Modding Soundcraft 600 (Master Channel first)

Dear,

I 'm modding my Soundcraft 600 and i need your help.
First i would like to mod the master channel.
Here is the schematic http://www.soundcraft.com/downloads/fetchfile.aspx?cat_id=user_guides&id=666 (Page 8).
I read a lot of post form Jim Williams how mods this boards.
That my conclusion to mod it.

Recap all the channel with Panasonic FR series el caps
Replace TR1 and TR2 by 2SA1084 transistor.
Install large bypass PSU electrolytic caps (C55, C56, C57 and C58 = 220uF/35V instead of 47uF/25V)  and bypassed with a 0.1uF Ceramic cap.
Replace AOP with super fast BurrBrown OPA1642  (1.8mA same as the TL072 so no need to upgrate the PSU)
Add Power supply bypass caps 0.1uF ceramic on each AOP.
Replace all Non polarized transitor with Wima 5i don't know what series ?)

What do you think about this mods?
And do you see other thing to do to improve my master channel ?

Best regards,
Xarolium

Hello,

If you do your mods in stages, you will be able to test for any changes that take place as you work through the module. By doing this you will be able to determine which mods make the most difference, which mods are really worth making, and which mods are a waste of time and money: not every mod is a good mod

A really interesting comparison will be to mod ONE signal path only, say the right path. This will leave you with the left path as a reference path that you can compare against..... and also keep you with a working path in the event of a failed mod that you can compare with and use as an aid to fault-finding. This is very useful when dealing with a board as densely packed as the 600 master.

This idea does have its limits because the power supply decoupling is common to both the left and right paths, so you will need to choose the point at which you do the power mod.

Cheers,

Gareth.

Dear Gareth,

Thank you for your advises.
My master Channel have some Crrr, Plok, MMMhh problem so i need to fix it.  So i telling me if I have to disassemble my channel master why not upgrade in the same time.
So do you think only large caps is a good start point ?

xarolium said:

I read a lot of post form Jim Williams how mods this boards.

Click to expand...

I would say, don't believe blindly everything that you can read on commercial sites.

Recap all the channel with Panasonic FR series el caps

Click to expand...

That's an excellent decision; this board is probably close to 20 years old now, so, yes, changing caps is a good preventative measure, although the electrolytic caps of the 80's and 90's have a much better life expectancy than the ones used in the 60's and 70's. 

Replace TR1 and TR2 by 2SA1084 transistor.

Click to expand...

I don't think that would bring any significant improvement. The noise factor of the 1084 is marginally better than the original 2N4403, by about 0.2dB, provided you increase considerably the operating current, from 1.5mA to about 6mA, which goes with a number of complex implications. Simply rolling transistors won't do much.

Install large bypass PSU electrolytic caps (C55, C56, C57 and C58 = 220uF/35V instead of 47uF/25V)

Click to expand...

Yes, that's a possibility that results from the size reduction due to progress of technology, and there are not many reasons why not taking advantage of it.
35V is not a necessity, considering the 17V rails. I would rather concentrate on temperature rating than voltage.

and bypassed with a 0.1uF Ceramic cap.

Click to expand...

Bypassing electrolytics with ceramics is a favourite pet of audiophools. Best case it does nothing, worst case it adds VHF resonance to the rails.

Replace AOP with super fast BurrBrown OPA1642  (1.8mA same as the TL072 so no need to upgrate the PSU)

Click to expand...

This is probably the most controversial suggestion. As it is implemented in the 500/600, the TLO there gives ample performance. With über-fast opamps, what you get is more risks of unstability, particularly  in the summing amps where the opamp is in the NFB loop with a BJT.  I would undertake this task only with a good o'scope and a good audio analyser (and my 40 years of expertise). Now you may want to do it, and there is no big risk there. Install DIL sockets in place of the TLO's and here you go... But don't expect much. The noise performance of the system won't be spectacularly different. There may be a minor improvement in THD, that you may discern, or not.
These opamps exist only in SMD form so you'll have to add adapters. 

Add Power supply bypass caps 0.1uF ceramic on each AOP.

Click to expand...

