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 Forum index » DIY Hardware and Software » Ken Stone designs - CGS
Synthacon feedthrough
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-VCO-



Joined: Jul 17, 2007
Posts: 3
Location: Stockholm

PostPosted: Fri Mar 27, 2009 3:48 pm    Post subject: Synthacon feedthrough Reply with quote  Mark this post and the followings unread

hiya people,

just finished one of my CGS pcbs (woohoo, my first day with my weller since...i can't even remember when! since i started working full time with electronics i've got very little time to build stuff. ironic really...), a cgs35 synthacon vcf. i still have to do some minor adjustments, such as the frequency range and the regular stuff. i did notice that the resonance pot's wiring on the pic on the page was reversed (or i was tired). anyhoo, simple to fix.

HOWEVER, when I hooked it up it seems I get quite a lot of feedthru - i can clearly hear the unfiltered signal in the background, especially when the freq pot is at zero. did i mess up or is there some kind of adjustment you can make? i did change the 2N2907 for a 2N5401 since i can get those through my job, but not the 2N2907. please help, i'd love to have a perfectly working module!

cheers
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andrewF



Joined: Dec 29, 2006
Posts: 1176
Location: australia
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PostPosted: Fri Mar 27, 2009 7:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

You may be right suspecting the 2N5401
I didn't look at the specs too closely, but it seems to be spec'd for lower voltages and currents than the 2N2907.

Assuming all else is correct, it would be a good starting point to swap in another PNP tranny.
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-VCO-



Joined: Jul 17, 2007
Posts: 3
Location: Stockholm

PostPosted: Sat Mar 28, 2009 4:11 am    Post subject: Reply with quote  Mark this post and the followings unread

Hmm, the maximum ratings for the voltages are much higher on the 2n5401 than the 2n2907, however the collector current (Ic) is half the 2n2907's. Maybe that's what causing trouble. Perhaps a BC327 could work? Its Ic value (collector current) is at 0.8A instead of the 2N2907's 0.6A, but all other values are quite similar. I don't want to order just a single transistor from the web with all the shipping and all that, it's just so much trouble for one little component. I can get all the other components through my work.

Are there perhaps any other transistors I could use in the 2N2907's place?
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andrewF



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PostPosted: Sat Mar 28, 2009 7:01 am    Post subject: Reply with quote  Mark this post and the followings unread

I didn't mean the max ratings, these circuits get nowhere near such levels - more the off and on characteristics.

my Steiners have A1015 PNPs, so other transistors can be substituted.
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