Eela s100 mixer - Direct output mod

[etfy]

Hi everyone, my first post here.

I just got myself an old Eela S100 16ch mixer.

It has been already modified

• added of 2 Socapex plugs wired to the Line and Mic inputs.
• removal of the vu-meters
• output section rewired, taking advantage on the fact that the connexions are 3 points but the circuit is unbalanced.

I am thinking of modifying it further.

• Recap all board and PSU
• Add post-fader direct output per input channel (16)
• Give it a new vu-meter

In this post I thought it would be good not to mix everything up and focus on the direct output only.

I had a look at the schematics [link] and spent a few hours to research about direct output modifications.
Apparently Eela offered the direct output option so I believe it’s doable

Here is the block diagram of the input section.


More details here with the input schematics



My assumptions

• unbalanced direct output is not a problem with max 2 meters from the mixer to the 16x ADC (Motu 16A)
• each direct output will need to be buffered
• power supply could be a problem depending on its specifications (i don’t have them yet the mixer is still on its way)
• i could use the installed Socapex plugs for the direct out but it might be cheaper cable-wise to use 2x DB25 instead

II wish to take advantage on the input transformer, eq and faders to multitrack several synths, effects and drum machines.
My goal it to make this mod as clean as possible sound-wise.
I am open to any suggestions to get the best out of this mixer and I will appreciate any help!

Cheers everyone

 

[ruffrecords]

Assuming you want the direct out to be pre-fader, I would just take straight from the top of the fader. A buffer should not be necessary as long as the input impedance of your interface is 10K or greater and this method eliminates possible power supply issues.

Cheers

Ian

 

[etfy]

Thanks @ruffrecords for the quick reply.
I just checked, the interface input impedance is 10K.
Would it add difficulties to take the signal post fader? I'm still thinking what would be best for my workflow.
Also could you confirm that going the unbalanced way would not interfere with the signal quality? I could eventually adjust the ADC sensitivity if a miss a few dBs relative to the master output.

 

[ruffrecords]

The post fader op amp is a little more heavily loaded than the pre-fader one due to the pan pot. The op amps used are only capable of driving a minimum load of 2K. A rough calculation shows that with the 10K direct out load connected pre-fader, the worst case load is about 2K8 so there is a good margin. If you connect it post fader then the worst case load becomes very close to 2K. You would need to make the connection to a point just after C20. In most normal settings the worst case load will be higher so you should be OK. (It is worst with the pan fully one way and both AUX sends at 100%).

Cheers

Ian

 

[guy_4]

Hello etfy,

Out of the impedance question, I think that your next issue will be not enough signal level to properly drive your A to D converter....
Think you'll need a nominal level of +4dB, with 18dB of headroom...
Not available on the Fader output...

I have modded many consoles with an additional buffer per channel to get a good Direct Out level, because of this issue.
Wired as Impedance Balanced, on a TRS jack on the channel back panel.
People love it ..

Best,
Guy