Tremolo pedal design

[suryabeep]

Hi everyone,
I'm thinking of building a tremolo pedal, but I'm not 100% sure I understand how to. I saw on some other threads that tremolo is basically using an lfo to vary the amplification of a transistor, but I don't quite understand this.

[Kipper4]

Think of the lfo outputting a wave.
Part of the wave is above circuit ground and part of it below.
If you think of it as when the lfo wave is at the top signal goes from input to output.
And when the wave is at the bottom the signal goes to ground through said resistor.
As a laymans explanation.

Probability a lot more to it.
I'm no expert.

[R.G.]

You're right. In fact, there is a huge amount more to it.

Tremolo is the cyclic variation of signal loudness. It's nearly always a sub-audio frequency amplitude modulation. Most common modulation rates are from perhaps one cycle per second to maybe ten or fifteen cycles per second. Higher frequencies are heard as a "growling" tone, which might be fun in itself, but that's another effect entirely.

You can think of tremolo as having a motor drive a volume control pot up and down, over and over. In fact, that's about an ideal way to do it, at least until your motor and mechanism wear out the pot. Most tremolos use one of two schemes: (a) variation of attenuation, much like the volume control example, or (b) variation of the gain of an amplifier stage. This second type is what the OP is suggesting.

@suryabeep: If you are not 100% sure you know how to design a tremolo, then, yes, you do not know how to do it. There is no one single way to get the cyclic variation in volume; instead there are many ways, and each of them requires understanding how that way works.  Here are a few ways that come to mind:
1) Use a series resistor and a shunt LDR to make an electronic "potentiometer". Use some electronic circuitry to drive an LED that cycles brighter and darker to make the LDR resistance change.
2) Use a varying oscillator signal to change the AC resistance to ground on the source of a JFET or MOSFET or emitter of a bipolar. This changes the AC gain, but not the DC bias, which is important in not getting distortion with your tremolo.
3) Use the LED/LDR setup to change the feedback or input resistance an opamp uses in setting gain.
4) Use a varying LFO ..current.. to change the gain of an OTA.
5) Use a varying LFO current to change the gain of a balanced multiplier array.
6) Use a varying voltage to change the gain of a VCA chip.
7) Use a varying very small balanced +/- current to change the effective resitsance of a diode bridge, as in Thomas Vox amplifiers.
Use a varying single current to vary the forward resistance of a single or multiple diodes; this suffers from only being nondistorting for very small, sub-25mV signals.
9) Use a JFET as a variable resistor instead of an LDR in schemes 1 and 3.

I could go on, but you see the issues. You have to know the desired action for the tremolo, AND know how to make the modulation circuit work.

[suryabeep]

Wow, that is a lot of information! Thank you, I'll try and read up on all of these when I can. Maybe I'll even build a mechanical tremolo with a motor But in all seriousness, I think that perhaps the LFO+VCA route is the way to go for me.

[FUZZZZzzzz]

Wow, that is a lot of information! Thank you, I'll try and read up on all of these when I can. Maybe I'll even build a mechanical tremolo with a motor But in all seriousness, I think that perhaps the LFO+VCA route is the way to go for me.

you really should build a machine tremolo with a motor! some inspiration

[PRR]

Tremolo: build a pipe organ. Put a box around the pipes. Put shutters on the box. Couple the shutters to a foot-pedal. One way, pipes soft; other way, pipes loud. Shake your foot, the sound shakes. That's classic tremolo.

Foot-shaking is tiresome, also interferes with other organ foot-work. An air- or electric-motor (very Victorian technology) can take-over that chore. The big theater pipe-organs were full of gimmicks like this.

With electronics, there are 789 different electronic approaches which are "better" than a flap on a box, better even than a windshield-wiper on a Volume pot. Programmed electronic volume control can be a lifetime study.

Don't re-invent wheels. STUDY the very-many trem circuits out there. You are not likely to self-invent anything that hasn't been tried before. You might *build* something "clever", like the spinning-disk gizmos, but hardly practical for professional musicians on tour.

[Transmogrifox]

STUDY the very-many trem circuits out there...

By re-inventing them.

...You are not likely to self-invent anything that hasn't been tried before...

But you sure as heck will understand it better if you try to invent one first.

In the work-place employers don't take kindly to tinkerers reinventing old technology, but in the personal basement laboratory the process of inventing is a lot of fun.  I have come to better appreciate and understand old designs after I have tried to invent the thing.

Invention is pedagogical.  Re-inventing the wheel because you want a wheel is foolish.  Re-inventing the wheel because you want to understand the deeper principles of physics in the design of the wheel is education...and then you understand well enough to design a wheel optimized for a special purpose.