Hi all, I’ve been enjoying my first DIY amp quite a bit, bringing it out for several gigs, tweaking a few things here and there, and seeing a trajectory of steady improvement with the voicing.
However, there is an issue which I don’t know how to address. I’m hearing an extraneous noise accompanying certain notes, it’s a kind of crunchy rumble. Sometimes I think I’m hearing a distorted sub-tone an octave down.
It only happens on certain notes, and they seem to correlate to mechanical resonance which you can hear if you tap on the tubes or the chassis. The same pitches you hear when doing this, can sometimes get excited into a slow feedback type of noise. The same pitches, when you play them on the guitar, get this extra crunchy whoosh-y rumble added. It doesn’t seem to make a difference how I set the volume on my guitar vs on the amp.
These are behaviors I can notice while playing at home. They’re maybe a bit too subtle to be noticed on a gig scenario. I’m playing louder on gigs, but there’s also other musicians playing and it just gets buried. It would doubtless be a better if the amp didn’t do these things.
Attaching the schematic. V1 is a C3G and yes I’ve got it running at really high gain, but again the offending sound doesn’t seem to care how hard I’m driving the input.
V2 is 6SN7 and this one seems to be the most sensitive, microphonically. The resonance seems to be localized there. I’ve tried swapping in different 6SN7’s, they all act the same. Drivers are 6SL7 and outputs are KT66. Generally the amp sounds pretty good, I’m just pleased it works at all, let alone well enough to play out with.
I hope that someone recognizes the behavior which I’ve described as best I can. Thanks for your thoughts.
However, there is an issue which I don’t know how to address. I’m hearing an extraneous noise accompanying certain notes, it’s a kind of crunchy rumble. Sometimes I think I’m hearing a distorted sub-tone an octave down.
It only happens on certain notes, and they seem to correlate to mechanical resonance which you can hear if you tap on the tubes or the chassis. The same pitches you hear when doing this, can sometimes get excited into a slow feedback type of noise. The same pitches, when you play them on the guitar, get this extra crunchy whoosh-y rumble added. It doesn’t seem to make a difference how I set the volume on my guitar vs on the amp.
These are behaviors I can notice while playing at home. They’re maybe a bit too subtle to be noticed on a gig scenario. I’m playing louder on gigs, but there’s also other musicians playing and it just gets buried. It would doubtless be a better if the amp didn’t do these things.
Attaching the schematic. V1 is a C3G and yes I’ve got it running at really high gain, but again the offending sound doesn’t seem to care how hard I’m driving the input.
V2 is 6SN7 and this one seems to be the most sensitive, microphonically. The resonance seems to be localized there. I’ve tried swapping in different 6SN7’s, they all act the same. Drivers are 6SL7 and outputs are KT66. Generally the amp sounds pretty good, I’m just pleased it works at all, let alone well enough to play out with.
I hope that someone recognizes the behavior which I’ve described as best I can. Thanks for your thoughts.
Those inductors are small through-hole ones, looking like film caps but heavier. They’re within the box so I’d have to run the amp open to evaluate the question. Maybe I’ll try that later, thanks.
There’s not very much doubt that V2 contributes the resonance, if it gets to singing that E above middle C, you can damp it by touching V2. However, placing the amp farther away from the speaker doesn’t seem to lessen the crunchy rumble sounds.
Maybe that note is always humming at a level I can’t necessarily hear, and the rumbly sound I’m getting from playing certain notes is an intermodulation effect
There’s not very much doubt that V2 contributes the resonance, if it gets to singing that E above middle C, you can damp it by touching V2. However, placing the amp farther away from the speaker doesn’t seem to lessen the crunchy rumble sounds.
Maybe that note is always humming at a level I can’t necessarily hear, and the rumbly sound I’m getting from playing certain notes is an intermodulation effect