 1980]
Sony TC-55 (an early compact — jacket pocket — mono portable) 41kHz (as low as I’ve ever seen) [Svc Manual dated 1972]

Reel Instrumentation Recorders

Honeywell 101 Medium Band: 4 MHz, Wide Band: 8 MHz [1977 manual] (note that the direct recording bandwidth on Medium Band was 600 kHz and 2 MHz on Wide Band at 120 in/s)

Racal Store / DS (Dual Standard) series 1.2 MHz [1982 manual] (note that the direct recording bandwidth was 300 kHz at at 60 in/s, the same wavelength limit as the Medium Band version of the Honeywell 101)

Aligning a tape recorder

Richard L. Hess — Sat, 02 Feb 2008 19:18:03 +0000

It seems some people new to tape are confused over how to align a tape recorder. This is the abbreviated version.

If you want to record on a tape recorder (and I do not recommend doing that these days as you’re just generating more tapes that will need to be transferred later) the first thing to do is get the playback correct.

CLEAN the machine.
If you haven’t done it in the last year or after a move (depending on the machine), demagnetize the heads and guides (using a strong demagnetizer like the Han-D-Mag).
Get a NEW (or trusted) calibration tape from MRL
The MRL tapes are supplied tails out. Rewind carefully and slowly onto a large-hub reel.
The first tone is a lineup tone, set for 0 on the VU meters of all channels.
If you are compulsive, the first time you do this, check the VU meter calibrations using an external AC voltmeter with wide frequency response. Most professional decks have very flat VU meters, so once you confirm that, you can just use the VU meters for the alignment.
There is a second lineup tone at different levels. If it is one of the -10 dB levels, take the machine out of playback cal and increase the level so that the meter again reads 0 VU.
On the 8 kHz azimuth section align the playback head azimuth (with an oscilloscope or a scope-application in the DAW) for minimum phase shift. Also check in mono sum.
Adjust the EQ trims (Trans-treble on the Studer A810/flashing treble light) for 0 VU.
On the 16 kHz tone, readjust the azimuth for minimum phase difference and maximum amplitude as above. Check in mono sum as well. It will never be perfectly stable.
Low frequency adjustment cannot be accurately accomplished off a test tape due to fringing unless the test tape and the play head track width is matched. However, one can often get close a test tape, but don’t necessarily tune for flat. It’s best to leave this alone if you can. The right channel of quarter-track machines will show more bass than the left as the fringing effect is coming in from both sides. Read the material on the MRL website.
Finally, recalibrate the playback level setting on the last tone. Leave the tape in a played wind on the reel it came on.

This completes the playback adjustment. Now you are ready for record adjustment.

Place a piece of blank tape on the machine (NOT your calibration tape from MRL)!
Record a 700 Hz tone at 0 VU on the meter when monitorin input and adjust the record level calibration for 0 VU when monitoring the output. Do this for all tracks.
Increase the frequency to 10 kHz (and drop it 10 dB at slower speeds, making up the gain in the uncal portion of the playback gain controls).
Decrease the bias level slightly so that you can find the peak. Then increase the bias past the peak until the 10 kHz level off the tape drops by the amount specified for that particular tape. It’s often somewhere around 3 dB. There are other, more precise ways to do this, but this should get you close.
Do a sweep of the high frequencies and adjust the HF record equalization for response closest to the response you got from the test tape. DO NOT try and improve the response from the test tape while adjusting record EQ as that will give you non-standard tapes.
Do a sweep of the low frequencies and then you can better adjust the PLAYBACK LF equalization.
Go back to 700 Hz and adjust for 0 on the VU meters when reading input.
Adjust record level control for 0 on the VU meters when reading output.

That should do it. I generally do a quick check flipping between input and output monitoring and you should hear no difference.

A word about levels. In the old days, I used to record at 185 nWb/m with Dolby A. With more modern tapes, 250 nWb/m will provide adequate headroom in most cases and may reduce the need for noise reduction processing. However, some have complained that 250 nWb/m is too low as it sounds too “digital” (i.e. “clean”). If you want to use tape as an effect, increase the record level to taste.

I really love recording with my Sound Devices 722 or somewhat less so with my MOTU 828 MKII, though there is nothing wrong with the MOTU that an RME FireFace 800 wouldn’t fix! Of course, now MOTU has the new 828 MKIII and it seems they have improved some of the things I complained about, but … twice burned (8Pre, also) … Anyway, I think that quality digital recording will capture sounds closer to the original than analog magnetic tape. This has been true in most tests run since the early days of digital recording and why most of the classical engineers who are looking for accuracy and not colouration were early adopters of digital. If you wish to record on analog that’s wonderful, but consider that analog tape is being used as much as an effect or sound-colourant as it is a storage medium. Also, remember that your legacy of tapes will be much more costly to preserve and migrate than digital files, although they may withstand neglect better.

Doug Pomeroy commented:

After aligning the deck for playback, per Richard\’s list, there is a simple way to set bias on any machine, recording on any tape. Use a 1000 Hz test signal and set bias current for maximum recording sensitivity (VU meter reading). Then for 15 and 30 ips recording, increase the bias until the
output level drops 0.2 dB. For 3.75 and 7.5 ips recording, decrease the bias until sensitivity drops 0.1 to 0.2 dB. One slight problem with this is being able, accurately, to read such small values on a conventional VU meter! (This method comes from Jay McKnight, of MRL Labs.)

Another method, also requiring a tone generator, is to record a low frequency, such as 30 Hz, at a very low level – at least 20 dB below normal operating level – and crank up the playback level enough to hear the output clearly, then adjust bias for the minimum amount of distortion (modulation noise, actually). This method allows one to easily adjust the bias by ear, listening for the cleanest reproduction of the low tone. The point of minimum modulation noise will very closely match bias settings arrived at by more elaborate means.

OF COURSE, after setting bias one must always go back and look at the high frequency response (10 kHz) and readjust the recording eq for flattest response.

Yes, bias setting is somewhat complicated, but it is good to remember it is always a matter of compromise, between the least distortion on the one hand, and the flattest overall high frequency response on the other.

Thanks for the comment, Doug. These are also good ways to set the bias. It is always a tradeoff. I no longer remember all the details, but biasing some old Magnetophonband Typ L from circa 1943 was a real challenge on a modern recorder as it is a homogeneous tape which means the \”magnetic coating\” is much thicker than on any coated tape, so the thickness loss is greater, and its basic sensitivity was far less than even something like 3M/Scotch 111.