Ring mod with adjustable frequency - suggestions?

[moosapotamus]

Actually, just recalling... I have done carrier modulation but not with the FA. Some time ago I added carrier modulation to JC Maillet's Nyquist Aliaser project http://www.lynx.net/~jc/nyquistAliaser.html. That was a lot of fun! My schematic is posted here https://moosapotamus.net/ideas/jc-maillets-nyquist-aliaser-project/ along with some sound clips.

I think doing something similar with the FA would have much more of a "hi-fi" sound, for lack of a better term.

[patricks]

I built this ring modulator from Parasit Studio, and i can recommend it :

https://www.musikding.de/xorcist_1

https://www.parasitstudio.se/uploads/2/4/4/9/2449159/xorcist_2_doc.pdf

There are two internal trimmers, Gate and Sensitivity, both are also very useful wired as external controls.

Not sure if this is exactly what you are looking for, but this project is cheap, sounds very good, and it will get you started in your Ring Mod Quest.

Only downside on this project is that you can't use the Ring Mod without the Fuzz. The Fuzz itself sounds amazing though, and you can blend it with the modulated signal. You can dial out the Fuzz signal with Blend fully CW, but the ring mod signal is fuzzy, a bit like an octave up/down circuit with the Blend control fully CW, set to cut the clean signal out of the mix.

Don't know if you are familiar with octavers, but those i tried tend to have also some more or less synthetic/glitchy/Lo-Fi octave sounds.
I mean, it's kind of dirty compared to a perfectly clean guitar signal.

From what i could understand, it's part of the analog nature of the process ?

Other good point is the momentary footswitch, allowing to toggle stuttering mod on or off. When it's off, the modulation acts a bit like an octave up/down effect, depending on how you dial the Frequency control. There' s also 2 internal switches, best wired as external toggleswitches in my opinion, allowing to change the action of the momentary switch (more info in the build docs). You can change the effect of the momentary in two different ways. Very useful to play with the effect while playing with the guitar.

On its own this effect sounds a bit raw, with some kind of Lo-Fi touch, but once combined with other circuits (reverb, delay, enveloppe filters...) it gets much more interesting and musical. It's also perfectly silent, no background noises. I often use a Meatball clone connected before it, and a Memory Man clone after it, with lots of feedback, for exemple.

I'd suggest to change all the internal trimmers and DIP switches into external controls.

Nice project, thanks for the recommendation! I'm starting to go down a bit of a rabbit hole and likely to put together a couple of designs based on some existing circuits cobbled together

Arguably overly complicated, maybe, but still thought provoking and worth including in any ring mod conversation...

https://moosapotamus.net/files/stompboxology-ring-modulators.pdf

I've built a few different ring mods and the Frequency Analyzer is my current fave. Could just use some modulation!

Oooh, some great reading material there, thank you. I'm about a third of the way through so far, it's a deep dive but it's logical to follow. I'm at the point where it's explaining the different circuits, so I need to read it on my laptop, the e-reader screen doesn't cut it cos I can see the text and the relevant circuit in the same view.

Neat idea modulating the carrier frequency!
I've been reading up on envelope followers from one of Mark's articles on GeoFex. Saw a reverb pedal project posted recently that uses one in a very sweet way

[patricks]

Arguably overly complicated, maybe, but still thought provoking and worth including in any ring mod conversation...

https://moosapotamus.net/files/stompboxology-ring-modulators.pdf

I've built a few different ring mods and the Frequency Analyzer is my current fave. Could just use some modulation!

I finished reading it yesterday, it gave my brain a workout in a good way! Lots of food for thought there, I like how the gate is implemented in the various projects too 🙂

[moosapotamus]

Yeah, gating the carrier is the way to go. Nulling doesn't always do the trick. The LM13700 VCA in the Penfold Fuzz Unit can be adapted to make a nice noise gate for silencing the carrier when you're not playing.
https://moosapotamus.net/ideas/penfold-fuzz-unit/
...and, there's tons of stuff you could do with the other half of the 13700 - LP filter, VCO (carrier), etc... 

[Mark Hammer]

I stuck a back-to-back pair of Schottkys in series with the RM path to the mixer on the EPFM circuit.  It subtracts about +/-300mv from the audio signal, but the threshold to pass signal is high enough to keep out pesky carrier-whine when you stop playing, and there's still plenty of output level left, despite the +/-300mv reduction.

[patricks]

Yeah, gating the carrier is the way to go. Nulling doesn't always do the trick. The LM13700 VCA in the Penfold Fuzz Unit can be adapted to make a nice noise gate for silencing the carrier when you're not playing.
https://moosapotamus.net/ideas/penfold-fuzz-unit/

That's a cool circuit. I like that it's a reverse ducking thing, rather than an envelop follower driving a compressor to silence the dry signal it's boosting the level of the effected signal.

