The VCO-555

carlo64 · Joined: Apr 02, 2020 Posts: 18 Location: Italia

Hi,
unfortunately after making the change I find myself with distorted waves like the hedefalk user and I can no longer fix them .. Crying or Very sad

wackelpeter · Posted: Sun Apr 19, 2020 9:48 am Post subject:

Then perhaps try another LM13700 and as i looked into my outprint of the schematic i saw that i reduced R34 from 100K to 56K, at least i marked it on the paper...

carlo64 · Joined: Apr 02, 2020 Posts: 18 Location: Italia

carlo64 · Joined: Apr 02, 2020 Posts: 18 Location: Italia

Ok! now I have a nice wide sine wave, but unfortunately when the frequencies go up I have all the waves very very distorted .. (the square becomes a trapezoid etc) will depend on the economic components

Thanks for support!
Carlo

wackelpeter · Posted: Tue Apr 21, 2020 2:00 am Post subject:

what fixed the sine?

and btw. can those distorted looks on your waveshapes come from your oscilloscope AC vs DC coupled?

carlo64 · Joined: Apr 02, 2020 Posts: 18 Location: Italia

elmegil · Posted: Tue Apr 21, 2020 10:56 am Post subject:

The mess in the middle looks like you haven't calibrated the triangle yet? (the "blip" near the zero crossing)

Going immediately to clipping on the sine shaper makes it look to me like whoever suggested this is trying to boost the signal *before* the shaper, and it's boosted WAY to much. Reduce how much you're boosting (dunno the specifics of the ckt at this very moment, and no time to go read up immediately).

edit: also looks like your triangle may not be centered about zero. That's another important calibration step.

carlo64 · Joined: Apr 02, 2020 Posts: 18 Location: Italia

Hi Elmegil,
I don't have a trimmer to adjust the triangle, how should I do it?

Yes, maybe the sine wave is at the limit, I have to try a compromise with the resistance value.

Thank you

wackelpeter · Posted: Wed Apr 22, 2020 6:35 am Post subject:

Without looking too much into it, i tend to say that you can adjust the offset if you play around with the values of R17 and R21.

elmegil · Posted: Wed Apr 22, 2020 7:01 am Post subject:

I must be remembering the wrong TH VCO, I'd swear there were trimmers for offset and the bump.

carlo64 · Joined: Apr 02, 2020 Posts: 18 Location: Italia

carlo64 · Joined: Apr 02, 2020 Posts: 18 Location: Italia

Aleencabralia · Joined: Feb 10, 2020 Posts: 5 Location: Brasil

Carlo, it was addressed in the previous page, it might be a fake op amp. Try and buy some tl074 from a trusted seller.
I built 3 of these and I´m having 2 problems: One is the tuning (Is my first osc built, so, pretty noob). I get the first 3 octaves, but the highr are sharp. I think I don´t get how the HF trimmer works: It´s like the calibration one? Like, when freq is flat, I move it even flatter, then go back, re-tune, repeat? Or it just "corrects" the freq? Tryed it in both extremes, HF are always sharp (When I tune them, The lower ones get flat). I matched the transistors using Ian Fritz method.
The other issue is that my sines are triangles! The round trim (I used a 50k in one and 100k in the other 2) just lower the amplitude a bit, the other one doesn´t seem to do anything!!
Any help is really welcome.

NuttyMonk · Joined: Jun 30, 2020 Posts: 63 Location: UK

wackelpeter · Posted: Wed Jul 22, 2020 1:58 am Post subject:

The trimmer is connected with two pins one of it's outer legs, and the wiper with the other outer leg conected together. Doesn't matter which one you're usig only the direction of the resistance getting higher or smaller would be the opposite.

Common practive to not keep legs on resistors or trimmers unconnected or floating... So the unused leg will simply be connected to the wiper...

NuttyMonk · Joined: Jun 30, 2020 Posts: 63 Location: UK

Thanks wackelpeter. I understand. I've seen that before in schematics and wondered about it but it makes sense. I guess it prevents the possibility of interference on the floating leg of the pot.

Thanks for the quick reply.

