Help me modify a console...

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datape

Well-known member
Joined
Feb 13, 2006
Messages
63
Location
UK
I have a DDA D series modular console. It sounds ok. Pretty clean. Could do with a few mods though.

The main issue at the minute is the lack of tape monitor channels. My workaround is this....

I plan to take a direct out from the mic pre, send this to my MOTU interface and then return this via the line inputs on the desk. The MOTU has a 'cuemix' matrix that will give zero latency monitoring. I plan to leave the desk in line mode all the time, so as long as the computer is on, I will be able hear the mic channels. I dont see this being a problem.

Here is a schematic of the mic pre.

67qz051.jpg


I guess that if I were to take a feed from the mic/line switch on the mic side this would give me an unbalanced output direct to the MOTU.

I would prefer balanced outputs. For this would I simply emlininate the TL072 IC1a circuit?

Would I use a transformer on the emitters of TR1 and TR2 and get rid of everything after the R22/R23 output balancing circuit?

Does anyone know what function the diodes serve?

Also I have already modded a couple of channels to have a transformer input. This was an optional extra for the console as shown in the diagram.

However the components C2/C3 R12/R13 C6/C7 R16/R17 C8/C9 all seem unneccesary. I wired the transformer primary to the junction of R6/C2 and R7/C3 and the secondary across C10, leaving the jumper wires open where the recommended DDA transformer would have sat.

The transformer used was a 'neve' type 10468 1k2:4k8. I havn't noticed any problems with the channel, and there is an improvement over the bass and a few extra dB of gain, but am I missing something without the extra capacitors in the path. As far as I'm aware less is more with components in the signal path.

There may be more questions to come about modding this desk, but for now I think it is enough to chew on.

Anyone have any thoughts on all this?

Thanks!!
 
You can't really get rid of those. The diodes are there to protect the op-amp, but the circuit doesn't work right without it there. I would take the output of that op-amp and run it through a balanced line driver. I like the OutSmarts drivers from THAT, but there are SSM and TI chips that work well, too. Use the pin on the LINE/MIC switch as a convenient (and safe) point to grab the output from. Don't do it directly from pin 1 of IC1a - it may oscillate. Check out the app notes of any of those driver IC's - they should give you a good sample circuit that you can just build.

You can also just use an 'impedance balanced' output, provided the input is balanced, it would work reasonably well and be cheap and easy to do. Take a 75 ohm resistor from the output of the mic pre (the leg of the line/mic switch), and that is the 'HOT' output. Take a 75 ohm resistor from chassis ground, and that is the 'COLD' output. Use 1% resistors.
 
thanks. I will try the impedance balanced output and see what it sounds like.

did you have any thoughts on how I had wired the input transformer to the circuit? is leaving those components out going to cause problems later on?
 

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