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today> Muied Lumens Frequencies
 Forum index » DIY Hardware and Software » Thomas Henry designs
The VCO-555
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gimble88



Joined: May 21, 2022
Posts: 18
Location: Oregon

PostPosted: Sat May 28, 2022 6:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

Well, it's pretty well fixed. The simulation you did was brilliant and pointed to the lack of gain at IC3d as the problem. Thanks so much for that.

We had to expect that with a set of symptoms as goofy as the ones I had that there was a pretty high chance of bone-headed-ness involved. Unfortunately, it was pretty extreme. In addition, I was focused on the 555 and it's interaction with the LM13700 so that's where I was most carefully checking components. Again the simulation made it clear where the problem actually was.

I remembered that as I was trying to get the oscillator to work after the rewire that I replaced IC3. Due to my not-so-great PCB design I found it easier to remove R22 as it was a little bit in the way of drag soldering the IC. Apparently, I replaced it with the wrong value. I believe there were a couple of the little 1206 buggers sitting on the bench and I must have grabbed the wrong one at the last minute as I installed it. I keep a meter with tweezer probes on the bench and check every part as I install. Well.... I guess almost every part. Embarassed

Thanks again for the patient replies and great ideas.

The only issue I'm chasing down now is that the sine amplitude is only about 6.5V PP. I know this design sometimes has lower output on the sine and mine was about 8V PP before the disaster.

I can't ask for any more help with this oscillator. For one thing it sounds good and if the sine output is low - hit the VCA harder.

I'll continue to sniff around but I have more modules to build including more 555 oscillators.

I gonna get to know that simulator, what a powerful tool.

Again, I couldn't ask for better or more generous help. Hope the vaccine booster blahs go away soon.

spence
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elmegil



Joined: Mar 20, 2012
Posts: 2169
Location: Chicago
Audio files: 16

PostPosted: Sat May 28, 2022 6:52 pm    Post subject: Reply with quote  Mark this post and the followings unread

Excellent!

You're quite welcome. I enjoy troubleshooting.

Falstad's simulator is a go-to for me whenever I'm looking at something and scratching my head. Doesn't always work because occasionally you'll have things (like Buchla) that push the components beyond their normal states, but it has helped me SO many times.
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