Cheers

NM

carlo64 · Joined: Apr 02, 2020 Posts: 18 Location: Italia

Resolved! I replaced the tl074 (new grrr) with old recovery smd with an adapter and now the waveforms are perfect. (just some small difference in output level but I'm happy!)
Thanks Aleencabralia and thanks to everyone!
Carlo

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

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

injektilo001 · Joined: Aug 21, 2020 Posts: 10 Location: Chile

Hello Everyone, I'm Jean Paul from Chile
I was wondering if somebody has a working single sided PCB and layout from this beautifull VCO for etching myself?
I've been looking like crazy everywhere.
(If somebody has the same kind of files for the Thomas Henry X-4046 it will be wonderfull too).
Hope somebody can help
Cheers from Chile

warpeggio · Posted: Sun Dec 13, 2020 1:56 pm Post subject:

Greetings, fellow synth nerds!

I've made a stripboard layout for Thomas' design. I was running low on stripboards in my parts bin, so my goal was to fit the whole shebang onto a single 93x55mm stripboard. I think the result will make some folks bristle, as I've broken some of the usual layout rules. However, i can confirm this layout works, as i've spent the weekend with it on my bench.

When constructing this board, my method was to work from left to right across the board, soldering 2-5 components at a time, which allows me to build up clusters of components relatively easily. The area around R14 and R32 is particularly prone to shorts, among some other areas. When you see that component legs may come together like that, its a good idea to slip some wire insulation over the component leads. You'll see examples of this on my board.

I will admit that i made errors both in the draft layout, and in my construction. Friends, you must stick with troubleshooting to get far in this hobby! My draft was missing 1 jumper wire, and 3 trace cuts on the left side of R36. The trace cut issues nearly overheated IC3. I made a construction error of omitting the jumper that ties the emitters of Q2/Q3 together, which resulted in the circuit having a narrow oscillation range in the supersonic.

Sorting all these issues out, the build tracked 1v/Oct nearly effortlessly. I am getting 5 octaves now with my inaccurate CV source. I will update when i am able to test with a precise CV input.

The BOM shows values for 15V supply as in the original schematic. The values for 12V supply are provided as well. Also, per Fonik's PCB notes, i've used his part numbering for R25, R26, and R55.

Changelog
v2020-12-13a: The colors on the power connector (PH1) on the right side of the board were wrong. This has been corrected.
v2020-12-13: Initial upload

20201212_222755.jpg

Description:

Filesize:

561.82 KB

Viewed:

125 Time(s)

This image has been reduced to fit the page. Click on it to enlarge.

20201212_223020.jpg

Description:

Filesize:

661.91 KB

Viewed:

157 Time(s)

This image has been reduced to fit the page. Click on it to enlarge.

TH555VCO.png

Description:

Filesize:

508.96 KB

Viewed:

209 Time(s)

This image has been reduced to fit the page. Click on it to enlarge.

NathanS · Joined: Sep 13, 2020 Posts: 3 Location: Iowa, USA

Some time ago I was taking an electronics course for a physics degree and was allowed to do an analysis of this circuit for the final project. This involved both bread-boarding the circuit, as well as writing a paper describing how it worked.

One of the things that resulted from this was a KiCad schematic which I've done quite a bit of tinkering on in an attempt to decompose it into its core functions. It has been my intention to make a real nice PCB from it as well; though the few attempts I've made haven't resulted in nice enough boards to make me want to give out those files as well --- not yet anyway.

Regardless, I figured I'd give out the schematic so far in the hope that it would save someone a ton of time if they had plans to transcribe the original to digital. Also included is a PDF print-out, in case someone is interested in seeing it without using KiCad.

I'd be interested in hearing any recommendations for modifications to the file to make it more understandable or more generalized. There is currently a lot more space for comments to be added, and I'm sure it could be used well.

Edit (2021-02-03): Changed out PDF to a properly formatted version that allows text selection. Updated the KiCad schematic to the version the PDF was plotted from. The only diffs in the schematic file are of a couple of connectors (J2, J3).

