[Not sure if this should go here or in the OT forum. Ended up here, anyway..]
Suppose you've taken up playing the electric guitar again after several years of almost no activity. I am looking over the collection of "effect pedals" I have, and have decided you want a really good tremolo.
[Let's just clear out the possibility of confusion here. The correct meaning of a tremolo is something along "a periodic variation in the volume". NOT a periodic variation of the frequency - the correct musical term for the latter is "vibrato". "Tremoling" is rocking the volume control, "vibrating" is rocking the tuning. (Never mind the tuning-altering mechanic device om e.g. Fender guitars called a "tremolo arm". That should have been a "vibrato arm", but the wrong term was used and got stuck.)]
So, I might be interested in building my own tremolo.I speculate that this kond of effect should be one of the simplest do get working (as compared to e.g. effects using phase shifted signals (phaser, flanger, chorus), or exploring saturated components (fuzz, distortion) or moving bandpass filter (wha-wha)).
Basically, what I think I need is a circuit that attenuates the signal, and where I can control that attenuation. Specifically, the attenuation should vary periodically over time.
I'd like to control
- Period (think 0 to perhaps 50 Hz)
- "Magnitude", i.e. maximum attenuation
- Waveform (nice sine wave, triangular, sawtooth ramping up or down, square...)
The typical box you buy has three knobs for these.
The signal should ideally be altered as little as possible - i.e. setting attenuation to zero should produce an output signal ideally identical to the input signal.
It seems most projects I've found isolates the waveform generation from the "attenuator" by e.g. a LED/LDR pair, so that supply/ground noise etc generated in the block that generates the waveform does not leak over into the signal that is attenuated.
Could I buy one instead? Of-course, but
1) I'd like to control the speed with a pedal that I already have (for those of you into these kind of things, it would work as an "expression pedal") - buying an expression-enabled box and the expression pedal ends up somewhere around $300-500..
1b) There are other effects I'd like to have that is not easy to build yourself, and where it pays off to buy quality stuff (curious? E.g a "compression effect box".)
2) Trying something like this will hopefully be fun
The waveform-generator could be a specific circuit, or an AVR that PWMs a signal that is filtered. If an AVR I'd need help with the filter as well, but doing it this way opens interesting possibilities. Example: When frequency increases attenuation could be decreased - so that you could go from a lo-freq very perceptible tremolo, up through something more staccato-like with the staccato eventually disappearing ending up with a clean signal.
I could envision something similar at the other end. Lowering the frequency below some threshold the thing goes into clean signal.
I'm sure there are a lot of interesting experiments I could do. Programming the thing will be up my alley. I am asking for your help with the analog hardware parts.
I know there are a lot of people knowing the ins and outs of analog electronics. That is certainly not my field of expertise.