Boss DD-2 modify - wet output mute during bypass

[bthm3288]

I'm using a boss DD-2 in an effects loop, with a dummy plug in the direct out.. this allows the "wet only" signal to be output from the main output. Works great!

The problem is, when the pedal is bypassed, the dry signal is then sent down the output.. not great.

I'm wondering if there's a mod that will kill they dry signal from being output from the main output, when the pedal is bypassed (when using a dummy plug in the direct out (or stereo out as it's called on DD-2).

Basically I would like the wet signal to be output, when the pedal is engaged.. and no signal to be output when the pedal is disengaged.

Any ideas appreciated! Schematic attached. Maybe I can add a switch to kill the dry at the mixer stage?

[ElectricDruid]

Following PRR's trick from another thread, one simple way would be to add a SPST toggle across C24. That will prevent Q5 from switching on (which it would ordinarily do in bypass) and prevent the dry signal getting to that de-emphasis mixer IC1a.

With the switch open the pedal is completely stock, and it doesn't require any modifications to the board, just a couple of wires tacked to the cap's connections.

[tommy.genes]

Ooh, I had wanted to do this years ago but never finished it. I still have the switch in the old DD-2 as well. It already has the high-cut and effects loop mods working.

I had been playing with the TANH() function in Pure Data recently and was impressed by how well it emulates a tape echo. I will have to do some research into an analog circuit equivalent and put that in place of the high-cut mod on the DD-2.

-- T. G. --

[bthm3288]

thanks ElectricDruid, I'll try adding a toggle switch across C24... does it matter which side of the cap I put the switch on? between the cap and ground?

Thanks!

[ElectricDruid]

I had been playing with the TANH() function in Pure Data recently and was impressed by how well it emulates a tape echo. I will have to do some research into an analog circuit equivalent and put that in place of the high-cut mod on the DD-2.

A differential transistor pair is the classic way to get a tanh response.

thanks ElectricDruid, I'll try adding a toggle switch across C24... does it matter which side of the cap I put the switch on? between the cap and ground?

I'm not sure I understand the question. The switch goes *across* the cap, and the cap is connected from the junction of D1/R26 to ground, so the switch will connected to the same points. I'm suggesting that you solder the switch wires to the same points where the two sides of the cap are connected. I don't understand "which side of the cap?" - both sides!!

[bthm3288]

thanks ElectricDruid, I think I misunderstood what you meant.. I get it now. I'll solder a switch across C24, as shown in red in the screenshot here -

[aviherman5]

I had been playing with the TANH() function in Pure Data recently and was impressed by how well it emulates a tape echo. I will have to do some research into an analog circuit equivalent and put that in place of the high-cut mod on the DD-2.

Do you mean modulating the signal by TANH function - similar to how other pedals add modulation to delay by modulating it by a SIN or triangle wave?

[ElectricDruid]

I get it now. I'll solder a switch across C24, as shown in red in the screenshot here -

Yeah, that's it.

[bthm3288]

thanks!!

[tommy.genes]

Do you mean modulating the signal by TANH function - similar to how other pedals add modulation to delay by modulating it by a SIN or triangle wave?

A TANH function looks like the plot below, and closely approximates tape saturation. This sets a top limit to how loud the repeats can be, so you don't get a speaker-busting unlimited increase in volume if you have the feedback gain above unity. With feedback approaching or even exceeding unity, though, this function does introduce more severe clipping, so at some point you lose almost all character of the original signal and you get that characteristic self-oscillating tape echo effect.

Here's an audio sample from my tests in Pure Data: https://donpancoe.com/shared/delay_oscillation_and_speed_test.mp3

-- T. G. --

[aviherman5]

A TANH function looks like the plot below, and closely approximates tape saturation. This sets a top limit to how loud the repeats can be, so you don't get a speaker-busting unlimited in increase in volume if you have the feedback gain above unity. With feedback approaching or even exceeding unity, though, this function does introduce more severe clipping, so at some point you lose almost all character of the original signal and you get that characteristic self-oscillating tape echo effect.

Woah...

Sorry for my incredible lack of understanding, but is it a function which maps volume to the amount of repeats? I've never heard something that convincing of a tape sound ever!

[edit] and if you're willing to share the Pure Data file, I'd love to play around with it!

[tommy.genes]

Think of it like a transfer function: for an input value of x, you get some output value of y. The function y = x (no change to the input signal) would look like a 45 degree line passing through the origin. The middle part of the TANH graph does look like that, meaning you get y = x for small values of x. But as x increases, the TANH function starts to limit and clip your signal.

This PD file doesn't include the sample file I was using to test it, but you could substitute your own or try it on live playing.

https://donpancoe.com/shared/stab-delay-test.pd

-- T. G. --

[aviherman5]

Thank you! Will play around with it!