[sdiy] DIY Mixer - please help!

[Scott Nordlund]

I highly doubt that you will be able to build a mixer that is competitive in price and/or quality with a commercial product.  It's probably best to just buy something used.  As you noted, the TX816 definitely needs a mixer, but it doesn't have to be particularly elaborate.  
 
The VCA-mixer thing is another can of worms entirely, it sounds to me like it should be a separate project, possibly as an "accessory" that plugs into mixer's inserts.  If you add more summing bus/aux send type stages, you can turn it into a large-scale "matrix mixer" that is very useful for feedback (in my experience, anyway).
 
But to build a complete mixer from scratch doesn't sound like a fantastic idea unless you're just made of time and money.

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> Date: Wed, 2 Sep 2009 21:47:44 +0100
> From: cheater00 at gmail.com
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] DIY Mixer - please help!
>
> Hi guys,
> It has come so far that I can't go on without a mixer, and, well,
> nothing I see on the market is satisfying to me right now. This can be
> of great use for modular synths as well since I would want it to be
> fully CV controllable. This is in part propelled by the fact that I
> have bought a TX816 which will need a proper mixer in order for me to
> be able to use it at all.
>
> I am currently collecting ideas as well as resources. It seems as
> though it's not so easy to find the schematics for most mixers that -
> at least I consider - are interesting. The first step is to come up
> with a good summing bus design. I think solid state is good for a
> start, but since it's all DIY, it'll be possible to swap it out for a
> tube stage if there's a need for that.
>
> I understand this list might not be the best forum to find out about
> this stuff - but I searched about for mixer/console DIY with people
> who actually *knew their stuff* when it comes to analogue music
> hardware and I simply couldn't find much interesting. If anyone has
> any recommendations, please do tell me. I trust the people here so I
> ask you guys first :)
>
> Here's a quick writeup of what I have in my brain right now. Most of
> it is probably wrong, so please correct me.
>
> What I am thinking of is a simple but effective modular approach which
> consists of:
>
> 1) multiple summing busses
> 2) multiple VCAs
>
> Each channel is one VCA that has CV inputs, a single input, and a
> single output to a single bus. Of course a stereo channel is that
> multiplied by 2. With a CV approach it's going to be very easy to
> control two channels with just the fader of the left channel, but
> that's a trivial comment.
> The bus sums and gives a single high-headroom output.
>
> The first thing to do is to make a good summing bus. I understand that
> to do this I will need to come up with a good op-amp design. What I am
> looking for is good headroom. Can someone recommend anything good?
> Supposedly the Harrison 4032c is pretty good. If you guys have heard
> the headroom in MJ's 'Thriller' - that's that. Has anyone got leads on
> that?
>
> As far as the mixer's format and general set of abilities, I am
> inspired by things like Manley mixers (EveAnna many positive
> affirmations to you if you can read this) and Chandler Limited (but a
> little less so because I haven't spoken to Mr Chandler or Mr Limited)
>
> I find that a fully voltage controllable design could be useful. For
> example a feedback compressor could be built which outputs CV that
> will be fed into the VCAs. Therefore the whole signal chain from the
> sound source to the recorder could be just two VCAs - I guess that's
> better if someone's looking for this sort of thing.
>
> Is there some interaction between the 'mixer strip' and the summing
> bus that I have left out? Or is my concept of how a mixer should be
> designed just plain wrong? :)
>
> Thanks guys
> Damian (probably wrong)
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