MUFF WIGGLER Forum Index
 FAQ & Terms of UseFAQ & Terms Of Use   Wiggler RadioMW Radio   Muff Wiggler TwitterTwitter   Support the site @ PatreonPatreon 
 SearchSearch   RegisterSign up   Log inLog in 
WIGGLING 'LITE' IN GUEST MODE

sinusoidal wavefolder
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author sinusoidal wavefolder
guest
i put together that barrie gilbert sine-shaper circuit i had discovered while researching for the OTA sine wave shaper paper:



it works as expected, but still needs some tweaking. its pretty fun, but has some glitches at deeper modulation (faster opamps might fix this). it goes about +/-550 degrees before the sine distortion gets bad, and +/-650 before it totally distorts and loses sine shape altogether. in the middle range, it can keep all harmonics below -60dB.

there are two ways to modulate with it. if you modulate the amplitude of the signal going in, it acts like a normal wavefolder, except the output is sinusoid, rather than a ramp wave. if you add an offset to the input, you are phase modulating. i will see about getting some videos up.
guest
and here is the transfer function:



it looks more like +/-720 degrees before distortion from this shot.
Dogma
Really cool smile

Audio?
SoundPool
looking forward to some audio/video. always on the lookout for interesting wavefolders. the distortion may actually give it some unique charm, no?
guest
it took some time to deal with youtube, but here are some quick tests. all of the modulation depths are set with some knob tweaking, so nothing fancy.



this is a basic run through of transfer function, with a triangle wave being amplitude modulated, as you might use a normal wavefolder.



this is a triangle wave being offset modulated (phase modulation at the output).



this is a saw wave being offset modulated with a slow sine wave. you can see tha the output remains a steady sinewave, with only the phase being changed with the modulation.



this is a saw wave being offset modulated with a fast sine wave, which is more akin to how PM would work.
nd595
Absolutely fantastic! Any chance to see the schematics and to buy a PCB?
mike.synthesizer
Great job.
guest
nd595 wrote:
Absolutely fantastic! Any chance to see the schematics and to buy a PCB?


once i get things finalized i will post a schematic. the circuit needs to be temperature compensated (well, should be, doesnt necessarily need to be). not sure if i will be making a product out of this or not.
cygmu
I try to avoid empty congratulations posts but that is absolutely great! So please accept my empty congratulations!
cygmu
Actually, I have a question: is this the article where you found the circuit in question?
B. Gilbert, "A monolithic microsystem for analog synthesis of trigonometric functions and their inverses," in IEEE Journal of Solid-State Circuits, vol. 17, no. 6, pp. 1179-1191, Dec. 1982.
doi: 10.1109/JSSC.1982.1051878

I might try to read it, along with your recent article.
guest
yes, thats the best paper for the topic. he also wrote one 5 years earlier which was an introduction to it called "CIRCUITS FOR THE PRECISE SYNTHESIS OF THE SINE FUNCTION". there are some tradeoffs in the design, mostly with the "bias factor" (how much overlap the differential pairs exhibit). right now im using a bias factor of around 3, which gives theoretical error of 0.2% (my circuit shows -60dB harmonics, which is similar). going to lower bias factors gives lower error, but higher temperature dependency, lower output signal, and a higher ratio between the normal signal (sine in the middle) and the overdrive signal (the saturation at the ends).
pirx
Fantastic wavefolder! Thank you for sharing this and looking forward to the schematic.
maltemark
Very nice PM-like action there. Like!
guest
so here is the current schematic:



im using +10V/-12V rails, and LM358 opamps. the transistsors are PMP4201 matched pairs. ideally all NPNs would be matched, and all PNPs would be matched, but thats not really possible like this.
guest
just did a quick temperature test. the distortion stays about the same over a pretty wide range of temperature. i hit it with the heat gun, and it stayed pretty consistent. the amplitude changed +14% with what was probably +50C temperature change, which is pretty drastic. i think it might be ok without temperature compensation, as amplitude isnt that critical.
Dcramer
Gads! I wish I could buy this! love
guest
im trying to figure out where the slight glitches at higher modulation come from, and i think its transistor mismatch. if thats the case, then there isnt a too much advantage to using matched pairs over hand matching, except for the very middle section when using it strictly as a sine wave shaper.

this then brings up the question: what would you prefer? a THMT PCB with transistor matching required, or an SMT PCB that is already populated?

i think im going to do a kit for this one, as it seems pretty useful. the circuit can be used to: 1. do low distortion sinewave shaping, 2. act as a quadruple wavefolder, 3. do PM or pseudo FM (there would need to be some leakage on the integrator to avoid slight offset voltages from saturating the modulator).
windspirit
Those transistor pairs are a bit daunting for some, I have soldered them before but they are quite picky. That being said wasn't there recently a thread talking about how difficult it is to match NPN with PNPs by hand? Is it more important to have all of the NPNs matched to the other NPNs and PNPs matched to other PNPs or is it important to have each NPN matched to the corresponding PNP?