...and, there's tons of stuff you could do with the other half of the 13700 - LP filter, VCO (carrier), etc... 

Oh no! That's dangerous talk! I'm already contemplating whether I could DIY a simple monosynth (dual VCO, noise, VCF, VCA, envelope) to replace an Arturia Minibrute I sold a little while ago...

I stuck a back-to-back pair of Schottkys in series with the RM path to the mixer on the EPFM circuit.  It subtracts about +/-300mv from the audio signal, but the threshold to pass signal is high enough to keep out pesky carrier-whine when you stop playing, and there's still plenty of output level left, despite the +/-300mv reduction.

That's such a neat solution, thank you

[moosapotamus]

I stuck a back-to-back pair of Schottkys in series with the RM path to the mixer on the EPFM circuit.

That's a great idea. Need to go try that mod on my EPFM ring mod. Thanks!
Did you put the diodes before or after the RING volume pot?

Back when I built it, I also added a spst switch between pins 6 & 7 on the LM565. Got the idea from JC Maillet's version of the circuit. It gives a different, sometimes less chaotic, sound by reducing the loop gain and locking the frequency range of the VCO... at least, that's what I get from the datasheet. 

[patricks]

Reviving the thread, I've started playing with the design on paper (well, virtual paper - Diptrace) again.

I'm basing this design on the EHX Frequency Analyzer (this schematic), substituting the AD633 with the AS3363 triple VCA suggested by Electric Druid.

The pinout isn't exactly the same, the AD633 has separate pins for each of the inputs, whereas the AS3363 has a single input per VCA block with a CV Mix and Vctrl pin.
In the EHX schematic the sine wave output from the ICL8038 is connected to one of the non-inverting inputs of the AD633 and the sine wave adjust pin is connected to both of the inverting inputs and the non-inverting input of the summing stage/multiplier.

@electricdruid with the AS3363 I'm guessing I'd just send the modulator signal to the input pin of the block and the carrier output from the ICL8038 (sine wave adjust pin if using the sine output) to the CV Mix pin?
Would it be best to have a voltage divider off the positive supply rail to provide the Vctrl pins with +2V for maximum current, or just leave them disconnected for simplicity (or am I barking up the wrong tree with this thinking?)
Last question, with the third VCA block in the AS3363 chip I'm guessing I'd just send the modulator signal to both input pins, correct?

[ElectricDruid]

@electricdruid with the AS3363 I'm guessing I'd just send the modulator signal to the input pin of the block and the carrier output from the ICL8038 (sine wave adjust pin if using the sine output) to the CV Mix pin?

Yes, that should work. It's a multiplcation and since A*B = B*A, it doesn't matter which way around it is in theory. In practice, it might be quieter one way than the other.

Would it be best to have a voltage divider off the positive supply rail to provide the Vctrl pins with +2V for maximum current, or just leave them disconnected for simplicity (or am I barking up the wrong tree with this thinking?)

It'll need 2V from somehwere, because the Vctrl controls the level of the CV MIx input (yes, you can control the control signal in this thing! And in either direction, from -100% to +100%)
If Vctrl is zero, you'll get no CV Mix signal and no output.

Last question, with the third VCA block in the AS3363 chip I'm guessing I'd just send the modulator signal to both input pins, correct?

Not *quite*. It's *almost* exactly the same as the other two stages, but if you look, you'll see that the two inputs *both* go to the +ve inputs, instead of one +ve and one -ve like the other stages.
So if you wanted to make the third stage like the other two, you'd have to send the signal into one input, and an inverted version of the signal into the other.

Good luck!

[patricks]

Sweet! Thank you!

In practice, it might be quieter one way than the other.

I hadn't thought of that, thanks, I'll try it each way and see.

It'll need 2V from somehwere, because the Vctrl controls the level of the CV MIx input (yes, you can control the control signal in this thing! And in either direction, from -100% to +100%)
If Vctrl is zero, you'll get no CV Mix signal and no output.

Oooh, the possibilities! I can see this being useful sending aftertouch CV to Vctrl if this were a synth application, or using it as part of a mod matrix.
I'm going to have to be careful, or I'll start trying to build a synth next... 

Not *quite*. It's *almost* exactly the same as the other two stages, but if you look, you'll see that the two inputs *both* go to the +ve inputs, instead of one +ve and one -ve like the other stages.
So if you wanted to make the third stage like the other two, you'd have to send the signal into one input, and an inverted version of the signal into the other.

