marshall valvestate 8080 hiss raw/growl

[meta11icafreak]

i have a marshall valvestate 8080 that just started growling when i turn on boost channel sounds like heavy rain.

it is only present when lead is pluged in (guitar or no guitar)
intensifys with more distortion
equlizer changes the sound from wind to heavy rain
i can still hear guitar but growl is 40% louder
volume controls growls volume
i can use clean channel with stompboxes etc.

what do i do. how do i test

 

[Enzo]

Probably an op amp went noisy.

The input jack has an extra contact used to mute the circuit when the jack is empty. That is why you can't hear it when nothing is plugged in.

You have discovered that certain controls affect the sound of this noise. That means those controls are after the source of the noise in the circuit.

 

[Nigel Goodwin]

There's really not a great deal that could cause it - for a start try removing the valve and see if it still growls without that. I'm assuming it won't, as it's probably either the valve duff (if you have one in something else, try it in and see if it cures it), or one of the three 'opamps' before it. One of those is a double, and more than an opamp (IC3) - but there's a second one (IC5) which you could try swapping over and see if the fault changes.

For the circuit see:

http://www.drtube.com/schematics/marshall/pc0689.pdf

 

[meta11icafreak]

its just started doing it on the clean channel. but obviously not as loud and distorted. when i unplug lead it sort of pulses but out of time for a few seconds. doesn't do it every time

also does it with distortion pedal

 

[01redcobra]

Wondered if you ever got to the source of this problem? Have a similar issue myself. Thanks

 

[hhh]

1. check the send and return plugs from the FXloop, sometimes the switched contacts in these jack give bad contact
2. check the solder connections on the big power resistors next to the tube and also check the power resistors in the power supply section (somwhere behind the on/off button

 

[01redcobra]

Enzo was right again, at least on the one I had in here. IC1 was the culprit!

 

[wahab]

A friend of mine has one with the same problem..
It was a power resistor that is so hot that it made
the soldering having a random electric contacting..

 

[Beauxdean]

Dog peed...

I have the same issue. My Valvestate 8080 was found in a trailer remodel and had been dog peed all over it and around it....some people. To treat this jewel like that.... Anyway, all the pots were sealed tight. I got all the pots and put them in. They work now and I've finally gotten the nerve to put power to it and test it. It works without blowing the fuse. Yah! Both channels have a small ground noise or something when powered up but not bad. The Normal channel works and sounds great but the boost channel is very cruddy sounding and acts like it's got a noise gate on it turned up WAY too high. I got a new 12AX7/ECC83S tube but that just does the same and makes it rougher. I changed out the R112 and R113 resistors even though they test ok because they get real hot and I wanted new ones with a bump more wattage. No change. I read here (where someone has an almost identical problem) that it could be IC1. In fact, 01redcobra that had this issue changed IC1 and that solved the issue. After reading this, I fired her up and touched the top of all the Ic chips with my finger. IC1 made the ground noise get louder when I touched it but none of the others did. You think that's it? I'm tired of this amp on my counter top! Any help would be appreciated!