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Revox a77 Abby road mod
Old 29th June 2017
  #1
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Brett 123's Avatar
 

Revox a77 Abby road mod

Hi there,

Does anyone know about this?

I can find two different versions on the web, not sure which one is correct ?

Either -
On the back of the input level pots there's 4 pins each. a black wire goes to pins 1 and 4, pins 2 and 3 are red and orange (i forget which is which off the top of my head - doesnt matter). Solder the ground wire to either 1 or 4, and the hot lead to the same pin as the red wire (nothing needs to be disconnected from the pots - as a matter of fact everything should stay in case you do want to still use the regular inputs for any reason)

Now, with my board setup, the input was HOT! I was hitting 0 at almost no gain on the controls even with a -10db unbalanced output, and I did have a load happening on the board - lost most of my signal going to my master fader - my VUs dropped from 0 to around -20. A 10k resistor in line with the hot lead on each channel brought it back. I'm reading "0" on the VUs at around the 3 on the inputs of the tape machine now. At max gain the needle drops back a little on mine (almost looks what happens when you do bias adjustment). I don't think there's ever a situation when you would even begin to hit that threshold so it doesn't matter to me. Maybe a 22k would be a little more accurate, but no worries, i'm happy.

Or
To modify the A77 to bypass the input board jumper pin 1 to pin 4 , and pin 7 to pin 10 with a 5k resistor, This eliminates the input board.
You can also replace R809 on the playback amp board with a 10 K trimpot to adjust the hi freq equalization on playback.


Any info much apprecited!

Thanks,

Brett
Old 27th July 2020
  #2
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drezz's Avatar
Could someone with the knowledge please explain how to do this 'Abbey Rd' mod please?

In simple layman's terms.

There's nowhere online with a definitive explanation on how to do this..................

C'mon Slutz, be that guy (or gal)

Old 29th July 2020
  #3
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drezz's Avatar
No one?
Old 30th July 2020
  #4
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Revox A77 modifications

not a clue what the Abbey mod is and frankly don't care.

since the early 1970's, users have bypassed the "mic" stage on the record board and fed the input level control via a set of step-down transformers such as the Neve 31267 or equivalent.

output stage mods are not really necessary.
If one needs +4 dBu out, use a set of external line amps.
Old 9th August 2020
  #5
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Brett 123's Avatar
 

Quote:
Originally Posted by cathode View Post
not a clue what the Abbey mod is and frankly don't care.

since the early 1970's, users have bypassed the "mic" stage on the record board and fed the input level control via a set of step-down transformers such as the Neve 31267 or equivalent.

output stage mods are not really necessary.
If one needs +4 dBu out, use a set of external line amps.
Three year old post
Old 9th August 2020
  #6
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Quote:
Originally Posted by Brett 123 View Post
Three year old post
Fifty year old subject.
Old 9th August 2020
  #7
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Quote:
Originally Posted by Bushman View Post
Fifty year old subject.
Lifelong pursuit
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