SSL 552 Summing Box

[helterbelter]

Regarding adding the GSSL sidechain circuitry to the 552 VCA's :
This week I have ordered a couple of Turbo boards. I'm going to turn a 4 channel SSL SL595 line amp (that uses VCA's as outputfader), into a GSSL compressor. Not sure when I'll be finishing it, but if it turns out well, the same modifications can be done to the 552.

Done the first tests today, it's promising to say the least.
I made a mistake on the GSSL board that I used for the experiment. The -12 v rail doesn't supply -12v (probably just a minor thing), but the SC circuit appears to be working.
The 552 compresses, but I have to do some tweaking to get it right. I'll set up a complete GSSL audiochannel, to make comparisons, and of course to be able to compare the compression ratios and settings while tweaking. But basically, it works.

Just so you know !

 

[kante1603]

Hi Paul,

wow,that sounds awesome.
If you need the GSSL pcbs for comparison-
I have one set left over (not populated though) from chef @ audiokitchen,rev#7 in pretty good shape.
Just to let you know before you must source them from anywhere else.

Rock on,

Udo .

 

[helterbelter]

Hi Udo,

Thanks, but I don't need it.

I have a GSSL board, but I only have populated the sidechain, not the remaining part.

 

[kante1603]

Hi Udo,

Thanks, but I don't need it.

You´re welcome

 

[DigitalMetal]

Sounds promising indeed !

Udo i still havent had time to test the level of my summing box as im rebuilding my studio setup at the moment and i have gear all over the place but once everything is settled down il give it a go.

Happy New year Guys!

 

[kante1603]

Hi guys,

just to inform you:Status quo on my build is that I have done 8 of the 24 channels of the NYD passive mixing network.
As my build consists of 3 x 8 channel blocks I thought it was a good time to debug/troubleshot this block first,then do the others.
Here are the results:
1)worked without any faults,all channels behave identical-cool.
2)Level drop with 1 signal routed to 1 bus is -18,5dB.
3)Center level drop is close to -3dB-nearly perfect.
4)Level fully down (ccw) or mute switch in is nearly -100dBU (as expected).
5)Fully balanced at all stages/modes.

So it all works-HURRAY!

Next is doing the other channels,after that I´ll hook it up to the SL552.
Will fool arround then with shunt resistors and see/hear/measure what happens.I will post the results here,maybe a pic of the network if you want.

Have a good time (I do!),

Udo.

P.S.:Have found some nice Penny & Giles 10k lin Faders with a travel path (is that right?) of 120mm-AWESOME (using it as masterfader!).

 

[kante1603]

Udo i still havent had time to test the level of my summing box as im rebuilding my studio setup at the moment and i have gear all over the place but once everything is settled down il give it a go.

No problem Neil,Pauls and mine behave identical,so I think it´s "by design".

Happy new year,

Udo.

 

[helterbelter]

All good news !
I expect 200R as shunt will do, but I have to testdrive it first, and here's the problem : The Motherboard of my PC died a week ago..... So, no audio tests can be done until I have built a new computer. 

Today I made some decent pics of my summingbox unit, will post them soon.

 

[kante1603]

All good news !
I expect 200R as shunt will do, but I have to testdrive it first, and here's the problem : The Motherboard of my PC died a week ago..... So, no audio tests can be done until I have built a new computer. 

Today I made some decent pics of my summingbox unit, will post them soon.

Hi Paul,

sorry to hear your computer died-that´s bad news.
200 Ohms as shunt would nearly be the same as NYD calculated for driving a mic preamp-hmmmmm....
Will do some tests,maybe it really works without?
Cannot verify the real loss I will get when all 24 channels are hooked up finally.As said I have a loss arround -18,5 dB with 8 channels,but with just Neutrik Minilyzer (high impedance!) attached.The values will be different after connecting the whole thing to the IMO I think.

Looking forward to see the pics of course!

Ciao,

Udo.

 

[helterbelter]

Regarding adding the GSSL sidechain circuitry to the 552 VCA's :
This week I have ordered a couple of Turbo boards. I'm going to turn a 4 channel SSL SL595 line amp (that uses VCA's as outputfader), into a GSSL compressor. Not sure when I'll be finishing it, but if it turns out well, the same modifications can be done to the 552.

Done the first tests today, it's promising to say the least.
I made a mistake on the GSSL board that I used for the experiment. The -12 v rail doesn't supply -12v (probably just a minor thing), but the SC circuit appears to be working.
The 552 compresses, but I have to do some tweaking to get it right. I'll set up a complete GSSL audiochannel, to make comparisons, and of course to be able to compare the compression ratios and settings while tweaking. But basically, it works.

Just so you know !

