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 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
Steiner Synthacon VCF
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j.dilisio



Joined: May 19, 2009
Posts: 186
Location: baltimore

PostPosted: Thu Aug 06, 2009 5:06 pm    Post subject:  Steiner Synthacon VCF
Subject description: no output?!
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Hello, I could use some help trouble shooting a Steiner VCF.
There's no output.
Power is reaching the board.
The wiring is correct.
Polarity of capacitors and diodes are correct.
Diodes test ok.
TL071 switched out, no change.

After a bit of testing I realized the 2N2222's I had were in backwards.
I have the middle ones in the attached chart. For some reason the emitter is on the other side for this type.

After switching them around they test ok,. still no output.

At this point I'm not sure what I have left to test.
Any ideas/help/direction would be appreciated.
I've attached a close-up of the board.
Thanks.


EDIT* I can hear the filter working when I turn the psu on and off, it's not loud. Also, I can hear the input signal bleeding through really quietly while it's on.


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j.dilisio



Joined: May 19, 2009
Posts: 186
Location: baltimore

PostPosted: Thu Aug 06, 2009 6:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

ok,. I found that bypassing that last resistor makes it a lot louder, about signal level.
Now it seems to be working ok except for the resonance pot.
When I turn it down, it attenuates the signal as well.
Also, it doesn't approach self-oscillation when turned up.

Is that how it's supposed to work?
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andrewF



Joined: Dec 29, 2006
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PostPosted: Thu Aug 06, 2009 6:48 pm    Post subject: Reply with quote  Mark this post and the followings unread

assuming you have PN2907 for the PNP transistor, it looks like it may be in backwards.
PN2907 datasheet

hope it is as simple as that. this filter is the best!
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hobgob_inc



Joined: Jun 09, 2009
Posts: 46
Location: Australia

PostPosted: Thu Aug 06, 2009 7:07 pm    Post subject: Reply with quote  Mark this post and the followings unread

So you're sure that power and ground signals are definitely getting to the board? Just asking this because this is probably the main problem i run into.

If using the crimp connectors i often find they make a poor contact so now i always solder them.

The only thing i could really suggest is check the resistor values, and then double check them. Even if your positive that they're all good. My reluctance to believe i could have dropped a wrong resistor value in often is my downfall.... And make sure that you have the 2n2222 layout from the actual manufacturer whos chips you are using.

Sorry if this stuff is all obvious just thought i'd offer what i could.

Luke
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j.dilisio



Joined: May 19, 2009
Posts: 186
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PostPosted: Thu Aug 06, 2009 10:03 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks guys.
I tried switching the 2n2907 around and that made it sound really crazy so I changed it back. Weird.
But it's working great now,. the 2k2 resistor in the resonance section just needed some adjusting. I ended up putting a 1k pot with a 1k resistor in it's place so now I can get really wild overdriven resonance if I want.
And with all that resonance there's a lot more signal so I put the output connection back to normal.

This ended up being really fun and made me want to fine tune the other modules I'm working on.
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haima



Joined: Jul 25, 2008
Posts: 40
Location: Melbourne, Australia

PostPosted: Sat May 15, 2010 1:12 am    Post subject: Reply with quote  Mark this post and the followings unread

hey guys. i'm also having a lot of trouble getting my CGS35 (PCB version 1.3) Steiner Filter working... Sad

LP and BP inputs don't pass signal at all and don't change when rotating the frequency pot, injecting CV into of the CV inputs or adjusting the "offset trim".

the hi pass input DOES pass signal, quietly (which implies the two transistor amplifier is working? - as the HP input is coupled to that via two capacitors, regardless of the state of the diodes?). but this input doesn't filter sweep either.

turning the "res" pot changes the level of signal injected into the 100n capacitor (or HP input) VERY slightly, maybe a 2dB or so)

the output TL071 amplifier seems to work - i can inject signal to the input and it will amplify a "fair bit" depending on the position of the 1M pot i have in the "level" pads for testing. not that this would effect the actual filter stage.

i've de-soldered one end of every resistor and measured. all values are correct, as per the screen print on the top of the PCB.

i've socketed all the transistors and tried various different combinations of PN2222A/2N2907, BC549/559, 2N3904/3906.

i tried replacing the two transistor amplifier with a opamp version, as per yusynth's version of this filter - no change.

i've tried replacing all the diodes, and capacitors - no change. tried putting wire links for the two "extra diodes" marked with the white dots. no change.

removing the pair of 2n2222 transistors at the bottom of the diode string has no effect on the sound - i.e. everything is the same with or without these transistors fitted - i feel like the problem probably lies in the "filter core" part somewhere...

i've attached a schematic with the voltages measured at different points - perhaps someone with a working filter could compare?

i'm at my wits end... it's such a small pcb - how dare it be such a pain!!! hahah. i've completed dozens of PCBs many times this big, no problems. i guess my luck had to run out...hahah

any ideas, tips, voltage measurements etc much appreciated!


