I’ve read Rene’s page a few times but I feel it’s a tad light on NTCs I will read the kassutronic post when I get a chance.
I was totally confused by the layout, thought this was some unusual exponential circuit typology I had not seen before… looking again it’s totally obvious 
lol
Here is a table of voltage vs frequency for anyone else working with the XR2206. I think this was with two .47uf film caps in parallel. It will scale with different capacitor values. The supply is +12V to gnd. Yes, the control voltage is negative wrt gnd and there is no negative supply to the XR2206.
| volts | freq |
|---|---|
| 2.851 | 20 |
| 2.744 | 53.2 |
| 2.471 | 160 |
| 2.366 | 202 |
| 2.244 | 249 |
| 2.069 | 318 |
| 1.815 | 420 |
| 1.619 | 500 |
| 1.335 | 612 |
| 1.061 | 722 |
| 0.726 | 857 |
| 0.429 | 976 |
| 0.375 | 1000 |
| 0.234 | 1056 |
| 0.008 | 1148 |
| -0.2178 | 1241 |
| -0.45 | 1339 |
| -0.852 | 1512 |
| -1.231 | 1673 |
| -1.737 | 1896 |
| -2.038 | 2096 |
| -2.988 | 3012 |
| -4.31 | 5549 |
| -5.46 | 11962 |
| -5.7 | 15338 |
| -5.86 | 18831 |
I think this is the schematic as tested. I do not think there were any last minute additions.
Anyone built Aidan Taylor’s Prism VCO?
Looks pretty simple. Maybe too simple. (No ramp wave output though. And no PWM, but that would not be hard to add.)
Here’s a new one for me, don’t like LCD screens but this is pretty interesting regardless.
Found some interesting stuff in the Erica synths DIY archive: GitHub - erica-synths/diy-eurorack: Erica Synths DIY Eurorack Modules
The VCO-3 uses something called the KR198NT1A, available here: https://synthcube.com/cart/erica-synths-diy-rare-parts
This archive is really cool, there are gerbers for everything, so if somebody wants to do a JLCPBC order, there are quite a few in here I’d be interested in, although some of them have harder-to-source bits.
They are all gone now but I did a run of the vco, vcf, and bassline. I ordered the weird ICs directly from Erica. I printed them really early when they came out and there’s been some fixes to the files since then. The vcf panel had a mistake but otherwise sounds nasty! The bassline is a doozy to build but sounds great except for a problem with the subosc which they apparently have a fix for that involves cutting a trace or two.
I have not built the vco yet tho
Pretty sure @ChristianBloch built his vco tho and posted about it somewhere
Yup, I built the VCO and it works like a charm!
I built the VCO but can’t get the octave switch to work. I built the bassline but it’s not working all that well. @ChristianBloch was there anything you had to do to the VCO or the Bassline or the VCF to get them to work correctly? They only sorta work for me. I thought there was something we needed to do to all of them.
@BlackDeath the Bassline module is said to be Erica’s most difficult module to put together and it really is a doozy. That ain’t no joke! Honestly, from what I have heard on the parts that are working I honestly wouldn’t bother building it again. I think the Weston Bass module that I put together is FAR superior to this Erica Synths one. I know it’s a VCO thread but am pointing that out since you mentioned Erica Synths modules.
An LFO maybe ?
As far as I remember, no. Just regular calibration.
Does your subosc on the bassline behave? Mine does not. Randomly switches between octave down and something else haha. I noticed they have a note for it on their updated build notes, let’s see if I can find it again
Edit—getting page not found error on ericas GitHub 
A bunch of vco circuitry in an epoxy block. FM and v/oct. Twenty pounds each. Used in the Pittsburgh V1 Oscillator.
Woah, i thought this was just a 7 seg display at first.
Google-fu brought me here:
This is really cool, if I understand it - I send this to JLCPCB, and with SMD manufacture, they send me a VCO core on a chip?
Doesn’t seem they’re quite there yet:
They use SMT parts but are designed for hand soldering. As there are parts on both sides of the board a substantial redesign might be required for automated assmebly by a pick-and-place assembly service.
(last update 2015)
Read through the topic but didn’t see an answer - I’m just wondering why you (or anyone else) is looking for a non 3340 VCO. Just for the sake of something different, or is there something else you want that you’re not getting?
I only have 3340 based VCOs so I’m curious if there’s anything I’m missing out on.
Either way, here’s two more.
A 555 vco and a 556 VCO. Eagle and Gerber’s are on GitHub, linked at the bottom of the page.
Note, I haven’t built either of these and don’t know if the 555 design is functionally different from the other based off the MFOS design linked elsewhere in the thread. I just finished building another module from this guy’s Gerber’s and have two more of his Curtis 3340 VCOs on the bench.
Some of it is nerdatry, but I’m actually looking for a chip/circuit that has direct sine wave output (no filtering circuitry required) with precise tracking in the low octaves to use as a main sub. 3340’s also don’t have easy “through-zero” FM, meaning FM sounds aren’t very musical as they don’t stay in tune. the SSI chip does have TZFM, but nobody has put together an open source schematic for it yet.
3340s are known to have some problems or at least pitfalls — the frequency variation with PWM, oscillations on the pulse wave edges, large differences in output signal amplitudes between waveforms come to mind. All of which can be dealt with in external circuitry but they complicate things. 3340s also lack features one might want such as a sin wave output, quadrature outputs, through zero FM. This is not to say a 3340 design is a terrible choice, but depending on one’s needs, something different may be better. It’s always nice to be aware of alternatives.