Does changing the biasing on U2A (the op amp in a loop with the current source at the very bottom) do anything interesting? I though that it could possibly be another interesting modulation point.
SoundPool
I don't mind SMD but those transistors look a little tough for me (I do have shaky hands but normally manage to work around it). Also I have ZERO interest in matching transistors, normally I'm not bothered by temp comp so much but when I need them I'm lazy and buy matched pairs. If I don't like to do it through hole I certainly won't want to hand match those tiny things.

I think leaving it small and SMD is nice though, regardless of if that means buying pre-soldered PCB. If it had power footprints for both Euro and MOTM/Serge and a couple caps for clean/regulating power (I'm guessing thats not included on here, right?) its nice that it can be multi-format compatible, or even small enough to be squeezed into something like a stand-alone mini synth. People would still have to run a few wires and make a panel of choice, so its not like it would eliminate it being DIY.
J3RK
Wow! That sounds excellent! Probably the smoothest non-digital implementation that I've heard.

applause
Isaiah
guest
This is fantastic!

So, the amount of folding is determined by the input amplitude, and adding a DC offset changes the symmetry, right?

A small SMT PCB (2"x2" or 2"x3"?) with 3M mounting holes and Euro/MOTM PSU footprints would be excellent.
Bonus points if you can squeeze an input VCA and mixer (for DC offsets) on there. hihi

Again, fantastic. Well done!
guest
windspirit wrote:
Is it more important to have all of the NPNs matched to the other NPNs and PNPs matched to other PNPs or is it important to have each NPN matched to the corresponding PNP?

Does changing the biasing on U2A (the op amp in a loop with the current source at the very bottom) do anything interesting? I though that it could possibly be another interesting modulation point.


only the NPN need to be matched to the NPN, and the PNP to the PNP. so no cross-matching required.

the bias on U2A sets the output gain, so that could be an AM point for the whole thing. im not sure how much feedthrough it has, though, or how well it goes to full-off, or effects on distortion at different levels, etc.
guest
Isaiah wrote:
So, the amount of folding is determined by the input amplitude, and adding a DC offset changes the symmetry, right?

A small SMT PCB (2"x2" or 2"x3"?) with 3M mounting holes and Euro/MOTM PSU footprints would be excellent.
Bonus points if you can squeeze an input VCA and mixer (for DC offsets) on there.


the amount of folding is set by amplitude, but offset changes phase, and not symmetry. basically, the input voltage determines the output phase, so Vout = sin(Vin), where Vin can go from +/-720 degrees. so if you have a saw wave of fixed amplitude that spans 360 degrees, it will make a sine wave. as you add offset, it still makes a sinewave, but instead of going from -180 to +180, it could be 0 to +360, or any other 360 degree span. so at slow modulation rates, you dont notice any change as you add offset. but, as the offset modulation rate increases, you travel over the sine function faster and begin to warp the output, giving that symmetry changing look.

i was thinking about putting 2 inputs, each with a VCA, going to a mixer, and maybe having one be switchable for the pseudo-FM.
Isaiah
guest
Ah, thanks for the explanation!
Yes, two VCAs and a mixer on the input of the folder would be excellent.
Perfect as a standalone module or as VCO add-on!
Isaiah
Also, what's the ideal input voltage range?
megaohm
Really cool circuit you have!
Love how it sounds.

Went searching for the paper and came across this which may relate and be interesting (page 12)?

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&cad=rj a&uact=8&ved=0ahUKEwivkrXppbHSAhUL34MKHWlVD44QFggoMAM&url=http%3A%2F%2 Fdocs-europe.electrocomponents.com%2Fwebdocs%2F0025%2F0900766b80025499 .pdf&usg=AFQjCNEQr_rCCzPF0RdVd6xQ-_o7fgIUIw&sig2=7y6xVUx_ndGz2QYIDbL3E g

Of course that chip is extinct!
Dead Banana
guest
yes, that was the chip they made from the original. it would be cool if it still existed.
guest
Isaiah wrote:
Also, what's the ideal input voltage range?


i havent yet set all of that, but the main circuit core runs at ~1mV/degree if i recall correctly. the input and output need to be scaled.
wsy
guest wrote:
i put together that barrie gilbert sine-shaper circuit i had discovered while researching for the OTA sine wave shaper paper:
.


