🛠️ ReVox A77 Reel-To-Reel + DIY Varispeed Mod, Part 1: How-to, Tape Echo / Dub FX + Demos 🔊

[@slavtrash]

this is amazing thank you for putting so much work into this.

[@scottschiller]

You are most welcome. It turned into a bit of an effort, mostly because I’m not an experienced electronics engineer. 😅

[@ghostexits]

There was a widely implemented varispeed modification for older A77's and a fair number of decks have it installed already--maybe 1 in a dozen A77's on ebay. It seems like these are always Mk2 or Mk3s. There were other standardized mods that one see's time and again in eBay, sales but sadly schematics for these mods haven't found a place on the internet yet.

[@scottschiller]

Interesting history and context, thanks. I think I’ve seen vague mentions of DIY varispeed mods for older (MK1-3?) models, but I haven’t seen any schematics outside of Studer / Revox’s own service manuals which connect to the capstan motor PCB typically found in MK IV models which uses ICs like the 555 timer.

[@ghostexits]

@@scottschiller You can identify the varispeed mod by an extra 1/4" jack placed an inch or two above the headphone jack. This is where the varispeed controller plugs in. It's always the same type jack: black, Cliff brand. These jacks weren't too common in the US, so I presume they were sold in kits to A77 owners. There was another amazing mod called "sel-sync" requiring an extra monitor card and allowing an A77 to play and record simultaneously so you could multitrack back and forth with only 2 tracks.

[@scottschiller]

@ghostexits Great info, thanks. I doubt I’ll be acquiring more tape decks soon myself, but this is handy for all to see. And, never say never. 😆

[@percaros]

Hey! This video was excellent, I'm going to apply some of the stuff you did here on my own. But wouldn't it be easier to tune the 10k pot with a sine wave going through the machine and a tuner?

[@scottschiller]

Thanks for watching, and I’m glad you enjoyed this one. Your idea to measure sounds more logical than my “by-ear” approach, certainly. 😅

[@Radar23]

very interesting.. unfortunately I don't have a nice revox but only a teac X3.. it's has similar speed control board internally with a NJM2903D IC (dual comparator) which is doing a similar PWM for the two stock speeds.. (3.5/7.5). This video has me considering designing a similar remote mod varispeed.. i see the Revox remote has quite a simple circuit, is the LM301 used to buffer the 12V supply to the speed adjustment Pot? What is the course and fine tune switch doing? Also tonally, you say this varispeed give a range of +-8.. any idea what that is in musical semitone ranges? thanks again

[@scottschiller]

Pardon the late reply on this detailed question! On the ReVox remote, I believe the "fine" vs. "coarse" switch affect the range of the varispeed effect. I believe "coarse" is the ∓8 range mentioned. I didn't try building the "fine" part of the circuit. If your Teac X3 is doing PWM and you have evidence to support building a varispeed control to get you somewhere between 3.5 / 7.5, that could be fun to look into - and I imagine others would appreciate it, too! I am not an electronics expert by any means, but I was able to test and sort out how to adapt the official ReVox Varispeed remote (for the B77 etc.) to work with the A77 MK IV. In terms of range, I feel like ∓8 is the better half of an octave. I did a few tests on the "Part 2" video, where I showed the range in the motor RPM and a few examples of what that also sounds like. Apologies again for the late follow-up, I hope this is of some help. Do follow up if you build anything, that would be neat to see!

[@tommychampion.mp4]

this is awesome! quick question - with a deck like pioneer rt707 which has a pitch control, would I naturally have control of the delay time ? hifiengine lists it as "± 6% Pitch Control" but im not sure if that means varispeed

[@quickstrike209]

????? I have this one as well

[@scottschiller]

Sorry I’m late in replying, my KZbin notifications stopped! 😬 Pitch control is *probably* “varispeed”, yes. One detail you should confirm, is if the feature works while you are recording. for example: I have a tape deck with pitch control, but the pitch feature only works when playing back sound. For the effect shown here, you want control during recording.

[@quickstrike209]

@@scottschiller Yes you can control the pitch during recording

[@dubdoodle7191]

Cool demonstration, what would the primary application / purpose be for a spd adjustment mod ?

[@scottschiller]

Dub-style echo effects, primarily - recording onto tape, then feeding that sound back into the tape which creates a “sound on sound” effect. I show some examples of this in the intro, and later on in this video.

[@scottschiller]

The variable speed bit allows “tuning” of the dub / echo effect in real-time, to match the tempo of the song - and/or, create some wild effects.

