-----Original Message-----
From: The Dark force of dance [SMTP:batzman@all-electric.com]
Sent: Tuesday, April 28, 1998 2:24 AM
To: List, Christopher
Subject: RE: Anybody played with the LM1036?

Y-ellow Chris.
Yea the 2164 has better specs. But (a). It's only a VCA and (b) it's
designed to be useable in a high-gain situation. such as microphone preamps
and surround sound steerage etc.

On the other hand the LM1036 is a line-level output stage. It not only
provides voltage controlled attenuation as opposed to amplification, but it
also provides equalization. The THD issues arise from the equalization and
you'll find that with other forms of equalization as well to a varying
degree. Some Audiophiles dis EQ for this reason. And the fact that the
LM1036 is an attenuator as opposed to an amplifier is a point of interest
that shouldn't be lost on you. Attenuation adds no noise to the source. The
chip may add a slight amount of noise over all as would any active device in
the audio path but the attenuation scheme will not add noise in of it self.

In practice these are of "CD Audio Quality". When used as a final preamp, I
doubt you'll hear any noise, distortion or other signal degradation under
normal use. Providing your input signal is within spec. With the controls
flat and the volume fully clockwise, the signal is unity gain through the
chip. If you put in 2 volts peak to peak you'll get out 2 volts peak to
peak. And 2 volts Peak to Peak is what a CD player is spoze to chuck out and
is generally enough to send a power amp into clipping. And even at twice
that level, the 1036 still has head room.

In a mixer, or in any audio system really, the rule of thumb is to do all
your amplification at the start. IE: you amplify your microphone at the top
of the strip. Then you let it trickle down. If you can possibly help it,
never include a gain stage after the initial pre-amp. Otherwise not only are
you amplifying the signal but also the noise of all the previous stages. In
a mixer app, the LM1036 could be used in two locations. Firstly it could be
used as the channel balance/eq/volume stage prior to the mixing busses.
Preceding it would be the mic/line preamp providing gain. The LM1036 would
save you about 20 bux worth of electronics per channel, provide better
consistency, over all long term quality, and save you a bucket load of board
space. Having already done this I can tell you that just mounting the pots
take up more board space than the rest of the channel components put
together. You could also use the 1036 in the final output stage. Though this
is less necessary than on the input and not usually provided in a mixer. You
would also need a couple of op-amps per channel as well to do the vitual
earth mixing followed by an inverter stage. Which of course depends entirely
on whether your channels were in or out of phase.

In a mixer of course, the voltage control range is largely unimportant. If
your aim was to automate the volume/balance, 0 -5 volts is fine. If your
using all 1036s then it becomes consistent. However in a synth you would
probably need to convert the CV. And off hand I can't immediately think of a
suitable scheme to do this. It would require a few stages of conversion and
it's stability would have to be looked at fairly carefully. But all this
depends on what you wanted to do with the output stage. If the synth it self
already had filters and a VCA, then this would be in addition to those
things and offer final, over all response tailoring. In which case, perhaps
your control would need to be less accurate.

Hope this helps.

be absolutely Icebox.
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