EXCELLENT!!!

I hope you realize that this is making me rethink continuing work on the FMO, don't you?

- Bill
nd595
guest wrote:

this then brings up the question: what would you prefer? a THMT PCB with transistor matching required, or an SMT PCB that is already populated?

i think im going to do a kit for this one, as it seems pretty useful. the circuit can be used to: 1. do low distortion sinewave shaping, 2. act as a quadruple wavefolder, 3. do PM or pseudo FM (there would need to be some leakage on the integrator to avoid slight offset voltages from saturating the modulator).


I would rather prefer SMT PCB, populated or not - can do all the soldering with a great pleasure! And tinkering with the thing - what can be better?
guest
wsy wrote:

I hope you realize that this is making me rethink continuing work on the FMO, don't you?


i sure hope not! as much as i love analog, digital is the way to go for FM.
wsy
guest wrote:
wsy wrote:

I hope you realize that this is making me rethink continuing work on the FMO, don't you?


i sure hope not! as much as i love analog, digital is the way to go for FM.


But there's flaws in digital FM / PM.... some people complain about the "low fi" or th "sawtooth". The FM Ogre samples it's
inputs at something well over 40 KHz, so the phase angle in TZPM has a "jump" that often. The jump is minimized by the software (there's
a predictor/corrector) but it's still nonzero.

You'd say "but it's up at 40 KHz or more" and you're right - but if you have some high frequencies already in the signal, you can get
aliasing frequencies that come on down into the audible range. Very minor, mind you, and audible only at very high phase angle mod
rates, but nonzero. Whether or not it's less audible than the distortion of this circuit is arguable.

- Bill
guest
i put some better opamps in (TL072) and its much, much cleaner. the distortion is down to -70dB on the harmonics on the middle range, and the clicks are inaudible for the vast majority of the range. at really high modulation you can hear them a bit in the background. at really low frequencies its a slight click, and at really high freuqencies its a bit of a hiss. i found some fun operating points while mucking around. overdriving it sounds really good with a high frequency saw wave. it can also be used to produce pure overtones at 2x, 3x, and 4x the fundamental. im tempted to put another transistor pair in there so the 5th can be achieved.

i think the remaining inconsistencies are from transitions between matched pairs, which is a bit hard to avoid in a discrete like this. im considering seeing what a pair of LM3046 can do for me. the matching is probably worse on that, though.
batchas
This is the kind of thread I like very much here on Muffwiggler applause

I like the videos of the tests too, like "test 1" for instance thumbs up
guest
ok, i did some tests with amplitude modulation using the current control port on the bottom. as it turns out, the emitter voltages dont go below 0V, so a ground referenced exponential converter can be used to create the current. the modulation bleedthrough isnt that great. i got it down to -60dB, but it was quite finicky, and -50dB will probably be more likely in practice. with a bunch more trimming it might get down lower, but i dont think thats worth it, considering how easy it would be to add a 2164 at the end. but, for envelopes and such, it seems to work pretty well. with it full off its -90dB or better for carrier supression. at really high (distorting) input ranges, the carrier gets forced through at full volume, but the final design will have clamping diodes to prevent this (the transistors shouldnt be driven like that anyways).
Clive
Well done, guest applause

The first video example shows the transfer function, which looks very similar to the Serge middle wavefolder. Can I expect that to do PM too?
gbiz
Fantastic work guest applause

edit: SMD please
xahdrez
Wow, love how this sounds. This is fun!

I'd definitely be interested in a PCB & Panel - I'd probably prefer not to have to match transistors, but it wouldn't stop me - either version would be appealing to me! Great work!
guest
Clive wrote:
The first video example shows the transfer function, which looks very similar to the Serge middle wavefolder. Can I expect that to do PM too?


yes, you can do PM with a wavefolder and a (optional) sine shaper afterwards. there was some discussion of this in the "analog phase modulator" thread that is currently active.
wsy
xahdrez wrote:
Wow, love how this sounds. This is fun!

I'd definitely be interested in a PCB & Panel - I'd probably prefer not to have to match transistors, but it wouldn't stop me - either version would be appealing to me! Great work!


