Possible to turn a Supa Trem (Tremulator) into a basic Ring Modulator?

[midwayfair]

I know in something like the tremulus lune that there's a way to just shrink a cap in the feedback loop of the LFO's op amp to bring the LFO into the audio range. Is there a similar simple method in something like this? I have a friend who's bugging me about ring modulators, and he'd rather add it on a switch to something that's already on his board. I just vcan't figure out what sets the maximum speed in this LFO.

[JohnForeman]

Jon,
not trying to hijack your thread, but i have a supa trem.  do you think it would be possible to put a vibrato mod on it that works like your blue warbler?
-John

[midwayfair]

Jon,
not trying to hijack your thread, but i have a supa trem.  do you think it would be possible to put a vibrato mod on it that works like your blue warbler?
-John

Not really sure.

~arph was working on a version of the blue warbler using an op amp, you could try to find his design to see how it's done there. I don't remember where he posted the first draft, though.

[Paul Marossy]

The ring modulators I have worked on use an MC1495 IC chip. I don't think you're ever going to get a ring modulator without the addition of that IC chip or something else that does the same thing. Look at the Maestro Ring Modulator schematic.

[slacker]

I think making the 2.2uF cap smaller will make the LFO go faster, hard to tell from that schematic. A LED/LDR combo probably won't do much at audio frequencies though, an LDR is too slow to switch on and off that fast.

[Jazznoise]

As has been said, most optocoupler based AM circuits roll off pretty steep after about 30 Hz, you'll hear the modulation index drop extremely quickly.

Opto-Fets are, by the spec sheet, a much better option. Haven't ever tried them myself, though.

[midwayfair]

A LED/LDR combo probably won't do much at audio frequencies though, an LDR is too slow to switch on and off that fast.

You're right, I hadn't thought of that! I'll relay the bad news.

I just hope he doesn't find out about the Ring Stinger and ask me to build one.

Jazznoise: Optofets have a tendency to distort in situations like what's shown in the schematic. I've been trying to get them to work for quite a while now.

[Jazznoise]

Reading up I'm seeing crazy figures, one particular person claiming they tend to distort after about 100mV of signal. I'm thinking that an active feedback path could be a cheeky solution to this (set up a non inverting amp, take the output and feed a max of 100mv through the Opto, then amplifty it with an inverting stage by something around ten and send it to the non-inverting amps input). It's abit crazy, but it might work. Balanced feedback pre-amps do something similar, but with no VCR element.

Have you found any difference when the signal has been DC offset?

[midwayfair]

Reading up I'm seeing crazy figures, one particular person claiming they tend to distort after about 100mV of signal. I'm thinking that an active feedback path could be a cheeky solution to this (set up a non inverting amp, take the output and feed a max of 100mv through the Opto, then amplifty it with an inverting stage by something around ten and send it to the non-inverting amps input). It's abit crazy, but it might work. Balanced feedback pre-amps do something similar, but with no VCR element.

Have you found any difference when the signal has been DC offset?

In Ray Ring's opto-FET squeezer, he simply uses a DC shunt to prevent the distortion. It works great -- the problem is that it's basically a bypass, and bypassing the variable resistance element in a tremolo ... well ... equals no tremolo. Maybe we should start a new thread and pick the community's brain.

But apparently the H11F1 is on a path to obsolescence anyway. I don't know how much effort is worth being expended over it unless there's an SMD part.

[Jazznoise]

I'm game if you're game.

Well the part was reintroduced recently, and there are surface mount versions. That aside, bizarre design challanges are the closest thing I have to soduku - I can never find my pens. Anyway, here's the possible idea I just brainstormed there. Signals upto 1V should be fine, over 1V and they'll begin clipping the Opto Fet.