chilton cm2 upgrades and transformer options

[mylesgm]

So I've just secured a Chilton CM2 with 6 channels of mic pres and 4 channels of stereo line pre, 2 aux and 2 bus.  This is a really neat little console with some suprising features.  Like belclere input tx's for the mic pre's (same as neve 54 series), sowter tx for line inputs, PandG faders, direct outs with tx output optional (missing from mine), 3 band eq with mid sweep that goes from 100 to 10k and low filters, phantom switching on each channel, large toroid tx for output (haven't sussed out brand), on board oscillator and talkback with slate etc.

Anyway I want to look at doing some upgrades adding the tx outputs on the direct outs and was hoping for some advice.  The manual with full schematics is here http://www.mik-el.no/manuals/cm2manualE.pdf
The opamps are ne5534 Low noise for mic standard ne5534 for line drive amp, tl071 and tl072 for eq's and filters.  Power rails are +/- 15v and 48v.

So my first thought is the output tx on direct outs.  I could use a 600:600 or a 10k:600 or perhaps I could use one of classic api's but they seem to be rated for a 75 ohm input and I can't see that this circuit would drive a 75 ohm load.  What about replacing the tl072's?

Anyway what are some of the things you see in the circuit that might benefit from a spruce up?

M

 

[mylesgm]

Thought I would add that the input tx is a belclere EN 8219.  Can't find any specs on it and CJ wont be cutting one of these up till I get an awesome replacement.

 

[rodabod]

If it's a 5534/5532 driving the output, then could could probably drive this into a typical 10K/10K output transformer, and possibly a 600/600 transformer depending on that transformer's primary inductance, and your opamp's series output resistance (couldn't find this while scanning through your PDF).

Roddy

 

[mylesgm]

what about swapping out the tl072's for te2072?
M

 

[mylesgm]

really, no other opinions?

M

 

[PRR]

It looks like a fine 1980s machine. EXCELLENT music was made on desks just like this.

What is wrong that it needs modding?

BTW: the "+48V" is really 32V. Most mikes won't care, a few might.

 

[PRR]

Page 19, 2-group output: change R3 R4 R15 R16 to 10K.

Channel direct outputs may use any good 600:600 transformer, if you REALLY need balanced outputs.

 

[mylesgm]

The 48v thing is worth knowing!  I worked on a Chilton QM3 for 5 years and we always had problems power Neumann TLM170 mics.  All other condensers no problems but the 170's just would not power on.  used external power supplies for them which was a pain. I remember testing that the desk actually put out 48v though and I did read 48 on my multimeter.  maybe the current was too low?
And wouldn't the drop in phantom voltage give a drop in mic headroom?

And why the resistor change in the 2 group output?

I do a lot of location recording and balanced outs are a must for minimizing noise.