Tremolo Pedals

[mcwilson]

Hey Everyone,

I am currently working on a Tuna Melt rehouse (currently in the not working state, but I think I know how to fix it). I was looking at the circuit and I noticed that the volume changes by a light variable resistor. Do all trem circuits work in a similar manner? I kind of expected something different.

I was really just curious about how most work.

Thanks,
Matt

[The Tone God]

There are alot of opto based trems but there are other ways to do it.

Andrew

[Transmogrifox]

I can't think that very many trems out there aren't opto-based.  Some may use an OTA. 

Just for the sake of learning, or for curiosity, check out the EA tremolo--it uses a JFET to change the gain on a single MOSFET stage, and is actually quite a simple circuit.

I have been tinkering with a pulse-width modulation scheme on the CD4066 chip.  This seems to work quite well as both a trem and a ring modulator.

There was also another amplitude control circuit by Luse (Luce?), an engineer associated with moog--Anyway, there was a link to the patent on this that showed up in one of the posts within the last couple months.  I don't know of any tremolo guitar FX that came from it, but it would certainly have been a viable circuit for the purpose.

Finally, these days the tremolo effect is an add-on in a digital FX unit, so it's reduced to a very simple and clean form though I tend to find them a little sterile compared to the analog trems.  Perhaps it's because the transfer of the LFO waveform to the resistance change tends to be more exponential in nature, and the resistor divider equation leaves a bit of a nonlinear relationship for LFO to amplitude transfer--enough to make a good sinewave LFO come out as a something else for shape in the amplitude.

[The Tone God]

I can't think that very many trems out there aren't opto-based.  Some may use an OTA.

The pulsar comes to mind. EA trem is another. Essentially FET based trems.

Andrew

[gez]

Penfold has done a number of OTA based trems in various books.  I like OTAs for trem myself.

[Paul Perry (Frostwave)]

I'm pretty keen on OTAs myself, but I suspect that ldr/led gives a better signal/noise. Anybody got actual figures??