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After months of attempting to design an amp with a nice tweedy overdrive, touch sensitivity, and Fender style reverb I've hit a wall where it seems that getting enough signal to overdrive tubes only causes a buzzy distortion tone that sounds terrible. Unfortunately I don't have a program capable of drawing schematics to show you my design, but I can at least explain the topology to you so you may have an idea of what I'm doing wrong, or if this is some other problem I haven't found yet.
v1a- Preamp (center biased)
v1b- Cathode Follower
into typical tweed Volume and Tone control
v2a- Gain stage (center biased)
v2b- Cathode follower
into Fender 6G type tone stack w/second Volume control
After this the signal splits with the typical blackface 3.3M carrying the dry signal and the 500pf cap carrying some signal to the reverb driver which is a paralleled 12at7 at high voltage off of the screen supply rail, and the typical blackface recovery design into a long-tailed pair phase inverter.
This was my first design, and at first I thought that maybe I had poorly designed the gain stage in front of the tone stack because it was only caused at high settings of the first volume control while the second volume control acted much more stable, so to limit the distortion I removed the volume and tone control and put the tone stack in it's place between the preamp and following gain stage. That lessened some of the fuzzier distortion that was previously there, but the buzzy sudden distortion was still left. So, thinking that perhaps somehow I was overdriving reverb driver I removed the cathode follower to leave the output impedance higher which didn't help, and I placed a 390k grid stopper on the reverb driver.
I have noticed now that the buzzy distortion is not really noticeable with the volume knob up high if the reverb knob is off, though it still seems that you can faintly hear it in the extreme upper registers of notes (possibly from the extremely high notes being passed to the next stage without much hindrance thanks to the 10pf cap and 3.3M resistor?) This now leads me to believe that distortion is coming from the second reverb recovery stage where the signals are mixed. However, I've been chasing this problem for awhile now, and am getting tired of attempting to come up with remedies...it especially seems odd that previously the first volume control caused this buzziness even at low settings of the second volume control...if I can make a schematic, and sound clip to demonstrate my problem I will, but for now I just would like to hear ideas from some more knowledgable people about guitar amps than myself to see if I'm doing something wrong (which I know may be impossible to tell until I get a schematic up), or if this design in general was a bad idea.
v1a- Preamp (center biased)
v1b- Cathode Follower
into typical tweed Volume and Tone control
v2a- Gain stage (center biased)
v2b- Cathode follower
into Fender 6G type tone stack w/second Volume control
After this the signal splits with the typical blackface 3.3M carrying the dry signal and the 500pf cap carrying some signal to the reverb driver which is a paralleled 12at7 at high voltage off of the screen supply rail, and the typical blackface recovery design into a long-tailed pair phase inverter.
This was my first design, and at first I thought that maybe I had poorly designed the gain stage in front of the tone stack because it was only caused at high settings of the first volume control while the second volume control acted much more stable, so to limit the distortion I removed the volume and tone control and put the tone stack in it's place between the preamp and following gain stage. That lessened some of the fuzzier distortion that was previously there, but the buzzy sudden distortion was still left. So, thinking that perhaps somehow I was overdriving reverb driver I removed the cathode follower to leave the output impedance higher which didn't help, and I placed a 390k grid stopper on the reverb driver.
I have noticed now that the buzzy distortion is not really noticeable with the volume knob up high if the reverb knob is off, though it still seems that you can faintly hear it in the extreme upper registers of notes (possibly from the extremely high notes being passed to the next stage without much hindrance thanks to the 10pf cap and 3.3M resistor?) This now leads me to believe that distortion is coming from the second reverb recovery stage where the signals are mixed. However, I've been chasing this problem for awhile now, and am getting tired of attempting to come up with remedies...it especially seems odd that previously the first volume control caused this buzziness even at low settings of the second volume control...if I can make a schematic, and sound clip to demonstrate my problem I will, but for now I just would like to hear ideas from some more knowledgable people about guitar amps than myself to see if I'm doing something wrong (which I know may be impossible to tell until I get a schematic up), or if this design in general was a bad idea.
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