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 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
Steiner VCF Reso problem
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Pehr



Joined: Aug 14, 2005
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PostPosted: Thu Dec 08, 2011 6:31 am    Post subject: Steiner VCF Reso problem
Subject description: too loud
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I've got three steiner VCF from CGS, the old version (green PCB).
Running on dual 12V.

One of the filters sounds good, but the two others have way too loud resonance and they start to resonate at too high frequency.

Where should I start troubleshooting for reso level/freq?

btw, the overall level of the filters is equal (no reso).

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Pehr



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PostPosted: Thu Dec 08, 2011 11:21 am    Post subject: Reply with quote  Mark this post and the followings unread

I think i'll try swapping transistors first
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Pehr



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PostPosted: Fri Dec 09, 2011 1:51 am    Post subject: Reply with quote  Mark this post and the followings unread

they sound good with no resonance
so I guess I'll have to take a look at the feedback stage

I'll try to post a scope-vid

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jumunius



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PostPosted: Fri Dec 09, 2011 1:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

Pehr wrote:
they sound good with no resonance
so I guess I'll have to take a look at the feedback stage

I'll try to post a scope-vid


IIRC, you might vary one of the 2.2k resistors, or use 3904/3906 transistors instead of those that are spec'd. There's more info in this thread.

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Pehr



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PostPosted: Sat Dec 10, 2011 1:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

It seems that I only have one filter of three that is not working. The one I previously thought was broken just has some extra resonance Very Happy

I've chaqnged all the transistors to BC-types now, and now it's not working at all.

weird

must be a solder joint or something...

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Abby Normal



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PostPosted: Sat Dec 10, 2011 9:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hi Pehr. if you went from the transistor "2n" type to "BC" type, the pinout is reversed between them. You might want to check the datasheet for the exact transistor that you're using for the correct pinout.
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Pehr



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PostPosted: Mon Dec 12, 2011 1:21 am    Post subject: Reply with quote  Mark this post and the followings unread

Yes, double checked with the datasheet to be sure. For bc the new layout is actually ok. It is 390x that should be reversed.
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