SSS #002 REDRAW DRAFT

[ViperDoc]

No and yes. JFET's are not known for consistency, so the source resistor is selected to get the desired operating point. The 2N3823 model in the sim required a 5k9 to more or less center the operating point, and it is likely some kind of average representation of that part. Some might prefer a hotter bias for more distortion.

Can you shed light on how you distinguish the operating point from the FET bias voltage vs. the gain setting on the 10K pot? Thanks.

[martin manning]

The 10k pot is just a level control for the output. Have a look at the FET biasing doc in the files section for the effects of the op point.

[GAStan]

The feedback for the reverb driver on the layout does not match the schematic. On the schematic the 2m2 resistor is connected to the potentiometer side of the 10k grid resistor. The layout has it connected directly to the grid. Is this intentional?

[martin manning]

The original hand drawn schematic had the 10k between the 2M2 and the grid. Should be a lot more feedback with the 2M2 on the grid, like Ryan's layout.

[GAStan]

I understand the layout version would have more feedback. I guess my question is "why?" Is the reverb too strong with the schematic version? Perhaps I just haven't been able to find a previous discussion on this, is there one?

[martin manning]

None that I can find or recall. Maybe Ryan or Erwin can comment?

[erwin_ve]

This has been discussed and tried: https://ampgarage.com/forum/viewtopic.p ... 58#p427558

Erwin

[martin manning]

Thanks, Erwin. I had to read on from there to find the specific reference: https://ampgarage.com/forum/viewtopic.p ... 42#p427842
Ryan seemed to favor moving the FB (2M2) to the grid side of the 10k, as shown in the latest layout. Do others agree?

[GAStan]

Thanks Martin and Erwin.

My conclusion is that this is a great opportunity to experiment and find one's own preference. Maybe even change the 10k resistor to a potentiometer, connect the 2M2 FB to the wiper and make it adjustable.

[rccolgan]

Sorry, I have not been following this thread too much. As for the reverb, the quick history that I recall is that when the original V1 LNFB was incorrectly 1M, the reverb seemed very weak by comparison. I focused on wet/dry mix afterward with some success but something still felt off. When it was brought to my attention to change V1 LNFB to 100K, the mix seemed much better going back to the 100k as well.

The swap between the 10k & 2.2M was either a tip I received from someone (likely) or based on observation of other amps. The stability of the reverb was not great with 2m2 in series with the reverb send pot. I also realized that feedback made much more sense with 2m2 and the 10k in series with the pot. Likely for stability and some RF rejection. I felt like this was correct so I added it to the layout. I tried to keep the layout clean and close to the original amp.

[GAStan]

Thanks Ryan, for the history lesson and posting all of the work you have done

[martin manning]

The swap between the 10k & 2.2M was either a tip I received from someone (likely) or based on observation of other amps. The stability of the reverb was not great with 2m2 in series with the reverb send pot. I also realized that feedback made much more sense with 2m2 and the 10k in series with the pot. Likely for stability and some RF rejection. I felt like this was correct so I added it to the layout. I tried to keep the layout clean and close to the original amp.

This is not clear at all (sorry). It comes down to where the FB is injected, before or after the reverb driver tube's 10k grid stopper. I gather after (grid stopper is not in the loop) is preferred.

[rccolgan]

The swap between the 10k & 2.2M was either a tip I received from someone (likely) or based on observation of other amps. The stability of the reverb was not great with 2m2 in series with the reverb send pot. I also realized that feedback made much more sense with 2m2 and the 10k in series with the pot. Likely for stability and some RF rejection. I felt like this was correct so I added it to the layout. I tried to keep the layout clean and close to the original amp.

This is not clear at all (sorry). It comes down to where the FB is injected, before or after the reverb driver tube's 10k grid stopper. I gather after (grid stopper is not in the loop) is preferred.

so making the 2m2/10k swapped per the schematic is what you're suggesting here? Definitely interesting if so! I always treated the schematic as a very close-to truth with a few exceptions.

[martin manning]

Hi Ryan, it's this. As drawn vs. the red. Your layout shows the red.

[GAStan]

The swap between the 10k & 2.2M was either a tip I received from someone (likely) or based on observation of other amps. The stability of the reverb was not great with 2m2 in series with the reverb send pot. I also realized that feedback made much more sense with 2m2 and the 10k in series with the pot. Likely for stability and some RF rejection. I felt like this was correct so I added it to the layout. I tried to keep the layout clean and close to the original amp.

This is not clear at all (sorry). It comes down to where the FB is injected, before or after the reverb driver tube's 10k grid stopper. I gather after (grid stopper is not in the loop) is preferred.

so making the 2m2/10k swapped per the schematic is what you're suggesting here? Definitely interesting if so! I always treated the schematic as a very close-to truth with a few exceptions.

Maybe Martin didn't catch your references?

I understood

2m2 in series with the reverb send pot

to mean FB connected between pot and 10k and

2m2 and the 10k in series with the pot

to mean FB connected between 10k and grid.

Did I get it correct?