New 'ultimate' SSL buss comp clone ;-)

[Rob Flinn]

Keith I will collate the info.

 

[radiance]

Thanks Keith! I copy pasted your post so I can print it. I probabely have to read this many times before everything makes sense but it'll save me buying a distortion meter :thumb: I guess I'll first try this method for my "normal" gssl clone with dbx202 gold cans, which I'm working on now.....

The "distortion meter info" part of this thread deserves a place in the meta's as well......

EDIT: ...ah, it already makes sense. I think this is doable with a DAW (for generating the 1kHz sine wave) and some kind of Berhinger Ultra Curve thingy (for the notch filters). Either way, I'll give it a try.....

 

[khstudio]

I have been watching this project since day one & have 2 boards, case & PS ready to go :green:

It would be ultimatly cool if one of you guys could compile ALL the info. :thumb: I've already built 2 GSSL's but I can say I don't care for it on my final mix buss :sad: I love my stereo imaging & feel I loose too much with the GSSL summing. It is KILLER on my Drum Buss though!!!

I have a few questions:
I only have 1 pair of 202x's but I have several 2151's & 218x's...
I'm not sure I understand why 4x Main VCA's are needed... is it possible to only use 2 (while using my 2151's or 8x's in the sidechains)???
It is only a Stereo L/R unit... right? ...Why 4?

I'm not sure if it's a bad idea but I was thinking about loading just the LEFT of one board & the RIGHT of the other with 2 sets of controls. AHHHH... maybe not (the more I think about it).

Back to question 1... if I NEED 4x MAIN VCA's can I just use 218x's?
(I guess I could just put the 202x's in my other GSSL if this is the case)

Thanks,
Kevin

 

[khstudio]

PS requirment's -
How many VA would you recommend? or Amps?

Do both Power Supply sections get loaded on each PCB?

If someone wanted to add the "Sidechain Filter"...How?

Is is possible to make a 2 ch. unit with separate controls (stepped threashold & Makup for matching) that would work like yours or the Original?

Sorry if my questions are dumb... just weighing out my options.

Kevin

 

[Rob Flinn]

[quote author="khstudio"] I have a few questions:
I only have 1 pair of 202x's but I have several 2151's & 218x's...
I'm not sure I understand why 4x Main VCA's are needed... is it possible to only use 2 (while using my 2151's or 8x's in the sidechains)???
It is only a Stereo L/R unit... right? ...Why 4?

I'm not sure if it's a bad idea but I was thinking about loading just the LEFT of one board & the RIGHT of the other with 2 sets of controls. AHHHH... maybe not (the more I think about it).

Back to question 1... if I NEED 4x MAIN VCA's can I just use 218x's?
(I guess I could just put the 202x's in my other GSSL if this is the case)

Thanks,
Kevin[/quote]

You can build this with just 2 202 VCA's. You will get the original SSL style detection.

The reason for using 4 VCA's is that you run an in phase signal through 1 VCA & an inverted signal through the other this reduces the noise in a similar way to balanced cables.

The only difference in using 4 VCA's is that the unit will be quieter.

I have just hooked mine up to a Phillips distortion analyser (all be it out of calibration) & it wasn't sensitive enough to trim the VCA's. I could make the adjustments to the normal GSSL with it, which means that it must be realy quiet !! :grin:

I am also just compiling the build info which I will pass to Keith for proof reading before I post it.

 

[matthias]

The reason for using 4 VCA's is that you run an in phase signal through 1 VCA & an inverted signal through the other this reduces the noise in a similar way to balanced cables.

that's the way it works in the alan smart c2

does anybody know how much the noise improvement is ?

