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 Forum index » DIY Hardware and Software » Thomas Henry designs
The VCO-555
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carlo64



Joined: Apr 02, 2020
Posts: 13
Location: Italia

PostPosted: Sun Apr 19, 2020 4:42 am    Post subject: Reply with quote  Mark this post and the followings unread

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
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wackelpeter



Joined: May 05, 2013
Posts: 461
Location: germany
Audio files: 10

PostPosted: Sun Apr 19, 2020 9:48 am    Post subject: Reply with quote  Mark this post and the followings unread

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...
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carlo64



Joined: Apr 02, 2020
Posts: 13
Location: Italia

PostPosted: Sun Apr 19, 2020 11:54 pm    Post subject: Reply with quote  Mark this post and the followings unread

wackelpeter wrote:
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...


Thanks, I'll try this too. I will also try to find a power supply at 15 + 15 instead of 12 to also do some other tests.

Carlo
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carlo64



Joined: Apr 02, 2020
Posts: 13
Location: Italia

PostPosted: Tue Apr 21, 2020 12:39 am    Post subject: Reply with quote  Mark this post and the followings unread

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
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wackelpeter



Joined: May 05, 2013
Posts: 461
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PostPosted: Tue Apr 21, 2020 2:00 am    Post subject: Reply with quote  Mark this post and the followings unread

what fixed the sine?

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

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carlo64



Joined: Apr 02, 2020
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PostPosted: Tue Apr 21, 2020 10:20 am    Post subject: Reply with quote  Mark this post and the followings unread

wackelpeter wrote:
what fixed the sine?


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



R34 from 100K to 56K!


AC if I use analog oscilloscope, automatically if I use economic hantek connected to the PC.
I attach some pictures, as the frequency increases (say after 3/5 kHz) the distortion increases

(I'm not very good, I still have to learn ..)

triangular and square
high frequency
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.

low frequency
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.

Carlo
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elmegil



Joined: Mar 20, 2012
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Location: Chicago
Audio files: 16

PostPosted: Tue Apr 21, 2020 10:56 am    Post subject: Reply with quote  Mark this post and the followings unread

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.
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carlo64



Joined: Apr 02, 2020
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PostPosted: Tue Apr 21, 2020 11:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

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
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wackelpeter



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PostPosted: Wed Apr 22, 2020 6:35 am    Post subject: Reply with quote  Mark this post and the followings unread

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.
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elmegil



Joined: Mar 20, 2012
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PostPosted: Wed Apr 22, 2020 7:01 am    Post subject: Reply with quote  Mark this post and the followings unread

I must be remembering the wrong TH VCO, I'd swear there were trimmers for offset and the bump.
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carlo64



Joined: Apr 02, 2020
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PostPosted: Wed Apr 22, 2020 7:59 am    Post subject: Reply with quote  Mark this post and the followings unread

wackelpeter wrote:
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.

and I thought I had found a vco with few adjustments Laughing Laughing

I will have to do some experiments!

Carlo
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carlo64



Joined: Apr 02, 2020
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PostPosted: Wed Apr 22, 2020 8:02 am    Post subject: Reply with quote  Mark this post and the followings unread

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


they would have helped me a lot
Sad
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Aleencabralia



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

PostPosted: Sun Jul 12, 2020 8:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

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.
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NuttyMonk



Joined: Jun 30, 2020
Posts: 5
Location: UK

PostPosted: Tue Jul 21, 2020 5:16 pm    Post subject: Reply with quote  Mark this post and the followings unread

fonik wrote:

anyways, here is a picture of a PTC mounted on top of a super matched pair for a 555VCO. i think you get the idea:

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


Thanks a lot!


Hi Fonik, love the way you have done the thermal mating here. What is the metal cap you used? Are they easy to come by?

On another matter i have a question about the "Sine Round Trim R24" trimpot in the schematic. Is it wired through directly as shown there with nothing connected to the wiper? If so it won't be a voltage divider and it also won't be a variable resistor. What gives? I'm relatively new to electronics so maybe i'm missing something obvious about how this is drawn and what it means.

Cheers
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wackelpeter



Joined: May 05, 2013
Posts: 461
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PostPosted: Wed Jul 22, 2020 1:58 am    Post subject: Reply with quote  Mark this post and the followings unread

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...

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NuttyMonk



Joined: Jun 30, 2020
Posts: 5
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PostPosted: Wed Jul 22, 2020 8:09 am    Post subject: Reply with quote  Mark this post and the followings unread

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
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carlo64



Joined: Apr 02, 2020
Posts: 13
Location: Italia

PostPosted: Sun Aug 02, 2020 11:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

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.
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