There's about 20 different quad matched NPN arrays 'active in stock' at DigiKey:

https://www.digikey.com/products/en/discrete-semiconductor-products/tr ansistors-bipolar-bjt-arrays/277?k=transistors&k=&pkeyword=transistors &pv74=85&FV=ffe00115%2C1f140000&mnonly=0&newproducts=0&ColumnSort=0&pa ge=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25

so it wouldn't be such a stretch to use these as the matched pairs (remembering to use them in the right order!)

- Bill
jhulk
yep you can i used that 300 series for the core chip design


so its easily done with quads
guest
ive been thinking about the matched quads. a lot of the 4-transistor dies are not matched, and have low beta transistors (3904, 2222). the main contenders for matching are THAT300 (6$), MAT04 (10$), and LM3046 (0.75$). the LM3046 isnt actually a matched quad, though, but might be as good as a bunch of matched pairs. there still ends up being at least one transition with the LM3046, and 2 with the quads, as the core takes 10 transistors. if i used quads, id bump it up to 12. by contrast, the PMP4201 cost 0.20$ and have better transistors and better matching than the LM3046. they are pretty close the the THAT300 in performance, but the MAT14 is amazing, and way better than them both.
jhulk
i chose that because they do npn pnp and dual npn/pnp quads

and are matched most of the new quad arrays are not matched but i have tested the 3904/6 varieties and they are close matched on the die a bit like using the same transistors next to each other on a tape which seem to be evenly matched as its done by robots now rather than a human tolerances are a lot higher.

i had one transistor left over in the quad npn all the others are dual npn/pnp matched pairs

on the later design which i also have a chip it uses even more as it has a phase control and for +voltage and -voltage and has a current biasing circuit for this that attaches to this basic core by the emitters connected transistor.

and attaches to the pnp current mirrors either end .

so i split it into 2 chips.

i like the mat chips do they do equivalent types like the that series.

i also like the bcm847/57 chips and the ls318/358 pairs.

the other reason i like using the that series and ls is because micross uk has the bare dies they have the octal matched transistors from that and lots of dies so that an asic can be produced so its easier to do the schematic capture using those devices as they have the dies so easy to add to a sub straight and inter wire weld on the prototyping machine which is a wonder to watch. on a magnified screen.
J3RK
I second the Linear Systems LS318 and LS358! They're excellent, and half the price of SSM22xx and a quarter the price of the MAT series. Nicely specced too. The LS318 and LS358 are the log-conformance parts. (great for exponential converters and such) They also have ultramatched pairs that aren't specced for this if I remember correctly. You can order them directly from Linear Systems, through Trendsetter electronics, and I think there are a few places in Europe that distribute them as well.
jhulk
micross uk has them

and why i like using them as im currently doing some chip designs that they are prototyping for me.
guest
quick question:

should the VCAs for this be linear or exponential? im thinking exponential so it more closely matches the FM algorithm, but linear would be easier, and would have a more clearly defined "off" state.
jhulk
exponential

the phase can be linear
Isaiah
guest
Which one will feel most natural when you manually open up the audio VCA?
To clarify, when I say "natural", I mean to avoid the situation you often find if a linear pot is used as an audio attenuator (where most of the pot's effective range is only across a small part of the pot's rotation, not spread out across the pot's whole rotation.)

Would it be difficult to implement both linear and exponential and enable the user to select either with a jumper, or header and shorting pin on the PCB?

Is it especially necessary that the (audio) VCA can close completely?
I'm not for or against it, just wondered. Obviously the PM VCA should be able to fully close.
guest
so, it depends a lot upon what people want to drive it with. linear envelope generators would work better with an exponential VCA, and vice versa. the attack portion is the part that sounds different between the two.

im leaning towards a dual scheme, like you suggest. basically a linear VCA driven with a current source that can be either linear or exponential, depending upon whether the signal is applied to the base or the collector of the reference transistor. it will require thermistors for exponential mode, which isnt too bad, except that panasonic is end of lifing the ERAV series thermistors that are cheap.
Isaiah
guest
Any news on this?
guest
synthcube should have a DIY "module" coming out soon. it will be just the core of the wavefolder in a 14p wide-DIP format. i have yet to get all the dcumentation finalized, but with a few opamps it can be built into a simple module.

there is also a eurorack module in the works, that would have been done by now except for some other things that came up. so it got back burnered.
Permette
Wonderful Guest !
Many thanks for that.

