Soundcraft 600 fixer upper

[FarisElek]

Last question. Is that IC2 and IC4?

 

[abbey road d enfer]

Last question. Is that IC2 and IC4?

That's correct.

 

[Johngoodmanson]

It's a problem that was reported to me by customersabout 30 years ago. The reason is that the Input Noise Current is modulated by the fader resistance. I suggested a simple ECO that resulted in swapping the 5532 in the post-fader amp for a TL072, since FET opamps have virtually no noise current. Indeed, the static noise will be slightly higher but there will be no more noise when cranking the fader.
Today, there are FET opamps that are quieter than the TL072, such as the OPA2134.
Even quieter are the OPA 1642, 1652 and 1656, but they are available only in SMD, so require an adapter, and may require increasing rail decoupling for stability.

Okay, I'm just a lurker, but I'm still freakin amazed when folks can get answers from THE SOURCE. I just want to express gratitude to all of the the badass MF's on this board that are so generous with their time.

 

[FarisElek]

Okay, I'm just a lurker, but I'm still freakin amazed when folks can get answers from THE SOURCE. I just want to express gratitude to all of the the badass MF's on this board that are so generous with their time.

Great point! I'm also VERY grateful. Thank you, Abbey!

 

[FarisElek]

That's correct.

On another thread you briefly explained a way to improve the ground using a garland of faston connectors. Could I trouble you to explain that in more detail? I really appreciate your help. This board is very close to where I'd like it to be. I just tracked my band on it and the recordings sound great.

 

[abbey road d enfer]

On another thread you briefly explained a way to improve the ground using a garland of faston connectors.

Can you find my post?

Could I trouble you to explain that in more detail?

The basic idea is to strengthen the 0V bus. It takes some ingenuity to find a way to attach a male Faston on the PCB, with a good connection to the O1 buse in teh vicinity of the pan-pot ground, and run a garland of female fastons.

 

[FarisElek]

Can you find my post?

The basic idea is to strengthen the 0V bus. It takes some ingenuity to find a way to attach a male Faston on the PCB, with a good connection to the O1 buse in teh vicinity of the pan-pot ground, and run a garland of female fastons.

I see. So my big question is where am I sourcing the 0v? Am I taking the 0v from the loom ribbon pcb to every individual input module via the garlands? Or maybe every few modules?

Actually, the modules are "star-grounded" via the connector boards; they are simultaneously hierarchy-grounded via the ribbon cable. The Ciletti mod replaces the hierarchy ground with a second star grounding.
Admittedly, the grounding via the ribbon cable is sloppy, so it works somewhat, but it's not as good as reinforcing the grounding where it matters most, i.e. at the module's reference ground, i.e. at pins 17, 18 & 19 of the main connector, where the loom connects. It involves running a garland of Faston connectors, that mate with a Faston-terminated wire soldered on the module, the end of the Garland being connected to the same pins on the Master module.
You don't have to cut the ribbon and you can do the mod on the modules without having to take off all the modules.
The concept of star ground is terribly misunderstood; what is good for meat puppet safety is not necessarily optimum for audio signals.

 

[abbey road d enfer]

I see. So my big question is where am I sourcing the 0v? Am I taking the 0v from the loom ribbon pcb to every individual input module via the garlands? Or maybe every few modules?

I think I have nothing to add to what I wrote previously. Connect the male faston to the 0V at pins 17, 18 & 19. Do it on every input module and every group and the master module.

 

[FarisElek]

Update!!!

I changed the wire from the faders to the pcb to some nice Belden wire and now the really annoying noise on the fader is gone. There is some very minor hiss when cranked but totally fine with me now.

 

[abbey road d enfer]

Update!!!

I changed the wire from the faders to the pcb to some nice Belden wire and now the really annoying noise on the fader is gone. There is some very minor hiss when cranked but totally fine with me now.

That is quite surprizing. Perhaps there was some kind of oscillation/unstability that teheshielded cable has tamed.
IIRC the original wiring is unshielded cable...

 

[swilliman]

Think I'll have to be dropping the OPA2134 into my SC600 as well now!

Thanks for the heads up, Abbey.

