Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: mbele on January 06, 2022, 11:11:49 am
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I've been struggling with this problem for a long time now... I have searched online for terms like "noise in the note sustain" and "noise riding note tail" with no luck, but I actually have no good way to describe the issue in concise way.
I started noticing it with the tube amps that I have built, and attributed it to bad wiring, old/scavenged parts, not enough signal filtering... (bad build). In the last few builds I specifically tried to address that aspect of the sound but couldn't figure it out. Then I heard it (in a less degree) with brand name solid state amp (pushed), switched arround guitars and cabs, and now I've trained myself to be annoyed by the hint of it :D
I have recorded an exaggerated example:
https://soundcloud.com/mihael-bele/se-cb2x12gb-2555a/s-VjJYkWiZH59?si=7feabd28032140bea07b2fca337a9aa5&utm_source=clipboard&utm_medium=text&utm_campaign=social_sharing (https://soundcloud.com/mihael-bele/se-cb2x12gb-2555a/s-VjJYkWiZH59?si=7feabd28032140bea07b2fca337a9aa5&utm_source=clipboard&utm_medium=text&utm_campaign=social_sharing)
Sample starts with guitar volume fully open and the tone rolled off, then the guitar volume is lowered so that artefacts disappear, then the volume is raised to a point where the artefacts appear, and finaly guitar is fully open (I switched pickups to check how the harmonics/low end affect the sound).
After the initial note attack, volume decays in wave-like fashion, crossing above and below the distortion treshold (resonance which is probably normal for that combination of notes), but the distortion character sounds to me like tonaly unrelated oscilation/motorboating (noise) riding a top of a note (like a torn speaker, or wiggling a bad or too long guitar cable).
So (finally :) my question is if this kind of distortion is something you've encountered in your tube amp building learning curve and solved (how?), or I should just not play the riffs that reveal that (with gain/eq set up like that).
Thanks!
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If you post the schematic of an amp so ppl can help you figure out if there is a problem.
Many tube amps does distortion, and its very common to lower the guitar volume to "clean" the tone, that is what sounds like in the audio you posted.
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uki, thanks for your reply.
I meant in a general way, applicable to shaping overdriven sounds in any tube amp, and if it sounds like an error symptomatic for a beginner's build.
I do not have the amp schematic (it's double cascode preamp into single ended amp), but the issue is applicable to other amps I've built, eg. 5F6-A: stock schematic + post PI master volume -> JJ6V6S, all voltages correct - just tested it again (my ears still ring :) and realised I may have another clue: turning the power off during the note decay, sound slowly dies while getting more distorted (until filter caps are discharged), which is normal, but in character similar to what I'm trying to describe.
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It’s just regular clipping I think. Maybe tweak signal level si that several cascading stages are pushed but not into hard clipping. Try removing cathode bypass of such stages.
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Thank you pdf64.