[sdiy] fun with KBD2e

[Schierl, Dan]

well, I see a sort of sawtooth with a flattened top (about 5 v p-p, centered at 12.5 v) at pin 5 of U2. just for the heck of it i replaced D1 and D2, but see the same result. bummer. 
 
C7 should be 33pF, right?
 
what voltages do you get for the gate CV?

________________________________

From: David Moylan [mailto:dave at westphila.net]
Sent: Tue 3/8/2005 9:27 AM
To: Schierl, Dan
Cc: synth-diy at dropmix.xs4all.nl
Subject: Re: [sdiy] fun with KBD2e


I put one of these together, and I also found some discrepencies, but nothing that prevented me from getting it working correctly.  I believe you should have a high frequency clock being fed into U3 and on the output, but the associated diodes/cap on the output should be rectifying/smoothing this into DC.  Check the signal input to U2 and see what you have there.  Maybe check the polarities on your diodes, D2, D1?

Dave

Schierl, Dan wrote: 

	hi list--
	has anybody had any experience with TomG's keyboard converter, the kbd2e? I recently put one of these together, and am getting some strange results. 
	 
	documentation is here:
	http://www.ele4music.com/pdfs/kbd2e.pdf
	 
	I noticed 4 or 5 discrepancies between the schematic and the pcb, and i believe I have corrected these. also, i noticed 2 discrepancies between the parts list and the schematic, and I think I got those right as well. the pitch CV out seems to be working fine, but the Gate out is acting weird--with key up I see about 14 volts, and with key down I'm getting a ~4volt p-p square wave centered around 12v, and from what i can see it has a frequency of around 50 KHz. tracing back a bit i'm reading a 30V p-p square wave on pin 5 of U3 (a 13600) at the same frequency.
	 
	any thoughts as to what i should check next?


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