I found out that there are tolerances of +/- 0,5 db in the output level of several vcas (that 218x) so there will also be tolerances in level of the both + and - output signals

is that a big problem..?


mat

 

[SSLtech]

Well, as Wayne (mediatechnology) also pointed out, there's also the benefit of reduced CV feedthrough. -Many VCAs will allow a small amopunt of the modulated control voltage to 'bleed-through' into the signal. With a muting circuit for example, this manifests itself as a quiet 'thump' behind the signal. In a compressor the DC excursions are usually smaller, and the fact that the audio doesn't suddenly disappear also tends to rather 'mask' the problem.

With the cross-pole VCA approach, the effectively reversed control voltages on half the VCAs mean that any slight leak-through is basically canceled... In the same exact way that a variable-mu compressor (which has colossal feed-through in any single pole) cancels out when the two poles are combined. -In the case of variable-mu, each pole's Control voltage appears massively on the signal, so any misadjustment of the balance tends to introduce this low-end 'thumping' modulating with varying GR. In a VCA the CV bleed-through is already very low and often ignored, but this circuit helps quell any feedthrough still further.

The benefits summed up are:

Improved distortion -perhaps by as much as an order of magnitude. -DEFINATELY easily measurable.

Improved input CMRR, since now both input legs have the exact same impedance... In the original Gyraf version, the cold leg has an effective impedance of 44kΩ and the hot leg has an impedance of 22kΩ... in the paralleled version, both legs have an input impedance of 15kΩ.

Improved output current drive. -The output should be able to provide the same performance into an impedance which is lower by a factor of two than the original design... in case you want to go leathering a hot output signal into a 600Ω input impedance for example.

Noise should be slightly lower. -Perhaps a 3dB improvement, though we may be into the realm of diminishing returns... the unit shouldn't really be noisy to begin with (unless you used 2001 VCAS perhaps).

I think those are the major points... but I do like to see people's eyebrows raise when I tel them that my compressor has 34 VCAs in it, and they're ALL being used, except for when it's in 'Gyraf' sidechain mode, when only 33 are being used!

Basically, when I put this in the bench, it exhibits mind-numbingly tiny readings of noise & distortion... amongst the very best of ANY unit I've ever measured.

However...

To the people who've been using this for the last 3 months, none of that means anything, nor has it been anything that they've concerned themselves with... -They LOVE the switchable sidechain. -They can't get over the fact that it changes the way the compressor operates. The Alan Smart doesn't do what it does, neither does anything else that they have, or anything else that I can think of.

The unit is worth building this way, even if only for the two sidechain approach.

Hey, Rob, -did you do that one yet? -if not, just wire up an SPDT switch to interrupt the sidechain signal of the slave at the summing resistor (next to the omitted one on the board) and switch it to either continue normally on it's way ("Oxford" SSL mode) or to meet up with the same point on the master unit, ("Aarhus" GSSL mode) and revel in the pleasure.

The single biggest demonstration of the difference in behaviour comes when you pan a tone from side to side on a mixing console. -In Oxford mode it compresses less in the center. IN GSSL mode it compresses more in the center.

THAT my friends, has been the revelation of this project. The difference is wonderful. THAT is the reason I can't prise the unit out of my friends' cold, clammy hands... and it's worth more than any distortion or noise measurements. -And it's why I reckon a couple more people should build it this way, because of the power it brings...

Nobody complains that the GSSL is noisy (unless they used 2001s and are doing very quiet music, perhaps) and nobody says that it's harsh or distorted sounding. Most of the test numbers that I foind I'd improved upon, I think are more than good enough in the original Gyraf version, so don't feel you HAVE to do this or yours will be unlistenable... but DO please take away that the behaviour of a twin-sidechain unit is markedly different, and THIS may be something that you will really enjoy.

Rob, I'd really welcome your comments on how you feel about the sidechain behaviour.

Keith

 

[khstudio]

Keith,
Thanks for the info.

Well I'm ready to get started but I'm not sure if I should do it your style (with 4 main VCA's - 218x) or with just 2x 202x that I have (that's all I have of those)? I think that would make it like the original. Man would a new board for this be cool!

Also, what about the power requirements? VA's?