BTW, POWER SUPPLY DRAW:

positive 15v: draws around 10ma (not sure exactly, my bench power supply shows "0.01 AMPS")

negative 15v: draws less than 10ma (not sure exactly, my bench power supply shows "0.00 AMPS")[/img]


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andrewF



Joined: Dec 29, 2006
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PostPosted: Sat May 15, 2010 9:14 am    Post subject: Reply with quote  Mark this post and the followings unread

this is probably not much help but -

be sure the transistors are installed correctly - some types have different pinouts depending upon the manufacturer, rare but it happens.

some steiners can be very sensitive and have a very narrow operating range.
probably when the two npn transistors at the bottom of the schematic are poorly matched (?) Smile
so it may be yours is working but you haven't found the region where it does anything - some careful tweaking of the offset trimmer might find the sweet spot.

from memory, most of the DC voltages you measured look about right, not sure about all of them
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haima



Joined: Jul 25, 2008
Posts: 40
Location: Melbourne, Australia

PostPosted: Sat May 15, 2010 6:10 pm    Post subject: Reply with quote  Mark this post and the followings unread

thanks andrew, i don't think that's it...

i've tried at least 5 sets of different types of transistors in that position, both reversed and the "right way" around, some matched for Vbe and Hfe...

also i don't think it's the trimmer setting - i've tried tweaking it a lot... and also removing the trimmer and frequency pot all together and putting a large amplitude LFO straight into just one 220k resistor at the cv summing point - not a peep...

i'm sure it MUST be something really simple - but i just can't find it...

take a look at takeda's voltages:

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

the only real difference to mine is the voltage on the emitters of the two transistors at the bottom of the diagram. he get's -6.4v - i get around -0.64v... i wonder if takeda made a mistake with his reading? or perhaps this points to my problem.

if someone could measure their working filter at that point i'd be really thankful Cool
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haima



Joined: Jul 25, 2008
Posts: 40
Location: Melbourne, Australia

PostPosted: Sun May 16, 2010 3:05 am    Post subject: Reply with quote  Mark this post and the followings unread

OK. so i re-built the whole thing on vero board - worked first time Very Happy

i get -0.64v on the emitters of the bottom two transistors - the same as the non-working pcb.

i'll post my results if i can figure out what's wrong with my original PCB version... or maybe i'll just stick the veroboard version behind a panel and get on with life...
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andrewF



Joined: Dec 29, 2006
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PostPosted: Sun May 16, 2010 6:23 am    Post subject: Reply with quote  Mark this post and the followings unread

Great! hope you enjoy it, the Steiner is such a wild filter

be nice to know what the problem was with the PCB version
but yeh....
onwards and upwards!!
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otherunicorn



Joined: May 11, 2008
Posts: 136
Location: Australia

PostPosted: Tue May 18, 2010 5:49 am    Post subject: Reply with quote  Mark this post and the followings unread

-0.64 volts is correct for the emitters. The base of one of the transistors is tied to 0V. The emitter can only go as low as the base-emitter diode drop. So the other diagram has an incorrect voltage written on it. That diagram also has the nearby -14.6 voltage specified as being positive.
As for the Vero construction working when the other didn't, it is possible you had a hidden bad joint that was corrected when you remade it. I had to repair two last week with similar faults - a lead cut short so that it didn't rach the solder, and a stranded wire that was insulated in a bead of solder by flux!

Or somehow I've managed to introduce and error to the artwork when getting the new boards made. I have had boards come back with spare tracks that weren't part of the artwork before!

A third possibility is that the offset trimmer is hard at one end, and it is skewing the frequency way off where it needs to be.

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

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haima



Joined: Jul 25, 2008
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Location: Melbourne, Australia

PostPosted: Wed May 26, 2010 5:52 am    Post subject: Reply with quote  Mark this post and the followings unread

thanks for the reply ken. it seems all that my PCB (version 1.3) of the filter is correct DC wise.. there's just some problem with the AC signal part. pretty sure it's not the trimmer - i tried all positions and even disconnecting it, no change.

i've checked repeatedly for bad solder joints and track lift off problems - couldn't find anything. there MIGHT be something there, but i couldn't find it.

is your pcb version 1.3 new? has anyone else successfully built one? i couldn't see any errors in the layout but i've only traced parts of it while looking for the problem.

i've actually got a problem with my veroboard version too (i seem to be cursed with this filter! Mad ). the filter works perfectly apart from a very loud hum/buzz that seems to be picked up via the LP input. it sounds like a disconnected ground wire kind of buzz, but you can filter the buzz completely away with the frequency cut-off knob all the way down.

