Ah, yes that is fun stuff. I have seen this sort of thing, sorting extremely tight tolerance ceramic sleeves for a fiber optic project and with wavelengths of sorted laser diodes.. You expect a Gaussian distribution within the stated bounds, but then it turns out that the manufacturer is dipping int...

measure that right at the output of the buffer amp. So I figured it out. Ableton's built in tuner goes whacky around the 3-5k range, I tried another vst tuner, same thing. A friend of mine suggested using my multimeter for hz measurements and I managed to tune it perfectly. Thanks again to all who ...

im not sure the saturated OTA is much different. i think the equation stays the same, but k is multiplied up at the expo converter rather than in the OTA. the expo reference current just becomes k*I. edit: OK I've convinced myself they are the same. I ran the numbers and get that the frequency of o...

That is helpful, thanks. So really it's pretty evident that if there is a max the Iexpo that can be delivered to the OTA, then as you decrease k, you lower the max frequency of the osciallator, all the way down to zero. Using a saturated OTA with FM signal being delivered to the expo doesn't have th...

Damn, now that I think about, you may be right. I think that if you decrease the FM index, then decrease the cap size to keep the same base frequency, the modulation depth will stay the same, because the same Iout of the OTA charging the smaller cap offsets it. Damn. My brain's gonna explode. So the...

so, is your current thinking that the HF linearity issue is solely the expo converter issue? for example, at full FM CV you get tracking to 10kHz, at 50% FM CV you get tracking to 5kHz, and at 10% FM CV you get tracking to 1kHz? Yeah, I think so. I mean, the OTAs are multiplying the DC value from F...

Well shit, guys. 2 pieces of good news: 1) Somehow, and I have never seen this before, something was wrong with that LM13700. I grabbed a few others from a new bag of them (Tayda), and voila, Iabcs are balanced. I can put 100R resistors on both Iabcs out of the expo and the waves are the same size. ...

Hmm, interesting indeed. So, I don't know if it is related but I found that after going back to the 100R Iabc resistors yeseterday, I had been checking the tracking without looking at both waves. What was happening was they were both the same size at low frequencies, and then diverging to the point ...

I did just realize I am violating this: "The limitations are that the signal current not exceed ID / 2 and that the diodes be biased with currents. In practice, replacing the current sources with resistors will generate insignificant errors." My Id is about 750uA right now, and with my low impedance...

was your test with various FM indexes done with the same frequency CV range, or the same output frequency range (increasing frequency CV as FM CV goes down). the latter will definitely shift down the frequency at which you see HF issues. also, if this is being driven by a PNP expo current pair, the...

Hmm, I'll have to look at that again. I'm pretty sure that the rolloff point of flatness in the v/oct response came down the lower the FM index voltage was. I agree in theory this shouldn't be happening, but if I'm looking at the same frequency range for a test at various FM indexes, this has to poi...

So I think I was effectively compensating for the balance with both the 20k resistors and the trimmer on one of the 4.7k OTA resistors. The major problem there is that 20k limits the top end Iabc too much. I went ahead and pulled those out and just put in some matched 100R resistors to take that out...

Would it make any sense to do something like this to improve Idiode on the 13700?

https://tinyurl.com/ycq5ra7t

Yeah, 555 is cool, but it uses dividers from the supply rails for the trigger points. Kind of defeats some of the purpose for a precision shcmitt trigger in this case without being able to have a stable 5V or whatever reference IMO. Other than that though, yes 555s are pretty awesome! Will check out...

this looks like a lot of fun! the waveforms look really good as well. The one thing that doesn't show up on this schematic is that I have to have a trimmer on one of the 4.7k resistors to the OTAs in order to make the waves the same amplitude. I also had to use those 20k resistors on the Iabcs to t...

cygmu wrote: ↑

Mon Feb 22, 2021 3:33 am

Looks very cool.

Before I tie myself in knots: am I right that the two op amps at the left end of the drawing have their terminals mis-labelled?

Yes, that is most definitely wrong haha! Was just quickly transcribing my schematic from notes to Kicad and clearly botched that!

Yes, I think the Serge QUO is basically a self-oscillating state variable filter. Neat that you get sin/cos tri and square directly from the core. Minimal processing to get a clean sine and saw from there if you want. Question: How would sync work in this design? Great question! :D I *think* the ca...

That is no accident about the form resembling a SVF! One can build a very nice sine wave TZ Vco using this mindset . doepfer has one as a product actually!

The one thing that doesn't show up on this schematic is that I have to have a trimmer on one of the 4.7k resistors to the OTAs in order to make the waves the same amplitude. I also had to use those 20k resistors on the Iabcs to the OTAs. If I use smaller and smaller resistors, the difference in wave...

Something new I've been working on the breadboard. I got the idea for this when reading Tietze and Shenk and this example of a quadrature function generator: quadgen.jpg I had actually been playing with making a trapezoid VCO, but then I realized one can very easily form the trapezoids by just summi...

There are 2 different DG403 in TH (on mouser anyway). There's the regular Vishay one and then Maxim's versions. The regular one is ok, but it has pretty high charge injection (60pC). The Maxim one is crazy expensive ($11) but looks improved on the specs. I haven't used this one. If you're ok with +/...

That is fast! Yeah, in this case I am using 3 comparators: 2 for a window that triggers the flip flop, and a 3rd which is a zero crossing comparator for one of the 2 signals in the quadrature feedback loop. Hysteresis on the zero crossing one would be most disastrous for that, so a no go there, or u...

Another one I just found, which is kind of an odd duck is the TL712. I tried it out and it is FAST. It has 3 state outputs and doesn't need a pull-up. It's interesting because it runs on single supply 0 to 7V, put has a huge differential input range. I tried it as a zero crossing detector on a a10Vp...

Can lm306 run off -12 / +12? Or just 0 to 12v? It's hard to tell from the datasheet. I *think* it's saying the max differential supply voltage is 30V I think so, the datasheet specifies VCC+ = 12V VCC- = -3 to -12V (unless otherwise noted) for the electrical characeristics. The only reason I know a...

Can lm306 run off -12 / +12? Or just 0 to 12v? It's hard to tell from the datasheet. I *think* it's saying the max differential supply voltage is 30V