[sdiy] [OT] Mixer upgrades

[Byron G. Jacquot]

>I recently picked up an '80s vintage Soundcraft model 200 SR mixer which I
>intend to use for recording purposes.  A look inside shows film type 2%
>resistors with either a blue or violet body color used throughout the unit.
> Does anyone know if these are carbon film or metal film?  It's generally
>known that metal film resistors generate lower internal noise than carbon
>resistors, if these are indeed carbon resistors, is it worth the trouble of
>changing them out with metal film resistors at least in the front end (mic
>preamp) section?

The only way to know for sure is to upgrade a strip or two, and A/B them
with the plain ones.

>The front end uses a 2SA1316GR differential pair feeding a TL072, any need
>to upgrade this area?

I've got a 600, which is very similar, and I've never had any issues that a
component-level upgrade would do much for.

If you want to help with the noise & crosstalk, then consider the following
path:

1> Upgrade the electrolytics in the power supply, then the master section,
then any rail-bypass 'lytics in the channels.  My 600 had some really crazy
issues with ripple.
2> Reground the channel strips.  Cut the ground from the ribbon connectors,
and run a heavier wire to a bussbar near the power entry point.  A great
article about exactly this:
http://www.tangible-technology.com/articles/200b.html
3> Experiment one strip at a time with removing/upgrading inter-stage signal
coupling caps.  They're all 'lytics.  If you trust other gear to not have DC
bias on the outputs, then the ones in the insert points and line inputs can
go.  The ones that block phantom power before the mic pre are essentially
mandatory (unless you drop in a transformer!).  Just replacing some of these
old, low-spec caps with new high-temperature ones might make a difference.

If you really need some good gain in some of the pres, consider one or two
of these cards: 
http://www.audioupgrades.com/products.htm

>Electrolytics are known for being less than perfectly linear, so is there
>any benefit in adding disc or film caps across the numerous electrolytics
>in the audio chain? 

In my experience, I replaced every 'lytic in the board with newer lytics of
the same value, but better temperature spec.  It seems to have better low
end (but that's also absurdly subjective!).  It also made the spontaneous
low amplitude clicking that a couple modules had completely
disappear...though I don't know if it was the caps, or the opening
everything up, cleaning it & reseating it that did the trick...

If youre not up for total replacement, then try a strip or two, and see if
they improve.

So did it come with a bus-extender cable?

Byron Jacquot