Re: [sdiy] DIY TR909 : noise !

[Roman]

	that's beautifull schematic :) 

	I especially like those comic-like comments and the "bass drum" thing in the middle. 

	You're a talented artist :) 
	Maybe I get it wrong, but you include the noise on purpose here, so what's the deal? 

	If you hear hiss when noise level is turned down to 0, it may be some leaking from noise circuit to output amplifier, or (a wild guess) some part of the circuitry has spurious 

	oscillations at HF causing audible distortion/noise when downconverted on VCA nonlinearities. 
	Roman
---- Wiadomość Oryginalna ----
Od: Jörg Schmitz 
Do: synth-diy at dropmix.xs4all.nl
Data: Thu, 17 Jun 2004 19:06:33 +0200
Temat: [sdiy] DIY TR909 : noise !

   Hi all !   at last I have managed to built my own TR909 - bass drum pcb. It works prettty well (see http://www.analog-synth.de/synths/tr909/tr909.htm (http://www.analog-synth.de/synths/tr909/tr909.htm) for details), but I found one problem : the output is a bit noisy. You can hear a little hissing noise, which seems to correspond to the envelope and therefore VCA activity of the VCA between the output amplifier and distortion diodes (controlled by "decay").   What would you suggest to eliminate that (not very loud) noise ? (Of course, this is not the noise of the noise generator, bleeding through somehow, this is tested...) Another opamp for the output-amplifier ? Something better than the TL072 ? Something better than the BC549 for the VCA's ?   cheers, Joerg

 
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