> it makes no difference if all the inputs are shorted to ground - still hums just the same.

> all the audio i/o wires are shielded (shield terminated at only one end).

> the entire pcb is enclosed in a grounded aluminium hobby box (i thought it might be EMI)

> it doesn't seem to be a ground loop with other modules - it still hums in complete isolation.

it's driving me a little crazy... anyone got any ideas? anyone had a similar problem with this filter?
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otherunicorn



Joined: May 11, 2008
Posts: 136
Location: Australia

PostPosted: Wed May 26, 2010 6:44 am    Post subject: Reply with quote  Mark this post and the followings unread

I've not had anyone else mention any failures building it. With a minor update like this one, I haven't built one myself yet, but do intend to especially since you have had problems. My problem is I am painting my workroom at the moment! I have checked the artwork yet again since you posted, and that appears to be perfect.

No idea about the hum. Stick your finger on the back of the board and move it around to see what affect it has. See if you can get it to change frequency, in which case it is NOT hum, but rather some sort of instability.

Ken

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haima



Joined: Jul 25, 2008
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Location: Melbourne, Australia

PostPosted: Wed May 26, 2010 8:25 am    Post subject: Reply with quote  Mark this post and the followings unread

thanks ken - i really appreciate your time. good luck with the painting!

i really like the sound of this filter, otherwise i would have just given up already Smile

as far as the hum goes, last time i was working on it i remember the hum seemed to be influenced by putting my hand near the diode string / capacitors in the filter section but i'm pretty sure it didn't change pitch - it was like my finger was acting as a antenna. this lead me to encase the module entirely within the pedal box... which didn't help much in the end.

i'm pretty busy right now so i don't know when i'll get another chance to look at it - but when/if i get to the bottom of the hum problem i'll post here in case it helps anyone.
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otherunicorn



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PostPosted: Thu May 27, 2010 5:39 am    Post subject: Reply with quote  Mark this post and the followings unread

I finished testing my version tonight, and it worked fine.
Worked with or without the 100k CV offset trimmer.
Build notes:
Ver1.3 PCB
I used 2N3904 and 2N3906 in this case (Note NOT 2N3906C or any other letter variant) . They are put in backwards with respect to the transistor outline on the PCB, using the spare unmarked base holes that are within the larger circular outline.
All diodes were installed.
+/- 15 volts used as supply.
The 1uF capacitor at the summing point of the CVs was causing the frequency to slowly drift. This capacitor was in the original design, presumably to de-thump the filter. I see no problem with leaving it out if you have this sort of problem.
I had to tweak the 2k2 in the resonance part of the circuit (connected to the emitter of the NPN in the amplifier) to compensate for transistor gain. A 15k across it brought it to the point where with the resonance full up, it was slightly ringing. A signal on the HP or LP inputs would then send it onto full oscillation, requiring the resonance to be backed right off to stop it, which is normal behavior for this design.

I hope this helps.

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haima



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PostPosted: Thu May 27, 2010 6:42 am    Post subject: Reply with quote  Mark this post and the followings unread

thanks ken - good news there's no problems with the PCB run.

bad new for me though - no easy explanation for my problems Laughing

oh well, i'll get to the bottom of it one day. too busy in the studio at the moment to spend any time at the bench.

hope the paint goes/went on smooth!
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MirlitronOne



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PostPosted: Wed Jun 09, 2010 1:18 am    Post subject: Latest victim Reply with quote  Mark this post and the followings unread

I appear be the latest victim of The Curse Of Synthacon.

I've built Ken's v.1.2 circuit on veroboard - six diodes and +/-12V supply. I've used BC547A transistors because they have the lowest gain of transistors I could match (about 250 - lower than my 2N2222s). As with the first correspondent, the symptoms are that any signal fed into the LP or BP inputs appears very weakly at the output, while the HP input produces nothing at all. The op-amp stage is working fine and the gain control works. The frequency and resonance controls make a small difference to the output level, and a square wave input comes out looking like a 'stepped ramp' if that makes any sense. I am an experienced veroboard builder and have checked the layout and component values many times, plus checking for shorts and bridges, etc. I've tried varying the value of the 2k2 bias resistor in the resonance amplifier with no effect.