Ah, good to know, thanks. The preceding stage will be a three way split off the buffer, one signal going straight through and the other going to each of a high- and low-pass filters based off the BYOC Brown Face harmonic trem. Blocks 1 and 2 of the AS3363 will get the unfiltered and high-passed signals, block 3 can get the low signal, and if I take a feed from the emitter as well as the collector then it should hopefully work like a cathodyne phase inverter and I can send each feed (one of which will be inverted) to each of the inputs for block 3.

Good luck!

Thanks heaps! I'll need it, the concept is getting more complex every time I come back to it 
I'll be putting an order in through your website in the not-too distant future

[Eb7+9]

Yeah, gating the carrier is the way to go. Nulling doesn't always do the trick ...

unfortunately gating the carrier produces glitchy tails ...
not a problem if you keep whacking the strings

it's also relatively easy to pull off


nulling otoh is way harder as it requires careful consideration of dynamic mechanisms produced by the circuitry in response to the clocking pulse

the aim is to first re-produce the offending (dynamic charge injection) glitch on its own - not mixed with signal
and then figuring out how to cancel it perfectly, or near perfectly, with a mixed (wet) s/h signal ... using a high CMRR subtractor, etc ...


I've only managed to do this twice, once in my Bleeding Aliaser (ver2 audio rate sampler)
demo'd here:

And more recently with a square-wave (ring mod) multiplier,
yielding simulated carrier rejection of 147db ...

https://viva-analog.com/wp-content/uploads/2022/09/Hmod-JCM2022.mp3


in practice both circuits exhibit perfect carrier nulling
but it also took a fair bit of design effort ...

[patricks]

Here we go, posting up a first draft of the schematic. Thanks so much to everyone who's offered ideas and advice so far!
It's based on the modern version of the EHX frequency analyser, with:

• switchable frequency range to go from ring mod to tremolo, BUT
• thanks to the evil genius suggestion from ELectric Druid to use an AS3363 chip and get three ring mods, I've added a frequency splitter borrowed from the BYOC Brownface harmonic tremolo
• there's a pair of back-to-back schottky diodes on the input to the mixer stage for carrier nulling, thanks to Mark,
• I've also used a DPDT switch as a SP3T to give options for sine, square, and triangle wave carrier signal
• I may add a simple compressor after the low pass filter that follows the input buffer

This is third in line to go on the breadboard, I'm testing out one more thing for my three-headed rat pedal, then next up is the Quadracomparator fuzz, and all of that testing can happen while I'm waiting for the AS3363, ICL8030, and LT1054 chips to arrive for this project.

I've scribbled notes all over the schematic to remind me what to test, things like the frequency range capacitor, filtering on the waveform signal, VCtrl voltage (should be fine at 2V with the mixer op-amps running at 12V), and pot values to take the signal from the AS3363 to the mixer stage (guessing at 25K log for a starting point).
I'm not sure whether using two op amps for the ring mod mixer stage is really necessary, that's copied out of the EHX schematic.
I'm thinking that if I take the signal for the clean blend from the output of the input buffer then I can do away with the EHX mixer and use the op amp currently used as the buffer feeding the clean blend as the output/ring mod buffer, to reduce the parts count by a dual op amp and the associated components. Or I might need an inverting buffer on one of the outputs of the low-passed harmonic trem section, come to think of it. Much to test!

@markhammer did you find that when you added the back-to-back schottkys to the mixer for the EPFM ring mod that the trimmer for carrier nulling was still necessary? I've got four inputs to the AS3363 chip currently and if the schottkys negate the need for the trimmer that'd be a bonus.

See what you think, any comments or queries most welcome.
I've got one other ring mod project in mind, inspired by this thread, that's next in line for drafting in Diptrace, I'll post it up when it's ready

[patricks]

Couldn't help myself, here's version 1.2 
I've:

• Taken the "clean" side of the clean blend from the output of the input buffer rather than splitting it from the input itself and giving it its own buffer
• Changed the output mixer from two op-amps to one (I think one of them in the EHX schematic was part of the filter on the output anyway)
• Switched around the connections to the inputs and the CV mix pins on the AS3363. This makes more sense in my mind, since the waveform from the ICL8038 is the carrier and the signal from the guitar is the modulator (and means less components for carrier nulling)

If it performs well, I've reduced the parts count by a dual op-amp, a trimpot, and a handful of passive components.
I finished testing the three-headed rat on the breadboard today, so I'm one step closer to setting this up and testing

[antonis]

I presume LF353 is powered from symmetrical dual-supply..

[patricks]

I presume LF353 is powered from symmetrical dual-supply..

Yes, that's right - the power supply pins are on a block down near the power supply section but I've just realised I didn't delete one of them when I deleted the other dual op-amp, I'll fix that up

EDIT: There we are, image updated