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

[martthie_08]

Purusha, I have it set up exactly like in your drawing, with the exception of the 220K resistor, which is 680K in my case for the THAT 2181LA chip.

 

[Purusha]

Marten,

also in the sidechain section? I deleted two resistors next to 47K if you noticed.

 

[martthie_08]

yes, also the sidechain, please look at the pic on my page, it is nearly identical.

cheers, Marten

 

[Purusha]

Yap, everything except the 680K :thumb:

 

[needlz]

Purusha, what does the "clean / colored - vca" knob do on your gssl and how is it wired in?

cheers

 

[Purusha]

[quote author="needlz"]Purusha, what does the "clean / colored - vca" knob do on your gssl and how is it wired in?

cheers[/quote]

It's a very simple addition. You probably know about the trimable 2181 VCAs, yes? OK, I just added the second pair of trimmers to them and a 4x3 switch. One set is for minimum distortion and the second set for more or max distortion.

 

[Fredrik]

What method can you guys recoment for the triming process of the 50k pot? That corp. seems to recomend feedin 1v 1khz signal on the input and monitor the output.

But what instuments should be used, an osciloscope?

I also have questions about the trimming of the sidechain vca. First I planned to trim a 1281 on the channel and once it was trimmed move it to the sidechain and solder a resistor on pin 4 that had the same value as the 50k trim was set to.

I had second thoughts though once i noticed the 47k paralell summing resistors on the input of the sidechain vca. According to THAT corps documentation the dist/noicelevel relationship is altered when changing the input/output resistors and since the input resistors on the channel vca is 15k I thought that the trimmed 1281 would not be correct once moved form the channel to the sidechain and now Im leaning towards using a 1280 on the sidechain and 1281s on the channels.

Whats your thoughts on this?

Regards

Fredrik

:guinness:

 

[martthie_08]

But what instuments should be used, an osciloscope?

maybe try googling audiotester, if you have a pc.

I also have questions about the trimming of the sidechain vca

I wouldn't worry about harmonic distortion of anything that is not in the audio path. It is not like the 2181's are way out of specs when not trimmed anyways. Just my opinion...

 

[Fredrik]

[quote author="martthie_08"]maybe try googling audiotester, if you have a pc.
[/quote]

I´m using mac unfortunately, but I hadn´t really considered a software solution I´m going to google for a similar app for the mac. :roll:

[quote author="martthie_08"]
I wouldn't worry about harmonic distortion of anything that is not in the audio path. It is not like the 2181's are way out of specs when not trimmed anyways. Just my opinion...[/quote]

Perhaps you are right, I have never heard these vca´s before.

Thanks for the input :guinness:

 

[Fredrik]

BTW, A bit of topic but does anybody know where I can download the graphics of the component side of the PCB that Purusha posted earlier in this thread?

 

[bluezplaya]

I am trying to get my GSSL to work. It passes audio fine and clean but no compression whatsoever. I am using 2180's. Do I need to omit pin 4 on them? And do I need to eliminate the 50k trimpots??

Thanks,
Adam
:sam:

 

[martthie_08]

hello, your problem is probably in the sidechain, but it has nothing to do with calibration. The 2180 series are pretrimmed and do not need anything on pin 4, I think for the audio path vca's you can omit the 10k on pin 4, the trimpot and the 68R on pin 4, just leave that off the board. For the sidechain, I think you can omit the 47R on pin4, but please check all of this for yourself, there are excellent documents on the THAT corp website and report back if think the above written is incorrect.

 

[bluezplaya]

hello, your problem is probably in the sidechain

Hey I'm not using the sidechain. But I will omit those resistors you mentioned.

Thanks for the input!
Adam
:sam:

 

[fucanay]

[quote author="bluezplaya"]

hello, your problem is probably in the sidechain

Hey I'm not using the sidechain. But I will omit those resistors you mentioned.

Thanks for the input!
Adam
:sam:[/quote]

Umm, if it's not working you aren't using the sidechain, but otherwise you need to be. It's part of the circuit. There is no other way. read more of the documentation on this project to understand how it works and what all the sections do.

Peace

Matt

 

[bluezplaya]

Oops!! Newbie Alert!!!

Haha. I will read up on it. I see the "sidechain" printed on the board now. I think I was confused with some kind of "sidechain mod" or something like that I saw in one of the threads. Or maybe it was a HPF mod or something.

Adam
:sam:

 

[bluezplaya]

Okay I am making progress. I found a major problem in the sidechain. TL074 was backwards!! But I am still having issues with it. Now the makeup gain works, but barely. The volume doesn't budge until I get the pot almost all the way up and then it increases just a little. None of the other functions seem to work. And all of this acts the same with the Bypass in and out.

Have I got the Bypass switch wired wrong? I've wired it according to the layout.

Adam

 

[tommypiper]

Marten and Purusha:

Did you use the 2150 in your sidechain, as in both of your drawings?

Would it be the same resistor values for 2181LB in the sidechain?

(I'm getting other ideas when looking at the datasheets, but I may be missing something.)

thanks.

EDIT: This project really hates me. :evil:

I tried the mods as depicted above and now my meter is pegging and it no longer passes audio - only buzz. I tried both 2150 and 2181s, same thing. Is there any way forward with this thing? I'm really having a miserable time.

 

[Purusha]

I wish I could help you. I have 2181LB all over the place and it works fine with all the mods. Though I have a 10K trimmer for the meter instead of the 2K resistor. I think it's set around 6K to get the 10dB meter scale for my G-SSL.

 

[tommypiper]

Thanks, Purusha. So you used 2182LB in the SC?

I only made the mods on one audio VCA channel so far, and tried a 2181LB there and it doesn't work at all - on either channel now - even the channel with the standard resistors doesn't work. No audio, only buzzing.

I've swapped VCAs around, no difference. Tried 2150A and 2181LB. Meter is pegged at most settings. Getting only buzz, no audio.

Purusha, tell me what your distortion was like before the mods? I had distortion, but only on fast release setting. Other settings sounded pretty good. It didn't matter how much gain reduction - the fast release, (and second fastest release sometimes) were distorting. Was your distortion like this?

I couldn't track that down, so I tried your mods which fixed the distortion for you. I thought my problem might have been like yours and the mods would improve the distortion. But now I have nothing. I guess my next step is to restore the original resistor values and see if it works again.

The poor board is getting beat to death. (I'm troubleshooting someone else's board.)

What can make the meter peg and buzz instead of audio?

 

[Purusha]

It's hard to say what you did wrong. Probably you have some shorts or cold connections from the mods. Reverse the thing and see what happens. It's not a different PCB from mine so it should work nicely with the mods I followed.