Calibrating the G-SSL with THAT2181 - share thread !!!

[RedNoise]

Thx BassC....

 

[intellijel]

hi,

i'm not a specialist, but according to :
http://homepage.mac.com/marten.thielges/gssl/calibration.html

with taht 2181LA :

4. remove the 10k resistor between VCA pins 5 and 3 on both sidechain and signal path VCA's.
5. For the signal path VCA's, change the 3K9 resistor from VCA pin 5 to V- to a 5K1 resistor. (only for signal path VCA - leave 3K9 on the sidechain)
6. For the sidechain VCA, remove the 47R resistor that connects leg 4 to ground (i.e. do not connect to ground - leave it as is)

hope it helps.

So if I have a 2181LA, should I only do those three mods mentioned above? what about 1-3?

Also are these absolutely essential?

I just finished my first gssl in a Purusha case and with the SSC. When the compressor is IN the meter shows compression but the audio effects are very subtle, even on what I consider more extreme settings (e.g. ratio:10, threshold almost all the way CCW).The makeup gain is definitely working so I just want to know if this is all symptoms of not setting up the 2181LA properly? or is there perhaps another issue I need to investigate?

 

[audiophreak]

Hi,

    I've used the THAT 2181BL08 - I see the calibrations for the LA, LB, LC - but not for BL or BL08 - Am I blind and just missed it ?  sorry if its been covered.

 

[regularjohn]

Hi,

   I've used the THAT 2181BL08 - I see the calibrations for the LA, LB, LC - but not for BL or BL08 - Am I blind and just missed it ?  sorry if its been covered.

they are the same thing

I believe LA, LB, LC refers to the version (A, B, or C) and AL08-U, BL08-U, etc refers to the packaging.  For through hole it's AL08, etc and for surface mount it AS08, BS08, etc.

 

[audiophreak]

Hi regularjohn ,
  Thanks for taking the time, Then having THAT 2181BL08, I should follow the calibration that is listed for the  2181LB  at this link http://diy.fischerworks.com/gssl_vca.shtml  ?

 

[regularjohn]

Hi regularjohn ,
   Thanks for taking the time, Then having THAT 2181BL08, I should follow the calibration that is listed for the  2181LB  at this link http://diy.fischerworks.com/gssl_vca.shtml   ?

yes.  although i think the 120K on the sidechain input (in place of the 47K's) is wrong, or at least i've never read about anyone doing that.  you might want to search around about that.  I always use the LA, so I can't personally comment on the LB.  everything else looks good though.

Bit of advice, you can save a couple bucks and use the LC for the sidechain VCA, because that VCA isn't used for passing audio, only for generating control voltages.  So the worse noise and thd specs won't matter there.

 

[audiophreak]

  Thanks for the help and tips regularjohn !

    I'm  just working out the last few bugs in a single unit as most have build, but am going to use it as a test bed for two more GSSL main PCBs with Turbo in a Dual GSSL 3U case with a similar layout as some dual LA2As I've seen pics of 

  Will post pics when done.

  Thanks again   

 

[CJ]

any news on the status of the 100K( ratio adj) resistor and the 2 47K's at the bottom of th page, when using the THAT 2181LC chip for the MNATS VCA's? It is the first resistor on th page below, thanks!

here is a link to the resistor choice page>
http://diy.fischerworks.com/gssl_vca.shtml

 

[Harpo]

any news on the status of the 100K( ratio adj) resistor and the 2 47K's at the bottom of th page, when using the THAT 2181LC chip for the MNATS VCA's? It is the first resistor on th page below, thanks!

here is a link to the resistor choice page>
http://diy.fischerworks.com/gssl_vca.shtml

For the 100K ratio adj. (later pcb revision has a 127K* silkscreen) substitute with 82K or 91K in series with 50K rheostat, initial value about centered.
With 33K feedback resistor in sc-VCA following I2V stage, keep both 47K sidechain summing resistors. More ideal value for Rfb might be 47K/SQRT(2)=33K234, but this is a little program dependant.
The 15K resistors at audio-VCA-input, located between on-board transformer and MNATS DBX202Cs outline (later pcb revisions have 27K silkscreened) will be 30K (=double value of the 15K I2V-stages feedback resistors, located below the silkscreen 'OUTPUT') to compensate for the +6dB at output balancer for overall unity gain in VCA bypass condition.

 

[CJ]

wow, great info, thanks!  ;D

 

[okdaniel]

So I've read through many threads but it's tough to find a definitive answer. I have 2181a vcas in the vca and the sc sections.

I'm using the newer rev 11 pcbs from pcbgrinder. Am I right to say that I should have a 3k9 and not a 5k1 for my sc vca, along with only 1 of the 47r resistors in? No 10k and nothing in the % space next to the 47r?

Planning on installing the expat audio turbo board once finished. Anyone know if it's alright to use a 2180c in the turbo board alongside the 2181a in the sc on the main board as long as I get the different resistor values right?

Hope this is the right thread for this. Seemed appropriate . 

 

[huuubert]

Hi,
could someone upload the gssl_vca.shtml file as the original website is no longer available.
Thanks!

 

[Script]

Those who search may find

https://groupdiy.com/threads/gssl-help-thread.47/page-431#post-1029346

 

[Script]

My gssl is fully operational except in turbo [...]

Posted in wrong thread. Better delete here and repost in:

https://groupdiy.com/threads/gssl-add-on-help-thread.65232/
There was at least one such problem IIRC.