Joined: May 04, 2007 Posts: 1734 Location: NM USA
Audio files: 54
Posted: Fri Nov 16, 2007 1:42 pm Post subject:
Analog XOR Subject description: (Whatever that means)
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!
Ian
NB: Edited to add modulation to schematic.
demo_a1.mp3
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xor1107b.gif
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Last edited by frijitz on Sat Nov 17, 2007 9:23 am; edited 2 times in total
Joined: Jun 09, 2007 Posts: 64 Location: Hackney Wick
Posted: Fri Nov 16, 2007 3:29 pm Post subject:
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?
Joined: May 04, 2007 Posts: 1734 Location: NM USA
Audio files: 54
Posted: Fri Nov 16, 2007 4:05 pm Post subject:
Usine Karate wrote:
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?
Hi Usine --
There's nothing at all critical about this circuit and anything you throw together should give interesting results.
I used a TL072 opamp. A 741 will show some slew-rate limiting (the pulse edges will be sloped) but I wouldn't worry about that unless you need very high frequencies or very clean pulses.
The threshold levels I stated are approximate and based on 12 V supplies. If you use 15 V supplies you might want to increase the 220k resistor to something 270k or 330k.
Thanks for your interest Please let us all know how this works out for you.
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. lol )
Great sound! I can't wait to build and modulate it!
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!!
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).
Joined: May 04, 2007 Posts: 1734 Location: NM USA
Audio files: 54
Posted: Sat Nov 17, 2007 9:30 am Post subject:
Hey folks ---
Thanks for all the interest
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?
Blue -- Thanks for doing the simulation. How involved was it to get the function put in?
Joined: May 16, 2005 Posts: 8932 Location: Birmingham, England, UK
Audio files: 19
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Posted: Sat Nov 17, 2007 9:52 am Post subject:
hey Ian! that's an interesting looking circuit
Thanks for posting it! _________________ ACHTUNG!
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Joined: May 16, 2005 Posts: 8932 Location: Birmingham, England, UK
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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 _________________ ACHTUNG!
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Joined: Mar 07, 2007 Posts: 4579 Location: London, UK
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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. _________________ Garret: It's so retro.
EGM: What does retro mean to you?
Parker: Like, old and outdated. Home,My Studio,and another view
Joined: May 16, 2005 Posts: 8932 Location: Birmingham, England, UK
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Posted: Sat Nov 17, 2007 3:05 pm Post subject:
EdisonRex wrote:
What's interesting is when you try input 1 and 2 in somewhat harmonically related relations.
mp3's??
EdisonRex wrote:
It's not really like a ring modulator.
yeah!!
I wish this course I'm doing would just hurry up and evaporate away There are so many more important things in life apart from writing reports on FMEA- like building this pseudo ring mod _________________ ACHTUNG!
ALLES TURISTEN UND NONTEKNISCHEN LOOKENPEEPERS!
DAS KOMPUTERMASCHINE IST NICHT FÜR DER GEFINGERPOKEN UND MITTENGRABEN! ODERWISE IST EASY TO SCHNAPPEN DER SPRINGENWERK, BLOWENFUSEN UND POPPENCORKEN MIT SPITZENSPARKSEN.
IST NICHT FÜR GEWERKEN BEI DUMMKOPFEN. DER RUBBERNECKEN SIGHTSEEREN KEEPEN DAS COTTONPICKEN HÄNDER IN DAS POCKETS MUSS.
ZO RELAXEN UND WATSCHEN DER BLINKENLICHTEN.
Joined: Mar 07, 2007 Posts: 4579 Location: London, UK
Audio files: 172
Posted: Sat Nov 17, 2007 3:13 pm Post subject:
v-un-v wrote:
EdisonRex wrote:
What's interesting is when you try input 1 and 2 in somewhat harmonically related relations.
mp3's??
EdisonRex wrote:
It's not really like a ring modulator.
yeah!!
I wish this course I'm doing would just hurry up and evaporate away There are so many more important things in life apart from writing reports on FMEA- like building this pseudo ring mod
I'll post some in the UK morning, if someone else doesn't beat me to it in the US evening or AU morning. Where's Krunkus, anyway? How long does it take to get back online?
Gonna play a bit more and see if I can't something resembling music come out of it. _________________ Garret: It's so retro.
EGM: What does retro mean to you?
