Interesting Dual Triode Compressor Circuit.

[SoulFetish]

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Okay! Big night for me. I might actually just suck a little bit less at LTspice (in that I was able to figure out how the directories/.inc/.lib/.asy/etc parts of the program work for the most part, and was able to actually open a working file without getting any f@#%ing error messages or missing parts.)

Now I just need to run some actual simulations and see what kind of analysis it can do. But, while I get into all that, I attached what I think might be a working schematic for you spice veterans. I used an existing file to create this one from an 18W asc file I downloaded once upon a time, but the tube library was changed to the one nickb uploaded in bea's 6L6PP 20W amp thread.

If someone wants to see if this is useful at all, here is a zip:
Dual_Triode_Compressor.zip
How'd I do?

[J M Fahey]

Yes, the second one is a voltage controlled resistor.
FETs are way better at that and bipolars work, only signal level must be kept low, 50 or 100mV TOPS.

Itīs the eons old Automatic Volume Control used in 60īs and 70īs cassette recorders,in that case rectifying speaker out signal.

Essentially same as the tube one, hgere first transistor attenuates, second amplifies and uses discrete diodes for signal rectification ; the tube one has a diode "hidden in plain sight", itīs the Grid-Cathode diode.

Notice the long time constant (100uF+10k) to minimize "thumping".

[SoulFetish]

the tube one has a diode "hidden in plain sight", itīs the Grid-Cathode diode.

Those sneaky little bastards!

[nickb]

-
Okay! Big night for me. I might actually just suck a little bit less at LTspice (in that I was able to figure out how the directories/.inc/.lib/.asy/etc parts of the program work for the most part, and was able to actually open a working file without getting any f@#%ing error messages or missing parts.)

Now I just need to run some actual simulations and see what kind of analysis it can do. But, while I get into all that, I attached what I think might be a working schematic for you spice veterans. I used an existing file to create this one from an 18W asc file I downloaded once upon a time, but the tube library was changed to the one nickb uploaded in bea's 6L6PP 20W amp thread.

If someone wants to see if this is useful at all, here is a zip:
[ATTACH]54216[/ATTACH]
How'd I do?

You're missing a ground connection. The model for the pot is missing.

I tried it out but I could not get it to work as drawn. I then first did a plot of Rp vs Vg1 for a 6SN7 with a constant 120v on it. After playing around with the Vg1 range I learned that 0 to -10V seem to be the useful range.



The other thing that seemed odd to me about the original design was the choice of positive grid voltage for the second triode. With positive grid volts you would have grid current and that stops the rectifier stage from working. Also, I had just learned above that the Rp change about 0V was not useful e.g. 0 to 1V gave a 7.2K to 6.7K Rp range. So I added a fixed bias to the second triode to make it work at all. I got around 1dB change for a about a 10dB change in input. Not exactly linear, or even monotonic. Note I reduced the output cap to eliminate DC drift from the output.



Still, I'd be interested to hear how it feels and sounds both before an O/D stage and just plain vanilla (no O/D). Needs a big drive signal.


PS: I should add that the spice models for grid current are not reliable. That could really throw things off.

[SoulFetish]

You're missing a ground connection.

That's no good.

The model for the pot is missing.

Figures, that's the thing that was tripping me up to begin with.
So, I was able to set it up in both Wine and the macOS version so the appropriate .lib files and schematic symbols were in the right directories. I downloaded a couple of .lib files with assorted potentiometer models to keep me covered.
How do I include the model needed?

[nickb]

You can just include the model right on the schematic:

Dual_Triode_Compressor - 2.zip

[SoulFetish]

You can just include the model right on the schematic:

[ATTACH]54225[/ATTACH]

okay, I saw what I did wrong (I think). after adding a global ground, I was getting an error that said Could not open library file "pote.lib" when I tried to use the "run" function, because I didn't have that library.
without drifting too far off topic, is that what you saw?

[nickb]

Didn't get to that point as there was no symbol for the pot. You will have seen the same problem if you tried to load my version above as I didn't include it. No symbol, so no lib reference.

[SoulFetish]

Didn't get to that point as there was no symbol for the pot. You will have seen the same problem if you tried to load my version above as I didn't include it. No symbol, so no lib reference.

That’s weird. I did see a pot in yours, but it was backwards and not lined up properly.

[nickb]

Then you have a symbol of the same name but different shape in your sym lib.