Turbo board VCA choice.

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Steve Jones

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Joined
Jun 4, 2004
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506
Location
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Sorry if this has been discussed already, but what THAT VCA is the Turbo board optimized for? The BOM specifies a THAT 2150, the silkscreen a 2181. Each of there VCA's need different resistors around them to make them work best. Without a schematic it's hard to tell which VCA should be in there, I guess I could figure it out by tracing some tracks. Anyone figured it out yet?
 
Steve, Any VCA you like is suitable.

The surrounding component differences between the 2151, 2150, 2181 and 2180 are all associated with low levels of distortion, and the Turbo sidechain is not concerned with them.

In fact the VCA configuration used in the Turbo is precicely the same as on the main GSSL board sidechain, so whatever VCA you used in the main sidechain is perfectly suitable for that... In fact if you think about it, most people don't worry too much about which they use for the sidechain because even an unthunkably massive distortion of 1% (to quote a cataclysmic example) means an envelope difference of significantly LESS than 1%, and the sidechain VCA is only responsible for generating a 'loudness envelope', so feel free to use whatever you have lying around.

I've happily tested 2150A, 2151 and 2180 in there, and all produce compression curves which overlay each other precisely.

Having said that, for the ultimate in restful sleep, I think that if you use the same type of VCA which you used in the sidechain position on the main board, it probably 'feels' like they should track the best that they possibly could.

Good luck with the build!

Keith
 
Thanks guys, I will relax now and go have a cup of Oolong (lovely) Oolong (lovely) Oolong (Lovely). I want milk in it, I want to see that spoon standing up.

Too bad the only pace to get HobNobs here is the English shop on Bondi Junction, now I have moved into the national park it's a bit too far to nip out for a pack.

Just finished building the 4 Turbo boards tonight, along with a dual LFO for my modular synth, so the smell of resin is in the air.
 
Keith,

Thank you so much for this. The turbo board makes the GSSL absolutely rock now. I find I can compress harder and faster than in 'standard' mode whilst still sounding good, and I finally can use it on a drum bus, which is what I built it for. :thumb: :thumb: :thumb: :thumb:

Something I noticed, whilst stuffing it - I had all of the resistors, caps and ICs lying around already, probably from building the SSL. This never happens to me - I always have to buy something! Was this part of the design philosophy, or just an accident. (I haven't checked the BOMs so might just be wrong).

Finally, is there a schematic around for this so I can learn a little about the differences. I had a quick search but it doesn't seem to be in any of the main threads. I also looked at the expat site, but couldn't find it there either.

Cheers!

:guinness:
 
[quote author="zebra50"]Something I noticed, whilst stuffing it - I had all[/i] of the resistors, caps and ICs lying around already, probably from building the SSL. This never happens to me - I always have to buy something! Was this part of the design philosophy, or just an accident. (I haven't checked the BOMs so might just be wrong).[/quote]
I'm not Keith, but if I understood it correctly it's a more or less exact duplicate of the sidechain you already have on the main-PCB, so that would explain it.

I'm not sure though whether Jakob had to make value- or other mods to 'translate' the dual-sc-original into the single-sc-Gyraf-version.

And for the same reason you'll have the schematic already :wink:
(see www.gyraf.dk)
But I assume you're looking for an 'isolated' schematic ?

Bye,

Peter not-Keith
 
Yep.

Basically it's a duplicate of the sidechain VCA section, followed by a duplicate of the precision rectifier section followed by a duplicate of the ratio section.

The fourth (and somewhat fortuitously spare, I might add) op-amp in the quad package is used to buffer the control voltage, because otherwise the second VCA would present a load on the driver and might slightly alter the GSSL curves.

But basically it's a duplicate of the GSSL sidechain bits, packaged to be much more convenient than wrestling with a double-build version, where there's a LOT more wiring, head-scratching and general furrowed eyebrows when trying to get it to work properly.

Keith
 
Just had another 'DOH' moment... penny dropping (more like a 2-pound coin!)

Everything makes sense now. This is now just running in dual-mono mode... right?

I've watched the video and read the threads on this yet I had it in my head that the two side chains were somehow different. I could see that they were similar, but I was imagining some subtle difference.

Thanks!
 
[quote author="SSLtech"]Yep.

GSSL 500.

Keith[/quote]

Nice, wasn't aware of the lunchbox-version,
let alone you guys went for a dual-mono possibility.


Bye,

Peter
 
WEll, the 500 is mono... just build two for dual-mono, and link "point c" and feed both VCAs from the output of just ONE of the time constant stages for true SSL stereo. (It's then up to the user to match threshold, makeup and ratio settings on both units, or just use them for mono only...

Keith
 
[quote author="SSLtech"]WEll, the 500 is mono... just build two for dual-mono, and link "point c" and feed both VCAs from the output of just ONE of the time constant stages for true SSL stereo. (It's then up to the user to match threshold, makeup and ratio settings on both units, or just use them for mono only...

Keith[/quote]
Aha, like that. Thanks for clarifying! :thumb:

Bye,

Peter
 
Hi !!
Just a lil point to be clarified for me...I have some 2181 LA , should I change some resistors in the turbo board???
Sorry for being so non-electronician! :oops:
thx.
 
I have just received a couple of THAT 2162 samples which are in QSOP package. I don't doubt that they are excellent VCAs but who was the complete and utter wanker who decided not to issue them in SIL package?
 
Hi !!
Just a lil point to be clarified for me...I have some 2181 LA , should I change some resistors in the turbo board???
Sorry for being so non-electronician!
thx.

Maybe nothing but Iam not sure
 

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