Parker: Like, old and outdated. Home,My Studio,and another view
Seemed a bit between PWM and RM to me, sound wise, but with a rough edge when the ingoing amplitudes get low (having envelopes before the circuit, as in example above).
Joined: Mar 07, 2007 Posts: 4579 Location: London, UK
Audio files: 172
Posted: Sat Nov 17, 2007 3:24 pm Post subject:
Blue Hell wrote:
EdisonRex wrote:
It's not really like a ring modulator.
Seemed a bit between PWM and RM to me, sound wise, but with a rough edge when the ingoing amplitudes get low (having envelopes before the circuit, as in example above).
yeah, it's a lot like other Ian Fritz circuits.
Harmonically rich, usually explains them in 2 words. _________________ Garret: It's so retro.
EGM: What does retro mean to you?
Parker: Like, old and outdated. Home,My Studio,and another view
Joined: Mar 07, 2007 Posts: 4579 Location: London, UK
Audio files: 172
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.
fritz_xor_example_edrex.mp3
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_________________ Garret: It's so retro.
EGM: What does retro mean to you?
Parker: Like, old and outdated. Home,My Studio,and another view
Joined: May 16, 2005 Posts: 8932 Location: Birmingham, England, UK
Audio files: 19
G2 patch files: 1
Posted: Sat Nov 17, 2007 5:20 pm Post subject:
Nice one Paul
Very 'fat' _________________ ACHTUNG!
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IST NICHT FÜR GEWERKEN BEI DUMMKOPFEN. DER RUBBERNECKEN SIGHTSEEREN KEEPEN DAS COTTONPICKEN HÄNDER IN DAS POCKETS MUSS.
ZO RELAXEN UND WATSCHEN DER BLINKENLICHTEN.
Joined: Mar 07, 2007 Posts: 4579 Location: London, UK
Audio files: 172
Posted: Sat Nov 17, 2007 5:29 pm Post subject:
v-un-v wrote:
Nice one Paul
Very 'fat'
you're welcome. It is rather fat, isn't it. I used a little filter but if you watch this shit on a scope you can see what it's doing. A typical cool Ian Fritz circuit. _________________ Garret: It's so retro.
EGM: What does retro mean to you?
Parker: Like, old and outdated. Home,My Studio,and another view
Joined: May 04, 2007 Posts: 1734 Location: NM USA
Audio files: 54
Posted: Sat Nov 17, 2007 6:12 pm Post subject:
Blue Hell wrote:
...
The blueish modules implement it with the modulation being done as well.
The rest of the circuit is part of the noodle I built around it. This one does not have the portamento mentioned.
Thanks Jan!
I don't understand the G2 well enough to figure out what you have set up. I would have expected two comparators to pick out signals (In1+In2) above and below certain limits then an AND gate to ensure both conditions are met. What you have done is equivalent to this?
Joined: May 04, 2007 Posts: 1734 Location: NM USA
Audio files: 54
Posted: Sat Nov 17, 2007 6:33 pm Post subject:
EdisonRex wrote:
...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.
In this case the waveshape control shouldn't have any effect, because rectangular waves always satisfy the threshold conditions no matter where the pot is set. If you have a chance to try out saw waves then the control should change the sound quite a bit.
I agree it's not all that much like a ring modulator. (Never understood why Korg called it that.) For example, if you feed both inputs the same saw wave, then you get a single pulse, whereas a true multiplier would give you sawtooth-like wave with a parabolic rather than linear rise.
I'd like to figure out how to get bell sounds with this. Any idea where to start?
I don't understand the G2 well enough to figure out what you have set up. I would have expected two comparators to pick out signals (In1+In2) above and below certain limits then an AND gate to ensure both conditions are met. What you have done is equivalent to this?
Your description was that the output should be one when the sum signal would be < 5V or > 5v and zero otherwise, and I tried to do just that.
I assumed 10 V would be the max signal level and mapped 10 V onto 64 "Clavia control units" (the max, well, the unit units count really, there is some headroom above that). And so I had to map 5 V to 32 units.
I have two >= comparators, one set to a fixed value of 32 and another that can be controlled by input units (voltage equivalent), modeling the modulation on the lower value (it can go too high here with improperly set control voltages/units).
The xor on the outputs of the comparators will give the windowing function like you described it ... I hope the following table will prove that
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Please let us all know how this works out for you.
lol )
There are so many more important things in life apart from writing reports on FMEA- like building this pseudo ring mod 
