marshall valvestate 8080 hiss raw/growl

meta11icafreak · 16th May 2009, 08:08 AM

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 · 16th May 2009, 03:08 PM

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 · 16th May 2009, 09:14 PM

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 · 18th May 2009, 03:54 AM

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 · 23rd February 2010, 05:23 PM

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

hhh · 30th March 2010, 01:25 PM

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 · 5th April 2010, 04:52 PM

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

wahab · 7th April 2010, 03:26 PM

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..

16th May 2009, 08:08 AM	#1
meta11icafreak diyAudio Member Join Date: May 2009	marshall valvestate 8080 hiss raw/growl 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

16th May 2009, 09:14 PM	#3
Nigel Goodwin diyAudio Member Join Date: Jul 2005 Location: North Derbyshire	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 __________________ Nigel Goodwin

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16th May 2009, 03:08 PM	#2
Enzo diyAudio Member Join Date: Sep 2004 Location: Lansing, Michigan	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.

18th May 2009, 03:54 AM	#4
meta11icafreak diyAudio Member Join Date: May 2009	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

23rd February 2010, 05:23 PM	#5
01redcobra diyAudio Member Join Date: Feb 2010	Wondered if you ever got to the source of this problem? Have a similar issue myself. Thanks

30th March 2010, 01:25 PM	#6
hhh diyAudio Member Join Date: Mar 2010	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

5th April 2010, 04:52 PM	#7
01redcobra diyAudio Member Join Date: Feb 2010	Enzo was right again, at least on the one I had in here. IC1 was the culprit!

7th April 2010, 03:26 PM	#8
wahab diyAudio Member Join Date: Nov 2009 Location: algeria/france	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..

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