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 Forum index » DIY Hardware and Software » MusicFromOuterSpace.com designs by Ray Wilson
transistor matching for VCO
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dylar



Joined: Apr 25, 2011
Posts: 51
Location: iowa

PostPosted: Mon Nov 07, 2011 12:51 am    Post subject: transistor matching for VCO Reply with quote  Mark this post and the followings unread

If I just pop in two 3904s instead of a matched pair, what do I lose?
I'm not clear on what drift and tracking loss are...
How severe would the effects be?
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Mongo1



Joined: Aug 11, 2011
Posts: 411
Location: Raleigh NC

PostPosted: Mon Nov 07, 2011 9:57 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
If I just pop in two 3904s instead of a matched pair, what do I lose?
I'm not clear on what drift and tracking loss are...
How severe would the effects be?


Of all the qualities of music, the ear is most sensitive to pitch. The better the match between the transistors, the more accurate your pitch tracking will be.
Drift refers to the way the oscillator reacts to changes in temperature. Unmatched transistors mean that if you tune the osc at room temperature, it will probably out of tune if the temp changes by a few degrees.
Tracking refers to the way oscillator converts voltage changes into pitch changes. If you set up the oscillator so 1V equals middle C (for example), you want 2V to be one octave above that, and 3V to be another octave higher exactly. Unmatched transistors can make this very hard to achieve.

If you don't make an effort to match transistors, you will probably not be very happy with the results. Ray has an excellent article on his website about how to do it, and it would be well worth your time.

Gary
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