Re: [sdiy] Multiplier vs VCA?

[Roman]

Multiplier doesn't produce FM!
Basic VCA IS multiplier, as it multiplies control voltage with voltage that passes thru, usually AC signal. Circuits that carry name "multiplier" usually do more than plain VCA, they can take negative voltage at input used in VCA as control voltage. VCA would then be totaly closed, while multiplier just reverses the sign of the output, as expected by math, meaning it reverses polarity of passed thru signal.
This property allows multipliers, or in another words ballanced modulators to be used in DSB-CS AM (dual side band, supressed carrier amplitude modulation). Plain VCA qould do only DSB AM, where main component of output spectrum is carrier whatever you do (carrier being here the signal that passes thru VCA).

It is possible to make 4-quadrant multiplier using 2 VCAs, I've seen the schematic somewhere on the web. The concept is to allow one VCA take care of positive control voltage, and the other of the negative control voltage.

what multipliers are available? I'll stick to one - AD633. Pretty good, rather cheap comparing to others.
VCAs - SSM2164, LM13600, LM13700, NE5517, CA3080, CA328, or discrete transistor circuit.

hope that helps
Roman

---- Wiadomość Oryginalna ----
Od: synthplayer88 at spymac.com
Do: synth-diy at dropmix.xs4all.nl
Data: Wed, 18 Aug 2004 10:51:04 -0600
Temat: [sdiy] Multiplier vs VCA?

>
>Hi guys,
>I was wondering if anyone could help me out to clear my confusion on using a VCA
>as a multiplier?
>
>I was under the assumption that a VCA ultilize a voltage to control the output
>amplitude eg.AM, whereas a multiplier ultilize a voltage to change the frequency
>eg.FM. Which leads to my question which is how can you use a multiplier to as a VCA?
>
>I know I must be missing something some where, thanks in advance.
>
>BTW, has anyone done a meta list of VCA chips and multiplier chips?
>
>Would love to know what's currently available out there to compare the functions
>and the sounds?
>
>Do they have actaully a "sound" of their own?
>
>regards,
>Scott
>
>
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