  I believe it was one of the (many) weaknesses of the 500/600 series - that was carried on in the 6000. They had opted for rail-to-rail decoupling instead of rail-to-ground, which almost everybody today know is nonsense. In order to do it right, you must add a pair of ceramic 0.1 at each opamp, very close. Ideally, the junction of the two caps should go to ground at the point where the stage load returns; this is not always easy to do with dual opamps. Others would opt foor connecting these to a "dirty" ground bus which, BTW, exists on the 600; they call it dustbin ground. The problem is that you probably won't hear any audible difference at first. These may appear on the form of subtle (or not) distortion, bird-chirps, swishes... Takes a lot of effort and determination to optimize decoupling.

Replace all Non polarized transitor with Wima 5i don't know what series ?)

Click to expand...

Again replacing caps with Wima is an audiophool's favourite. In the master channel, I don't see any cap that may be replaced with a Wima, certainly not the 30p that are in the monitor section.

xarolium said:

My master Channel have some Crrr, Plok, MMMhh problem so i need to fix it. 

Click to expand...

I had a 600 that gave me headaches with all sorts of noises; turned out it was a defective loom. Went perfect after replacing the loom. IDC connectors can be a pain.

abbey road d enfer said:

I had a 600 that gave me headaches with all sorts of noises; turned out it was a defective loom. Went perfect after replacing the loom. IDC connectors can be a pain.

Click to expand...

Thank you for your help. I just want to know what is a "loom"?

xarolium said:

abbey road d enfer said:

I had a 600 that gave me headaches with all sorts of noises; turned out it was a defective loom. Went perfect after replacing the loom. IDC connectors can be a pain.

Click to expand...

Thank you for your help. I just want to know what is a "loom"?

Click to expand...

The loom is the ribbon cable with IDC connectors that runs across the desk and connects all the modules.

The loom is the ribbon cable with IDC connectors that runs across the desk and connects all the modules.

Click to expand...

Ok thank you.  i will try with a other one but i really expect that my problem come from faulty old caps, i hope so

Lot´s of great advice in this thread!
From my experience with  Soundcraft desks I´d start with inspecting all ribbon wires and insert jacks. Recapping is a good idea and makes more of a sonic difference than chipswapping. While you´re at it increasing all coupling caps might be a fine idea because Soundcraft´s beancounters made them very small.
You did realize that Jim William´s suggested chip is SMD? You´d need adapters and solder SMD parts. Then you still have to tame that chip in case it oscillates. Do you know how to do that? Like John said the original chips will give you all you need. There should be a valid reason to swap chips, not only believing that it will sound better. I.e. something like a TL072  used at insert sends which are supposed to drive 600 Ohm input gear in your scenario.

@Gareth: did you design the 600?

jensenmann said:

@Gareth: did you design the 600?

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Yes, Jens, I did design much of the desk, with various bits of involvement with Douglas Self (mix amps & oscillator coming to mind).
I guess you spotted my name, initials and signature on various of the drawings.......

Yes, I did. We´ve been chatting about the 8000 in the past over at the analog console forum. So it was obvious that you must have been involved with that board, too.

jensenmann said:

From my experience with  Soundcraft desks I´d start with inspecting all ribbon wires and insert jacks. Recapping is a good idea and makes more of a sonic difference than chipswapping. While you´re at it increasing all coupling caps might be a fine idea because Soundcraft´s beancounters made them very small.

Click to expand...

I've got the patch bay one my SC600 so i don't think problem come from the Insert jacks.
And i got the same sound problem on Studio out, Mix out and Control out so i don't think it's a Ribbon cable problem too and it looks like pretty new and not bend.
I think and i hope it comes from the inter-stage coupling caps before the fader (C8,C108, C11, C111).
I will replace it and come back with news.

So after changed some caps, the noise is gone but i still have a little creaking who appear sometime when master is full.
I replace all Inter-stage coupling with 220uF  25V nichicon fine gold caps, 
I replace the 2.2uF local decoupling caps by 10uf nichicon caps, C7,C107,C3 and C103 by 100uF Elna Starget, C12 and C112 by 47uF nichicon fine gold.

My question is do i have to add 0.1uF ceramic Cap between local decoupling cap to silence this creaking?

xarolium said:

My question is do i have to add 0.1uF ceramic Cap between local decoupling cap to silence this creaking?

Click to expand...

