[sdiy] sync circuit woes

David G. Dixon dixon at interchange.ubc.ca
Thu Nov 20 18:35:24 CET 2008


The input resistors to a summer can be any value.  The ratio of the feedback
resistor to each input resistor gives the gain for that input.  Hence, a
summer can do more than simply add multiple inputs; it can weight those
inputs in the sum by multiplying each one by a scaling factor.  Think of it
as a weighted summer.

David G. Dixon
Department of Materials Engineering
University of British Columbia
309-6350 Stores Road
Vancouver, B.C.  V6T 1Z4
Tel 1-604-822-3679
Fax 1-604-822-3619

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-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Dan Snazelle
Sent: Thursday, November 20, 2008 9:24 AM
To: music.maker at gte.net; sdiy
Subject: RE: [sdiy] sync circuit woes

I thought that in summer circuits, the feedback resistor HAD to be the
same value as the summing resistors! i thought that was what made
summers work properly. i feel very stupid right now.
Ok, so if i was using 100k, i can maybe try a 47k?
also...in my GUITAR PRE opamp, i am using a non inverting opamp with a
10k to gnd resistor and a 100k feedback resistor for a gain of X10 but
it still isnt really loud enough compared to the other mixer inputs. SO
i was thinking of bringing it up higher BUT i dont want any distortion.
(there is already a dirty switch for that)
so what do you guys think i could get away with before distortion?
maybe 15x? i was thinking of putting in a 150k on the feedback
thanks so much-diy

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