Reverb Wet/Dry Mix Problem, Part 2: 2-Channel Passive Resistive Mixer w Different Zs

[tubeswell]

1) Should we take resistor 1 (1M) into account?

No. 2, 3, 4, 5, 8 and 9 determine the overall AC load for the recovery stage AFAICT. The 100k between the verb insertion points also plays a part, depending on which other resistor you are looking at. These same resistors also happen to form the overall AC load for the V1 stage.

2) Should resistor 6 (5K) matter also (as the top leg on a voltage divider involving V2P and resistor 5 (220K)?

No resistor 6 is not part of the AC load for the recovery stage or the V1 stage.

[dchang0]

Oh, I see. So the operative word is "load," here, meaning that we ignore the reverb driver and tank and only concern ourselves with what interfaces with the grid on V1B?

I'll modify the Thevenin diagram I drew, then.

[dchang0]

Okay, now I'm lost. I removed the resistors that don't matter (and the whole reverb driver stage and tank).

But this diagram doesn't make sense to me where the reverb recovery rejoins the signal path. The B+ points also pose a problem, because they seem to be floating out in space. I can easily see the first B+ at the left as being the Vin source while trying to solve for Vout at the output, but what happens with the second B+ (labeled (C)) on the reverb recovery stage? Do I treat that as another voltage source in parallel with the first?

As drawn, wouldn't the 100K mix resistor (R2) end up getting shorted out by the wiper on the 100KA reverb pot if the pot were turned all the way up?

See this diagram, please:

[tubeswell]

This is how I think the AC load is for the recovery stage with:

1) both the reverb level and vol pots maxed. I looked at this again and this revision makes more sense to me. The 'first two' resistors in the load are in parallel, and the 'last three' in the load are parallel legs of a voltage divider and now the output is where it ought to be. It should be pretty easy to work out what goes where from here with various settings of the pots.
2) the vol pot maxed and verb pot cut (totally dry). Note that with the reverb level pot cut, the 220k plate resistor for the recovery stage is no-longer part of the AC load for V1.
3) the verb pot maxed and the vol pot cut (totally wet)

(based on your last complete schematic).

Pretty sure these are right (finally). These change all my earlier answers. I blame the xmas season for my earlier indecisiveness. (Sheesh)

[tubeswell]

Ho-hum. its boxing day here already and I am bored. So I thought of trying to solve this because I need something too occupy my brain.

I have attempted to map the respective AC loads for either V1 or the recovery stage, when both the Reverb level pot and the Vol pot are at 50% resistance. And this is where it gets murky for me.

(But I'm pretty confident the AC loads, for either V1 or the recovery stage, are straightforward as I described in the AC load schematics in the post before this.)

The trouble is, when you start moving the reverb level knob and the vol knob, I am not absolutely certain what happens to the AC load in respect of the 'passive' triode, which is why I have shown those parts of the circuit in green on the attached schematic. Intuition tells me that the plate resistance of the 'passive' triode, would act to put a 'brake' on the AC that might otherwise be loaded through the respective plate resistor. In either case, there would be a signal at the grid of each triode in any event, which would (probably?) tend to override the 'passive' AC load effect from the other triode?

Hopefully somebody brainier than me (and someone fitting that criterion wouldn't be hard to find) can shed some light on this so we all can learn. Otherwise merry xmas to ya.