The desk did not need 0.1uF caps when it was in production, so assuming that the ICs are as-per production spec (TL072 and NE5532, etc), the answer is that you do not need to add ceramic caps.

Changing only electrolytic caps that were in the original design would not add a requirement for more caps to be added.

Have you modded both left & right paths so you can compare performance with and without modification?

G J C.

xarolium said:

And i got the same sound problem on Studio out, Mix out and Control out so i don't think it's a Ribbon cable problem too and it looks like pretty new and not bend.

Click to expand...

The loom is common to all modules; you cannot exonerate it. The problem I experienced before was not due to a bend,  it came from a contaminated IDC contact, that was totally invisible.

Have you modded both left & right paths so you can compare performance with and without modification?

Click to expand...

I didn't mod any thing on the master channel yet, only replaced capacitors .

The loom is common to all modules; you cannot exonerate it. The problem I experienced before was not due to a bend,  it came from a contaminated IDC contact, that was totally invisible.

Click to expand...

How can i test it ? Do i have to buy an other one to know if the problem come from the IDC cable ?

xarolium said:

The loom is common to all modules; you cannot exonerate it. The problem I experienced before was not due to a bend,  it came from a contaminated IDC contact, that was totally invisible.

Click to expand...

How can i test it ? Do i have to buy an other one to know if the problem come from the IDC cable ?

Click to expand...

You may build one yourself; the components are not too expensive. You don't need the expensive tool; use a standard vice. You don't need to build a complete one, just a short one that would cater for a restricted number of modules, so you can test all the signal paths.

You may build one yourself; the components are not too expensive. You don't need the expensive tool; use a standard vice. You don't need to build a complete one, just a short one that would cater for a restricted number of modules, so you can test all the signal paths.

Click to expand...

You was right the noisy master problem come from the bad IDC cable.
I replace it and now i've got a perfect recap working board

thank you for your help

xarolium said:

Dear,

I 'm modding my Soundcraft 600 and i need your help.
First i would like to mod the master channel.
Here is the schematic Soundcraft - Professional Audio Mixers (Page 8).
I read a lot of post form Jim Williams how mods this boards.
That my conclusion to mod it.

Recap all the channel with Panasonic FR series el caps
Replace TR1 and TR2 by 2SA1084 transistor.
Install large bypass PSU electrolytic caps (C55, C56, C57 and C58 = 220uF/35V instead of 47uF/25V) and bypassed with a 0.1uF Ceramic cap.
Replace AOP with super fast BurrBrown OPA1642 (1.8mA same as the TL072 so no need to upgrate the PSU)
Add Power supply bypass caps 0.1uF ceramic on each AOP.
Replace all Non polarized transitor with Wima 5i don't know what series ?)

What do you think about this mods?
And do you see other thing to do to improve my master channel ?

Best regards,
Xarolium

Click to expand...

xarolium said:

Dear,

I 'm modding my Soundcraft 600 and i need your help.
First i would like to mod the master channel.
Here is the schematic Soundcraft - Professional Audio Mixers (Page 8).
I read a lot of post form Jim Williams how mods this boards.
That my conclusion to mod it.

Recap all the channel with Panasonic FR series el caps
Replace TR1 and TR2 by 2SA1084 transistor.
Install large bypass PSU electrolytic caps (C55, C56, C57 and C58 = 220uF/35V instead of 47uF/25V) and bypassed with a 0.1uF Ceramic cap.
Replace AOP with super fast BurrBrown OPA1642 (1.8mA same as the TL072 so no need to upgrate the PSU)
Add Power supply bypass caps 0.1uF ceramic on each AOP.
Replace all Non polarized transitor with Wima 5i don't know what series ?)

What do you think about this mods?
And do you see other thing to do to improve my master channel ?

Best regards,
Xarolium

Click to expand...

Did you ever do these mods? what do you recommend?

Viceroy is a cat said:

Did you ever do these mods? what do you recommend?

Click to expand...

I believe you should have understood that:
Replace TR1 and TR2 by 2SA1084 transistor. is useless
Replace all Non polarized transitor with Wima is not pertinent
Replace AOP with super fast BurrBrown OPA1642 may be counter-productive
Recap all the channel with Panasonic FR series, Install large bypass PSU electrolytic caps and Add Power supply bypass caps 0.1uF ceramic on each AOP is recommended