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.

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.

Related posts

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.

Related posts

The punch cards were found and converted. This is a much happier fate than that suffered by the original IRIG 14-track 1-inch tapes of the Apollo Moon Walk from 1969! I am currently digitizing 14-track 1-inch seismic tapes surrounding the Mount St. Helens eruption in 1980.

Many analog and digital formats are becoming harder to recover. David Crosthwait at DC Video lists many at-risk video formats that he can transfer. I was contacted today by someone wondering if I knew where to transfer QIC DC-600A data tapes. I said I did, and sent him to Chris Mueller who can transfer many formats including most QIC formats.

The point is, however, I don’t know how much longer all of this equipment will be workable. Ten years is pretty much a certainty. Fifty years is a very long time. Please, search your archives now for obsolete formats that still need to be converted. There are people who can still recover content from a wide variety of formats, but we and our equipment are all aging, as the Library of Congress pointed out. They had to repair the punch card readers before the Kennedy data could be captured. It’s getting more and more common to hear: if you want me to recover that data, first I have to restore the old player.

I have given up maintaining an 8-track cassette playback machine as the call wasn’t there. I sold it to another restorer, so let’s hope he will bring it back to life. Little by little, the less-widely used formats will fade away. My first 7-track 1/2-inch IRIG tape recovery in 2006 came to me after a long search in North America and Europe with no success. At that point, I did not own any real IRIG machines (I now own several). I used a modified audio recorder and a 1/4-inch 4-track instrumentation machine for the FM demodulation. So there are not many people capable of playing IRIG instrumentation tapes. I don’t think there are too many people able to recover 9-track data tapes.

Please, before it’s too late, bring your data into the 21st century. Be prepared to be told at some point in the future “it’s too late–no one can do it”. Another piece of luck was finding some old tape machines in someone’s garage for the recovery of the Lunar Orbiter images. They were almost lost. There are so many formats and all of them require dedicated hardware to recover the data.

The formats that I am still accepting are:
—Digital Files on CD, DVD, hard drive, USB drives, etc.
—CD
—MiniDisc (normal stereo, not porta-studio multitrack)
—PCM-F1 on VHS or Betamax
—Sony DASH (3202 or 3402) 2-channel reel

I will, however, attempt to play digital tapes in other formats that I used to accept as stand-alone projects if there are one or two in a larger collection that I am digitizing and the machine still works. These formats include:
—DAT
—Digital Compact Cassette (DCC)
—20-bit ADAT (8 track)
—DA-38/DA-88 DTRS tapes (8 track)

DATs have become especially problematic of late, and I have decided not to risk my remaining machines attempting to play them. I recently discovered, when attempting to play a client DAT, that two of my four machines, which I had considered backups, were non-functional after having been in storage for about a half-dozen years without use. I also have a personal collection of DATs that I need to transfer.

One thing that appears to be happening is that DAT tape may be in need of baking. I have had success with one tape, but more research needs to be done.

As with all formats, my ability to transfer them is limited by available working machines. While I did not make a big announcement about dropping 8-track analog cassettes, it was uneconomical to maintain the machine for that format as well, and I sold it.

I have listed other resources that might be of assistance on this link for dedicated digital audio formats and this link for digital audio formats that used an adapter with a VCR.

An example is here.

Last October, when my friend Christopher Campbell visited to exchange knowledge** with me, he brought along a Quasar Sensor Loupe from VisibleDust. I had to have one. It is designed for showing dust on digital SLR camera imaging sensors, but its built-in lighting and 7X magnification make it perfect for looking at the magnetic viewer. This link appears to be a new and improved version. They also make a smaller version (called the Mini) which I have never tried, but you can look at it here. It is a little bit less expensive as well as being smaller.

Details about this system can be found here.