 

[FarisElek]

That is quite surprizing. Perhaps there was some kind of oscillation/unstability that teheshielded cable has tamed.
IIRC the original wiring is unshielded cable...

Ahh, that sounds possible. I replaced all the caps and opamps to original spec but I fear the regulators in the PSU need replacin' as the psu is very quietly making the same noise as the fader was. I've been really hard-core ignoring it though

 

[FarisElek]

I've 100% traced the buzzing from the fader to the torroidal transformer in the PSU. It buzzes regardless of load. Turning the transformer lets a little less leak into the audio, but it's still there.

 

[abbey road d enfer]

I've 100% traced the buzzing from the fader to the torroidal transformer in the PSU. It buzzes regardless of load. Turning the transformer lets a little less leak into the audio, but it's still there.

The PSU is supposed to be placed far enough from tehemixer itself. That's why there is a rather long cable.
Did I misunderstand something?

 

[FarisElek]

The PSU is supposed to be placed far enough from tehemixer itself. That's why there is a rather long cable.
Did I misunderstand something?

Ah, I see. Pardon my lack of knowledge. I have it racked up about 3 feet from my mixer as I figured that was enough but I see now I'll have to find a better solution. I appreciate the help. I've had all my questions answered then.

Thank you,
Ryan

 

[abbey road d enfer]

Ah, I see. Pardon my lack of knowledge. I have it racked up about 3 feet from my mixer as I figured that was enough but I see now I'll have to find a better solution. I appreciate the help. I've had all my questions answered then.

Quite often, you'll find the PSU lying on the ground under the console.

 

[FarisElek]

Ah geez. I just realized my master fader doesn't track properly. I had been testing it between 0 and +10 so I hadn't realized as you go below 0 it fades a little then jumps back up, and then fades a little, and then jumps back up, over and over until you get to the bottom and it stays off.

 

[abbey road d enfer]

Ah geez. I just realized my master fader doesn't track properly. I had been testing it between 0 and +10 so I hadn't realized as you go below 0 it fades a little then jumps back up, and then fades a little, and then jumps back up, over and over until you get to the bottom and it stays off.

Looks like a mechanical problem. You can open the fader and maybe fix it.

 

[FarisElek]

No luck on fixing it. Am I wrong to think this may be a suitable replacement?

https://www.mouser.com/ProductDetail/Alps-Alpine/RSA0K12A1013?qs=YMSFtX0bdJDDCro05rKppg==
Using opa2134 in the preamp position of the input channels is such a noticeable improvement in clarity that i'm actually a bit taken back by it. Not interested in doing it on every channel as I'm fine with the TL072's. But it's cool to have them on a couple channels

Do you think there is anywhere else on the board in which opamp replacement's or light modifications might be worthwhile? Not trying to hot rod this board, but simple modifications I'm interested in.

In particular, would replacing the 5532 with opa2134 in the C/R amp be worthwhile?

Also, I have a version 5 board. Is the trans-amp mod worth doing? And what exactly do I do? I've heard Jim Williams explain it a few times on GS but the person he talked to about it then had problems with oscillations and I've already dealt with enough recapping the channels and fixing all the problems it already had from the years of improper care.

 

[abbey road d enfer]

No luck on fixing it. Am I wrong to think this may be a suitable replacement?

Well, it looks the part. My memory is not so clear about the lever.

Do you think there is anywhere else on the board in which opamp replacement's or light modifications might be worthwhile? Not trying to hot rod this board, but simple modifications I'm interested in.

In particular, would replacing the 5532 with opa2134 in the C/R amp be worthwhile?

No, there is nothing to gain here. You may try replacing IC2 & 4 on the Master module, though.
I assume you have the Standard output modules (one fader, two tape returns); then you may try replacing IC2.
In both cases, I don't think the difference would be spectacular.

Also, I have a version 5 board. Is the trans-amp mod worth doing? And what exactly do I do? I've heard Jim Williams explain it a few times on GS but the person he talked to about it then had problems with oscillations and I've already dealt with enough recapping the channels and fixing all the problems it already had from the years of improper care.

Do you mean for the summing amps? I don't remember a version of the 600 that doesn't have transamp summing amps... Can you post a link to such mods?