[sdiy] Single-supply operation of a SSM2164 VCA/MLT04 analog multiplier?

[Ishaan Dalal]

> Is it cheating to generate the negative supply ?  There are many charge
pump
> converters (Intersil 7660 for example... and many from Maxim ... max680
iirc)
> that could generate a negative supply.

This is supposed to be a "digital design" project, and I'm already up to my
head in analog stuff :-), would like to avoid as much analog as possible
now. More practically, the noise sources on this project (constructed on
solderless breadboard) are already enough of a pain, without adding the hum
of the switcher into it.

    Anyway, I played around with the MLT04 for quite a while tonight. For my
purposes,
it works (almost) perfectly off a single +5V supply (analog ground = 2.5V).
For a 1.5 Vpp signal, and a control voltage from 0 (2.5) to +2.5 (5)V, it
swings the output from ~0V to about 2 Vpp, which is good enough for me. The
only problem I noticed is that for a low multiplier, output below about
0.4-0.5 Vpp begins phase-shifting very noticeably (on the oscilloscope) --
the sound isn't any different (though I only tested it with square waves),
and besides, the amplitude at that stage is low enough to pass unnoticed.
Bumping up Vcc to >= 7V solves this problem, giving perfect control over the
0V to Vcc/2 range. I'm fine with the +5V approach though. The MLT04 also has
less stringent I/O requirements than the SSM2164, and happily, looks like it
is working out for me.

Cheers,
Ishaan