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 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
Steiner Synthacon VCF
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Just_Andrew



Joined: Jul 31, 2016
Posts: 4
Location: Canada

PostPosted: Sun Jul 31, 2016 1:37 pm    Post subject: Steiner Synthacon VCF Reply with quote  Mark this post and the followings unread

Hey everyone,
New to electro-music!
Trying to wrap my head around the Steiner vcf and having a long and difficult battle. I purchased a ken stone board and having a hard time getting things working on that as well. I'm only getting sound through the bp and the filter isn't doing anything. I'm guessing the op amp is Working as it should as the output level is working fine. But I'm not sure how to get the filter starting up. I'll look at the voltages tonight, but if there's nothing wrong with that stuff could some one look at pictures (when I post them) to see if I've missed something on the board?
I've tried all the transistors I have in there 2n2222/2n3904/bc547 and I only have 2n3906/bc557 for the pnp's but no change in the problem.
Running -/+ 15v
Really I'm just trying to find some one out there to help.
This is my first modular build and I'm hoping to build more of these filters (8 in total!) if it sounds the way I'm expecting.
I also have more builds in the works and it would be nice to know that I have people to help me out if I run into trouble.
Cheers
Andrew
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Just_Andrew



Joined: Jul 31, 2016
Posts: 4
Location: Canada

PostPosted: Sun Jul 31, 2016 7:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok so I have some voltages
So going from left to right here are
T1
E) -0.74 B)-0.09 C)-0.74
T2
E)-0.74 B)0 C) -0.74
T3
E) 0 B) -0.03 C) 0
T4
E) -0.54 B) 0 C) 0

Ic1
1. -14.75
2. 0
3. 0
4. -14.9
5. -14.75
6. 0
7. +14.94
8. 0
I'm not sure where things go wrong but something is not right. Any help would be great.
Andrew


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Just_Andrew



Joined: Jul 31, 2016
Posts: 4
Location: Canada

PostPosted: Sun Jul 31, 2016 7:27 pm    Post subject: Reply with quote  Mark this post and the followings unread

It's only letting me do one picture at a time...


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prgdeltablues



Joined: Sep 25, 2006
Posts: 222
Location: UK
Audio files: 12

PostPosted: Mon Aug 01, 2016 6:29 am    Post subject: Reply with quote  Mark this post and the followings unread

Hi, and welcome!

Hard to tell from the pictures, but there is something wrong around the transistors. The emitters of T1 and T2 are pulled to V- through 3k9 and 82R, so ought to show something more like -14V. T1 Base ought to relate to the CV so should show a positive voltage. Check that the offset trimmer is producing 0 at its wiper (for the moment, no need to trim offset yet!). Then check that the wiper of the Frequency pot goes from 0 to +15V as you rotate the pot. That voltage ought also to show up on the base of T1.

Assuming that is all OK, my next guess would be that you have one or more of the transistors in backwards. Never assume all 2N3904 or whatever have the same pinout - different makes do vary. you need to check how yours are, then carefully assess against the PCB and the schematic. Best way is to use a transistor tester, but if your DMM (i'm assuming you have one!) doesn't have that function, try removing T1 and turning it 180degrees - my experience is that they are either EBC or CBE (ie B in the middle). Other flavours do exist though!

hope this helps!

Peter

PS you didn't say which version you have. I've assumed the one labelled CGS35, not CGS35 euro
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Just_Andrew



Joined: Jul 31, 2016
Posts: 4
Location: Canada

PostPosted: Mon Aug 01, 2016 1:12 pm    Post subject: Reply with quote  Mark this post and the followings unread

Hey, thanks Peter.
I have the cgs35 (1.3version).
I'm sure about the pin out as they have it printed on the transistors themselves. I'm worried that pnp transistor is getting a (-) at the emitter. That doesn't seem right.
I'm getting the correct response from the frequency pot and the wiper on the trimmer is set to 0. But all the voltages are the same as before. So I think I need to find out why the emitter on the pnp is negative and not +13 like in Ken's post on voltages.

Edit** I found two issues!
390k in place of 390r is going to mess a few things up! That's what I get for not organizing my resistors properly. Embarassed
Also the 3.9k on the negitive side at the first transistor was doing something weird so I swapped that out and now the filter is working. Some of the voltages aren't exactly on,but I think I'm a little closer to the end of the dark tunnel!
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