[sdiy] JP8 Gate circuit issue

[Tom Wiltshire]

My guess is that it was intended to be driven by an open-collector output. E.g. by another transistor that looks much like the one you've got. That'd explain why there's R127, a pull-up, and it'd also explain why the circuit is inverting, since the open-collector output would be high when not switched on with just the pull-up attached.

To modify it for a 0-5V input, just take R127 out. If it doesn't switch on properly, reduce R128.

HTH,
Tom

On 31 Oct 2013, at 19:31, Jack Jackson <jackdamery at hotmail.co.uk> wrote:

> Hey all, I'm trying to get this gate circuit from the JP8 working. As far as I can tell you should apply 5v logic signal to the base of the transistor and it should output 15v positive gate. I can't get any change from it. I'm using correct resistor values, and a 2N3904 for the NPN. Any ideas?
> 
> http://flic.kr/p/h9o13k 		 	   		  
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy