Runoff Groove Tri-Vibe hiss, pop, and a mod idea

[Kailem]

Hi Folks,

I recently built a Runoff Groove Tri-Vibe pedal.  It is a kit ordered from musikding.de using the PCB from TH Custom Effects. (build instructions and schematic found at that link.)

The pedal is working as expected except for a couple of small issues that I've noticed.  I'd also like to ask about the feasibility (and level of difficulty) of adding a tremolo mod.

The issues, which I hope come through in the video here, are that:

• There is a hiss, whoosh, or just generally a small amount of noise when the pedal is engaged.
• The on-off-on switch makes quite a loud pop, and the 3pdt footswitch makes a small pop.

I've tried to highlight these issues at the end of the video, where I mute my guitar and turn up the amp.  Watch from 1:15 on.

Using my multimeter, it does seem like there is a voltage difference between the pin and sleeve. (I believe about 0.5 mV) that can pop up to about 40 mV when the switch is switched.

There is a great thread here that explores the hiss and whoosh, but, as far as I can tell, the issue was never resolved, just a resignation that perhaps that OTAs are inherently a bit noisy.

Any ideas for what could be the culprit here, for either the hiss or the pop?  Any tips or help would really be appreciated.

I've also wondered about the feasibility of including a switch to turn this into a tremolo effect.  Since a nice sine-wave LFO is already being created, could that be used to modulate volume instead?  I would love to incorporate that extra versatility into this pedal, but maybe that's too much to ask for in one package

I haven't done any mods except to not include the rate-indicating LED, as I wasn't sure how to engage and disengage it with the footswitch.  Additionally, a musikding.de 3pdt pcb is used on this project.

[bluebunny]

Welcome!

OTAs aren't quiet.  I think you have to live with the whoosh - it's part of the tri-Vibe charm.    I've built one of these using the same TH board and don't recall that it was particularly noisy.  YMMV of course.  And I don't recall any popping on either switch.  The schematic doesn't show a pull-down resistor at the input, so you could add one (1M from input pad to ground on the board).

The speed indicator LED is always on, no switching required: just drill a hole (if you haven't already got one) and mount it directly on the PCB and let it poke through.

Dunno about the feasibility about having a switched tremolo function.  I suspect you might be switching out/in so many bits, you might as well just build a tremolo pedal. 

BTW, nice socks. 

[r080]

Welcome to the forum!

I just finished a Tri-Vibe using Aion's board. I have the pop on the mode switch, but not on the bypass. There is definitely a pulldown resistor on Aion's board.

Regarding the tremolo idea, it might be possible. If you search the site, you will see some discussion of using this chip as a tremolo, along with some watch-outs. The Tri-Vibe has the OTA set up as a variable all-pass filter. Switching a few components could turn it into a variable gain amp, but right now, it is past my understanding of OTAs. My gut says to just swap the feedback capacitors for resistors. However, the board already has the LFO connected to the OTA. The Tri-Vibe LFO does make a sine wave, but then exponentiates it to work better for phase shifting. You would have to deal with that to make it sound nice as a tremolo.

http://www.geofex.com/Article_Folders/VCA%20Applications.pdf

Google search site:diystompboxes.com lm13700 tremolo

[Kailem]

Thanks for the tips! (And the sock compliment.)

I tried adding a 1M pulldown resistor, but it seemed to have no effect.  I also tried resoldering a few joints that I thought might be suspicious, but that had no effect either.  It sou D's like the hiss may just be part of the circuit, and that is OK.  Maybe one day I'll try replacing the ICs to see if it cleans up.

Adjusting the feedback resistor is what I had thought for creating a tremolo effect, but I will do some research before I attempt anything or post again.  Thanks for the resources r080!

[r080]

Depending on how you have the LED implemented, it might be worth trying to disconnect the LED and see if you still have popping. Sometimes when you switch the power to the LED on and off, it affects the power to the rest of the circuit enough to hear it. There are tricks to fix that.