steppenwolf
Well-known member
Hi everybody!
I know this is not really a guitar amp forum, but I was still hoping that somebody has a hint for me!
I have a problem with my Marshall JTM45 amplifier, and I need help cause I simply don't find the solution.
Let me describe it first:
The JTM45 ist handwired, no PCB, new tubes, BIAS ok all voltages seem to be all right.
The Problem:
The Amp doesn't have headroom, even with lower power singlecoils, it distorts to early compared to other JTM45, moreover the distortion is somehow fuzzy, scratchy for lack of better words...
The components are all top notch, SOZO caps, Mercruy Magnetics Iron, swapped tubes, nothing changed...
First, I tried to put a 1kHz sine through it and watch it on the scope.
I noticed, that there is a tiny 'notch' on the edges of the sine that rises up or down depending on the setting of the volumeknob...
This phenomena is there already after the phase inverter, so it is no cross over distortion.
When I go up in frequency(I stopped @ around 4kHz), this notch is more and more apparent. When I turn the presence knob all the way up to ten, the notch nearly disappears...
has anybody an idea what it could be, I searched for days but I simply don't find the problem...
Thank you!
Have a nice day,
Stefan
I know this is not really a guitar amp forum, but I was still hoping that somebody has a hint for me!
I have a problem with my Marshall JTM45 amplifier, and I need help cause I simply don't find the solution.
Let me describe it first:
The JTM45 ist handwired, no PCB, new tubes, BIAS ok all voltages seem to be all right.
The Problem:
The Amp doesn't have headroom, even with lower power singlecoils, it distorts to early compared to other JTM45, moreover the distortion is somehow fuzzy, scratchy for lack of better words...
The components are all top notch, SOZO caps, Mercruy Magnetics Iron, swapped tubes, nothing changed...
First, I tried to put a 1kHz sine through it and watch it on the scope.
I noticed, that there is a tiny 'notch' on the edges of the sine that rises up or down depending on the setting of the volumeknob...
This phenomena is there already after the phase inverter, so it is no cross over distortion.
When I go up in frequency(I stopped @ around 4kHz), this notch is more and more apparent. When I turn the presence knob all the way up to ten, the notch nearly disappears...
has anybody an idea what it could be, I searched for days but I simply don't find the problem...
Thank you!
Have a nice day,
Stefan