Cheers !
guest
ive been filling out the documentation for it. got the basics up, a few more schematics will follow.

http://wiki.openmusiclabs.com/wiki/SineCore
trip
Great! Thank you for sharing. Can't wait to try this out, the demos sound incredible.
homeless_peep
That looks neat! I based my triangle to sinewave converter on that paper of yours,and even designed a (non optimised) version using the lm3046 bjt array. I experimented with folding using opamps and diode clipping (not a sinewave shape) on a guitar pedal and the sound is very distinct. distorted but in a very "original" way, almost like adding a weird reverb effect to it. the noise was terrible though and i never got down to revisiting that again.
folding can be used to implement real time, non linear frequency multiplication- might be a good start for an additive vco thing...
guest
thanks for reporting your experience, its great to hear someone built it up. the overdrive on it is pretty good. did you use 2 x LM3046?
trip
I quickly threw together a messy layout of the differential schematic on the wiki that should fit in 4hp - boards are untested / still on their way. Will report back when they arrive. If anyone's interested in the files I'll upload them somewhere.
homeless_peep
guest wrote:
thanks for reporting your experience, its great to hear someone built it up. the overdrive on it is pretty good. did you use 2 x LM3046?

no. 3 of the trannies make up he non linear stage and he other two make a voltage adder. i then used a differential opamp stage to convert the output to single ended. never got down to constructing the circuit because I only have smd lm3046 available, but he simulations look good. i can upload the schematics and simulations when i get back home later today.
it was designed as part of a chapter on my thesis, demonstrating how your saturation-cusp canceling method can be implemented with discrete differential pairs. the circuit i actually used is based on your OTA one, with some slight changes (can also share later).

attachments show the sinewave and sawtooth waves, derived from the triangle output of my vco. i have more measurements as well, that go way beyond the audio range (100khz+), the sinewave is satisfactory up to 10-15khz.
guest
the OTA one looks like its working well. the transistor one sounds like a discrete OTA version and not the barrie gilbert implementation?
homeless_peep
guest wrote:
the OTA one looks like its working well. the transistor one sounds like a discrete OTA version and not the barrie gilbert implementation?


exactly. It implements the exact same functions as the OTA circuit, but skips the whole current mirror part (inside the IC, in order to obtain a current output).
It is more complicated in terms of external components and value calculation (I tuned most of it by guestimating and trial-error), but might prove to be slightly cheaper to some extend (especially if you use some of the super tiny transistor arrays available nowdays).
Temperature stabilisation might be a desirable thing here. Using two LM3046 you can have both differential pairs in two different ovens (one for each IC), yielding a more consistent result. To be honest, I'm not sure how important that is in our field. I could hardly notice 1% distortion at those frequencies (3Khz+), so that's close to good enough for me, but I could certainly hear the harmonics in doepfer's "standard VCO", so it surely is a big improvement.
All in all, I think the OTA circuit was a very good idea. I don't see why I would look for anything different/better for generating a high quality audio sinewave from a triangle. (unless OTA's eventually become obsolete).
homeless_peep
I actually forgot to upload the transistor version. Here it is, along with the simulation result and a true sinewave of comparable amplitude, as a reference.
guest
looks good. you could probably do away with the second transistor diff amp summing stage, and just sum with opamp diff amp. i think there is a good example of a buchla vco using that method, although i cant remember offhand. that would definitely make it cheaper than an OTA, although the total price difference is pretty small if youre using both halves of an LM13700.
homeless_peep
the second D. pair is available in the package anyway, so I just went on and used it. However, you're right, and it can serve as the thermal oven for the saturating part instead.
trip
I was really excited by the demos of this, so threw together a board of the differential schematic... it sounds amaaazing! Needs a dual vca paired with the inputs to get the most out of it, but I like that it can fit in 4hp on a single board. I made a stupid error on the schematic for the mod pot, but otherwise it seems to be working fine - the offset pot has a fairly large deadzone either side of the centre of the turn, I've yet to measure it out.



ps. I don't really know all that much about best practices for board layout, any advice much appreciated![/img]
guest
the offset has a really wide range, and maybe too large. you can increase the 150K resistor at its wiper to reduce that. right now it goes from into saturation on either side, so that an input signal can pull it out.

the build looks good.
guest
i may have selected the 150k assuming a 5V supply, which means a 300k would be more appropriate for 12V supply. i have a few different designs on this right now, and i may have gotten that value confused with another.
trip
Grand thanks, I'll try swapping it out later.
trip
Had a bit of time to play around some more with this - I swapped out the offset wiper resistor to 300k and got more range on the pot. Increasing the input amplitude seems to clip the sine function into a square wave really early though, and the folding has a bit more of a pwm characteristic than a wavefolder. Scope shot of the amplitude sweep is here:



Could this be some more passives related to the voltage rails need changing?

