SuperFast! a sine wave tremolo and ring modulator

[~arph]

This is basically the modulation section of the ringdroid v2 (which I never actually finished yet)
It uses a XR2206 function generator IC as an analog multiplier. Something I stumbled on on a Japanese synth schematics page.
I have seen XR2206's being used in modulation pedals before, but only as the modulation signal source, not as the modulator itself.
It's a small and simple circuit, other than some other sinewave ringmods out there.

It has two knobs, frequency and volume and one switch tremolo/ringmod.
The trimpot is for trimming out the carrier wave. When building this, set the pedal to ringmod mode and adjust the trimpot until the modulation frequency is inaudible.

I had some adventures in getting the clean blend circuit to function as expected in both trem and ringmod mode. Due to the different nature between amplitude modulation (tremolo) and ring modulation. (thanks ElectricDruid). In the end a simple resistor on a switch (that I needed anyway) sealed the deal.

I haven't tried it with humbuckers. So if you are getting some distortion, reduce the gain in the input section. (lower R5 to 10k).
If you like a tempo indicator, you can hook up an LED to pin 11 of the XR2206. This probably needs some extra circuitry as I get some noise if I do this directly (via a resistor to vcc).
No sound samples, but I think you all know what a sine wave tremolo sounds like. as for the ring mod sounds, listen to something like fairfields randy's revenge and you get the idea.

I hope someone tries it and please let me know what you think. And if you spot any errors or improvements, please share them.

Arnoud

[Mr. Lime]

I think arph talked about this circuit.



Ring modulators always caught my attention somehow and I've got really good results with the Phonic Taxidermist (Maplin Voice Vandal) circuit which is basically a CD4060 oscillator feeding choppers. More or less a high frequency tremolo. Modulating the frequency control gives some really cool ring mod sounds.

Now what is the XR2206 doing different?

I understand the circuit above is in sine wave mode due to the closed connection of pin 13 and 14. Ring mods seem to prever sine waves but what waveform exactly does the CD4060 put out?
There's no external switch to chop the input signal, so what happens between input and output of the XR2206?


Thanks a lot!

EDIT: here's my Phonic Taxidermist ring mod schematic:
http://www.mediafire.com/convkey/f0ce/pg8xvrd884sdgae4g.jpg

[~arph]

Yes, that's the one.  the beauty here is that the XR2206 is the function generator and multiplier rolled into one IC.
A lot of other sine wave ring mods use two chips for this.. eg. a LM13700 and an AD633
What the XR is doing is multiplying the generated sine wave with the incoming guitar signal.

[Mr. Lime]

Ahhh, thanks for the clarification!

So there's a significant difference between multiplying and chopping waveforms.


How about chopping the already multiplied "ring modish" output signal?

The infamous Lovetone Ring Stinger is multiplying the guitar signal with a carrier signal formed by a VCO which is modulated by a LFO.
Modulating the frequency of the XR2206 with an LFO should work fine but is the XR2206 capable for a triangular carrier signal just by breaking the connection of pin 14/13?
Frequency range seems to be defined by the caps on pin 5.

In the graphs are multiplied vs. chopped signals and a multiplied signal which is chopped.

[~arph]

Hey yes you can do triangle too, but be aware that there is a substantial difference in output volume

[soggybag]

Where is the schematic? I'd like to see this one.

[~arph]

It was here yesterday 

[Mr. Lime]

Seems to be back..

Well according to the Datasheet the triangle is approximately twice the sine wave output!

Some people suggest to put a low-pass filter infront of the multiplier, has someone experience with this making it variable?
Also the squarewave output looks interesting to me. The oscillator freq has a maximum of 1MHz so we could devide the square wave with a CD4040.
This offers /2, /4, /8, /16 division steps and for example /32 to get into typical tremolo range (3,5 -6 kHz).


Any suggestions what to do with the square wave output?
I think chopping the already multiplied waveforms leads to chaos and wouldn't sound useful..
There's no way to select the square wave output as carrier signal, right?


EDIT: to compensate for triangle/sine output the resistor on pin 3 has to be halfed for triangle

[Mr. Lime]

Maybe it's a better idea to put a chopper tremolo into the clean path, so it's parallel to the ring modulator. With the division selected to classical tremolo range and the ring mod in tremolo speed it probably sounds a little like in the video at 4:30..

[Mr. Lime]

Some suggest to put a  low-pass filter infront of the multiplier. Either on the guitar input side and/or the carrier side.
Fairfield Circuitry Randy's Revenge seems to have such a LPF to archive the bell like sound.

Here are some ideas:
Portamento/Glide control on the LFO output to soften the edges of the waveforms.

2nd order Sallen Key on the guitar signal side.

Is there a point of making the Q variable so the mids can be controlled?
Should give a wide range of multiplied waveshape sounds, doesn't it?