[@Synth2000]

Will you share your mod / varispeed control eventually?

[@scottschiller]

Yes! I have "Part 2" almost done and will be publishing it very soon. Stay tuned. Most of the circuitry is covered here in Part 1, but I may be able to provide more detail on exactly how I wired things up.

[@romainscordia3507]

Thanks for your video! I would like to do it on my Revox too but my timer IC is a mc1455p1, is that going to work?

[@scottschiller]

You’re most welcome, Romain. My machine also had the mc1455p1, listed as a replacement for / equivalent to the 555 - but I suggest you confirm this for yourself before you start doing any wiring! 😅

[@romainscordia3507]

@@scottschiller After checking the mc1455p1 datasheet, it's the same IC. Just to be sure before starting : BLK is ground, can I connect it directly to the ground on the board? same for ORG with 12v? And also can I use "CV" indication on my board to connect WHT to pin5? Best regards and thank you for sharing this video!

[@scottschiller]

Thanks, I hope this works OK for you. I recommend disconnecting power entirely and having the machine off when making or changing any electrical connections. You don’t want to connect the wrong thing or short anything. I accidentally fried the original 1455 chip on mine somehow, in this process. 😬 I don’t have the schematics in front of me, but carefully review what I’ve highlighted in the diagrams. There should be more and maybe links in the description, too.

[@tristanpolliandersen3524]

Great video !!!!

[@scottschiller]

Thanks! This one took many hours to make. ;) Stay tuned for more - I have yet to build the "remote" control box, etc.

[@leonard.c]

great! thank you for this video

[@scottschiller]

Thanks for watching. This is a two-part series, with a third on the way. Stay tuned.

[@StuffnSuch]

Would the varispeed remote work with a Mk III?

[@scottschiller]

I’d say it’s unlikely, but doesn’t hurt to check. If your capstan motor PCB has “IC’s” (integrated circuit chips) on it, then it should have a NE555 (timer) IC like on the MK IV and you may be able to build a varispeed circuit for it. However, it depends on whether or not your particular board has chips. I believe with the MK IV, they were new at the time - but these machines are modular, so it’s possible that some of these boards can be swapped out with newer ones and still be compatible. Don’t quote me on that, but I recall something like that being mentioned somewhere.

[@sinuscasehornung2531]

Yes 🎉

[@Radar23]

Just picked up a B77 mk2.. Need to make me a remote varispeed box!

[@Radar23]

The story continues.. I'm in Australia and paid $1500aud for the B77 mk2.. In great condition.. Now wooden panels but well maintained.. That's about $900 USD.. Surely that's a decent price.. Haha.... Looking forward to getting the dub feedback varispeed Prince Fatty style happening..

[@richardramirez8909]

Hi,will this mod work on th mk1? Thanks

[@scottschiller]

It is not likely, but it depends on what version of the motor control board your machine has. At the time, integrated circuits like the 555 timer IC (“chip”) were new. If you see chips on your board like mine, then varispeed may be possible. I believe the MK IV was the first model to have ICs on the board, but these machines are pretty modular and boards can be swapped out to some extent. I am not sure what compatibility is like, I have only ever worked on my on MK IV model.

[@seravenerdi]

If a 1-7/8ips 3.75ips model is upgraded to a 3.75 - 7.5ips, how can this be achieved ? Just replace capstan spd pcb ?

[@scottschiller]

I am not familiar with the 1-7/8 to 3.5” process, but my guess would be that if everything is driven by the capstan motor speed control PCB - and, if upgrading is compatible - then you could try the varispeed approach with a PCB that has the 555 or equivalent IC chip. Before you go down this road, I recommend checking that you can upgrade or swap the PCB and that it will work with your existing conversion work.

[@seravenerdi]

@@scottschiller Will do Scott. I also got a 7.5ips B77 and see the capstan is identical. Suppose I should start with the service manual and compare pcb parts. Revox are very modular that way

[@scottschiller]

Good thinking, and I agree. It was pretty neat opening up the machine and seeing the layout of all those modules.

[@klinkske]

very good! You replaced the rifa with rifa??? Why?

[@scottschiller]

Sorry, totally missed this comment. Not sure if I have "newer" RIFA caps; I didn't work on those. Let me know if so, and I'll nag my tech / service guy if I have to. ;)

[@arturasb]

great video! what app did you use on your phone for sampling? :)

[@scottschiller]

Thank you! Some was just music from my phone, and a bit of a DJ set I recorded previously. I was scratching a bit within Alglriddim’s “djay” app earlier on.