Hmm, I didn't make a mistake, the 79L12 is defective..... took me quite some searching to discover this. Anyway, fixed it, and did some more testing..... :

the opamps in front of the 552 VCA's are setup as inverting, so the 552 works as expander instead of compressor..... This means that I'd have to use an extra opamp to get it correctly.

Not a big problem, but all in all, it's not a straight forward mod to do anymore. It might be easier to take out the VCA's from the SSL boards, bend two pins of each VCA, and wire these to the 202 emulation parts of the GSSL..... Or something similar.

 

[kante1603]

Hi Paul,

sad to hear,but this seems to be way too much work to put in to get acceptable results from it,no?
Thanks a lot for all your efforts!
Some of us even have the originals (520 and 510),others have build the GSSL (which is a f*****g good bus compressor).

I´m still focussing on my NYD-build and do the tests with the shunt resistors.It´s on hold at the moment as I´m waiting for 2 more Lorlins (MBB;not easy to get,but found them at banzai music) which I seem to have killed  by overheating (?)during all the heavy soldering jobs I had to put in there-it´s now arround 1.900 solderpoints just for the passive mixer-puuuuuuhhhhhh......;but I´m close to complete it-as said "just" swap Lorlins.
Meanwhile I started to design the inserts part which will be huge too,have done the controlers so far and started building the relais circuits on veroboards.

Will report back hopefully next week when I´m done with first tests on the behaviour between passive mixer and the 552.

Heads up Paul

Cheers,

Udo.

 

[helterbelter]

Well..... I'll continue this quest, hahaha. I'm going for Keith's ultimate setup, but then with an SL595 as quad line amplifier.

There are a few ways to solve this issue, and even though it takes time to figure out what to do, once it's clear, it could be that it's pretty easy.
I want to have a minimum of mods on the 552, and currently, there are 4 points the connect the 552 to the GSSL board, leading to 5 modifications :
1/2. remove 2 resistors, and wire 2 pads to the GSSL SC inputs (in front of the 47K resistors).
3/4. Remove 2 other resistors, and wire these to the CV to VCA pads on the GSSL.
5. remove 1 trimmer
That's it so far.
(I have removed lots of components that aren't needed though. The post VCA opamps and caps, obsolete logic switching, everything that consumes power that hasn't got use anymore, is taken out.)


As said, an extra opamp would be needed, but, I could also add more modifications to the board making the opamp obsolete.
But now it's time to decide which way to go.

Just to give you an idea which choice I'm looking at :
1. An extra opamp (for each channel) : There are at least 6 opamps not used on the GSSL board, but these are all setup as non-inverting, so, there has a bit of twiddling to be done to be able to use a few of these. I could choose to go this route,. but it makes the work look a bit ugly. Especially if it'd be necessary to lift a few legs of the opamps.....

2. Modding the 552 : This means that (on the GSSL) the 5534 of the 202 emulationcircuit has to be fitted, and the output must drive the VCA pair in the 552 : In the 552, 2x 2 5534's have to be removed, the output of the first one has to be connected to the wire coming from the 202 emulation circuit, and the output of the second 5534 has to be connected to 0v, IIRC...

The second option appears to be the easiest one, so, I'll try that first.




on a sidenote : the 520 is a VCA buscompressor, but it's not entirely the same as the GSSL compressor.
The 510 is a channeldynamics module, gate/compressor/expander, an awesome tool for sure, but not meant as buscompressor.

 

[kante1603]

The second option appears to be the easiest one, so, I'll try that first.

Cool!I´m highly interested in where this ends up Paul!

on a sidenote : the 520 is a VCA buscompressor, but it's not entirely the same as the GSSL compressor.
The 510 is a channeldynamics module, gate/compressor/expander, an awesome tool for sure, but not meant as buscompressor.

I know ;D-remember we had them on our consoles;I´ve used them very often-always pretty useful tools,and the 520 on a bus is simply killer!

Cheers,

Udo.

 

[helterbelter]

Back on track !  ;D
And..... even more simple than initially thought, hahahaha !
Still some tweaking to do to get the amount of compression right, though.
And for some reason the gainmake up doesn't work.......

So.... Back in business, haha !

And... in the meantime I discovered something wicked, that I can use for an idea I had somewhere in the very back of my head. : )

Very fun to do, and I learn a lot !

 

[kante1603]

Hey guys!

Success:Have my little passive mixer set up (just on a mounting panel but hey...) and connected it to the SL552.
Sent 1Khz at 0dBU thru the whole stuff with all channels muted (therefore only the 2 x 10Ks "seen" on the bus) except of channel 1 and switched to left and right bus alternating.

1.:It behaves exactly as before with just using summing resistors having a boost of 6dB.
2.:Shunt resistors nearly do not have influence on it (-0.7dB with 240r and -0,3dB with 620r)-therefore can be left out-cool!
3.:Switching input to center position gives a drop of nearly exactly -3dB-supercool.