The voltages I get from the circuit points are consistent with those shown above (given that I'm using 12 V supplies) except at the collector of the left-hand transistor of the differential pair (the one whose base receives the CV), which varies very little from +7.9V as the frequency control is varied. The collector of the right-hand one of the pair varies from about +3V to about +8V as the frequency control is adjusted. The base and emitter voltages are more-or-less as indicated above. I have have swapped out the first transistor, tested all the diodes and checked and re-soldered everything in this area. No change.

If the two collector voltages track one another, surely there is no change in the voltage across the diode chain? This is what I don't understand. I'm wondering if the resonant circuit is simply resonant at entirely the wrong frequency. Meanwhile, my beard is getting greyer and thinner and if anyone has any suggestions, I'm all ears!

Phil

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otherunicorn



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PostPosted: Wed Jun 09, 2010 1:26 am    Post subject: Reply with quote  Mark this post and the followings unread

That sounds like the diode chain is being reverse biased. Are you sure you are driving the correct base with the CV?
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MirlitronOne



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PostPosted: Wed Jun 09, 2010 4:15 am    Post subject: Reply with quote  Mark this post and the followings unread

I think I have it right, but it is the kind of mistake that I might make... Wink

Many thanks for the suggestion!

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MirlitronOne



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PostPosted: Sat Jun 12, 2010 5:06 am    Post subject: Reply with quote  Mark this post and the followings unread

Crying or Very sad

Okay, I still have all my hair but I am developing a pronounced facial twitch thanks to this build.

You're right, the diode chain IS reverse biased. This is because the collector voltage of - let's call it Q1, as in the original Nyle Steiner circuit - is permanently stuck at 8V, and I can't figure out why. The transistor is good; the base voltage varies with the frequency pot from -10 to +40 mV; but the collector voltage doesn't budge. Meanwhile, Q2's collector merrily scans from 4.5V to just over 8V, never quite reaching a high enough value to forward bias the diode chain. And I can't see why.

Yes, I've checked all component values. I can't find any shorts or breaks or miswirings on the build. And I can't see how the collector voltage of Q1 can remain static as the transistor is turned on and off at the base. It's back to the breadboard on this one.

[BTW: the gains of the BC547A transistors I used for Q1 and Q2 are about 190, not 250 as I stated earlier.]

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otherunicorn



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PostPosted: Sat Jun 12, 2010 5:25 am    Post subject: Reply with quote  Mark this post and the followings unread

I take it from your comment that you have compared the circuit to the original diagram in Nyle's article too.

What are you doing for the CV? Do you have the initial frequency pot there? Have you tried reducing the value or the resistor in series with it? Is it between the +VE and 0V , not -VE and 0V?

Ken

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MirlitronOne



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PostPosted: Sat Jun 12, 2010 5:36 am    Post subject: Reply with quote  Mark this post and the followings unread

The CV input is as per your v1.2 - two inputs, each via a 220k resistor, one fed from a 100k pot between +12V and earth. 1k resistor and 1uF capacitor to earth. Capacitor is correctly orientated.

Thanks for your quick response!

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MirlitronOne



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PostPosted: Sat Jun 12, 2010 6:21 am    Post subject: Reply with quote  Mark this post and the followings unread

Just swapped the 220k resistor for the 47k used in Nyle Steiner's original circuit, and also took the 1uF smoothing capacitor out of circuit. Both Q1 and Q2's collector voltage ranges increased slightly and the overall result is the same - no filtering yet...
Sad

Can you confirm that Q1's collector voltage should vary over several volts with adjustment of the CV?

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otherunicorn



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PostPosted: Sun Jun 13, 2010 4:08 pm    Post subject: Reply with quote  Mark this post and the followings unread

Left TR is the one with its base connected to the CV
Voltages given are the collector voltages
CV Left tr Right tr
0V 5.8V 4.7V
4.3V 4.4V 6.0V
15V 3.0V 7.5V

So yes, the left collector voltage does vary with changes in CV, and the two collector voltages move in the opposite directions to each other.

Ken

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MirlitronOne



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PostPosted: Sun Jun 13, 2010 5:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks again, Ken.

Well, there's my problem - right transistor is behaving, left transistor ain't. It's GOT to be something trivial, but I just can't find it. Mind you, this has been one of my "stupid" weekends, where everything has been - what was that marvellous phrase from Scott Stites? - oh yeah, "a great batch of loser cakes drenched in fail sauce."

Back to the veroboard tomorrow, if I can swallow those cakes. Confused

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