Edit (2021-08-16): Fixed wrongly connected wire in the sawtooth shaping sub-circuit. R20 was connected to U4 through pin 2, where it should have been connected to pin 7. It was making some interesting ramps, anyway... Embarassed

The schematic as a whole was revised. It's a bit more organized and hopefully more understandable as a result. A few more references were linked in, and my notes were expanded on a bit. R27 and R24 were changed based on Fonik's suggestion a ways back in the thread. Lastly, the OTA's unused buffer's input was grounded - which I'm hesitant to claim makes any difference.

I did make a PCB using this version which I just finished putting through its paces. I haven't checked how well it tracks, but it sounded good and I'm reasonably confident no major bugs are present at the schematic level now.

Thomas_Henry_555VCO.pdf

Description:

Download (listen)

Filename:

Thomas_Henry_555VCO.pdf

Filesize:

134.38 KB

Downloaded:

2902 Time(s)

Thomas_Henry_555VCO.sch

Description:

Download (listen)

Filename:

Thomas_Henry_555VCO.sch

Filesize:

57.75 KB

Downloaded:

228 Time(s)

wallybob · Joined: Sep 26, 2015 Posts: 7 Location: Iowa

Thanks a lot for posting the KICAD schematic file for this!

Alfredo · Joined: Nov 20, 2008 Posts: 52 Location: Spain

I have this board that someone gave me for free. Look very similar to the Fonik one and sound fantastic, all potentiometers work as it should as well as the modulation inputs. Only problem is I can't calibrate because the HF trim R36 doesn't do nothing,maybe the person who designed the board made a mistake, anyway my knowledge is not sufficient to detect the problem.
I show you some images of the plates in case someone can see the problem.
Any help appreciated, thanks!

https://www.youtube.com/watch?v=co-Rp9sCECs

BACK.jpg

Description:

Filesize:

2.79 MB

Viewed:

137 Time(s)

This image has been reduced to fit the page. Click on it to enlarge.

FRONT.jpg

Description:

Filesize:

3.72 MB

Viewed:

143 Time(s)

This image has been reduced to fit the page. Click on it to enlarge.

ESTA SI.jpg

Description:

Filesize:

4.31 MB

Viewed:

156 Time(s)

This image has been reduced to fit the page. Click on it to enlarge.

elmegil · Posted: Sun Feb 07, 2021 2:03 pm Post subject:

Did you mirror your bottom-side scan around with software? Normally there's no way to scan it so that the holes on one side line up directly with the holes on the other, but that's what it looks like to me.

So the circled leg of R36 is supposed to be ground, it ties to D2 where D2 is also supposed to be ground. I would verify the continuity between those two points, that your solder joint there was good, and that both points show continuity to ground. That would be the most likely cause for a problem.

If that all seems correct, next thing would be to measure the cathode of D1 when things are powered on and verify that you're seeing control voltage there, that tracks the linear FM input with the pot all the way up. Then measure the wiper of the trimmer and make sure that it's changing when you turn the trimmer. It is possible that the trimmer is defective if your solder joints are solid and it doesn't do anything.

NathanS · Joined: Sep 13, 2020 Posts: 3 Location: Iowa, USA

It looks to me as if R2 and R23 should be swapped around. At least according to the original schematic, R2 should go to ground and the trimmer R1, but it's going out to D1 and IC3-pin7 - as R23 should.

Thus in that pcb, R2 should be 22 kOhm while R23 should be 390 Ohm. Does this match up with how it's been put together?

Alfredo · Joined: Nov 20, 2008 Posts: 52 Location: Spain

Hello elmegil, thnaks for your answer. I scan the board with a desktop scanner and mirrored with photoshop, then I followed the tracks and drew them with a Sprint Layout software so the image of the third photo is the same as the board.
Verified continuity between circled leg of R36, diode and ground, I tried various trimmers, this timmer seen don't do nothing, no changes in pitch or voltage when turn it. I thing the PCB has a routing error but i don't have enough knowledge to compare schematic and board Sad

board 2.jpg

Description:

Filesize:

5.37 MB

Viewed:

120 Time(s)

This image has been reduced to fit the page. Click on it to enlarge.