Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: knebiter on January 01, 2021, 01:28:48 pm

Title: Tone Stack distortion
Post by: knebiter on January 01, 2021, 01:28:48 pm

Hey all,
Just finished an amp that is the marriage of Merlin's High Gain Preamp and the AX84 20W Power amp. Seemed to start up OK after one bad 12AX7 out of the box. While poking around measuring voltages and stuff I took the scope to the preamp and am a bit confused as to what I saw. Attached are pix before and after the coupling cap immediately preceding the Treble/Bass tone stack. I guess I expected just attenuation based on frequency applied but at the onset of clipping the waveform really looks funky. Is it normal for tone controls to shape the signal this much? Integration of the square wave perhaps?  :dontknow:
Thanks for looking.
Joe

Title: Re: Tone Stack distortion
Post by: PRR on January 01, 2021, 02:17:32 pm

It's possible. Without detailed plans it is impossible to say if it shows a problem.

How does it sound?

Title: Re: Tone Stack distortion
Post by: knebiter on January 01, 2021, 02:39:48 pm

It sounds like it has a bit of hair or sizzle, guess I should have upped the skat to begin with.
Was more of a general question if that is normal for a tone stack to do.

Title: Re: Tone Stack distortion
Post by: thetragichero on January 01, 2021, 03:46:34 pm

that's about what i get on my tek 453 (with its square wave test signal) on amp tone stacks. i take it as the controls working
how it sounds is what matters to me  :dontknow:

Title: Re: Tone Stack distortion
Post by: shooter on January 01, 2021, 04:46:53 pm

Quote

I guess I expected just attenuation

measure on the "right side" of C22, I suspect the scope is messing with the TS, I quit looking "inside" TS's for that reason.

Title: Re: Tone Stack distortion
Post by: knebiter on January 01, 2021, 04:55:28 pm

OK, thanks for the sanity check guys.