Modulating dry/wet parameter with an expression pedal [amp reverb]

Started by fryingpan, May 24, 2021, 12:51:28 PM

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fryingpan

One of the features that I miss the most when it comes to amp reverb is the capability to dial in reverb level (actually the dry/wet ratio) with an expression pedal, so I wish to implement this in my preamp. I can only see three solutions though:

- use a voltage controlled resistor (not any FET, as signal levels and resistance range are too high) and use the expression pedal as a voltage divider
- use an encoder linked to a very simple microcontroller (some PIC chip) and use the expression pedal as a voltage divider
- send the dry, the wet and the output signal in a 3-lead + shield cable to the expression pedal

The easiest would be the first, but there don't appear to be many suitable VCRs around.
The second would probably be the most doable nowadays, even though I wanted to avoid having digital stuff in my preamp (mostly to avoid digital noise in the signal in the form of EMI).
The third would probably never work right.

Ideas?

iainpunk

a 3 wire connection, one carying +9v which goes to the pot, 22k lin, they have stopper resistors of 1k in series which are connected to the other cables, and both other cables go to the LED side of a vactrol inside the amp.
basically a crude current control.

cheers
friendly reminder: all holes are positive and have negative weight, despite not being there.

cheers

PRR

I don't think you understand all your options.

There's many kinds of "voltage controlled resistors" and they all suck somehow but different ways.

They used to sell "VCRs" which were selected JFETs, but that market faded.

The return level from the tank, ~~10mV, will not overload a standard JFET L-pad; there may be a hiss compromise. Note that JFET L-pad was a much-used FM radio processor, and we didn't complain. But it needs tweaking.

Opto-resistors and LEDs are another path.

Tubes?

But in this the twenty-first century (schizoid man) the most direct path may be a THAT Corp VCA. These were used by the shoebox-full in those very large analog mixing consoles favored by those big-hair bands; also mixed-down ALL music styles for a couple decades (until the all-digital path you wish to avoid).

http://www.thatcorp.com/Blackmer_Voltage-Controlled_Amplifier_ICs.shtml
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fryingpan

Quote from: PRR on May 24, 2021, 08:43:09 PM
I don't think you understand all your options.

There's many kinds of "voltage controlled resistors" and they all suck somehow but different ways.

They used to sell "VCRs" which were selected JFETs, but that market faded.

The return level from the tank, ~~10mV, will not overload a standard JFET L-pad; there may be a hiss compromise. Note that JFET L-pad was a much-used FM radio processor, and we didn't complain. But it needs tweaking.

Opto-resistors and LEDs are another path.

Tubes?

But in this the twenty-first century (schizoid man) the most direct path may be a THAT Corp VCA. These were used by the shoebox-full in those very large analog mixing consoles favored by those big-hair bands; also mixed-down ALL music styles for a couple decades (until the all-digital path you wish to avoid).

http://www.thatcorp.com/Blackmer_Voltage-Controlled_Amplifier_ICs.shtml
A VCA is a perfect choice, of course, but I was thinking it's like using a bulldozer to hammer a nail. Can a VCA be used to modulate dry/wet though? The obvious application for a VCA seems to be, well, simply controlling the amplitude of the reverb signal, which can be OK (set the balance between dry and wet with a pot, and use the VCA to control reverb level), of course I could use two VCAs and use them as a "balance" control but that seems awfully overengineered.

ElectricDruid

If you want to control the the levels of two signals, using a VCA seems reasonable to me - after all, that's what they're designed for. As to over-engineered, it's a one chip solution, so no, I wouldn't say so.

AS3360 is a cheap VCA. LM13700 is maybe even cheaper. THAT Corp stuff has better specs and prices to match.