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

[Greg]

Purusha man, you're going mod crazy !!!

The sidechain highpass pot, changing the 47K summing, the 1K to CV, and the threshold pot mod will all interact with one another. Honestly, it seems like you're just doing a bunch of mods without taking the time to think about what they're doing.

First, for threshold adj, either use the sidechain highpass, or some other method... not both. If you use a different method, just set the sidechain at unity gain.

I think the point I'm trying to make it that perhaps some of your mods are interacting with each other. As always, I recommend getting the unit up and running stock so you know how the original behaves then mod to taste. If you start off with the modded version you have no reference to whether or not you made improvements or not.

But it seems that you are close, and I can't wait to see a nice stack or GSSLs finished.

 

[Purusha]

Thanks for your concern Greg, much appreciated :thumb:

Just for the record, I built first the unit with the original value elements and find the unit to be very off balance in regard to the threshold and ratio and making way too much distortion when compressing only a few dBs. Than I followed all the mods which I got from Reggie who used the same VCA. So far I think I am very near but still need some more tweaks regarding the threshold and maybe ratio also. I have 7 more G-SSLs ready to be tested and they are all done with the original value elements so I can always compare if needed.

Don't worry Greg, I just like experimenting
:grin:

 

[Greg]

You speak of distortion. This should be of concern. There should be no distortion with a few dB of compression. This is an aggressive compressor, so you might hear pumping. Can you describe the distortion?

 

[Purusha]

It looks like I had some success after all with all those mods...

... after listening again carefully to the sound of compressor I can say that there is no distortion going on at 6dB or even 12dB of GR but the sound becomes grainy when I apply a lot of GR for example when I turn the threshold to the max then sound becomes very distorted or grainy. I don't know how much GR would that be since my meter doesn't work at that point anymore but it might be OK after all.

How does your G-SSL sound when you apply max GR?

 

[Greg]

[quote author="Purusha"]How does your G-SSL sound when you apply max GR?[/quote]
Like total crap because there's probably 20dB or more of compression...

You might know this but just thought I'd mention:
db loss = 20*log(Vout/Vin) in case you want to make a quick calc.

 

[Purusha]

Thanks, so it's OK after all. :thumb:

One more thing, I noticed that my meter's pointer doesn't deflect immediately when the song is paused, but it deflects immediately when bypass is applied. It goes down very very slowly. Does anyone know why?

 

[Purusha]

Greg, are your 7815 and 7915 regulators also so hot that you can't hold them for more then 5 seconds?

And I didn't wire any extra stuff to the G-SSL yet... I have two more LEDs, the HP filter, overload LED mod plus relays for true bypass :wink:

 

[Greg]

For deflection, is your release set slow? Change it to fast.

Yes, the regs are going to be warm/hot. This is another can of worms, but all those LEDs won't affect the regulators. You need to pull DC for them pre-regulation. Same for the relays.

The only additional components that will pull more current through the regs is the sidechain opamps your adding.

 

[Emperor-TK]

OK, I editied my original post. I think I was only confusing the issue. What I was trying to say was that it's easier to use the pre-trimmed 2180 series VCA's if you haven't bought the 2181 series already.

The info in this thread is great and I wasn't trying to contradict it at all. Volker's page lays out how to use the 2181Lx series very well. Just note that the 1M resistor feeding the 50K trimpot will change to different values depending on whether you use the LA, LB, or LC VCA.

http://groupdiy.silentarts.net/martthie_08/gssl/calibration.html

One final thing I noticed that may or may not have been discussed, is that the 47R resistor on pin 4 or the sidechain VCA could technically be deleted for all 2181Lx VCA's. There is an internal resistor from pin 4 to pin 2, and this external resistor would parallel that one. It is however only the sidechain, and noise isn't really an issue (hence no trim pot).

-Chris

 

[Purusha]

[quote author="Greg"]For deflection, is your release set slow? Change it to fast.

Yes, the regs are going to be warm/hot. This is another can of worms, but all those LEDs won't affect the regulators. You need to pull DC for them pre-regulation. Same for the relays.