Have a minor issue with hum,therefore bad THD but this is just a quick setup to proof it all working;propper grounding will be done in the box of course.

Next steps are my insert and ms matrix,frontpanel design etc.Will keep you posted.

Attached a pic of the quick setup.If you want to see more detailed pics of the passive mixer please tell me as I´m not sure if it belongs to this thread (allthough it´s about turning an SL552 into a summing box,hahahahaha....).

Cheers,

Udo.

 

[helterbelter]

Ha, tonight I'm doing a bit more experimenting with the GSSL add-on !

And yes Udo, your passive summing thing does belong here.

Regarding the shunt : This is also on my to-do list, but my list is a bit too long, and I haven't look into the shunt thing yet.


The knobs by the way, they're cool ! Where did you get these ?

 

[kante1603]

Regarding the shunt : This is also on my to-do list, but my list is a bit too long, and I haven't look into the shunt thing yet.

As said I don´t think it is necessary at all.

The knobs by the way, they're cool ! Where did you get these ?

From Banzai Music,a bit fiddly to mount because it has 2 set screws;massive aluminium;here´s a link (also available in black,the german word for them is "Knebelknopf"):

http://www.banzaimusic.com/Harmony-Knob-Silver.html

O.K.,some further pics of the passive mixer then:

The panel measures only 24 x 20 cm;I ended up in ca.1900 solder points,so yes:A lot of work sir-and much more to come!

The wiring (looks a bit messy at the moment because the loose wires are for status leds;will be mounted later direct on the frontpanel-they go through the holes next to the mute toggle switches):







Some further impressions-as said this is not the front but only a mounting panel:









That´s it for today;it was a big step for me.Tomorrow I´ll be back to "normal" work,hahahahahha...... 8)

Cheers,

Udo.

 

[helterbelter]

Wow, looking great !

Regarding the compression mod : This is going to work. I have got it working, it sounds like a luxurious GSSL, but the compression ratios aren't the same yet. The IMO's ratio response is like 75 percent the amount of compression compared to the GSSL VCA.
The gainmake up isn't working yet, but that has to do with something else because the GSSL audio channel doesn't respond to the gainmakeup pot either. I do need to tackle this this before I can really say all is working.

But for now, this is what needs to be done to get it working :

And, the good news is that the mod is really simple.
-You'll need a GSSL board (and preferrably also a turbo board). Stuff the Side chain electronics, and the 1712 and 7812 regulators.
Then unto the 552, for both channels :
-remove 2 resistors.
-lift one leg of a 5534, solder a wire to it, and attach that to the GSSL board (This is the CV),
-solder a wire to an empty pad, and wire it to the GSSL (this is the sidechain audio.)
-Maybe remove a trimmer.

That's all. It's less work than building a complete GSSL.

When all is correct, I'll let you know how to do this in detail.

But first I'll have to get the ratio right. I think that changing 2 resistors will do the trick.

 

[helterbelter]

Done.  ;D

Here's the test jig :

The part of the GSSL that needs to stuffed. Without the 7815/7915 combo. But it needs the frontpanel PCB of course.

The mods on one of the 2 IMO boards. This needs to be done on both boards.

-remove 2 resistors.
-lift one leg of a 5534, solder a wire to it, and attach that to the GSSL board (This is the CV),
-solder a wire to an empty pad, and wire it to the GSSL (this is the sidechain audio.)
-remove a trimmer.

The ratio is now precisely tracking with the GSSL channel I set up for comparison.
It was very simple after all : I replaced 2x 1k resistors with 1x4K7. (for each channel). These 2x1K resistors are in front of the compression 21xx vca. (1 in the 202 emulation, and 1 in front of the 202 emulation).  This is the only difference.

So, get yourself a GSSL board (and preferrably also a Turbo board), a bunch of components, and upgrade your 552 to a mastersumming amp/ masterbus compressor !

As said, I'll work out the details soon, including scanned schematics with notes, and then I'll update the first post !


Soon I can start building my "Ultimate" version.
The completion of my console is very, very close nearby, mwoohahahaaah !

 

[kante1603]

Hi Paul,

this is just AWESOME!
Back from a big TV-liveshow I found your pics just by accident.Thought I have missed something because notification doesn´t work anymore (my web provider changed software completely;now lots of bugs in it at the moment).
Have seen that you just made an edit on this post,so that´s why.....
Paul-this is simply a fantastic work you´re doing,and thinking about having some of those modules left plus GSSL boards this mod is becoming a must-have for me!
I agree that a turbo-board is a must (thinking back on my first GSSL after adding the oxford mode,hahaha....killer!)

Thank you so much for sharing all of this!
And I´m very very curious about seeing the pics of your console.

Keep up your good work and thanks again,have a nice weekend,

Udo .