Revox A77 - copy a 15ips tape on a machine that does not have 15ips in a DAW

R

rob aylestone

Well-known member
I'm still away but cannot confirm this one? If somebody gives me a 2track 15ips half track tape, the only half track machine I have tops out at 7.5ips. They want the tape content on a USB stick as an mp3. If I record this at the half speed, then double it in the DAW, has anyone tried this and got any strange artefacts? I'm thinking that the slow, low recording can just have the sample rate changed and it should be fine? There could be issues with the EQ of course, 15ips tapes often being different, EQ wise - but what do you all think?
 
You can try it - and see what the results are like - 15ips is an amazing sound that I don't think doubling 7.5ips will achieve - deep bass - the crack of the snare - the guitars sound etc...I don't think it will be nearly as good - I would see if there is a 15ips machine you could use.
 
That's what's in my head. What is on the tape is the same. just coming off the tape at half speed and an octave down - easily fixed. I can wait till I have time when back home, but am struggling to think what the extra difference is. To be fair, the difference I hear normally between 7.5 and 15 is just a bit more top end I suppose I could just play it back on the four track? just sum 1 and 2 and 3 and 4?
 
I've transferred 30ips tapes at 15ips in the past and doubled the sample rate in the .wav file header using Adobe Audition. The results were fine - but this was probably helped by the playback machine using IEC equalisation which scales nicely with speed. The 15ips IEC eq is 35uS while the 30ips AES eq is 17.5uS which means that a 30ips tape played at 15ips will automatically have the correct eq applied. I don't do this much nowadays because I have machines that work at 30ips but it certainly works.

This eq scaling still applies if you play a 15ips IEC tape at 7.5ips with IEC eq but if your tape uses NAB eq then you will need to apply a little eq correction later. I'd be tempted to play a NAB tape with the IEC eq setting because the IEC eq only affects the high end so you can apply a 3180uS filter on the low end and the appropriate correction on the high end. The MRL website has a useful document that gives the eq corrections needed to go from almost any eq to any other -


If you play a 2 track tape on a 4 track machine then you may find the bass is slightly boosted due to fringing effects. Nothing really insurmountable though.
 
Well - I've bought a different machine, now I just need time to record some things and see how things go. I found a non-ebay, really nice A77 Revox from a retired fella who has a hobby - refurbishing Revox A77 machines. I drove down to Southend - about 100 miles from me, and it's in amazing condition - everything perfect and he's even added a few extra brackets to the case, as the machine's original case has a few quite weak corner joints - so he's reinforced them. I'm very pleased with it.
 

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Revox machines use a servo controlled capstan motor and so AFAIK it should be quite easy to mod the speed control to give 15ips? Yes the EQ will be wrong but only the HF turnover point which I would guess would need just an extra cap in the playback EQ?

Or Rob you could buy my 15ips Teac A 3440!

Dave.
 
And now ladies and gents... Next up, a tour of Mr. Aylestone's home. We'd like to introduce you to Mrs. Aylestone, but we can't seem to locate her.

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Dave - can't be done this way, because the driver for the motor not only alters the frequency, it alters the voltage - there's a whacking great transformer in there - and to double the speed takes the motor over it's maximum rated voltage. Revox simply used a larger diameter capstan. Apparently somebody did make machined sleeves at one point but they've vanished now.

Spantini - please don't joke - Mrs appeared at the office yesterday - she'd not been there for months, having filled half the home studio with my 'junk' she put there while I was away working for 10 weeks. So the home studio is full, and when she walked into the office she had a fit.
 

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"Dave - can't be done this way, because the driver for the motor not only alters the frequency, it alters the voltage - there's a whacking great transformer in there - and to double the speed takes the motor over it's maximum rated voltage. Revox simply used a larger diameter capstan. Apparently somebody did make machined sleeves at one point but they've vanished now."

Ah, that wasn't obvious from the schematic I found. Making one of those sleeves would be child's play for skilled lathe owner or someone with a CNC machine. I wonder if Sweetbeats has any dope on the subject?

Dave.
 
ecc83 said:
Ah, that wasn't obvious from the schematic I found. Making one of those sleeves would be child's play for skilled lathe owner or someone with a CNC machine. I wonder if Sweetbeats has any dope on the subject?
Click to expand...

If you add a sleeve to the motor you need to move the motor backwards to keep the tape path correct (you can do it without moving the motor on a Brenell or Ferrograph because they use pressure pads). This isn't that easy to do on an A77 (especially an older A77) and poor tape to head contact was a problem with many of the early high speed mods for the A77 which didn't move the motor. The B77 is designed for both sizes of capstan but I believe you may have to move the motor between different mounting holes to compensate.

Edit - on a B77 you have to change the motor completely according to Ted Kendall.
The motor needs to be replaced rather than just the capstan shaft as the motor mountings are offset according to the capstan diameter to keep the driving surface in the correct position with respect to the heads.
Click to expand...
 
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jamesperrett said:
If you add a sleeve to the motor you need to move the motor backwards to keep the tape path correct (you can do it without moving the motor on a Brenell or Ferrograph because they use pressure pads). This isn't that easy to do on an A77 (especially an older A77) and poor tape to head contact was a problem with many of the early high speed mods for the A77 which didn't move the motor. The B77 is designed for both sizes of capstan but I believe you may have to move the motor between different mounting holes to compensate.

Edit - on a B77 you have to change the motor completely according to Ted Kendall.
Click to expand...
NEVER 'king easy is it?! I wonder how much difference a sleeve makes for a one off dupe job? And yes, I have used a Brennell and knew that used a capstan sleeve (do I remember more than one?)

Dave
 
ecc83 said:
NEVER 'king easy is it?! I wonder how much difference a sleeve makes for a one off dupe job? And yes, I have used a Brennell and knew that used a capstan sleeve (do I remember more than one?)

Dave
Click to expand...
Yes - there was more than one on a Brenell. The speed switch has two sets of numbers - one for the small capstan sleeve (1 7/8 - 7 1/2ips) and one for the large sleeve (3 3/4 - 15ips). As far as I remember, you had to use one of the sleeves because the pinch roller wouldn't make contact with the capstan if no sleeve was fitted. I've got one sitting in the garage with some transistor electronics that I made from a Mullard design in a Henrys Radio catalogue. I still have the original valve electronics too although they weren't working very well when I last tried to use it some 40 years ago.
 
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