Mixer Master-section upgrade, advice needed

[MrZpliff]

I've got this Soundtracs Topaz 32/8 mixer.

I'm thinking of maybe upgrading the master-section with a couple of better op-amps and get balanced out.
How/what would you do. Should I go for some nice Lundahl-transformers (for example) to get balanced out ?

My soundcard is Presonus firestudio with Balanced inputs, Input Impedance 10 kΩ.
Voltage supply is +17V/-17V.

What do you think ? Should I bother ? sounds ok as it is, but you know how it is... modding is fun

The op-amps are NE5532:s. Suggestions of Op-amps and transformers would be most welcome.

 

[Nora]

The schematic you've shown is for the fader amp, post insert. Most results will be obtained when changing the actual mixbus amp, ie the inverting amplifier directly on the l-r bus. I've had some good experiences with 2025-like opamps feeding a line out transformer. You'd have to make a new pcb though.

I find the difference between ne5532 and expensive opamps like bb to be very small and not worth the extra power consumption and possible side-effects. I understand many people here see discrete opamps as inferior to most modern devices, but imo there is a noteable difference, especially when driven at high levels. 

 

[conleycd]

For your actual mix buss you could consider Jeff's active combining amplifier (ACA).  Basically a mixer using the inverting opamp.  You can find a build support somewhere around here in the Lab.  Or go to his website www.classicapi.com

You can throw in a 2520 discrete layout.  With some modding - maybe a bug up design you could use a IC like a OPA2604.

But otherwise - the section that you have show is just the tail end of your master fader.  Lots of great stuff has been built around the NE5532/5534 so... if it ain't broken... don't fix it?

If you are driving a long cable and are concerned about noise you can build out an impedance balanced output check out Bill Whitlock's paper from Jensen-transformers.  Top of page 3 http://www.jensen-transformers.com/an/an003.pdf

Modify his example based on what your actual circuit is.  This provides easy connection to unbalanced and balanced inputs.

Of course, you could always just through some iron on the end...

CC

 

[QUEEF BAG]

c 147,148 & 171,172  .68uf ?
is i just me, or are those coupling caps real small for an IC circuit?

i would think 4.7uf to 68uf  would be more expected for a polarized cap there.
but that is moot 'cause someone will say 'yank those things and put in AD chips with
super low offset, better chips, no caps'.
personally i'm ok with 5532

OH, yes! and the the summing amps (mix amps, ACA, whatever ya wanna call them)
are more important as Arno said.  high gain stage.  all yer channelss dump into the summing
amps through resistors so they need to make up gain. cleanly. elegantly.
nice spot for the application of discrete components.

 

[MrZpliff]

Thank's guys !

As you've noticed I got the wrong section... shame on me, but you know what I meant anyway 

For now I think I just strap a couple of transformers on the output to make it balanced.

A DOA is an interresting option. I'll read up on the subject. As you say I'll probably won't be able to hear any
difference if I just change the IC-opamps.