Author Topic: Tremulus Lune tremolo pedal produces loud harsh fuzz  (Read 1468 times)

Joe_Shroe

Tremulus Lune tremolo pedal produces loud harsh fuzz
« on: April 10, 2018, 05:12:00 PM »
I'm working on recreating this Tremulus Lune pedal but am using my slightly modified schematic seen here. This is the wiring setup for my stompswitch. The problem is when I switch the effect on, the pedal will turn my sound into a harsh and incredibly loud fuzz which leads me to believe there's some serious DC leakage in the circuit. I measured DC on the input and output decoupling caps and replaced both of them, but they're still measuring DC voltage. On the input I get 0.20v and on the output I get 0.25v, although the voltages tend to gradually spike sometimes. What should I do next to eliminate this problem?

bean

Re: Tremulus Lune tremolo pedal produces loud harsh fuzz
« Reply #1 on: April 10, 2018, 05:50:43 PM »
Two things:

You have the input impedance to the first op-amp stage set too low. You want a minimum of 220k for each resistor, where you have 47k. The TL has them at 1M, IIRC.
Second, depending on what type of photocell (or vactrol) you are using it's "on" resistance might be very low. Meaning that you gain recovery (50k trimpot) is too high causing distortion.

ElectricDruid

Re: Tremulus Lune tremolo pedal produces loud harsh fuzz
« Reply #2 on: April 11, 2018, 10:13:34 AM »
What's the purpose of the 1K resistors across the two LEDs? I'm curious...

Also that 1nF cap across the 50K gain trimpot is going to eat your treble if it's set to 50K - works out at roll-off from 3.2KHz.

Thanks,
Tom

bean

Re: Tremulus Lune tremolo pedal produces loud harsh fuzz
« Reply #3 on: April 11, 2018, 10:32:33 AM »
What's the purpose of the 1K resistors across the two LEDs? I'm curious...

It pulls the LED all the way dark for more depth on the trem effect. Without the 1k across the LED the difference between light and dark tends to be more narrow.

Digital Larry

Re: Tremulus Lune tremolo pedal produces loud harsh fuzz
« Reply #4 on: April 11, 2018, 10:43:38 AM »
I had some loud harsh fuzz recently and it turned out to be a bad solder joint on a feedback resistor in an op-amp circuit, so it was just operating at its open loop gain.  I'd double check your solder joints.
Digital Larry
DSP tinkerer and former transistor twister

Digital Larry

Re: Tremulus Lune tremolo pedal produces loud harsh fuzz
« Reply #5 on: April 12, 2018, 10:49:41 AM »
Not that it would make a fuzz tone, but the wiring of the "spacing" pot seems suspicious.  With the wiper not connected to anything it won't do anything when you turn it.
Digital Larry
DSP tinkerer and former transistor twister

Danich_ivanov

Re: Tremulus Lune tremolo pedal produces loud harsh fuzz
« Reply #6 on: April 12, 2018, 07:55:03 PM »
I think that generally this method of producing tremolo has a high chance of being "fuzzy", it depends too much on a switching device. I much prefer pulling signal to the ground, like in a schaller tremolo for example.
« Last Edit: April 12, 2018, 10:20:37 PM by Danich_ivanov »

Joe_Shroe

Re: Tremulus Lune tremolo pedal produces loud harsh fuzz
« Reply #7 on: April 13, 2018, 12:03:18 AM »
Update: the tremolo actually works only if I jiggle around some components just right, not even joking. The main cause of the problem seems to be when I twist or bend the wires for the SPEED pot which will cause the LEDs to either stop working, shine continually, or pulse at a slower speed. However after compulsively checking the solder points and continuity, and also replacing the wiring completely, the SPEED pot seems to be hooked up just fine so I don't know what the issue is. It seems there must be a bad solder joint somewhere but everything checks out okay with my continuity tests. I don't know if this is a problem that can be diagnosed online since the problem stems from my build quality instead of the schematic itself.

You have the input impedance to the first op-amp stage set too low. You want a minimum of 220k for each resistor, where you have 47k. The TL has them at 1M, IIRC.
Bypass mode works just fine though, and it's only when the effect is switched on that I hear fuzz. As a matter of fact, on the rare occasion that the tremolo does work after I jiggle it around just right, the sound is a bit distorted. Would this be coming from the second op-amp stage?

I had some loud harsh fuzz recently and it turned out to be a bad solder joint on a feedback resistor in an op-amp circuit, so it was just operating at its open loop gain.  I'd double check your solder joints.

I've been checking every solder point and testing continuity and they all seem fine to me, but there must be a whack solder joint somewhere because the LEDs start and stop working at random times as I described above. Honestly I suspect it's just a dumb mistake I made somewhere and I've been driving myself crazy trying to find it.

Not that it would make a fuzz tone, but the wiring of the "spacing" pot seems suspicious.  With the wiper not connected to anything it won't do anything when you turn it.
The numbers next to the pot (1 and 2) are the lugs. It was easier for me to visualize if I drew the schematic that way instead of drawing the pots at a 90 angles.


ElectricDruid

Re: Tremulus Lune tremolo pedal produces loud harsh fuzz
« Reply #8 on: April 13, 2018, 05:28:10 AM »
You could try sticking a resistor (10K-50K maybe) across the LDR temporarily with the LFO op-amp pulled out. That would allow you to see if the audio path part is ok. If you still get weird noises, you've got a problem in that part of the circuit. If it's all fine, then the problem is in the LFO, and potentially in the gain range given by the LDR/50K combo if you find crunches higher level inputs.

HTH,
Tom

Joe_Shroe

Re: Tremulus Lune tremolo pedal produces loud harsh fuzz
« Reply #9 on: April 14, 2018, 05:14:08 PM »
SOLVED: Fuzz went away after I adjusted the 50k trimpot on the second op-amp stage, I had it set too high initially.

chemosis

Re: Tremulus Lune tremolo pedal produces loud harsh fuzz
« Reply #10 on: December 12, 2019, 08:41:42 PM »
ive built a few tremulus lunes from pcb and vero and I usually get a slight distortion noise/hiss effect when I strum. I always use vtl1 vactrols

tubegeek

Re: Tremulus Lune tremolo pedal produces loud harsh fuzz
« Reply #11 on: December 12, 2019, 10:57:22 PM »
ive built a few tremulus lunes from pcb and vero and I usually get a slight distortion noise/hiss effect when I strum. I always use vtl1 vactrols

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