You can see there's a fair bit of noise on the output as well, nothing too noticeable when it's mixed with a signal.

Here's the schema I made the board from:

guest
looks like youre getting the right number of folds, so its just a matter of amplitude of the input signal if you want to avoid clipping.
slow_riot
have been looking for a waveform modifier circuit and this is just fantastic, thanks for posting!

if someone can PM me this PDF I will be eternally grateful smile

B. Gilbert, "A monolithic microsystem for analog synthesis of trigonometric functions and their inverses,"
guest
i put it up on the oml site

/files/trig.pdf
slow_riot
Amazing thanks, the biasing part isn't immediately obvious and there is quite a big change from the first Gilbert iteration to the second.

I've been playing around with an OTA version as I have a bunch of them sitting around, but I might use your drop in part.

Have to agree that this circuit is really interesting.
guest
in the original paper from 77 there is a third configuration that uses transistors of different emitter areas to do biasing.

ill ping synthcube to see how the drop in boards are coming along.

i built up a 14 transistor version, and it sounds really good, but i think thats the limit of how many folds you can do without putting the transistors into reverse conduction.
hexinverter
What a fascinating circuit! The vast majority of the mathematical derivations in Gilbert's paper are well above my head, but the theory of operation is pretty neat. The paper from '82 features a glimpse into the IC implementation which presumably made its way into the AD639. That was cool to check out.

I've been playing around with the different configurations that Barrie proposed in his papers in simulation. Pretty cool to observe the levels change around the network while varying the network base voltage, Ex. I then built a couple practical circuits on the breadboard, including the SineCore implementation. Getting some rad sounding vowel tones out of this! Phase modulating with a ramp wave as source is pretty fun.

I figure I'll share my little experiments with the circuit here as well!


The circuit in test in the following screengrabs is the SineCore configuration, running off of +/-12V power. The source signal is a 10Vpp triangle wave, with amplitude adjusted manually through a potentiometer. The current sources are set to ~103uA (~6V bias, 750ohm network resistors), just as in the SineCore "basic connections - differential" configuration.



I seem to be getting some high frequency oscillations during transitions on the output differential amplifier. Adding some capacitance in the feedback path of the opamp seems to have quelled this. 100pF is what worked best for my messy breadboard, but your mileage my vary. [EDIT for clarity to anyone skimming the thread: Guest corrected me, 47pF is probably better, thereby keeping the cutoff above 20kHz. Also, impedance matching the diff amp nodes by placing a second 47pF over R9 in my schematic below, is a good idea]






During folding, the output levels approached around 20Vpp (as in the previous 'scope shot). This resulted in the output opamp clipping a bit. I used a TL0xx which isn't rail-to-rail, so clipping occurs somewhere just a bit more than 20Vpp when on 12V rails. Altering the tail current through the NPN diff pairs ('Bias current control' in the SineCore documentation) made the output amplitude closer to 10Vpp. Increasing the resistor R17 in my schematic to 200k (from 100k) brought the current down to ~120uA, from ~240uA. [EDIT: the SineCore schematic is revised to have what is the +12V node in this schematic below changed to GND. In effect this will solve the overdrive issue, and there's no need to change R17 if your current mirror is connected to GND instead of +12V!]





Peaks no longer clippy! This is fun!

All in all this makes a nice sounding little wavefolder! And in a minimal configuration makes a nice sine waveshaper. I was researching low distortion sine waveshapers and that's how I stumbled upon your OTA-based waveshaper improvement paper, Guest. Thanks for sharing your discoveries! And cool to see that Synthcube will be making some handy SMT boards available for everyone to play with. nanners
guest
great work! ive been digging into the circuit a bunch more lately, as im working on a complete module version. i settled on 47pF in the feedback path, just to keep the frequencies up to 20kHz. i also used a capacitor across R9 in your schematic, to keep the impedances matched.

also, thanks for pointing out the excessively high drive. the 100k to +12V is incorrect, and was meant to go to ground.
hexinverter
guest wrote:
great work! ive been digging into the circuit a bunch more lately, as im working on a complete module version. i settled on 47pF in the feedback path, just to keep the frequencies up to 20kHz. i also used a capacitor across R9 in your schematic, to keep the impedances matched.

also, thanks for pointing out the excessively high drive. the 100k to +12V is incorrect, and was meant to go to ground.


