An idea I had about making an affordable reel to reel tape head preamp that exceeds the limits of the medium

[Shinano]

I was thinking today about reel to reel, as I love the format. But what I don't like is the large amount of distortion, low SNR, etc. The record and playback electronics being so old, can likely be improved to better than the medium, as that aspect of the machine is likely holding performance back. Then I thought, "What if there was an external tape head preamp built to SOTA specs in THD, SNR, etc. Then the only variable is the tape itself and the heads." With that, I remembered that the output voltage off the heads is very low, so that could add difficulty, as more gain would be needed. Then I thought, "What about a CD player output section? Maybe the output voltage from a DAC chip is similar enough to the tape heads that the output section from the CD player could be modified to be a tape head preamp?" I say a CD player, as the outputs usually measure well enough, not having much distortion, high enough SNR, etc. I did a quick search on output voltages of DAC chips and tape heads. Looks like a Philips TDA1541 (chosen as reference due to it's popularity. Likely easier to find information on.) output voltage is a max of 25mv. A tape head looks to be a max of 6mv (not a particular one. Just what I could find quickly.).
All the preamps I've seen are tube based, or just crazy expensive. Maybe I'm overthinking things with the whole CD player output stage thing, and there's something that could fill the role perfectly that I don't even know about, since I'm not a DIYer. Surely, in this era of audio, where low distortion and high SNR is widespread and affordable, something can be made to exceed the specs of reel to reel's capabilities, while remaining affordable. I don't know what to do about playback EQ yet, but I don't expect it to be a problem, especially when digital parametric EQ is so prevalent. I would appreciate the input of people who actually know how to design this kind of stuff, as I have no clue how to. I just had an idea that I wanted to share, since there may be more people here that have a similar problem with the format.

 

[sergeauckland]

Having worked with Ampex and Philips professional tape recorders in the 1970s, the limitations were always the tape. Electronics were even then well able to have the sort of distortion and noise figures close to CD, but the tape was the limitation. The point of Dolby Noise Reduction was to adjust dynamically the frequency response of the record signal to then decode it on playback and thus reduce the noise. Nothing was done about the inherent distortion of tape due to non-linear magnetic effects, but Dolby SR addressed some of the limitations of tape regarding HF saturation. . Given that the main use of tape was to record for release on LP or 45rpm singles, tape noise and distortion was deemed adequate and not the limiting factor.

By the late 1970s, with CD on the horizon, digital tape was the next development, and analogue tape development pretty much stopped.

A reel to reel stationary head digital recorder could be what you're looking for, but frankly, apart from doing it as a hobby project 'because you can' anything on tape seems rather pointless when solid-state recorders are ubiquitous. DASH recorders should still be available from the usual sources.

S.

 

[EERecordist]

Audio tape has an EQ standard defined by the NAB (US) or IEC (ROW). Think like RIAA for vinyl discs. Then the record and playback is dynamically adjusted to the specific tape formulation referenced to a calibration tape.

To do that in analog takes several amplifier stages.

I think some kind of auto-eq/calibration would add value.

Pretty sure you could find a used bias-record-playback channel with a schematic and a theory of operation. It is the tiniest of markets to make high-performance professional reel-to-reel third party electronics. So they are expensive. Maybe with the audiophile interest in reel-to-reel, there is more of a business case. I wouldn't bother with cassettes, the track width is tiny.

 

[MaxwellsEq]

I worked on Studer professional tape machines. The amplifiers were better than the tape. This was true of any professional machine.

 

[Shinano]

the limitations were always the tape. Electronics were even then well able to have the sort of distortion and noise figures close to CD, but the tape was the limitation.

Makes sense. I wasn't thinking in regards to the professional machines, as no doubt they had the best preamp designs at the time, and wouldn't have been a hinderance, but more for home machines. I have a Tandberg 10XD 4 track (and Teac A-3300SX. But there are no measurements here for that one.), which going off the measurements on this forum (granted, who knows the state of the electronics inside, as it wasn't stated it was serviced), direct pass-through was yielding about -67db THD+N. Which is a long way off the SMSL PL200's THD+N of -98.6. So I think there's room for improvement in that regard. I've always wanted a pro machine, but given their cost, I thought I would instead focus on making what I do have perform the best it can, preferably on a low budget.
Edit: That Tandberg is 1/2 track. So mine would measure worse, being 1/4 track.

 

[mhardy6647]

A decent MM phono preamp can (i.e., should ) be easily adapted to serve as a good preamp/EQ for a tape head.

 

[sergeauckland]

Your Tandberg would be about 3dB worse on noise being 4 track.

Of course you can replace the replay amps with something more modern, and you could redesign the record amps similarly, but the limitation would still be the tape. What you could do at 'sensible' cost is to source a pair of Dolby 361 units or better still Dolby SR, but even then it won't be as good as a digital recorder, and for Dolby to track properly between record and replay, the machine must be immaculately lined up.

I think you have what you have, and trying to improve on that will be either disappointing or expensive.

S.

 

[Shinano]

Your Tandberg would be about 3dB worse on noise being 4 track.

Of course you can replace the replay amps with something more modern, and you could redesign the record amps similarly, but the limitation would still be the tape. What you could do at 'sensible' cost is to source a pair of Dolby 361 units or better still Dolby SR, but even then it won't be as good as a digital recorder, and for Dolby to track properly between record and replay, the machine must be immaculately lined up.

I think you have what you have, and trying to improve on that will be either disappointing or expensive.

S.

Yeah, working with consumer machines isn't ideal. I've wanted to try those Dolby units before, as what seems to be the best noise reduction system would be fun to see the results with and without it.

 

[Shinano]

Alright, maybe this wasn't even a problem to begin with. I knew tape distortion was high from the start, but even -67db is .04% THD+N. Which honestly isn't terrible. I think I'll throw this idea into my bin of crazy reel to reel ideas (more like "What if this worked?" kind of things.). Which include using an 8 track 1/2in tape machine to record two channels across the full width of the tape, via splitting the signal before it gets to the machine, and then recombine after the machine (which I learned that wouldn't give much improvement in SQ.), and (I never shared this one, as it's even dumber than the last one. Besides needing so much extra work, and not even being possible without custom tape heads.) having a setup where you have two mono recorders, one for left and right, that record each channel separately. The problem with that is wow and flutter would make syncing audio hard. So my dumb thought was "Just put timecode on the tape, put it through a box (what would be in it, I don't know.), and just buffer it so the audio would be synced to the timecode." Which would be great, if you don't have the variable of record wow and flutter, and also the playback wow and flutter. That's why I quickly ruled this one out. I appreciate everyone's input on this. You've been very helpful in helping me get a better look at things. Which I now know that it's silly to pursue this idea of mine, as it likely won't make a huge difference for the amount of effort needed to make such a thing.