So a friend recently brought over his Traynor YBA-2 (EL84 - volume, bass, treble knobs) and we both agreed it sounded way worse than my YBA-2 (cathode biased 6V6 - volume, tone). There was a crappy buzzing type octave distortion that fizzled out as the notes died down. (The amps are so different that it is very confusing that they even share the same name, but I wasn't expecting his to sound straight-up "Bad" when overdriven.
Here's the schematic:
I decided to throw it on my bench and probe around to try and figure out why this thing sounds so bad. Immediately I noticed that the distortion is very asymmetrical before it even hits the tone-stack and volume knob. Unlike my 6L6 YBA-2, this one has two gain stages back to back before the tone-stack and volume control.
Here are some scope shots (VOLUME @ 4, BASS+TREBLE @ 5:
1: Signal Generator input. 1Vpp sine.
2. Output from first gain stage after C1. 12Vpp nice sine.
3. Output from second gain stage after C3. 90Vpp hot mess.
4. Speaker output.
1. Signal before PI before C7. 2Vpp hot mess.
2+3. Outputs of Phase Inverter. 40Vpp
4. Speaker output.
So you can see after the second gain stage, the distortion is very asymmetric and then only gets worse after the output section as the crossover distortion is added. This certainly explains the octave sounding buzzy distortion that faded with the notes decay.. This is definitely not how my YBA-2 looks in the scope. I desoldered and tested the resistance of everything associated with the first two gain stages and they all match the schematic, no DC passing through the coupling capacitors.
- Is this the expected behavior of this schematic?
Here's the schematic:
I decided to throw it on my bench and probe around to try and figure out why this thing sounds so bad. Immediately I noticed that the distortion is very asymmetrical before it even hits the tone-stack and volume knob. Unlike my 6L6 YBA-2, this one has two gain stages back to back before the tone-stack and volume control.
Here are some scope shots (VOLUME @ 4, BASS+TREBLE @ 5:
1: Signal Generator input. 1Vpp sine.
2. Output from first gain stage after C1. 12Vpp nice sine.
3. Output from second gain stage after C3. 90Vpp hot mess.
4. Speaker output.
1. Signal before PI before C7. 2Vpp hot mess.
2+3. Outputs of Phase Inverter. 40Vpp
4. Speaker output.
So you can see after the second gain stage, the distortion is very asymmetric and then only gets worse after the output section as the crossover distortion is added. This certainly explains the octave sounding buzzy distortion that faded with the notes decay.. This is definitely not how my YBA-2 looks in the scope. I desoldered and tested the resistance of everything associated with the first two gain stages and they all match the schematic, no DC passing through the coupling capacitors.
- Is this the expected behavior of this schematic?
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