Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Wanabejimi on March 27, 2021, 08:00:10 am
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Problem: I have some unwanted trailing distortion trailing notes. It sounds like someone tearing paper. It occurs when the amp is turned up above “3”.
The amp is a Princeton Reverb circuit with a 5881 power section. Both the PT and OT are built for that. Other mods include a frondelli master volume from Rob Robinette’s website (replaces the two 220k resistors in the phase inverter circuit with dual gang 250k pots). Per the Hoffman layout, I have 1.5 k resistors on the screens of the power tubes. I have a 470k grid stopper on the phase inverter.
I do not have a scope, but I did use an audio probe on the amp. I was surprised by the amount of gain going into the PI….even at low volume.
Thanks!
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Problem: I have some unwanted trailing distortion trailing notes. It sounds like someone tearing paper. It occurs when the amp is turned up above “3”. ...
I think you mean, "As the note trails off, it sounds fizzy and not smooth."
If correct, turn the volume down. Or put away the microscope. :icon_biggrin: Most amps sound like that when the player artificially gets obsessive about micro-details in the amp's sound. I vividly remember listening to the same "flaws" in my 1967 Princeton Reverb 25 years ago.
If you step back, play a song in the context of a band-track, those little flaws are inaudible.
On another forum, a guy discovered the sound of "power supply ghosting" (really the distorted guitar sound creating intermodulation distortion with power supply ripple due to high power output) but only after connecting his amps to a load box to crank the snot out of them while recording quietly. Odd sound with the guitar on its own, but sounds "thicker" in the context of a band (where it can't be distinctly heard).
That guy also found out from several of us (including an amp manufacturer) the only way to get rid of his noise is huge amounts of power supply capacitance, until the amp sound stiff an uninviting at lower volume. Gotta pick the lesser of two evils.
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+1 on that HBP!!
I chased that once too... only to find out all my amps suffer from it. Think It's dirty wallpower.. I gave up making a fuss out of it and now I simply re-love all of them.
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Problem: I have some unwanted trailing distortion trailing notes. It sounds like someone tearing paper. It occurs when the amp is turned up above “3”.
The amp is a Princeton Reverb circuit with a ... frondelli master volume ...
That seems a poor choice, as low settings will tend to provide a partial bypass for the cathodyne's cathode.
Why add a master vol after a cathodyne anyway :w2: