Revox B77 Level pots: how to use 25K instead of 5K ?

[david winter]

Hi,

The two original input level pots drifted and the recording levels weren't matched. I therefore put two new originals from Studer, but they no longer have the same value. Moreover, they are double 50K pots instead of single 5K, causing the level to jump from none to high at only position 1.5 or 2 even after putting both in parallel to get a 25K equivalent. This also causes the sound to cut when the cursor goes out of the resistive portion and reaches the real ground. Can I bypass thos pots with 5K resistors ? Studer told me to put a 25K in parallel but I'm not sure. It doesn't cost much to try, but I wanted to know if anybody already experienced this and knows how to fix the trouble. Thanks !

 

[LDS]

Why don't you just get some 5K pots?

 

[cyrano]

If the pots are linear, you could easily change the value with a parallel resistor. But I guess these are probably log pots and that's not that easy. A parallel resistance will change the curve.

Have a look here:

http://www.ultimate-guitar.com/forum/showthread.php?t=1319500

But 5 Kohm pots are fairly common, so why don't you get these? Or are the Revox ones non standard mounting?

 

[david winter]

The problem is, those pots have a very specific mounting. I have hundreds of pots in stock, but Studer models are only available from them or on a used machine. And they are obviously expensive: 65 euros including VAT per pot.

 

[cyrano]

And no way to open them up and replace the carbon part with a new one from a standard pot?

That's what I do if possible...

 

[david winter]

No way to do that, I thought about it but the pot is maintained by small rivets and the size of the resistor is not standard.