Revox A77, convert from Normal to High Speed

I bought another Normal Speed motor (direct buy a High Speed motor was too expensive and risky) and tried to convert it to High Speed by increasing the capstan shaft diameter from 4.5mm to 9mm (some say 9.05mm, not very important since speed can be post-calibrated).
The most important factor is the capstan diameter variation tolerance which means the workshop's lathe must be well calibrated and precise.

[@harveysvintageaudio]

I also love working on Revox, nice channel.

[@dchatz]

Thank you

[@imsaint007]

Love that convertion and you can reverse it any time to original speed👍👏👏

[@brotherspock8180]

It's an honor to sub your channel. These A77 videos are the best on KZbin.

[@dchatz]

thank you sir

[@mteixido9]

Great video again ! super useful info!

[@andrewjohns6036]

wonderful Great stuff keep going

[@dchatz]

Thank you

[@EasyMusic36]

Hi, I've been looking at your work, I think it's a good idea to convert a standard motor to another HS, but nothing more. The first thing is that speed is directly related to the EQ of the PCBs, so both playback and recording, as well as the motor control PCB. The values of its capacitors and resistors are different, because the standard model (3 1/4-7 1/2) all its electronics are designed for that model, and not for an HS model. You can get rid of doubts by placing an original recording in 19 and 38 cm, which I mean that, will not sound the same as in an original HS machine with all its original electronics and mechanics. You get these explanations in the REVOX manuals available online. Any way, good job!!!

[@dchatz]

you are correct that rec and PB preamps have different electronics but I think the speed control board is the same. Proff. conversion would require messing with the electronics of the preamps but I am just a hobbyist so I will not mess more. What I only did was turning the equalization down from the trimmer on the rec preamp. Further more I like the boost on high freqs that result from this. Like that also and keeping the old motor I can revert the machine to normal speed anytime. But yes you are correct. Proffesional conversion would require changing stuff on the preamps.

[@MateusMachado]

Great job. I would like get some help to solve a sensor noise (whistling). It only happens on 7 1/2 speed. I see you removed the motor and so on, although I don't don't how you calibrated the sensor back. Is it so hard? Could you help me on this?

[@unequally-tempered]

Is there flutter audible on this?

[@dchatz]

Unfortunately there is. For my home amateur specifications, it is acceptable. It only comes down to how accurate the workshop's lathe is. The less tolerance there, the better the results. I had to try twice (seen on the video) to get an acceptable result. If anyone tries this, it must be very clear to the store that tolerance must be to the bare minimum. Better to make it a bit bigger (say 9.10-9.15mm) to be able later to take out some material in case it not very well made. Speed is adjustable so diameter accuracy is not that important.

[@dubdoodle7191]

How many A77 machines do you have presently ?

[@dchatz]

1 mk3 converted to HS, 1 mk4 . 2 total

[@dubdoodle7191]

@@dchatzYou're on your way to collecting - the ReVox acquisition virus is manifesting !

[@bobsbits5357]

hi did you know there was a deck that used A77 deck in side ut was a 8 track 1/2 deck the thing is the one's i have have very heavy wear all over them yes i know the motors very well i have a slow model same as you it's very ill with wear

[@duncan-rmi]

this messes up the tape path. you'll change the angle that the tape takes off the r/p head. the factory HS machines have the motor mounting drilled differently so that the centre of the fatter capstan sits further back & gives you the same angle off the head. the tape isn't supposed to touch the guide in between except by its edges.

[@dchatz]

But i did exactly that. i lifted the motor to a new position. I even show exactly how i did it.

[@duncan-rmi]

@@dchatz my apologies- I didn't get to that bit! 😞

[@dchatz]

@@jonvincentmusic the man apologized so lets just forget about it.

[@jonvincentmusic]

Literally 3/4’s of the fekking video is about how he adjusted the motor mounts to correct the tape path, but nah why watch the video when you can just try to be a smartass instead.

[@duncan-rmi]

@@dchatz thanks. & he's deleted his comment & fcked off without apologising himself. 😂

[@davidspendlove5900]

My A77 runs at 7.5 ips and 15 ips

[@dchatz]

then you are lucky enough to have an original HS version. You don't need to convert anything

[@fickfehler3866]

You must have had to change the capstan speed control pcb also, no ?

[@dchatz]

not at all, the motor turns at exactly the same speed. No need for motor control replacement. The tape speed is increased only by increasing the diameter of the capstan shaft. Everything else remains the same.

[@imsaint007]

That's smart move like in the racing bicycles gears @@dchatz