When I am not using the VisibleDust viewer, I use my older Surefire L4 LED flashlight for illumination of the viewer, although any good LED flashlight, such as those from 4Sevens and Fenix, would work. I still think the Zebralight in the full-flood mode is the ultimate headlamp for hands-free working—there is no hotspot.

Finally, a note about the viewer images. The majority were made with a Nikon D100 digital SLR camera (6 MP, APS-sized sensor) and a Nikon 60 mm f/2.8 autofocus Micro (macro outside of Nikon-speak) lens. Although the reticle of the B&L magnifier is shown in some of the images, the lens of the magnifier was removed and only the Micro-Nikkor lens was in the image-forming path.

**Christopher is an artist, photographer, large-format image printer, and is involved in tape restoration. I helped him with tape recorder and electronics skills and he helped me with colour profiling, Lightroom and Photoshop tricks and techniques, and camera image sensor cleaning. It was a good time, I think we both learned a lot from each other. Funny thing about knowledge…when it’s shared both parties win!

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.

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.

As I stated here in 2006, there is a 4 dB ambiguity at 16 kHz.

Many things conspire to make this 4 dB ambiguity essentially meaningless in a generally low-fi medium. The only reason I’m mentioning this now is that I’ve been bombarded with email from more than one participant in this discussion and apparently there may be some editorial judgment attached to what is posted.

Jay McKnight has graciously permitted my posting of his comments to me:

The problem, I think, is that people now-a-days are used to measuring digital equipment with digital measuring equipment, and think that precision measurements are always possible. As you well know, THIS JUST AIN’T SO WITH AN ANALOG MAGNETIC TAPE RECORDER! We try hard, and often come close, but there are just a lot of complicating factors, and most engineers are not aware of them.

For instance, there has NEVER been a measurement standard for tape flux vs frequency (“frequency response”) in ANY format. I have published on it (link here), but when we approached the IEC committee way back when, they said “we don’t write measurement standards like that”, which I think really meant “don’t confuse me with facts, my mind is already made up”.

There is also a problem revealed in the excessive spacing loss document, here . We suspect that this is the cause of the discrepancy in the wavelength-response  of the Philips cassette calibration tapes, but they would never admit that. Note that the German Open Reel calibration tapes even at the higher speeds 15 in/s (380 mm/s) also show this problem.

Note also that the AES Standard for measuring the medium-wavelength fluxivity ( AES Standard AES7-2000 (r2005): AES standard for the preservation and restoration of audio recording — Method of measuring recorded fluxivity of magnetic sound records at medium wavelengths (Revision of AES7-1982)) does not exist as an IEC standard, and we think that the amplitude of the medium-wavelength fluxivity on the German Open Reel calibration tapes at the higher speeds are about 10 % in error (link here).

When we approached BASF with these problems on their Calibration Tapes circa 1978, they said something to the effect “Your measurements are probably right, but we’ve been doing it this way for years, and we’re not going to change it now.”

So between the technical problems and the political problems with the IEC Committee (which, to a great extent WAS Philips and BASF), plus the fact that this is OBSOLETE technology, I think that trying to solve the problem with a 4 dB error at a 3 um wavelength on a cassette tape is futile. Take it for what it is. If it sounds bad, fix it as best you can.

To this, I might add that a colleague (and former member of the Ampex Standard Tape Lab) who would prefer not to be mentioned by name (and I can understand why after this week’s barrage of emails) has noted in at least some high-end cassettes back in the 1980s and 1990s that, if put away in storage for a year, they would lose substantial amounts of high-end. Some might have lost close to 10 dB at 10 kHz.

This high-frequency loss due to aging has never been studied, but it is one potential explanation for the very poor Dolby tracking with older tapes.

The same colleague also noted that in his measurement of cassette calibration tapes all of them were hot at the high end. The ones prior to the Prague Compromise were hotter than the ones after, but all were hotter than what the standard states.

