[sdiy] Cheapest, simplest but still reliable VCO & VCA for polyphonic project

[David G. Dixon]

Karl,

Check out Thomas Henry's VCO-1 design on Scott Stites' excellent website:

http://mypeoplepc.com/members/scottnoanh/birthofasynth/id33.html

This triangle-core VCO sounds very nice and is very cheap, using one OTA
(and the obligatory pnp expo converter transistors), a few opamps, and some
discrete transistors.  It has a sine shaper and a pulse generator with PWM.
I'm going to build a pile of them for myself (with a few alterations,
including building them as duals with added hard sync, added saw shaper, and
wave morphers to blend either sine or triangle with pulse and/or ramp, with
the latter two fed through opamps with variable gain from -1 to +1 to get
varying degrees of reinforcing or cancelling waveforms).  So far I've only
simulated it in Multisim, but it all seems to work exceedingly well.  I've
substituted LM13700 for the original CA3080 (hence the dual design).
Multisim's CA3080 SPICE model is kaput, so I couldn't actually compare them,
but I doubt the change makes any measurable difference.  I also used 2N3904,
2N3906, and TL072/4 throughout (I love cheap!).

I'm thinking of using a THAT320 matched quad pnp for the expo converters.
At about $4, it will cost more than the rest of the circuit combined (not
counting the tempco, of course)!

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

The information in this email and in any attachments is confidential and
intended solely for the attention and use of the named addressee(s).  It
must not be disclosed to any person without the writer's authority.  If you
are not the intended recipient, or a person responsible for delivering it to
the intended recipient, you are not authorized to and must not disclose,
copy, distribute, or retain this message or any part of it.

-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Karl Ekdahl
Sent: Thursday, January 08, 2009 10:52 AM
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] Cheapest, simplest but still reliable VCO & VCA for
polyphonic project

Hi list, so i wanna make a poly synth and as usual i'm looking for the
cheapest possible VCOs and VCAs that'll still cut it. Note; i'm not after
absolutely perfect pitch or anything, in fact i'm going analog to avoid
this.

>From what i can see online the simplest okay option seems to be the ASM-1
style VCO, yes? For this design, how important is it to use a ca3140, i've
seen similar designs using standard TL0XX opamps. Also i've seen design
using LM394 instead of MAT-02 and recent discussions have even suggested
that any discrete transistors from the same batch are matched enough for it
to work straight-off, is this true for a poly synth? As for tempcos, is
there a big difference inbetween 3300ppm and 3900ppm, my experience tells me
that SMD is good here because you can very easily glue the resistor directly
to the transistors with very good thermal contact - any sources for these?
Anything else i should think of?

Next question is in regards to the fact that since i'm doing a poly synth
where one set of knobs controls all the voices, i'll have to make *every*
parameter voltage-controlled, so i'll need a hell of a lot of VCAs. Any
suggestions on good, cheap and very low parts-count VCAs? I'm guessing a
LM13700-design.. ?

Thanks

Karl


      __________________________________________________________
Låna pengar utan säkerhet. Jämför vilkor online hos Kelkoo.
http://www.kelkoo.se/c-100390123-lan-utan-sakerhet.html?partnerId=96915014

_______________________________________________
Synth-diy mailing list
Synth-diy at dropmix.xs4all.nl
http://dropmix.xs4all.nl/mailman/listinfo/synth-diy