Analog XOR

frijitz · Last edited by frijitz on Sat Nov 17, 2007 9:23 am; edited 2 times in total

A while back I built an XOR circuit ("digital ring modulator") to use with my various pulse waveform generators and shapers. Rather than using a digital IC I used an opamp design that I found in an old EN App Note. It worked just fine.

But then I got curious about what would happen if I fed it continuous (non-pulse) waveforms. After some head-scratching and calculations I figured out that what the circuit does is to go high whenever the sum of the two inputs is between -5V and +5V. And it does indeed produce some interesting ring-modulator type sounds.

To increase the circuit's versatility, I put in a pot that allows the lower threshold to be varied from the negative supply up to the upper threshold. So the output goes high when the sum of the signals is between x and 5V, where x is between -12 and 5V. I've just started to play with this, but it seems pretty cool.

Here are the schematic and a very short mp3 clip. For the clip, two TRI waves were sent into the unit via VCAs. The VCAs were run by envelopes from the AD/AR I mentioned in another thread. One AD is delayed from the other, which is set for a monostable-driven AHD envelope.

Enjoy!

Very Happy

Ian

NB: Edited to add modulation to schematic.

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Usine Karate · Joined: Jun 09, 2007 Posts: 64 Location: Hackney Wick

This looks very interesting Ian. I would like to try it out this weekend. Is there however a recommended op-amp that you would use? I have lots of old 741's I'd like to find a home for, would these be okay?

Would different op-amps lead to differing thresholds re. -5v to +5v?

thanks, usine.

frijitz · Posted: Fri Nov 16, 2007 4:05 pm Post subject:

toppobrillo · Posted: Fri Nov 16, 2007 4:14 pm Post subject:

cool- sounds nifty!

mosc · Posted: Fri Nov 16, 2007 7:56 pm Post subject:

I love this circuit. Very Happy

Very creative. Splendid... too much coffee

frijitz · Posted: Fri Nov 16, 2007 8:18 pm Post subject:

Rykhaard · Joined: Sep 02, 2007 Posts: 1290 Location: Canada

MANY thanks Ian!! I'm just working on a multiple circuit utility panel at the moment with some optional spare space! One of these (at LEAST how you've shown) is going in!! (Desire to VC it has struck, immediately. Wink

lol )

Great sound! I can't wait to build and modulate it! Very Happy

mono-poly · Posted: Sat Nov 17, 2007 3:49 am Post subject:

And another simple great sounding circuit bij Ian!

StephenGiles · Joined: Apr 17, 2006 Posts: 507 Location: England

Ian, if the shape control could be replaced by a vactrol arrangement providing a similar voltage range, (probably not easy!) which is driven by an envelope follower control voltage derived from a guitar connected to one input, and say the output from a PLL (4046 perhaps) connected to the other, also driven by the guitar, we might have some interesting results. What do you think - on my desk 9am Monday morning!! Wink

Blue Hell · Posted: Sat Nov 17, 2007 8:05 am Post subject:

Toyed a bit with this idea on the Clavia G2, very nice!

It was nice to put a bit of portamento (like 20 .. 30 ms/oct) on one of the ingoing oscillators - which were tuned 7 semitones apart (and playing some tune together).

Dynamic shape control is very worthwhile as well Very Happy

frijitz · Posted: Sat Nov 17, 2007 9:30 am Post subject:

Hey folks ---

Thanks for all the interest Exclamation

Per requests I added a modulation section to the schematic. It's not obvious what the best way to do this is, but the one drawn works pretty well. I used a "switch hitter" so the sign of the modulation can be changed (zero modulation when pot is centered). The schematic in the original post has been updated.

Steven -- do I get a bonus, boss? Wink

Blue -- Thanks for doing the simulation. How involved was it to get the function put in?

Very Happy

Ian

v-un-v · Posted: Sat Nov 17, 2007 9:52 am Post subject:

hey Ian! that's an interesting looking circuit Very Happy

Thanks for posting it!

Blue Hell · Posted: Sat Nov 17, 2007 10:30 am Post subject:

v-un-v · Posted: Sat Nov 17, 2007 10:42 am Post subject:

I think that was probably my first ever encounter I had with Jan all those years ago, on the NM@code404 list. And it was a 'digital' ring modulator patch for the Nord. Very similar stuff. very easy too Very Happy

EdisonRex · Posted: Sat Nov 17, 2007 2:52 pm Post subject:

Hmm. Decided to whip it up on a breadboard and try it out. Took about an hour to get it to work. Odd little thing. What's interesting is when you try input 1 and 2 in somewhat harmonically related relations. It's not really like a ring modulator.

v-un-v · Posted: Sat Nov 17, 2007 3:05 pm Post subject:

EdisonRex · Posted: Sat Nov 17, 2007 3:13 pm Post subject:

Blue Hell · Posted: Sat Nov 17, 2007 3:15 pm Post subject:

EdisonRex · Posted: Sat Nov 17, 2007 3:24 pm Post subject:

EdisonRex · Posted: Sat Nov 17, 2007 4:30 pm Post subject:

well, v-un-v reminded me I can whip off mp3s at will here, and as I did build the circuit, here's some sound. I used square waves, although you can use others, it still ends up somewhat pulsed sounding, being a comparitor-ish thing. I tried to play a bit with the waveshape thingy but mine isn't behaving I think. Anyway, like I said, it's not really a ring mod nor is it PWM, but it's certainly rich.

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v-un-v · Posted: Sat Nov 17, 2007 5:20 pm Post subject:

Nice one Paul Smile

Very 'fat'

EdisonRex · Posted: Sat Nov 17, 2007 5:29 pm Post subject:

frijitz · Posted: Sat Nov 17, 2007 6:12 pm Post subject:

frijitz · Posted: Sat Nov 17, 2007 6:33 pm Post subject:

Blue Hell · Posted: Sat Nov 17, 2007 7:18 pm Post subject: