LarMar master volume squeal ab165

[jb83]

I just installed a LarMar in my ab165.  Everything is great on the bass channel.  I can crank the volume to 10 with no issues.  On the normal channel, I get a squeal when the volume hits about 7 on the dial.  Any ideas?

[SEL49]

Dis it squeal ***BEFORE*** the mod? If not, then you miswired the pot. Just swap the two wiper wires. Any better?

[jb83]

Dis it squeal ***BEFORE*** the mod? If not, then you miswired the pot. Just swap the two wiper wires. Any better?

Didn’t squeal prior to the mod.  So can I just swap the red and yellow wires on the board?

[SEL49]

yes

[jb83]

yes

Well, I swapped those two, and the amp sounded like it was melting down (loss of negative bias?).  Possibly a lead dress issue that’s only not affecting the bass channel since the master volume wiring is further away from that preamp section of the board?

[SEL49]

Well, I swapped those two, and the amp sounded like it was melting down (loss of negative bias?).

Bias should have been unaffected. More likely, the NFB phase was correct to begin with and when you swapped the wires the NFB became positive phase and caused oscillations. So, put the wires back as they were originally.

Possibly a lead dress issue that’s only not affecting the bass channel since the master volume wiring is further away from that preamp section of the board?

Shielded wire will probably help. I suggest shielded twisted pair (STP) cable.