Speck M72 master section mods with Speck, Neve, and CAPI summing

[yosh]

I bought a Speck M72 line console about 6 weeks ago. Sonically, it is pretty transparent with just a bit of euphonic "mojo". There was an integrated patchbay which did not have enough room for all our outboard, so I rewired the console to TRS ins and outs. This left an empty space about 11 inches wide. Hmmm...how to fill?

The M72 is a split style console with the 16 buses appearing on 16 pots in the master section with no L-R assign or solo or insert features. In my workflow I definitely favor a more inline approach, so I decided to make a new add-on master section and add 16 bus faders with switches for solo, independent L-R assign and insert engage. Why stop there? I thought it would be cool to have a switch which would change the summing amps. I like the Speck sonics for transparency so that would be one option, and then how about the other two classics, Neve and CAPI? I went with 2 Neve 1272 amps and the CAPI 2ACA-BO. All the connections to the new master section are on DB25 to keep things modular and make it easier to work on.

So far so good! I have the master section almost finished. I just need to install balanced line drivers for the Speck master and balanced line receivers for the studio monitoring section of the existing Speck master. The bus switching I did all point to point. If I did it again I would probably do circuit boards :-\

The summing switch is pretty awesome. Very different flavors especially when pushed a bit.

 

[Rocinante]

Awesome.

 

[XAXAU]

Nice! How do you switch between the different summing amps? I'm thinking about the different bus R's!

 

[yosh]

Nice! How do you switch between the different summing amps? I'm thinking about the different bus R's!

I left the same bus Rs on the channels for all summing styles. I then tapped where all the console channels come in to the master section for L/R summing and moved it to a 6 pole 3 way switch. The switch moves where the channels go to get summed and it moves the different summing outputs to the console mix out.

 

[Rocinante]

How did you handle the voltages, considering the API wants + - 16 and the Neve wants 24v?  You just added a psu? On board or off?  Or did you regulate from the Speck psu?

 

[yosh]

I used the power ones at +/-16 that are powering the Speck to power the API and I have a bench power supply that is currently powering the Neve at +24. So far no issues with grounding, though I wasn't sure initially how that was going to work out.

 

[XAXAU]

I left the same bus Rs on the channels for all summing styles. I then tapped where all the console channels come in to the master section for L/R summing and moved it to a 6 pole 3 way switch. The switch moves where the channels go to get summed and it moves the different summing outputs to the console mix out.

Sorry, noob alert here! Are bus resistors the same as summing resistors?

The 2-ACA-BO use 47kohm and the EZ1290 (that I'm building atm) use 598ohm for 16 channels.

Would like to be able to switch between API & Neve just like you!

 

[yosh]

Yes, I'm using bus resistor and summing resistor interchangeably. Not sure if that's technically correct? In the Speck M72 the bus resistors are 10k. I left those as-is and changed the appropriate resistors in the CAPI ACA to get the correct gain. The input connections for the Neve are to tie the L/R summing bus to the input transformer high and connect the low tx leg to ground. Not sure if this is the best way for the Neve, but it seems to be working well for me.