6v6 JTM build noise/hair on notes

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bhyatt1
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Re: 6v6 JTM build noise/hair on notes

Post by bhyatt1 » Sun Aug 02, 2020 2:36 pm

So, I just got back on to let you guys know... Today I had an idea. I plugged in a 5u4gb that I had just for shits and giggles. Noise is gone. I have tried swapping power and preamp tubes and have basically gutted this amp multiple times just to try and fix the noise and never thought of noise in the rectifier tube. I am so relieved and so amazed at my stupidity because sometimes the solution is one of the simplest. It just never crossed my mind. Now to rebias witht he 5u4 and I should be good. :shock: :what: :stars:

bhyatt1
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Re: 6v6 JTM build noise/hair on notes

Post by bhyatt1 » Sun Aug 02, 2020 3:48 pm

Alternate OT hooked up and no difference. I swapped the rectifier tube from a 5y3gt to a 5u4gb just because it was something I was playing with anyways... Rebiased and ALMOST thought that the rectifier tube fixed it, it seems less noticeable but I believe it was only because I seem to be getting a little more drive (I thought higher plate voltage did the opposite :what: ) but either way I've about given up. With the amp at the driven tones I was wanting (Eric Clapton/Hendrix--y tones) it isn't as noticable. When i want clean marshall I have a 50w 1987 clone for that stuff. Kinda like just dealing with the ghosting and what not on old jtm45s. I've heard those things over the years on recordings and never had a problem with it... Why start worrying now?
That said, I am still open to suggestions... :rock:

danman
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Re: 6v6 JTM build noise/hair on notes

Post by danman » Mon Aug 03, 2020 6:13 pm

Sorry that you haven't been able to track down the issue yet. Have you tried posting this problem over at the Marshall Forum? Many of the members here are active over there and they may have some fresh ideas to try.

bhyatt1
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Re: 6v6 JTM build noise/hair on notes

Post by bhyatt1 » Tue Aug 04, 2020 5:32 pm

The problem with a scope is that I do not have an isolation transformer... Which I've been told was an issue.

bhyatt1
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Re: 6v6 JTM build noise/hair on notes

Post by bhyatt1 » Tue Aug 04, 2020 7:17 pm

Oh and before I was warned about that, I did find that the only place I noticed any thing strange in the signal was at the phase inverter... I will recheck today when I get home

bhyatt1
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Re: 6v6 JTM build noise/hair on notes

Post by bhyatt1 » Sun Aug 30, 2020 12:31 pm

UPDATE... When presence pot is bypassed completely my problem goes away. Checked solder joints... Maybe a bad pot?

danman
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Re: 6v6 JTM build noise/hair on notes

Post by danman » Sun Aug 30, 2020 6:38 pm

Possibly. I think that I mentioned early in the thread about how sensitive the wire leading to the presence pot can be. I believe that you have already tried moving the wire around a bit but it couldn't hurt to look at it again. It can definitely add noise into the circuit if it couples with some of the sensitive wires leading to the tonestack. Good luck!

bhyatt1
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Re: 6v6 JTM build noise/hair on notes

Post by bhyatt1 » Tue Sep 01, 2020 3:48 pm

I attempted using shielded wire on the presence pot, but there was no change in the issues.

danman
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Re: 6v6 JTM build noise/hair on notes

Post by danman » Tue Sep 01, 2020 6:09 pm

It may be the higher frequencies from the presence circuit that is causing your noise issue. You can try bypassing the nfb resistor on the board with a small cap. Try 100pf across the resistor. You can go slightly lower if the amp gets a bit dark or higher if the noise is still present.

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