Help: Volume Dropout in Mesa Quad Pre

[zeuch]

Hi Guys,
Has anyone ever suffered from an extremely low volume on clean channel 1 of the quad pre?
I used to turn the master knob to 3-4 but yesterday I forgot to turn it off then this morning I could barely hear the sound by turning master knob to 10! All the other 3 channels work normally. I tried to exchange tubes from different slots but it didn't help. What could the problem be? Any idea or suggestion will be appreciated! Thanks!

 

[mcr23]

No but my Ch2 has lower volume on higher settings than Ch1. I even tried replacing the 12AX7s and it didn't really help.

 

[straitouttahell]

No but my Ch2 has lower volume on higher settings than Ch1. I even tried replacing the 12AX7s and it didn't really help.

I had the same problem when I had a Quad. I solved it bypassing a resistor which is there only for noise suppression purposes, but I really can't remember which resistor it was

 

[daveyboogie]

It's my guess you've got an LDR issue, man. I doubt it could be tubes as it would affect Lead-1 channel also. Look at the signal path:

http://www.tubefreak.com/s-main.gif

If it's only affecting Rhythm-1 channel then looks to me like LDR-2 (or 3). It could also be the Lead-1 isolation: LDR-10. Change them all. I did!

New LDRs from RS or T.A.D.

You'll have great fun removing the PCB from your Quad.

Enjoy!

 

[zeuch]

Thx for the reply!
As you said, it turns out to be the LDR problem. Now I'm trying to replace them myself. Not an easy job for me