Slight channel bleed

[torcamaniac]

Hi,
my modded JTM60 has some slight channel bleed from Boost channel to clean. Not too bad but noticable. Very faint and buzzlike.
I found out that if I turn down the gain knob in boost channel, there is no bleed through to clean channel anymore. I did replace the relays after doing other mods, but don't think they are the problem and I suspect a capacitor somewhere.
Also, I replaced the four elkos C102, C106, C109 and C110 (22uF 450V) as a part of recap job after the mods. Used the same values as original but from Panasonic. Also replaced the C7 on VR6 with same value capacitor 100pF but from Silver Mica.

Here is a schematic with the mods:



And the original schematics:

[Enzo]

I am not sure why a cap would be at fault, they are shared by all channel circuits. You have crosstalk. That is why a lot of modern amps ground the signal path in the high gain channel when it I snot selected.

[torcamaniac]

Could it be that because of removal of C120 (it was connected from input grid of V2 to ground) I removed the input signal from going to ground??? This was one of the mods. Just removing C120 and putting it in the place of R104. If not could you give me some suggestions how to ground the signal path of the boost channel?
Anyway, before the mods there was no crosstalk. Relays are also soldered the same as the original ones were.
The only breaks in the circuit were the removal of C120 and C105 (to get the clipping diodes out of circuit). All other mods were only value replacements of some resistors, caps and a voltage divider right after V2 stage going to Volume Pot VR6 (here I used a 100K after C121 connecting with 22K to ground. From the point between the resistors to VR6).

Thanks Enzo

[Enzo]

A 470p cap to ground is just a rolloff, snipping some highs off the signal. The signal doesn't "go to ground" really. It is a non-adjustable tone control, how about that?

I don;t know what you did to the amp, unless you increased the gain of the dirt channel so it has a hotter signal.

As to grounding the signal path, you can do just that. Use a free relay contact or add a relay or a JFET and ground off the signal path in the dirt channel whenver clean channel is selected.

[torcamaniac]

A 470p cap to ground is just a rolloff, snipping some highs off the signal. The signal doesn't "go to ground" really. It is a non-adjustable tone control, how about that?

I don;t know what you did to the amp, unless you increased the gain of the dirt channel so it has a hotter signal.

As to grounding the signal path, you can do just that. Use a free relay contact or add a relay or a JFET and ground off the signal path in the dirt channel whenver clean channel is selected.

Cool thanks Enzo.

Yeah, because I removed the clipping diodes from V2, I also increased the gain a lot eventhough I balanced the signal level somewhat by installing voltage dividers right after this stage.
I guess I'll have to check about grounding from the relay.
There are two DPDT relays. RL2 is where I should look at I guess?