Oooh, I hadn't thought of impedance matching those nodes! Thanks. Seems obvious now, I guess it could also likely add some distortion to the overall function. Raising the cutoff seems like a good idea as well. Correct me if I'm mistaken but it could have a pretty noticeable impact when modulating with higher frequency PM or FM as well? hmmm.....

Very cool, looking forward to seeing your module! screaming goo yo
guest
there are definitely harmonics going well above 20kHz with PM, so it depends upon your hearing. i cant hear anything above 18kHz anymore, so i probably couldnt tell the difference. sometimes there are sonic effects if the signal is passed through other modules or mixers. for example, although you cant hear higher frequencies, they can still distort and overload amplifiers and then you hear those effects.

if you put a pot or CV on that 100k (200k in your case) resistor, you can adjust volume into clipping, or just modulate the amplitude.
wavefold
loving how this sounds, keeping an eye on this, definitely eyes...
daynehacks
Anything ever happen with the possibility of a DIY euro module??
guest
the main difficulty with a DIY is the super small transistors involved. i was talking with synthcube about having that portion of the circuit be put in production, but i havent heard back in a while.
slow_riot
I've been looking for a reason to use a bunch of OTAs and this is quite a good use for them, getting some matching between diff pairs and simplifying the output.

U can change the current amplifier driving the bias nodes to use single small resistor pushing a larger reference current into an opamp feedback network with all the PNPs in parallel. Personal taste and availability of board space notwithstanding.
guest
quick update: just heard back from synthcube, and boards should be getting in soon.

slow riot: whats your plan with the OTAs? are you using the inidividual diffpair configuration (rather than the one i used with all the emitters tied together)?
slow_riot
guest
thanks for posting that up.

one thing i thought was a bit nicer about the diffpair versions as compared to the stack of emitter coupled transistors, was that biasing was easier. you didnt need to use current mirrors, and could drive it single-endedly. is there an advantage to the differential drive youve shown? i could imagine that it would improve symmetry, and maybe improve accuracy as the impedance seen by the diffpairs are equal.
Permette
Looking forward to seeing it available at Synthcube.
Wonderfull work !
Thanks for that.

Cheers
Rex Coil 7
~wooosh~

the sound of this entire thread going right over my head

neato sounds, pretty pictures on the scopes

neato and pretty is good things
trip
I made another rev of my 4hp board a while back, the 12v instead of ground going to that node was what was causing my clipping issues as well. I made a pcb panel for it so it can be a permanent fixture in my case as well, it turned out quite nicely. Getting some amazing timbres out of this thing, huge thanks to guest for sharing his work!!



The two big pots are the attenuators for the incoming signals and the small one is the phase offset. Which may seem a bit backwards, but it was difficult to fit 3 full sized pots and all the components on one pcb - I also assumed that the initial phase would be more of a set and forget type parameter, but now I often find myself reaching for it... I'm happy with this though, any of the additions I would have made would have made it an exponentially more complex project, and I figure guest still has a full module coming down the line?
guest
thanks for sharing, your module looks awesome. how much phase angle does your phase knob adjust? this is one of the things i wasnt sure about for the module im doing (all finalized, going into production real soon). i settled on +/-180degrees, with a solder jumper for +/-800 degrees.
goldenhours
This is all very nice. Following to see where it's going.
trip
My pot gives +/- 180 degrees of phase angle, it's really nice to push the phase mod into and out of saturation to give things more edge.

Was so busy putting the thing together I didn't check the features fully and realised I'm not getting folds anymore d'oh! Going back over to see what else I might have changed from the last rev that could have caused this.

I'm excited to see what you've come up with for the final version!
trip
Ah I caught it, pin 5 J2 - the top of the 51k resistor network is missing a connection to vcc.
guest
this finally made it into a module by WOMS (west oakland music systems). i put a few quick videos up:



there are more at the oml channel:

https://www.youtube.com/channel/UCIvT8tGiPe4eD_3h1PPwNOA
Bartimaeus
Did this ever make it to Synthcube? I'm not finding anything when I search Sinulator.
diophantine
Yes, I just noticed this thread for the first time - has anything been made available DIY? It looks awesome!
guest
synthcube will be getting it soon, but dont know the exact time frame. right now they have the very-DIY breakout board for the sinecore modulator. the breakout board has approximately half as many folds, but you can stack two of them in parallel to get the same depth as the sinulator module.
jorg
WOW! Great job!
cygmu
I love this circuit so much. Finding out about it here sent me down a huge Barrie Gilbert rabbit hole which has been some of the most enjoyable circuit-studying I've done. Thank you guest for your amazing work here.