Maybe I should hold off loading the boards until the info is compiled to save a headache or 2 :green:

I'm ready & excited about this one :thumb:

Kevin

 

[Rob Flinn]

[quote author="khstudio"]Keith,
Thanks for the info.

Well I'm ready to get started but I'm not sure if I should do it your style (with 4 main VCA's - 218x) or with just 2x 202x that I have (that's all I have of those)? I think that would make it like the original. Man would a new board for this be cool!

Also, what about the power requirements? VA's?
Kevin[/quote]

Kevin the info is being proofed at the moment. Hopefully we can put it up tomorrow or very soon.

I suspect that if you just did the mod using single 218x or if you did it with just the pair of 202, you would be very happy either way. As Keith says the main thing is changing the side chain. Even using the single218x the GSSL is very quiet.

Mains transformer I used was 30VA which is overated for the job with 2 x 0-18v secondaries.

 

[khstudio]

Very cool :thumb:

I'd like to get started a little tonite - should I load one board completely or just the left side of one & right of the other. I'm going to try the 2x 202x's since I have them (unless you guys think the 4x 218x would beat it?)

I'm only confussed because this project & the pics are dealing with ALL 4 VCA's in the main path. Hope that makes sense.

kevin

 

[SSLtech]

Yes, you can load up just the left side and the complete sidechain on each board, then couple the sidechains as described. Remember to use a 2-pole ratio switch, and wire one pole of it to each of the two ratio boards. You need to stuff only one set of attack/decay componente (the tantalum caps and associated high-value resistors on the switch boards).

Keith

 

[khstudio]

:EDIT: I loaded both left channels... working on the SC's now.

My biggest confusion is the control board hook-up?
I'm just going to load the sections you said then get into that later.

Also are all the power supply components REALLY needed twice :?:
Would it be OK to just jumper the rails to the other board ?
Or is there too much current draw on the regulators?

This would cut down on parts needed.

I took a good hour of running mixes thru my GSSL tonite before starting & I can't wait to hear this thing... love the compression "Style" but not what it does to my stereo mixes.

Thanks,
Kevin

 

[khstudio]

How many "New" Pro mixes do you think hit one of these on the stereo mix buss out before mastering?

I do a lot of rock bands & I really like mixing with a buss comp strapped acrossed the L/R out... it helps me determin the balance of energy between instruments & frequencies... & drive my mixes into it instead of slammin the crap out of my console out (which does work sometimes)

All I really have is my GSSL & a FATSO (Empirical Labs EL7)
The Fatso does a pretty good job but it seems softer & it cannot be adjusted.

Kevin

 

[Rob Flinn]

Here are the notes for the build. Can the next few builders please give feedback, so that we can amend any errors (hopefully there won't be any)

Ultimate GSSL mods

SEE PAGE 10 OF THREAD FOR AMENDED INSTRUCTIONS !

 

[ChrioN]

This might seem a little out of the blue, but where can I get those pushbutton switches? Are they hooked up to relays?

 

[SSLtech]

Good work Rob. I've edited the first post in the thread with a link directly to your post immediately preceding this one, for full instructions. -If there are any errors or omissions, hopefully we can update that post to contain the latest info.

:thumb:

keith

 

[SSLtech]

The switches are EAOs, they're not cheap (not evan a little bit cheap!!!) but they're good, and authentic looking. They are DIFFICULT to come by, be warned, and that's the last of my stash, unfortunately...

Keith

 

[ChrioN]

[quote author="SSLtech"]The switches are EAOs, they're not cheap (not evan a little bit cheap!!!)
Keith[/quote]

Just checked them out. Nope, they ain't cheap, not even one tiny little bit...

 

[Whizard]

The EAO switches are stock items at ELFA in Sweden since decades.
I have been using them quite a lot, great quality. But not the cheapest kind no...

So you could easily get them Chrion.

 

[SSLtech]

Damn... I wish I lived in Sweden...!

Just not now... in WInter! :green: