Noise Issue with my Metro Build

[Krinkle]

I've had my Metro built since June and I love it except for one thing. Occasionally I get a crackling/whooshing noise, like white noise, quite a lot like static. If I put the amp on Standby and turn it back on again, most of the time it goes away. If I play long enough it usually becomes a big enough issue where I just stop playing because I get sick of flicking the Standby switch, which doesn't get rid of the noise all the time.

I initially thought that it was the filter caps so I put different ones in there. Then I thought it might be bad solder joints so I got a bigger tip and re-wetted all of the filter cap joints. I thought that I had a pretty clean build so it's pretty disappointing when the noise shows up. At the same time I still can't believe I have what I consider to be the equivalent of a '68 Marshall. Great job George.

I'm also wondering if it might be the EL34's. I bought the new Mullard's from George, and I'm not sure if anybody has had any problems with them.

Here are my gutshots. Any suggestions are appreciated. By the way, I am a tech so this is embarrasing. I do plan on bringing the scope home from work but I really find that most problems are not rocket science and don't require it.

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Thanks,

Darrin

[demonufo]

Now I have had exactly the same sounding problem with a modded Epi valve junior that I bought from a guy who fitted it with all sorts, and it turned out that the fault was with the standby switch.
It seemed that it was actually making contact with both sets of terminals at the same time, rather than switching between them.

It's worth a go anyways. Certainly a cheap fix if it is the case. Let us know whichever way.

[Krinkle]

My Standby switch is the big red 3PDT to allow the lower voltage "variac" effect so I don't want to just replace it. I'll have to check it out though, I have to get my head around what could cause a defective switch to cause the noise. How did you find the problem? I've been mostly using the lower voltage, a la VH, so I think what I'll do is use the regular high voltage position to see if it still happens. Thanks for the suggestion.

[neikeel]

A whooshing noise like heavy wind blowing a gale makes me think a preamp valve.

Crackling more like arcing, poor contact etc.

Have you tried switching it on in the dark to inspect for flashes etc?

[demonufo]

I should've stated that the standby switch on mine was a three position, light duty switch. Up was for triode, middle for standby and down for pentode.
I just replaced it on a hunch of the guy that built it.
Basically it kept intermittently giving off a real loud crackly white noise.
But yeah, you should look to the preamp tubes before looking at anything else really. Always suspect tubes first.

[Krinkle]

Sorry, I left out some information. The noise does not increase or decrease when I turn the volume knob up or down, so the preamp section is ruled out.

[demonufo]

That doesn't necessarily rule out a preamp tube though. I'd still try swapping.

[VelvetGeorge]

Agreed. Try tube swapping. And if you suspect output tubes, try running them in pairs to isolate the bad one.

Also worth trying:

move the amp to a different room, wall circuit

in the head case, out. For the shielding

reflow any suspect solder joints


George

[Krinkle]

I thought about it after I wrote it. I have to try everything, whether I think I've ruled it out or not.

I used to maintain/write and test software at GE as part of my tech job. I always found that when I had a bug that I couldn't find/fix, it was always a flaw in my logic, which I initally thought was fine.

I have more preamp tubes that I can swap in so I'll try that first.

I moved the amp to a different room to try to rule out crap coming out of the wall. Even though I'm in a different room, it's still in the back of my mind (the GE job was designing and manufacturing power company protection and monitoring equipment, the money we pay for the garbage that comes out of our outlets disgusts me). I'll probably grab the scope at work and monitor it if I don't have luck anywhere else.

I was going to try the output tubes in pairs, as well as putting the quad in another amp (I built a London Power Standard from TUT5 which has individual bias pots so it would be really easy to do).

Good stuff, thanks.

By the way, GREAT job on the amps George, every friend that comes over to hear it is floored and you WILL be hearing from all of my guitar playing buddies as soon as they gear up their cash.

Also, thanks for the interest and suggestions demonufo.

Darrin

[VelvetGeorge]

Many thanks! Glad you like it.

Let us know what you find.

george

[Krinkle]

I'm afraid to say it but as soon as I vowed to diligently look for and find out what was making the stupid noise, it stopped happening.

I had the chassis on my bench for about 2 months, playing it for a while, and stopping when the noise started. I grabbed a spare 12AX7 and swapped the first preamp tube. I played for about an hour and no noise. The next day I put the original back in and played for another hour, still no noise. Been playing or about a week, different volumes, etc, no noise.

Since then I have been EXTREMELY happy with the sound of this amp. I put it back in the head case and brought it back into the main room in my basement. On Sunday my Wife and kids went to a movie and I played for about 3 hours straight. Just my Strat with a SD '59 straight into the amp. I used my IPOD as a reference for the VH tone and I was as close to FW as I ever have been. Still some tweaks I want to try but I am seriously happy with this amp.

I bought a Presonus Inspire recording device and although my first attempts at recording with my Shure 57 sucked (I'm pretty sure it was my mic placement, straight into the center of the cone), I'm looking forward to making some clips to get some feedback.

Before I found Metroamp.com some people at other forums were pretty discouraging about getting the VH sound so I wasn't sure that I'd ever get to this point, or if anybody could. I've waited 30 years for this.

Thanks George!

[Mars Hall]

I had a similar experience with my jtm45 ri. At first I thought it was eating preamp tubes. I would replace v1, the noise would go away for a time. Then the same noise returned, replaced v1, went away for awhile.

I'm glad I saved the tubes. Turned out to be a cold solderjoint. On the amp, there is a yellow wire that goes to v1. It hits a lug with a jumper to a lug on the oppisite side. It turned out to be the little jumper wire was making intermitten contact. So whenever I relaced the tube it would make contact for awhile, then vibrate loose later.

Just to be sure check all those connections. When I replaced just replaced the tube, it might work fine for a week, or a month. Eventually it lost contact. If your problem creeps up again, I'd bet that's what it is.

[Krinkle]

Thanks. If the noise happens again I'll just pull the chassis out of the head and wet the socket joints.