[@urbanlypure]

Hi great video, what OHMs did you go for with the potentiometer?

[@scottschiller]

Per the original circuit diagram for the varispeed remote, I used a 10K-ohm linear pot.

[@a.stockton4817]

nice, also whats the dj app on your phone

[@scottschiller]

Thanks. This is Algoriddim's "djay", which is pretty great. Available on iOS and Android, and desktop Windows / Mac as well.

[@klinkske]

a shame my a77MKiV is old board- it can't have the B77 mod :(

[@scottschiller]

If you look on eBay, you might be able to find a compatible IC-based one for a reasonable price. YMMV, at your own risk etc. Note that mine is an A77, but the capstan motor control board is IC-based with the 555 timer; that's the important part making this possible.

[@ryal1]

How does one determine if an A77 is compatible ?

[@klinkske]

kerry gatt it needs a black component on the board under the transformator. A Trim pot. If it does notnhave this, it is the wrong board. You can see this if you remove the case, easy. Check this video at 2 min 53 when Scott swapps it.

[@ryal1]

klinkske Turns out I got the right one! Thanks for clarifying 🙏

[@klinkske]

any chance to sell me all i need to mod my mkIV (with the wrong electronics inside, seems like the first iV's are not the same as the later iV's?)

[@scottschiller]

I'm afraid I don't make or sell kits for this sort of thing, unfortunately, as it really isn't plug-and-play. You need a machine with the right IC-based motor control PCB, _and_ then you also have to wire up the DIY varispeed controller circuit to a few places on the board; that means you have to open up the machine, etc. Even when you have one with the right PCB, my $.02 on this is, "here be dragons." I think some tinkering, hardware, and electronics experience is needed to feel comfortable doing this work. I took the chance of building and wiring up my own external Varispeed circuit - and it _did_ work after some mistakes, but it felt quite risky; I assumed I might break the machine along the way! I was lucky in that I didn't break anything, but I did fry one 555 timer IC and had to replace it. Thankfully, that was the only thing that broke. I do see ReVox motor / speed control PCBs on eBay sometimes, e.g., www.ebay.com/itm/REVOX-A77-Speed-Control-PCB-Board-Card-Reel-to-Reel-Part-1-077-724-Rx111/324200470240?hash=item4b7bda96e0:g:6ZoAAOSwmGde6RZt - this has the 555 timer IC. *However*, I have no idea if this would "just work" if you put it in your machine. It's not clear to me if you can mix and match different PCBs in a particular machine. Mine happened to have the IC board when I got it, I didn't have to change or swap out anything. While these are designed to be reasonably serviceable (especially vs. today's surface-mounted microscopic electronic parts etc.), there's still a chance you might break something trying to open the machine just to get to this card, or while unplugging all the cables and so on; it is a non-trivial amount of work. If you can, a safer approach would be to get a B77 MK II model (not the MK I) that has varispeed built-in on the front panel, a smaller dial. I think it has only ± 2 in range, you need an external control to get the the ± 7 range - but it's a start. With a B77, you could either try to find the external varispeed remote ($$$), _or_ try building your own version of the circuit I did and then making your own control which you could connect via 4-pin DIN plug into the B77's remote control socket.

[@klinkske]

@@scottschiller thx, but i remember the video from Prince Fatty - he said 'don't buy the B77' while he was demonstrating the vari speed on the A77 mkIV- i guess it might be because the B77 does not do the slow speed like the A77 - i want muddy tape echo's for DUB- i want a revox that goes as slow as the one he used in the video. I guess you have seen that video too?

[@scottschiller]

@@klinkske Ah, yes! That's how I got started on all this, hah - Prince Fatty's "Masterclass" video on dub techniques - right around the 26-minute mark. kzbin.info/www/bejne/d56oqIaCqrqVqasm48s What Prince Fatty's saying is, he thinks the B77 only comes with tape speeds of 7.5 and 15 IPS - whereas the A77 has 3.75 and 7.5 IPS. The lower 3.75 speed, slowed down even further with varispeed, can be helpful when you want to work with lower-tempo music. I _think_ there are B77 models that have 3.75 and 7.5 though, per this page. Worth a look. www.reeltoreel.de/worldwide/B77.htm Even if you can only find a B77 with 7.5 as the lower speed, I wouldn't rule it out entirely; I have some things running at 7.5 IPS here and in my more recent videos, and you can still bring the speed down a fair bit.

[@klinkske]

@@scottschiller thanks, i think i just scored the right A77 mkIV - i tried to send you a email with some questions.