Marshall Vs100 Clean Channel Breakup

[yanyan39]

Hi I have a Marshall vs100, It's been noisy and unreliable for a while. I've taken it apart and found a capacitor and input jack with multiple cold joints on the preamp board so have fixed those. The amp is now much improved, but there remains a problem on the clean channel, As the volume is increased there is nasty breakup which responds to louder playing. Both distortion chanels are fine so i don't think it's the power amp. I have the schematic and was wondering if this problem could be a faulty TL072 chip in the preamp, any ideas how best to proceed with sorting this. I'm pretty sure there are no more bad joints on the preamp board and I've used contact cleaner and all plugs, sockets, pots and jacks.

thanks for any help.

[ansil]

very well could be but if the same schematic i am looking at here is yours then i would look into the m5201 replacement. they are quite sheit and noisy. raven and kustom use them as well.

you can build a simple audio probe check out geofex.com

[yanyan39]

Thanks for that, will check it out.

[yanyan39]

Ansil, you were spot on, changed the chip and all is well. Thanks

[ansil]

Good deal.yeah those ics are terrible. Tge mil spec ones are beter. I made a little perf board design and a relay ti use regular dual opamps. Couple that with a computer header pin set and a dip socket and your good to go