Marshall Valvestate VS65R Static

[rudi246]

Hey guys. I have a Valvestate vs65r that makes a static noise while it is on. The static is independent of the volume or any other controls. In fact, it even does it when nothing is plugged into the amp. It stays the same volume and although I can still play through it, it's very annoying since I would like to record with it soon.

The static noise started after I resoldered some things since it was popping at times. I also replaced the 4 large capacitors and the transistor at T4 because I thought I burnt it up.

If anyone knows what could cause this I would really like to know so I can fix it.

[rudi246]

I checked my solder joints today. I even resoldered some things that I already resoldered and I am still having the issue. If anyone knows what could cause this please help me out!

[Mick Bailey]

Would you post a schematic, or link, so we're talking about the same version?

Has the original 'popping' fault cleared? the main thing is to establish whether the fault is in the preamp or power amp section.

[rudi246]

The popping was being caused by a ceramic resistor that was wiggling which I fixed by resoldering it. While I was doing that I decided to resolder other things to be on the safe side and I think that's where I screwed something up.

Here are the schematics
Preamp 1 of 2
http://www.drtube.com/schematics/mar...65-60-02-1.gif

Preamp 2 of 2. I replaced capacitors C6 and C7
http://www.drtube.com/schematics/mar...65-60-02-2.gif

Power amp. I replaced capacitors C11 and C12 as well as Transistor T4
http://www.drtube.com/schematics/mar...vs65-61-02.gif

[Mick Bailey]

With the amp turned off, removing CON1 will isolate the power amp. Power back on to see if the noise is still there. If so, there's a problem somewhere in the power amp.

Could even be noise on a supply rail - not impossible for one of the replaced caps to be faulty. Set your meter for AC and measure each rail to ground.

[rudi246]

Ok I will try that when I get home. I doubt it's a capacitor since I replaced them after the hiss started. I figured it would be a good idea to replace them given the age of the amp. I suppose it's not out of the question though.

[rudi246]

Well, pulled con1 and fired it up. No static. So that means it is somewhere in the preamp correct? Could it be caused by heating a component too long with the soldering iron? I resoldered the two white ceramic resistor, the tube socket, and the 2 tiny capacitors (c24 and c11) and two other tiny things next to them (zd2 and zd1) not sure what those are. I had also resoldered the input jack but that was before the static started happening.

By the way I pulled the tube and powered it up and it still had the static so it's not the tube.

[Mick Bailey]

Ok, you're looking at anything before CON1, So reconnect it for further testing.

You say that the controls don't make any difference. Double check to make sure and turn everything to zero. Still got the noise? Switch channels and see if it stays the same.

The components you mention are part of the DC supplies to the op amps and needs to be clean. Set your meter to AC mV and check the +/- 15v rails with respect to ground. One of the Zener diodes (ZD1 and ZD2) or caps replaced could have been overheated. If there's supply noise then even with the controls zeroed IC7 would be injecting signal noise if the supply is noisy.

[rudi246]

Everything at zero, no guitar plugged in, clean and od channels, with or without reverb tank plugged in. No difference whatsoever. Unfortunately, I don't have a meter. I know I need to get one with all of the electronic work I do. Those tiny capacitors and zener diodes shouldn't cost too much to replace so I will try replacing those. Maybe I'll get a meter while I'm at it. Thanks a lot for your help, by the way. I would have never thought to run it with that connector unplugged. I thought for sure it was the power section since the volume didn't change.

[Mick Bailey]

I wouldn't replace a component unless I suspected it to be faulty. My guess is one of the Zeners has gone noisy, but for me I'd want to see some noise on one of the 15v lines before replacing one or both. They are cheap parts, though and sometimes it's cheaper to replace a component than spending time testing. My caveat here is that the pads and tracks are easily lifted when removing components, so any unnecessary desoldering/soldering should be avoided. Or be very careful not to overheat the pad.

The volume won't be affected if there's noise on the op-amp supplies, because you have an op-amp after the last control with this particular amp. At the outside IC7 could be dying, but because the noise started after re-soldering the Zeners, that's kind of a smoking gun.

[rudi246]

Well I guess I'll take a trip down to the local electronic supply store and try and match these zener diodes. Also gonna look at some meters. Can't wait to start recording with this thing. It's a good sounding amp, just needs some TLC.

[Enzo]

They are just 15v zeners. 1N4744 or similar.

[rudi246]

Can I just get any 15v zener diode? They look like this...


The schematic is hard to read but it looks like BTY03C. It's 15 volts but I can't seem to find the wattage if that matters.

[g1]

15V 1watt, same as 1N4744 or equivalent.

[Mick Bailey]

Wattage only matters if you go lower - the device will probably overheat or short out if you do. Higher power rating is fine.