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Tremolo pedal schematic

TomA1234

TomA1234

Jul 27, 2009
1,342
50
Fareham, England
#1
Calling out to effects and electronics gurus, :)

I have been thinking about making a tremolo pedal of my own design (with my knowledge from AS level electronics) and have come up with a possible circuit for it.

The basics for my idea so far are this:
Multiple chopping waveforms (square/triangle/sine)
The chopping wave forms will be generated through a PIC, digital to analogue converter and high/low freq relaxation oscillator.

The PIC will be wired up to increment and output a binary number every time the high frequency oscillator pulses. The DAC will take that binary number and convert it in to an analogue voltage that will control the feedback voltage on the op-amp.

I will use these outputs to (hopefully) modulate the gain of the pre amp in order to create the chop effect.

The output from the pre amp is then fed in to 3 cut filters (treble, bass, bandpass) which are then fed into a summing amplifier with a variable gain for each channel, in effect creating the ability to boost frequencies if I want (I will add in a bypass for this).

The circuit diagram is below.

Any comments/suggestions/errors that you have on it will be appreciated. :)

Thanks,
Tom
 

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  • Tremolo circuit.png
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#2
I'm pretty sure your crude vca is not a vca, but just clips the signal more or less.
Your EQ is a waste of parts, try something like this:
Link Removed
If you really do want a shelving filter for the hi-pass I thhink you can omit C5.

No reason to have external clocks on the PIC, do that in code. And run it off of a crystal.

I'd suggest, if you want to go with a digital LFO you take a look at this:
[Invalid or Expired Link Removed]
Invalid Link Removed

good luck :)
 
#4
Thanks for the comments so far, I shall replace the current EQ with the suggested one. Is the suggested one a boost as well as cut?

To be honest, I had no idea if the varying gain op amp would actually work, so thanks for saving me the frustration of it not working properly. :)

The FET seems a good alternative to the gain varying op amp, and I shall boost the out signal using the eq to prevent volume loss.

I am using an external clock on the PIC so that I can more easily alter the speed of the LFO (frequency=1/0.5RC) and program the pic to increment on each pulse, I shall have to look up crystal oscillators to see how that could be used, however, the schmitt trigger NOT gates come in packages of 6, so using more than 1 relaxation oscillator won't take up too much room.

With the EQ, the diagram appears to not run the op amp on +/- voltage, wouldn't this result in clipping at the output?
 
#5
You just hook a crystal with a fixed frequency up to the PIC and set up a real-time loop with one of the timers on it. Then you either vary the loop-speed, or change the speed at which it goes through the look-up table.

I really really suggest you got through the documentation I linked, to get some more theoretical knowledge, both on tremolos and micro-controllers.
There is a link from musicpcb to a detailed description of the code used on the PIC there.
 
#6
TomA1234 said:
Is the suggested one a boost as well as cut?


With the EQ, the diagram appears to not run the op amp on +/- voltage, wouldn't this result in clipping at the output?
Click to expand...

yeah it'll be boost and cut.

also, look at R11 and R12 in that schematic. They split the source voltage in two. It's then applied to the noninverting opamp input so it'll shift the ac signal up by 6vdc.
 

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