A small clarification: on the triangle sine shaping video it is stated that turning up the gain gives the 2nd, 3rd, ... , 6th harmonics, but I think it's actually the 3rd, 5th, ... 11th harmonics, as compared to the fundamental, right? I can't see a way to get even harmonics by shaping a triangle wave with this circuit.
jorg
Barrie Gilbert is the soul of analog electronics. Most of our analog synth technology would not exist without him. And I believe he's still alive and well!
guest
cygmu wrote:
A small clarification: on the triangle sine shaping video it is stated that turning up the gain gives the 2nd, 3rd, ... , 6th harmonics, but I think it's actually the 3rd, 5th, ... 11th harmonics, as compared to the fundamental, right?


hey cygmu, thanks so much for catching this. you are right here. i updated the blurb on the video with the correction.
cygmu
Thinking a bit more... can you get even harmonics from a triangle by changing the offset? I guess the gain would then take you through all the evens. Is that right?
guest
yes, i think you are right again. but, its not a fixed offset, its actually more like a unipolar gain, so the offset needs to scale with the amplitude. with the triangle wave, the peaks of the triangle wave have to conicide with the peaks of the sinewave to get a pure tone. each time you amplify the waveform so it can stretch to another peak, you get another harmonic. but, if you amplify in a bipolar fashion, the triangle wave extends in each direction, so you have to go an extra peak in each direction, so an increase in 2 harmonics. if you start in a position that gives the 2nd harmonic (by adding a fixed offset), you can use a bipolar amplification to give all the evens. but, if you use a unipolar amplification, so you only stretch your waveform in one direction, you can get all the harmonics up to the 12th i think. this could be accomplished by adding a DC offset to the input triangle wave, so it goes from 0V to 5V, and then run that into the VCA input. if you add a negative 5V CV to the MOD input, that will rest the 0 point to the beginning of the sinewave shaper, so you can get all 12 harmonics, and not just 6. ill have to try it out, as thats pretty crazy if it works.
synthcube
Bartimaeus wrote:
Did this ever make it to Synthcube? I'm not finding anything when I search Sinulator.


we do have the sinecore pcbs here, and hope to have the sinulators here april/may 2019
guest
just tested out the triangle wave + offset setup, and it does give 1-13 harmonics. the harmonics get a little shakey, as both offset and gain need to be perfect for a perfect alignment, and its a pretty wide range for that sort of precision.
cygmu
That's fantastic. This circuit is wonderful.
atl
I bought one of the retail WOMS units, and it is a fun little beast.
Rob Kam
There's nothing about the Sinulator at Synthcube nor at WOMS?
guest
sorry about this. the first units were on sale at perfect circuit, but those sold out, and there has been a delay in getting more in stock. i know WOMS has them in inventory, they just need to get to the distributors.
LektroiD
This looks like an awesome project. When they become available again, I'd be interested in one.
guest
ill keep you posted. should be ready later this week.
Dogma
me too please? Ive been looking at this project for ages
brilliant smile
basicbasic
Is this similar to how the Happy Nerding FM-Aid works? I love that module but would prefer a DIY option.
guest
it does a similar thing, but i think its a different approach. the fm-aid looks like a wavefolder followed by a sine shaper. this allows the various other waveshapes to be created before the sine shaper. the sinulator does wavefolding and sineshaping in one step, so you only get sine output. there are 2 options here: the sinulator, which is a prebuilt module, and the sinecore modulator, which is a just a breakout board for the core of the sinulator, and the user has to build some buffer amps and a faceplate for themselves. the sinulator is equivalent to 2 sinecore modulators cascaded.
guest
well, that was a long "week". perfectcircuit has them in stock again:
https://www.perfectcircuit.com/west-oakland-sinulator.html

and WOMS has a website up for it now, and you can contact them directly as well:
http://www.westoaklandmusicsystems.com/modules/sinulator/index.html
MUFF WIGGLER Forum Index -> Music Tech DIY  
Page 1 of 5
Powered by phpBB © phpBB Group