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 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
steiner vcf troubleshoot
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Luka



Joined: Jun 29, 2007
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PostPosted: Thu Nov 13, 2008 7:24 pm    Post subject: steiner vcf troubleshoot
Subject description: need some voltage measures from some finished/working modules
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im trying to work out some bugs in my steiner vcf
i am trying to be conservative with my part stock and not simply keep replacing all the transistors.

i can get the unit to self resonate at all inputs
i get all pass on the HP
i get no pass on BP
i get no pass on LP

the freq knob and 2n2222 seems to be working as i can FM the the oscillating resonance


btw should the output electro be 1uf or 10uf as the pcb says 1uf and the schem says 10uf?


a few readings

2n2907
emitter: 12.75 (notch side of can)
base: 12.35 (middle)
collector: 3.5 (opposite side of notch)

my metal can 2n2907 is orientated the same as the markings on the ReV 1 board. so im wondering if this seems correct?

post 390R > 12.76

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Luka



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PostPosted: Fri Nov 14, 2008 3:17 am    Post subject: Reply with quote  Mark this post and the followings unread

what does this section from the 2n2907 datasheet mean?

does the emitter > base voltage suggest that the emitter maximum rating is 5v?


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Blue Hell
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PostPosted: Fri Nov 14, 2008 3:31 pm    Post subject: Reply with quote  Mark this post and the followings unread

Luka wrote:
what does this section from the 2n2907 datasheet mean?

does the emitter > base voltage suggest that the emitter maximum rating is 5v?


All three values say something about voltages at which the transistor might be destroyed (when current is not kept under control).

* -VEBO is the reverse Base Emitter voltage with Open (not connected) Collector.

Reversed in this case means (as it is a PNP transistor) that the Emitter voltage is lower than the Base voltage. This is not the normal working mode of the transistor, but rather the voltage at which the BE junction starts to go into Zener mode, i.e. it starts to conduct in a direction that is not the normal conductance direction. 5 V is not an unusual value for VEBO for transistors, most designs will stay out of that region.

* -VCEO is the Collector Emitter (Open Base) break down voltage. the voltage at which (destructive) current will start to flow although it is not supposed to (because no Base current flows out).

* -VCBO is the Collector Base voltage with open Emitter at which the device will break down on that junction.

All values are not unusual for lowish power transistors, and they are not prohibitive for "normal" low voltage circuits. The voltages you measured on the device are well within specs and do not indicate the transistor to be malfunctioning as far as I can tell. I can't tell from your numbers but it could still be that you exchanged the Emitter and the Collector (that would make it into a not so good working transistor), but you'll have to look that up in the data sheets ... the one I saw (here, the Siemens one) BTW mentioned that the metal can is connected to the Collector, so be sure that the can is not touching anything.

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Luka



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PostPosted: Fri Nov 14, 2008 4:11 pm    Post subject: Reply with quote  Mark this post and the followings unread

thanks Jan

i might contact laurie at elby and see if there were any quirks with the pcb i was sent. ill take some photos of my build too.

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

im going to try break this circuit down into sections to see what is working and what isn't. im a little vague on how the diode ladder becomes a variable resistor. where is the best spot to probe to see if my CV is working. would it be at the left side of the diode ladder or would i measure DC offset before the 100n cap?

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PostPosted: Fri Nov 14, 2008 4:24 pm    Post subject: Reply with quote  Mark this post and the followings unread

When your CV goes up the leftmost 2222 should conduct more, bringing it's collector voltage down and it's emitter voltage up. This in turn causes the rightmost 2222 (the emitter conected to the leftmost, I see a third 2222 now) to conduct less, and it's collector to go up. This causes more current to flow through the diode chain, which makes the diodes behave as a lower valued variable resistor.

There is no DC feedback, so this should work regardless of what the 3rd 2222 and the 2907 do exactly.

What is the problem you have?

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Luka



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PostPosted: Fri Nov 14, 2008 4:33 pm    Post subject: Reply with quote  Mark this post and the followings unread

well i am getting all pass from the high pass input, a low amplitude all pass from the band pass input (perhaps it is band-pass but i can't tell on my scope, i know that the square wave doesnt look sqaure when it comes out but it sounds roughly the same and no pass from the low pass input.

the frequency pot seems only to have any effect when i get the filter to self oscillate with resonance.

my diodes have been checked, they are all healthy and in correct, i think my transistors are in correct ( checked with datasheets / schematic / board layout) and ive given the continuity of the board traces a good work over.

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PostPosted: Fri Nov 14, 2008 4:47 pm    Post subject: Reply with quote  Mark this post and the followings unread

Ok, so it is able to oscillate ... it must be doing something right ... are you getting a "normal" frequency range (when oscillating) when turning the CV pot?
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Luka



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PostPosted: Fri Nov 14, 2008 6:05 pm    Post subject: Reply with quote  Mark this post and the followings unread

the freq range pot doesnt seem to interact with the audio signal unless it is in self-oscilation
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Luka



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PostPosted: Mon Nov 17, 2008 4:53 pm    Post subject: Reply with quote  Mark this post and the followings unread

re-built in mini-vero board ghetto-steiner version

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

im know the pcb is proven and working but it is
funny that this version works and the pro-pcb didn't

Smile

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PostPosted: Mon Nov 17, 2008 5:02 pm    Post subject: Reply with quote  Mark this post and the followings unread

Cool
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Paradigm X



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PostPosted: Tue Feb 15, 2011 5:16 am    Post subject: Reply with quote  Mark this post and the followings unread

Luka wrote:
re-built in mini-vero board ghetto-steiner version

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

im know the pcb is proven and working but it is
funny that this version works and the pro-pcb didn't

Smile


Cool, thats exactly what im planning.

Any hints or tips would be great.

Cheers

Very Happy
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