Low parts count zener-inductor waveshaper/modulator

cslammy

Hi there, was messing around on the bench and stumbled on the schemo below. Output goes from a cheap distortion pedal sound to reasonably good balanced modulator effects depending on what you put in.

Stripboarded in about 5 minutes. this is like 8 parts, super super simple.

Anyone else have variations or know of this design in the wild. hard to believe it's new, but for me it was a complete accident. Then again I almost never use inductors for anything except power so new for me anyway.

BTW variation for this design and more detail on my blog:
http://audiodiwhy.blogspot.com/2018/10/discovery-by-accident-super-low-parts.html

8 parts.PNG

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gabbagabi · Posted: Fri Oct 12, 2018 12:45 pm Post subject:

any chance to see some scope-shots Input-vs-output?
would be nice, just to get more sense out of it.

cslammy · Posted: Fri Oct 12, 2018 12:48 pm Post subject:

I was going to do another blog entry with before and after WAV files, but doing scope shots as well is a great idea. I'll do that too. Thanks for the suggestion.

gabbagabi · Posted: Fri Oct 12, 2018 11:59 pm Post subject:

u could also just open the wav in a audioeditor and screenshot the waveforms there, but Scopies are somehow more elegant.

i understood that it is acting like a RM?
can u may run a test where u feed in the same sine in both signal and carrier in?
This is a special task for an RM, it acts then as a frequenzy-doubler, cos it is performing sin²

the other standard test would be sin&saw, the frequenzy of the one should be an uneven multiply of the other eg 1khz/3khz or 1khz/5khz 1/7 .....
this is to see how it is performig the phase inversion when the carrier is going thru zero, means that the saw is running backward then

Posted Image, might have been reduced in size. Click Image to view fullscreen.

cheers, gabi

cslammy · Posted: Sun Oct 14, 2018 12:04 pm Post subject:

AlanP · Posted: Mon Oct 15, 2018 12:09 am Post subject:

http://www.madbeanpedals.com/projects/Retrograde/docs/Retrograde.pdf

The Tychobrahe Octavia uses a tranformer. (Schematic is on the last page.)

PHOBoS · Posted: Mon Oct 15, 2018 4:42 am Post subject:

just a quick note: I am not so sure if that zenerdiode across the inputs is such a great idea, as it pretty much
shorts them when the voltage on input 2 is lower than the voltage on input 1.

cslammy · Posted: Mon Oct 15, 2018 9:30 am Post subject:

cslammy · Posted: Mon Oct 15, 2018 9:31 am Post subject:

gabbagabi · Posted: Tue Oct 16, 2018 2:33 am Post subject:

dont worry about it is a RM or not Cool

it would just be nice to see how it is behaving

cslammy · Posted: Fri Oct 19, 2018 2:18 pm Post subject:

OK Blog post is done. Sound demo, scope photos.

I might create a PCB if there is interest.

http://audiodiwhy.blogspot.com/2018/10/zener-synth-distortion-alive-and.html

Comments appreciated. Phobos: I only buffered one of 2 inputs, seems OK to me, what do you think?

gabbagabi · Posted: Sat Oct 20, 2018 4:21 am Post subject:

cool!

very nice soundworks indeed, 2:35 is of course my favrorite, but also the low amplitude sine part, those little extra noises, nice

cheers, gabi

PHOBoS · Posted: Sat Oct 20, 2018 9:32 am Post subject:

I don't think a buffer is really necessary, but a good idea nontheless, as long as you have at least a resistor in series with one of the inputs
it should be good. For the "Son of Zener" I'd buffer the input connected to the transformer or you could buffer both for good measure.

Sounds pretty cool, not what I expected.

cslammy · Posted: Sat Oct 20, 2018 12:27 pm Post subject:

[quote="PHOBoS"] For the "Son of Zener" I'd buffer the input connected to the transformer or you could buffer both for good measure.

Resistance across the primary side of the transformer is only about 50 ohms so I agree, it's safe to buffer it. I ended up buffering both inputs.

Thanks.

Psynth · Joined: Jul 18, 2018 Posts: 34 Location: UK Audio files: 8

Interesting circuit. I've played around with it in LTSpice, and it seems to behave like a cross between a ring mod and a logic gate. Basically the diodes, being zeners, can conduct in both directions, but with different threshold voltages (the zener voltage in the reverse direction, and the normal 0.7V diode forward drop in the other direction).

Putting in identical sine waves to both inputs results simply in the same frequency at the output. But putting in say 440Hz and 880Hz produces a sort of anharmonic series of diminishing amplitude, at 1320Hz, 1.76kHz, 2.2kHz etc.

It also seems, in spice at least, that the transformer is not essential for the operation of the circuit (though it may impart musical colour). The attached screenshot shows the transformer replaced with the two diodes feeding both + and - inputs of an opamp.

Not breadboarded yet though, so don't know what this would sound like in practice.

Peter

Screenshot 2018-10-21 23.16.39.png

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Psynth · Joined: Jul 18, 2018 Posts: 34 Location: UK Audio files: 8

Got round to breadboarding this. Very good sounds from such a simple circuit. I've not used a transformer, and have added opamp buffers and an additional moderator input- which acts like a sort of VCA.

Schematic attached (for a dual version).

A quick sample is attached. This is just two sine waves, at 178 and 280 Hz. At about 20 secs I start to turn the 'mix' pot up, then play with the 'mod' pot and the 'offset' pot. At about 1.15 I put a triangle LFO into the 'mod' input. From 2.12 onwards, variously changing the sine wave frequencies, then from 2.50 swapping the LFO out for an audio frequency saw - from 3.30, this is controlled by a sequencer.

Peter

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Zener demo.mp3

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