The only additional components that will pull more current through the regs is the sidechain opamps your adding.[/quote]

Yeah, I had my release on auto, it's so damn slow that I thought something is wrong :green:

Sorry for bothering you Greg, but can you suggest where exactly to pull the voltage for the LEDs and relays?

 

[Purusha]

Emperor-TK, how is your G-SSL progressing, finished yet?

 

[Purusha]

[quote author="RogerFoote"]Purusha

You pull the pre regulator dc off of the + pad on the unused bridge rectifier.[/quote]

Thanks, I thought so. The only thing I don't know is do I need to add some resistors or something else before the LEDs?

 

[Purusha]

Emperor-TK, just being curious, have you finished your G-SSL?

 

[imo]

i am a bit confused on the summing resistors. Are you referring to the pairs of 47k's on the output, and consequently replacing the 4 with 4 120k's, or am i looking at the wrong resistor?
Thanks
Ian

 

[Purusha]

We are talking about these 47K resistors

 

[Emperor-TK]

[quote author="Purusha"]Emperor-TK, just being curious, have you finished your G-SSL?[/quote]

Yes, almost. My case arrived yesterday and it needs to be mounted still. Other than that, I need to trim the meter better. The 1K meter resistor gives me about 24 dB's at full scale (1mA Modutec meter). To summarize, I'm not using any add-ons, such as the side chain mod, etc. I used 2181LB's this time instead of the 2180's I mentioned before.

- took out the 68R next to VCAs
YES

- replaced the 10K with the jumper next to the VCAs
YES

- replaced the 1M resistor with the 220K
YES

- replaced the 100K to 120K on the right of the TL074
I used 122K

- replaced the 100R with 51R right of the TL072
NO

- replaced the two 47K summing to 120K
YES

- soldered the 47K to the +leg of the threshold pot
I used 20K. The lower resistor value allows for greater range on the threshold control. With the threshold turned all the way down, 20K has the comprssion kick in around -50dBFS (running my DAW at +4). 47K has it kick in around -35dBFS. The upper limit is not effected (threshold set at max has no compression for both). A 1KHz sine wave was used for testing.

And lastly, I deleted the 47R resistor on pin 4 or the sidechain VCA. I did this for no other reason than technically it's not supposed to be there. I don't suspect that it will have much effect on the circuit. I doubt that I will even A/B it to see if I can tell a difference.

 

[Purusha]

Did you check your ratios yet?

Are you satisfied with how the threshold reacts by using your mods? If everything works fine I'll follow your mods and see what will happen. I am very close with mine but not there yet :green:

One more thing, can you meassure the voltage on your main VCAs 3rd leg with 1Khz - 0dB, ratio 10:1 and threshold fully CCW? I wanna know what you are getting.

 

[Greg]

[quote author="Purusha"]One more thing, can you meassure the voltage on your main VCAs 3rd leg with 1Khz - 0dB, ratio 10:1 and threshold fully CCW? I wanna know what you are getting.[/quote]
I might do this as well on my two GSSLs. One uses 2180LB and the other DBX 202. Should be interesting.

 

[Greg]

Thanks Roger. I don't even remember which version of the 202 I put in there. I will say; however, that the one with the 202s and WIMAs is hands down the best of the 5 SSLs I've made. So I might not go muck with it even if it's off spec. But I am curious just for kicks.

 

[Emperor-TK]

Pursha,

First I have to point out that these aren't my mods. In fact, I cut and pasted from earlier in this thread.

Here are some screen shots from my calibrations. They show the effects of the two different threshold resistors:

Here is the Excel file too.

here

You can get the local ratios from the data here. Note, that I don't do simple two point ratio measurements because the response is not quite linear, even after the knee region. This is seen in the data, but is also shown well in this graph:

I'm going a little overkill here, but I am interested in the shape of the knee as a function of ratio as well. These plots show this effect.

When I put together my chasis, I'll do the voltage measurement for you.

-Chris