Excessive noise while jumping channels on JTM50

[jrewing]

Hi Guys,
So I have been playing my newly built JTM50 with channels bridged as I like the sound. I go in the normal channel, and then out of the normal channel into the bright channel. Really nice tone. Anyway, when both volumes, the treble, and presence are dimed, it gets very noisy and makes a weird feedback noise. Is this normal? The amp is otherwise very quiet even when very loud on either channel.

Thanks

[toner]

It seems normal to me unless there's a drastic increase in noise when jumping channels. It will naturally have more noise than using just one channel but it shouldn't be a huge difference. Make sure the patch cable you use to jump the inputs is high quality. You can also try different tubes in V1 to find one that may have less noise.

Cranking the presence can cause squealing or feedback. You can try moving or shortening the negative feedback wires to fix this, especially the one that connects to the presence pot.

[Reeltarded]

Hmm... Unplug the instrument input cable and see what is different about the sound with the same settings.

There is a simple condition i have considered where you might accidently have 2M reference to ground from the inputs. That would do something brashly unexpected. Brash.

that said, toner is right, and usually will be i think.

[jrewing]

Well, I can have both channels and the presence on 10, and the treble on 9, but when I go to 10 on the treble, it makes a bit of a weird noise. Any other suggestions or causes?

[Coot Boy]

If you are close to the speaker this will cause a very high pitched oscillation with the treble and presence dimed. Just in case that's what's happening with you.

[Reeltarded]

Or close to the head. Have you chopsticked your tonestack wiring? The wire to the treble cap and the wire to the PI entrance.

The presence too. Make sure everything drops straight down to the floor, and as short as it can be to still work on easily.

You have 250p/56k TS? I notice one of my amps with a 250p but cascaded makes a little itchy ick around 9.75 treble if I am standing less than 2 feet out, but only then.