Hybrid Passive mixer/monitor controller

Right then. Not sure if this is an original idea but I?ve personally never seen anything like it either here or in the market place. (it might not exist because it might not be a very good idea!!!)

I want a 24 channel passive, balanced summing mixer similar to the Fulcrum and many discussed here. I also want a transparent, built in active make-up gain stage that can be used when a coloured mic pre isn?t being used for make-up gain (most likely the design on Fred Forssell?s page using discrete opamps and DC servos and a switching feature to remove the active stage when a more coloured mixer is required). I also want a calibrated monitor level controller (as suggested by Bob Katz) ? I toyed with the idea of a passive stepped attenuator after the Forssell active stage but that just seemed quite inelegant (attenuating, amplifying then attenuating again).

Since the passive mixing network is already attenuating the signal to somewhere close to an appropriate level to send it to active monitors or a power amp, could I not just put a balanced output driver on the end of the mix buss? I realise some level adjustment will be needed, but surely its better to amplify the mix bus a tiny amount (or most likely, attenuate it a bit more) than to passively attenuate it in the mix network, amplify any noise picked up by about 30dB then attenuate the whole lot to the right level to sent it to the monitors?

Can I have both stages working simultaneously? I.e. Have the Forssell active stage (or whatever) going to the DAW and the output driver going to the monitors both connected to the mix busses without them interfering with each other?

Am I barking up the wrong tree?

Mark Lewis

... by the way, i know that the extra fidelity from not having the make-up stage can't really be stored digitally, (the make-up stage is needed to bring it back up to line level for recording), but it might be nice to have anyway considering it won't be expensive to impliment.

perhaps i could have a switch that selects the actual mix that will be recorded and the "pure" mix without the extra gain stage.

ML

Hi Mark,

Interesting idea, I've also been thinking about a 24 channel summing amp that would be switchable for passive and amplified output. I hadn't even considered the Bob Katz recommended metering, however! My initial idea was to make something more plain vanilla, no pans, no channel gains, possibly mute switches.

Instead of having a switch for the various types of out.. maybe offer both pair of outputs on the back of the unit.

Please keep us posted about how you progress. My approach would be to build an 8-channel prototype to play with before diving into 24 or more channels.

cheers~
Jay