Mixer circuits

[media at mail1.nai.net]

>.....I know this is against the spirit of synth-diy but it is a real
>hard job to get a ultra low noise diy mixer...

Right, and it's impossible to build one cheaper than you can buy.

>....the idea here is that as you add identical signals each with noise, the
>noise (if truly random) only adds as the square root of the number of sources
>and the signal adds arithmetically... with modern low noise SSM series from
>AD i doubt very much if this strategy is worth while

Not that I know anything about discrete transistor arrays, but how quiet
does this thing have to be??  Almost all commercial mixing boards use
op-amps.  I've held different Neve channels in my hands and looked at them
-- all IC's, every one.  You don't even need discrete components to build
quality mic pre's -- most megabuck consoles use chips from Analog Devices
(OP27??).

If I were to bother to build a mixer I would use all tubes (valves) and
build something I couldn't buy.

>a low noise DC mixer for CV, now that could be useful, say with 4 inputs
>and 4
>outputs, also the 16 knobs very pretty....

I think I saw one of those 4X4 mixers in a Serge catalog -- at about the
price of a used car :)  While I'm thinking of Serge, I remember they had
all of these uncommon utility modules -- scaling buffers, schmidt triggers,
inverters, comparators, divide by "n" counters . . .

PEACE OUT :)
MARK