Mod for Soundcraft 200sr?

[Brian]

Hi everyone,
this is my first post here but i've been visiting the forum for some time now. before i get to my question, let me thank you all for providing your expertise in public for all of us to take advantage of. It's an invaluable resource.

My question is on modifying an 8 channel soundcraft 200sr (very similar to the 200b) mixer. I would like to add direct outs to the individual channels, for use with a DAW. I'm currently using the channel inserts as outputs, with the 1/4" plugs pulled half way out. I'd like to add the outputs for two reasons: one, to free up the inserts so that they may be used as originally intended, and two, so that i can vary the gain AND output level before sending the individual signals to my DAW.

Is this a feasible modification? The only stuff i've read about is people replacing the opamps in the master section, which really doesn't concern me as i rarely use it as a summing device.

Thanks from another solder-sucking newbie,
Brian

 

[jrmintz]

Welcome! Can you post the input channel schematic?

 

[Brian]

I have a PDF file users manual, but no schematic. I've contacted soundcraft hoping to find one. I'll post again if i recieve a reply.

 

[SSLtech]

You would need to use a 10dB gain buffer, and 'sniff' the outputs from the wiper of the fader, before the pan-pot. The buffer will likely have to be a moderately high-ish impedance, and take it's output to a direct out socket on the back.

That should do it for you. -the only thing to look into is whether the fader wiper is in correct polarity, or polarity-reversed... they might possibly be relying on a re-flipping of the signal polarity at the summing amp... I'd have to look at it to be sure.

Keith

 

[Bjorn Zetterlund]

What chip comes after the channel fader? I have an 800B, and that uses a 5534 as the fader +10dB amp. Wouldn't be surprised if it's the same on a 200. If that's the case, you can probably get away with another 'split' off that 5534's otput. If you can't find the schem, get back with what the chip is after the fader...soundcraft never used anything too fancy, so this should be quite a solveable problem. Most likely you will find that the wiper of the fader goes to one end of a capacitor, the other end of which is connected to ground via a fairly high value resistor (probably a good 47k or so if you have 10k faders) and straight into the +ve input of an opamp, such as the 5534.

Bjorn

Hey Keith...wouldn't it need to have a buffer after the fader? Sounds like you're assuming it doesn't (in which case a hi Z buffer with +10 as you mentioned does the trick...in fact it does the trick regardless of wether or not it does have a post fader make-up amp)?

 

[jrmintz]

Wouldn't be surprised if it's the same on a 200.

Yes, my old 200B was all 5532s.

 

[Brian]

I just pulled out one of the channels, the only chip i see close to the fader wiring is a TL072cp. (according to google, it's a Low Noise JFET Dual Op Amp) Could this be in place of the 5534 Bjorn mentioned? And if so, (i'm really showing how green i am here...) which of the connectors is the output i should split? There are 8 pins on the TL072cp, i assume that the best way to locate the right one(s) is to look at what components are immidately following each of these traces, right?
Thanks alot for all the responses, i'll boil some coffee and try to figure this thing out!
_Brian_