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Revox A77 varispeed mod? Recorders, Players & Tape Machines
Old 18th August 2007
  #1
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dlmorley's Avatar
Revox A77 varispeed mod?

I'm thinking of setting my A77 up as a tape delay but it doesn't have varispeed to adjust the timing. Is there a simple mod I can do to give it varispeed??
Thx!
Old 18th August 2007
  #2
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Hi
It should be possible but get yourself a copy of the schematics and look if there is a varispeed 'option' as 'standard' but otherwise you could attack it and remote connect the speed adjustment pot which I think it has.
Matt S
Old 19th August 2007
  #3
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dlmorley's Avatar
Quote:
Originally Posted by Matt Syson View Post
Hi
It should be possible but get yourself a copy of the schematics and look if there is a varispeed 'option' as 'standard' but otherwise you could attack it and remote connect the speed adjustment pot which I think it has.
Matt S
Thanks Matt
I just found the schematics online, so will see if I can find anything
David
Old 19th August 2007
  #4
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Hi
I believe that there is a high voltage transistor controlling the power to the capstan motor which regulates the speed. A 'tacho' ring on the motor generates pulses which give speed feedback.
This is all from memory but it was about 30 years ago.
I don't know how much 'vary' you want and whether it will manage it smoothly but as the motor does not have a 'gearbox' as such it should be possible as it ranges from 7.5 to 15 IPS (or other speeds).

Good luck
Matt
Old 20th August 2007
  #5
Motown legend
 
Bob Olhsson's Avatar
 

You just substitute a pot for a resistor in the motor circuit.
Old 20th August 2007
  #6
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dlmorley's Avatar
Quote:
Originally Posted by Bob Olhsson View Post
You just substitute a pot for a resistor in the motor circuit.
Nice. Thx!

Just need to find which one
Old 28th August 2007
  #7
Gear Nut
 
Goreski's Avatar
 

Servo pot for vari-speed

schematics for the A77are on line at both Studer LA and AnalogRules.com (my site) for free download
I believe you will have to cut out the trimpot P201 on the servo board and bring this into an external pot for vari-speed adjustments.... the pot as shown in the schematics is a 1k pot, but I would choose a greater value - say 2.5K and a 10+ turn pot.
the A77 is NOT designed as a vari-speed unit - I would expect severe wow and flutter beyond a few percent change in speed.

Goreski
Old 28th August 2007
  #8
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dlmorley's Avatar
Quote:
Originally Posted by Goreski View Post
schematics for the A77are on line at both Studer LA and AnalogRules.com (my site) for free download
I believe you will have to cut out the trimpot P201 on the servo board and bring this into an external pot for vari-speed adjustments.... the pot as shown in the schematics is a 1k pot, but I would choose a greater value - say 2.5K and a 10+ turn pot.
the A77 is NOT designed as a vari-speed unit - I would expect severe wow and flutter beyond a few percent change in speed.

Goreski
Many thanks Goreski
As it's for tape echo, wow and flutter may not be an issue (may in fact be nice!)
Will try this out soon...
Old 9th January 2015
  #9
Gear Maniac
 
thomasdf's Avatar
Has anybody tried that? I am in the process of recaping my A77 and this could be a cool mod... Thanks!

Thomas
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