# Marshall valvestate Fizz



## deadear (Nov 24, 2011)

8080 valvestate has got a whole lot of fizz for some reason. Worked fine when I parked it a month ago and now all kinds of Fizz. Come on amp techs I replaced all the pots about a year ago and I am not going to give up on it.


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## nonreverb (Sep 19, 2006)

Solid state is not easy to diagnose in person let alone on a forum. There's a myriad of things could be going on. If I was to guess based on what I know and have seen, there MIGHT be a bad opamp. They tend to go from time to time....cap may be bad, the tube might be bad too....hope that helps a teeny bit. 
You might consider bringing it to a good tech with experience with this type amp.



deadear said:


> 8080 valvestate has got a whole lot of fizz for some reason. Worked fine when I parked it a month ago and now all kinds of Fizz. Come on amp techs I replaced all the pots about a year ago and I am not going to give up on it.


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## Wild Bill (May 3, 2006)

deadear said:


> 8080 valvestate has got a whole lot of fizz for some reason. Worked fine when I parked it a month ago and now all kinds of Fizz. Come on amp techs I replaced all the pots about a year ago and I am not going to give up on it.


This may or may not be the problem but it's the sort of thing that could and might also cause a lot of others.

When I get a ValveState in my shop the first thing I do is get the circuit board out. This is a pain in the asss but it allows me to touch up almost all of the circuit board solder connections with a bit of heat from my soldering iron. You see, Marshall ValveStates suffered from terrible quality problems with their board soldering. Often as the amp gets older some of these connections start to act up. They can go open, intermittent or develop a high resistance, all of which screw up the amp!

Once that is out of the way, it can be amazing how many problems just disappear! If not, at least one area of possible suspects has been eliminated, making tracing deeper problems more clear.

Wild Bill/Busen Amps


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## deadear (Nov 24, 2011)

Well I changed the three line IC chips on a whim. Lucky to get out of it and it still works. Soldering that board was a nightmare. Still noisy but I can live with it , it is good for practice. Thanks for the input guys.


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## dcole (Oct 8, 2008)

The relative simplicity of tube amps becomes apparent when you start troubleshooting solid-state stuff.


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## deadear (Nov 24, 2011)

Bump this up for the new amp tech's on here. Maybe they have some input.


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## jb welder (Sep 14, 2010)

Glad to see you haven't thrown in the towel, sorry I missed this thread first time around.
I take it the hiss is in both channels, and you have tried replacing the tube?
Is the hiss still there if you plug into the FX return jack?
Which exact IC's did you replace (designator names from schematic)? There are several more than 3 in the audio path.
The M5201 IC's I have sometimes found problematic. The 5201 chips are obsolete and can be rare/expensive. The new equivalent is NJM2120D or JRC2120D (or 2121). Also the newer versions may actually improve performance due to better specs.


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## deadear (Nov 24, 2011)

http://www.drtube.com/schematics/marshall/pc0689.pdf Yes I replaced #3,#5 and #7 on a suggestion from someone on You Tube. I got 5201 chips on E bay out of the Orient but like someone said they are probably counterfit. I have changed tube also. I have a Ohmn meter to work with ,and the jack is good. Yes both Channel fizz and the treble will changethe pitch. Guitar in the effect loop (return)works good with no noise when the blend is on full effect setting.


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## mhammer (Nov 30, 2007)

1) have the speakers been changed? Sometimes, an amp can be designed based on what is going to be heard with the existing speakers. If the stock speaker rolls off treble sufficiently that fizz isn't heard, then a change I speaker may reveal what is not a decline in performance, but rather a (weak) plan in the original design.

2) Is the fizz there _all the time_, clean or dirty, or simply an undesirable element of any overdriven sound? try lifting the ground end of each pair of LEDs on the board (the basis of the amp's clipping) and see if the fizz disappears.


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## deadear (Nov 24, 2011)

Original speaker. I have Marshall Celestion G12T . My friend has the same amp and his is dead quiet.http://www.youtube.com/watch?v=yAiG90MByOc. This is similar up to 1 minute mark.Peddles up front cut some of the hiss.

