Pareidolia Tremolo Plus TAPLFO3 clicking

[lars-musik]

I just built the Pareidolia Tremolo and because I couldn't find the XR2206 LFO generator chip in my workshop (that I am sure I ordered about two years ago but that I seemingly did not store away correcty) I thought it might be a good idea anyway to build it with a tap function. So I hooked the circuit up to Tom's fantastic TapLFO3C and – voila! – it works quite good.
However, if I choose a square wave, the tremolo clicks very loud. Tom did implement a smoothing routine to his code especially for such incidents to smooth of the edges of the wave but still the clicking is very present. Do you have any idea where I could add some more de-clicking? My experience with non-optical tremolos is somewhat limited.


Thanks a lot!

Lars



Click here for larger version:

[ElectricDruid]

You could try just sticking a capacitor to ground after R30/1K. Incidentally, that resistor was only included in the original schematic because it went to the output - it prevents large current flow if someone shorts the output.
But to be honest, I think the solution is probably a bit deeper than just sticking another cap on it.

I'd also have a look at the biasing of the original LFO vs the TapLFO. The filter circuit you've used was intended to replace a Schmitt Trigger/Integrator LFO, so it includes an offset to produce an output from about 2V to about 7V. That may not be what you need to drive your FETs, and if it's pushing them too far, perhaps that would make a click. They need to be kept in a region where their behaviour "Voltage in -> Resistance Out" is reasonably linear. I can't work out from the datasheet exactly what output range the XR2206 might have been putting out, but it does look like it's broadly similar, which is hopeful. But without the detail, it's hard to be sure.

Also I note from the XR2206 datasheet that the chip doesn't work on a 9V supply, so the original circuit probably used 12V. Does that affect anything else?

I also note the original circuit only uses the Triangle/Sine output from the XR2206, so there's no guarantee that the circuit can be made tick-free with square waves. Maybe it can, maybe it can't. But I'm just pointing out they didn't try. I would be concerned with DC levels on the FETs, since any rapid switching of DC is going to produce audible thumps and bumps. That's physics we can't get away from.

HTH,
Tom

[Kipper4]

I'm having trouble reading the drawing, my eyes are getting worse.

I hope you work it out Lars.

[lars-musik]

Hi Tom,
thanks a lot for looking into the matter. The master himself, great!

so it includes an offset to produce an output from about 2V to about 7V. That may not be what you need to drive your FETs.... .... But without the detail, it's hard to be sure.

Yes, that is indeed a problem. The technical specifications on this site https://electronics-diy.com/Function_Generator_XR2206.php
says the XR2206 puts out 0-3V for sine and triangle and 8V for square at 9V input. I have no idea if it means total voltage swing or not but it already hints towards a huge difference between square and sine.  The datasheet states an output amplitude of 60mV peak per kOhm resistance at pin3 (on page 12). However, they calculate 13V for an example with a 50 kOhm resistance. No idea how to figure that out.

It seems I still have to wait for my re-ordered XR2206 and just measure what the original circuit does.

Also I note from the XR2206 datasheet that the chip doesn't work on a 9V supply, so the original circuit probably used 12V.

Another unsolved mystery for me. The originally traced circuit had a 7809 in the power section, yet the pedal specifications said it could be run from 9V-18V. That doesn't make any sense as I seem to recall that the 78LXX  need a 1 or 2V higher supply to function correctly. And even then I'd end up with a stable 9V that makes me 1V short according to the XR2206 datasheet. So I left the regulator on my board.

I also note the original circuit only uses the Triangle/Sine output from the XR2206, so there's no guarantee that the circuit can be made tick-free with square waves.

On Harold Sabro's site somebody reported that he used the XR2206 for square waves in the Pareidolia and also got a  severe clicking. So maybe it won't work.



If I reduce the Level on the TAPLFO I might be able to still tremoloe enough and reduce the clicking. Maybe I put that voltage divider in as a trimmer and adjust the depth of the effect via a blend circuit....

I'm having trouble reading the drawing, my eyes are getting worse.

Hi Rich!
There's a link at the bottom of the original post for the original resolution image.... Just in case.....

Or download it here (you're to far away to borrow my glasses....)


Thanks all!

Lars

[lars-musik]

To conclude this I finally got around visiting someone with a DSO to adjust the amplitude of the TAPLFO to the original XR2206 sine wave. The max V-p-p of the XR2206 is at just 1.7V at a 12V supply. So I adjusted the tapflo via the Level CV and take a clean blend circuit for depth control. The square has to be tamed via a 3,3uF cap to prevent it from ticking. Not square anymore but still an addition to the solitaire sine wave from the original.

I think I REALLY like the outcome. Thanks for your help Tom!

[ElectricDruid]

Good work Lars! Glad to hear you got it sorted.

[lars-musik]

Thanks, Tom.

I had an even better idea whilst walking my dog to spare me the hassle of a clean blend. I measured the max CV of the TAPLFOs level pot for the sine to match the XR2206's level (1.9V) and put another voltage divider on the +5V of the Taplfo's level pot to bring it down to that 1.9V. Works perfect.

[lars-musik]

Finished! Great, I think.
The etch was also quite good, but it looks super shabby now. I don't mind that. Spaghetti inside, so won't post any gutshots but rather spend my time designing a better, combined layout for TAPLFO plus Pareidolia.

[ElectricDruid]

Nice work! Are there any other 16 waveform tremolos out there?! You might have something unique there, and if not unique, certainly unusual.