A hot calibration tape will cause the repro EQ to be turned down. Adjusting record EQ to match playback EQ will mean that the tapes recorded on a machine calibrated with a hot calibration tape will be hot. Tapes recorded on machines that meet the standard will play back sounding dull on machines calibrated with the hot calibration tapes.

Please note, according to  IASA TC04 IEC Type I tape reached its final equalization curve in 1974, and that was 3180/120 µs, and the change was in the low end from 1590 to 3180 µs. IEC Type II and IV tape reached their final equalization in 1970, and that was 3180/70 µs.

I received an urgent phone call yesterday from a man who had digitized several reels of 2″ 24-track analog recordings that he wished to re-mix.

The tapes were originally recorded in about 1978-1979 and he said that he needed them to have Dolby C noise-reduction processing applied to the files.

I did a bit of research, as that did not sound correct from an historic point of view.

Here is an approximate chronology of the major noise-reduction systems and their dates of introduction:

DOLBY
A – 1967 (pro)
B – 1971 (consumer)
C – 1983 (consumer/prosumer)
SR-1986 (pro)
S – 1990 (consumer/prosumer)

dbx
I (pro) & II (consumer) – 1971

Telefunken (later ANT)
C4 – 1977

He later wrote me back saying the engineer was pretty sure it was Dolby A.

When I applied Dolby A, Dolby B, Dolby C, dbx I, and Telcom C4, only the dbx I sounded close to correct.

Fortunately, dbx I is less critical than the Dolby noise reduction systems for accurate level setting, since there are no test tones digitized along with the audio.

This work requires playing the digital files out through the D-A converter and then re-recording them via the A-D converter.

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

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.

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.

As with much equipment–and especially with lower-cost equipment–the performance specifications and the actual operational data is not published. There are reports of the H2 clipping on the line inputs in some of the reviews and it appears that a lack of understanding how the inputs were configured exacerbated that situation.

There is nothing wrong with the line inputs on the H2. BUT there are some caveats:

1. DO NOT use the input level control on the line inputs to go below 100 or the preamps will clip before the signal reaches 0 dBFS.
   ALTERNATE WORDING (thanks Greg H.):
   Set Zoom H2 RECORD LEVEL to 100 or greater to avoid clipping at the Line In preamp stage.
2. Use an external attenuator with the gain set at 100 to avoid overdriving the line inputs.
3. The noise floor is not spectacular, but is not too bad. With the inputs terminated in 150 ohms, the peak noise was -70 dBFS, but that improved to about -85 dBFS or better, measuring it as an A-weighted rms figure, which is how most noise is measured. While this certainly isn’t what one would expect out of the Sound Devices, it is far better than the 50-60 dB(A) that one can achieve with an analog cassette tape without Dolby.
4. The maximum input level to the line input should be no more than -5 dBV or -3 dBu.
5. Try to avoid clipping as there appears to be a delayed recovery in some instances.

With this information, you can optimize a pad between the source and the H2 line input so that the recorder is never overloaded. Try to keep the levels as high as practical as there is a relatively limited dynamic range. On the other hand, I have found that the recorder noise is not objectionable even when I’ve boosted the levels 20 dB for a quiet choir piece from our church. The room ambience totally swamps the recorder noise–at least as far as I hear.

The H2′s internal mics are reasonably good for many purposes. While I still prefer the SD722 for many things, I think the H2 is one of the better oral history conversation capturing devices I’ve seen. It uses SDHC cards which may require a new card reader. Don’t use the built-in USB connection unless you’re recording MP3 files as you’ll be there all day. The internal card-reader mode is limited by the USB 1.1 interconnection. This interconnection is adequate, however, for using the H2 as a 16-bit live audio interface/microphone connected to your computer (at either 44.1 or 48 ks/s). The unit will record up to 96,000 samples per second, 24 bits,   but many of those bits will be noise.

Please let me know if this has helped or if you have any questions or comments.This work was done with version 1.50 of the H2 firmware.

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.

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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 moiré 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.

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.