Lift the ground ? I will try this.


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## deadear (Nov 24, 2011)

I went back into it and really don't want to pull the board out to get at the solder side of the board. So all I could do is tug on the LEDs but that did not do anything. I figure this is a common problem with these amps and there would be a standard repair. What is the purpose of the LEDs in layman terms when they can not be viewed from the amp face. Are they for service purpose and if so what can be learned from them ?


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## jb welder (Sep 14, 2010)

The Led's are used in the clipping circuit for the OD channel. I think what Mark meant was IF the noise was just fizz in the OD channel, then disconnecting the Led's may help pinpoint the problem. 
But from your post, it sounds like the noise is in both clean and OD channels, and for either channel, the treble pot affects the noise?
If so, one IC common to both channels that is before the treble controls is IC1.
You could just replace it, or you could try this: in OD mode, ground (with a jumper) the junction of C43 and R11. Is the noise still present? A similar test for the clean channel would be to ground pin 2 of IC2. In either case if the noise is substantially reduced, IC1 is the likely cause of the noise and should be replaced.

You said you replaced IC's 3,5,and 7, the 5201's which you got from China. Normally, any extinct or rare chips that magically appear to be stockpiled or re-issued from China are highly suspect. But we'll ignore that for now.


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## Church-Audio (Sep 27, 2014)

You have got some good advice already... Take a chopstick turn the amp on and bash the board with it if you get crackling you need to pull the board and reflow all the joints with quality solder and a quality iron. If you don't want to do it maybe hire a tech. it's quite common for these Amps and fender solid state amps to have this issue. As others have said. I charge two hours labor to do this job. I use a microscope and a super bright light that shows any cracks or bad solder joints. I basically reflow all the joints because if one failed others will not be fare behind. I have seen some horrible hack jobs by techs using shitty soldering gear and to much heat.

- - - Updated - - -

If the chopstick does not find it and it's fuzzy on all modes it might need a new output device I have them in stock here. But I don't sell parts.


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## deadear (Nov 24, 2011)

Update. Thanks for all the input everyone. I went back at it and re soldered the pots and jack figuring would not hurt might have had a bad joint. I had been over the board a year ago so did not redo this. No better no worse but one thing I do not understand is why do peddles cut some of the hiss to a level not to bad for for playing at home at a fairly loud level. Not enough to get the cops at the door but loud enough to enrage your family members.


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## dtsaudio (Apr 15, 2009)

> Lift the ground ? I will try this.


Don't do this. mhammer said lift the ground end of the LED's.

The predominate noise source is going to be IC1 if it's an opamp. However it may be something else related to the opamps - the +/- 15V power supply.
opamps need to be decoupled from the power supply by small local capacitors (22ufd). The further away they are the more unstable they can become in high gain situations. I suspect you have one oscillating. The 15V regulators may also oscillate if you have a bad cap. 
The problem you're going to have is you need a scope to track it down. Otherwise you have to start replacing caps.
I suspect this because you said you parked it for a month. A borderline cap could have failed just sitting there drying out.


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## deadear (Nov 24, 2011)

I forgot to mention I did bang around the board with a plastic pen ( no chopstick in the house) trying to get some kind of crackle from a bad joint or hair line crack in the board tracks. I would take it to a local tech but at this point I don't think it would be worth pumping more money into it. Thanks guys.


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## jb welder (Sep 14, 2010)

Try replacing IC1. They're cheap and you don't have much to lose.


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## mhammer (Nov 30, 2007)

dtsaudio said:


> Don't do this. mhammer said lift the ground end of the LED's


What HE said. Thanks, Dan and JB. Good catch.


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## deadear (Nov 24, 2011)

Thanks everyone for all your input the amp is fixed and running like a new one.


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## jb welder (Sep 14, 2010)

I have confirmed that replacing IC1 did indeed solve the problem.


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