Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: warioblast on April 25, 2020, 02:11:09 pm
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Well, I think what I have are ghost notes. My amp sounds slightly out of tune when I'm playing; particularly single notes on a clean setting. Both channels are affected. It's like having a soft vibrato effect engaged.
I did a quick search and it looks like a frequent problem on old Marshall amps. Most of the recommendations I have seen talk about replacing the filter caps. The 2 can caps 50+50uF are brand new. The 33+33uF is 3 years old, it hasn't seen a lot of usage, but I soldered & unsoldered it many times...
I have a 33+33uF cap in my reverb tank I could possibly take out...
Besides replacing the filter caps, what else should I try to modify.
I put a switch on the relay to make sure it was transparent.
I tried different preamp & power tubes.
:help:
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What exactly did you try to rule out the relay? Bypass it with an additional switch or remove it from the circuit?
Something I've run into is capacitive bleeding through the relay. At the point where you select between the 2 channels, you have an un-attenuated signal from the other channel right on the other side of the "open" relay switch and juuuust a little sound gets through (enough to be heard though!)
If you turn down the channel you are using and turn up the channel you aren't using, do yo uhear any evidence of sound bleeding through like I describe?
If you turn down the channel you are not using does this reduce or fix the problem?
If this is the cause, the way to fix it would be to kill the signal earlier in the unused channel-- not allow the full volume signal to get to the selector relay. You could do this with another selection at the input, or using a relay to short the signal to ground somewhere.
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I just put a switch between the relay and its power supply. As I have had problems before with a relay that was inducing hum when powered up.
So yes, technically I didnt rule out the relay.
I thought I was done with my relay problems... I struggled this week to work with a 6V heaters powered relay, that was giving me hum. I'm now using a 24V relay. I haven't really played with clean settings during that time, but I thought it was odd that I didnt notice this "ghosting" before, because it's noticeable.
92Volts, thanks for the lead ! :wink:
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Besides replacing the filter caps
I wouldn't replace 1st, I would grab some Ecaps and gator-clip in parallel with the existing and "see" if that changes or fixes the ghost notes.
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If you turn down the channel you are using and turn up the channel you aren't using, do yo uhear any evidence of sound bleeding through like I describe?
If you turn down the channel you are not using does this reduce or fix the problem?
I tried it but I didnt hear any changes. Just to be sure, I hard-wired the plexi channel, without the relay. The problem was still there.
Besides replacing the filter caps
I wouldn't replace 1st, I would grab some Ecaps and gator-clip in parallel with the existing and "see" if that changes or fixes the ghost notes.
The only E-cap I have around was a 220uF. Anyways, I put it across C10. I didn't hear any changes. And while I was doing those tests, moving stuff around ... at one point, I strummed my guitar with the volume on 0.
I was like WTF, could it be !?
I was using my strat. And with no amplification, the guitar sounded out of tune. I didnt have an amp for 2 years, so I didn't played electric guitar very much. And when I did I used my tele.
I plugged my tele, no signs of ghosts. Plugged my Les Paul, no signs of ghosts.
Plugged the strat back, ghosts city.
Like I said, last week I was working with this amp and a 6V relay, and the guitar I used for my tests was my go-to tele. It make sense now that I didn't notice ghosts because I was having none.
Thanks for your concern guys :thumbsup::hello:
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troubleshooting 101;
verify all test equipment works and is calibrated :icon_biggrin: