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Old 3rd March 2015, 01:58 PM   #1
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Default Circuit Tweaking Challenge (sort of)

So this is most likely in the wrong area, but this is where I've gotten a lot of help with the same types of questions as I'm asking now.
Soundcraft 200 Delta Mixer. Bought it from Craigslist and once researching, I realize after a full recap (Nichicon and Wima's, about 1,000 of them), this can be a studio quality mixer. I also read up about some Jim Williams mods. But since those are $150 a channel, no one says what they are. (Which is good, that's the guys job!) So, since I have 24 channels to mess with, I thought I'd ask here for circuit opinions.

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

Stable op amp upgrades would be very nice to know, I have some ideas, but again, I'd like to have input. The power supply is a CP450, recap and new rectifiers are on the docket.
Here's a thread with the (maybe) correct schematics. It combines Delta, Venue, and Delta Theatre so I'm not quite sure.

Last edited by Mooly; 3rd March 2015 at 02:03 PM. Reason: Fit pictures inline
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Old 4th March 2015, 02:01 PM   #2
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Looks like quite a sensible circuit overall (schematics are hard to read though).

What are the supply voltages like? Could be anything from +/-12 to +/-18 V.

That's a whole bunch of faders likely in need of some TLC. I hope you are prepared for this.

I'd say you could probably do better than TL072s for the input and EQ nowadays. IC1 should be something suitable for medium-high source impedances (3-10k), with either FET input or some kind of input bias current cancellation, good CMRR, and half-decent output driving. Medium-low current consumption preferred. IC2 similar but with low input impedance nonlinearity. Hmm. LM4562 seems close but its current noise isn't terribly low. Doesn't anyone make a dual with cascoded FET input?
BTW, I wouldn't trust the circuit to give symmetric input impedance with the gain adjustment like this. That's just a hunch though, and would have to be verified by simulation.

The balanced output amps could use something even beefier than the trusty NE5532... LM4562/LME49720/LME49860-ish.
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Old 4th March 2015, 02:18 PM   #3
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Default Circuit Tweaking Challenge (sort of)

Quote:
Originally Posted by sgrossklass View Post
Looks like quite a sensible circuit overall (schematics are hard to read though).

What are the supply voltages like? Could be anything from +/-12 to +/-18 V.

That's a whole bunch of faders likely in need of some TLC. I hope you are prepared for this.

I'd say you could probably do better than TL072s for the input and EQ nowadays. IC1 should be something suitable for medium-high source impedances (3-10k), with either FET input or some kind of input bias current cancellation, good CMRR, and half-decent output driving. Medium-low current consumption preferred. IC2 similar but with low input impedance nonlinearity. Hmm. LM4562 seems close but its current noise isn't terribly low. Doesn't anyone make a dual with cascoded FET input?
BTW, I wouldn't trust the circuit to give symmetric input impedance with the gain adjustment like this. That's just a hunch though, and would have to be verified by simulation.

The balanced output amps could use something even beefier than the trusty NE5532... LM4562/LME49720/LME49860-ish.
Sorry about the schematics. The PDF link I put in seems to have disappeared.....

Rails are -\+ 17V. I am ready as I ever will be for the faders, worth it! I'll do some simming with it, thanks for the idea, not sure why I didn't think of that.
I have a boatload of TI op amp samples, most of which you recommended. I'll probably go with LME49720 for outputs, I've had good experiences with it. Thanks!
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Old 4th March 2015, 02:22 PM   #4
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got any pic's of your new bundle of joy.
i liked the delta i had use of for the better part of 12 years i miss it...
i used it for live sound applications as well as some recording projects worked great in both circumstances.

only problem i ever had was assignment buttons sticking but that was in a heavy touring season with no time in the schedule for maintenance even the crew was hard pressed to find shower time(stinky tour as i recall...)

Last edited by turk 182; 4th March 2015 at 02:29 PM.
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Old 5th March 2015, 04:05 AM   #5
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Default Circuit Tweaking Challenge (sort of)

Buyer is in Vegas, so I don't have the mixer quite yet unfortunately so no pictures except for these uninteresting ones sent by seller.
Click the image to open in full size.
Click the image to open in full size.
Something odd however, the first two inputs are not DLX, then 18 are, then another 4 aren't. No dual inputs and they all have only four auxes, maybe slowly I'll look on the bay for the full input modules.
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Old 5th March 2015, 11:05 AM   #6
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so it's a 24 channel mainframe mine or i should say the one i had was a 32.
i hope it comes with a roadcase.
it looks like this one has some corrosion forming on it.

Last edited by turk 182; 5th March 2015 at 11:09 AM.
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Old 5th March 2015, 12:38 PM   #7
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Default Circuit Tweaking Challenge (sort of)

Quote:
Originally Posted by turk 182 View Post
so it's a 24 channel mainframe mine or i should say the one i had was a 32.
i hope it comes with a roadcase.
it looks like this one has some corrosion forming on it.

Yeah, wish it was a 32. I think that corrosion might just be residue from something (hopefully). It doesn't come with a road case, but I'm happy the power supply included is rack mountable!
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Old 5th March 2015, 12:48 PM   #8
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as long as it doesn't get shipped in a cardboard box all should be well.
i once purchased a TAC Scorpion console (used) that arrived with a 1/3 of the controls sheered off because the supply was in the same box.
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Old 5th March 2015, 09:40 PM   #9
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Quote:
Originally Posted by turk 182 View Post
as long as it doesn't get shipped in a cardboard box all should be well.
i once purchased a TAC Scorpion console (used) that arrived with a 1/3 of the controls sheered off because the supply was in the same box.

*Seller in Vegas
Very sorry. That must have made no sense. I'm in Minnesota and should've picking it up Saturday sometime.
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Old 6th March 2015, 03:53 AM   #10
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Default Circuit Tweaking Challenge (sort of)

https://www.gearslutz.com/board/geek...chematics.html

Post 7
Wondering about a input transformer.
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