GSSL VCA Variations and Resistor Value Changes

Hello gang,

There seems to be quite a lot of discussion about what changes need to be made to the GSSL resistor values when using different VCAs than are called for in the original using the DBX2150. I am trying to assemble a list that will make these changes easier for people, and therefor make the various breeds of GSSLs sound their best.

Being that the GSSL was based around the 2150, I won't include that. It's right on the overlay. The chips I'd like to compile lists for are 2180LA/LB/LC, 2181LA/LB/LC, and 2155(somebody is using these right?).

I will be glad to host this information after it is complete, but I need The Lab's help in compiling it. I've only built a GSSL with the 2181LBs so far and I'm even confused about what changes are being made.

The general idea be like this: http://fucanay.fischerworks.com/diy/gssl/gssl_vca.html

Anyone who wishes to contribute can post right in this thread and I'll start getting the information put into the table. Once it's completed I'll see if Jakob can add it to the GSSL meta.

EDIT: I am also setting up a webpage for DIY information. If anyone has anything they'd like to add to it, feel free to contact me. I have plenty of hosting available.

Check it out: http://diy.fischerworks.com/

Thanks,

Matt

Just a few suggestions.

You can also include the info about adding the resistor (47K, 27K or 20K) to the threshold +leg for taming the threshold a bit. :thumb:

Maybe you can also put somewhere the info that 330R resistor should be added between the + and - legs on the meter if you are using the 0.1mA meter instead of 1mA. This would help us newbies a lot. :green:

[quote author="Purusha"]Maybe you can also put somewhere the info that 330R resistor should be added between the + and - legs on the meter if you are using the 0.1mA meter instead of 1mA. This would help us newbies a lot. :green:[/quote]
This information is actually on the schematic.

i am about to use the 2155's, adn will let you know the progrss

ben

I'd like to keep this VCA related if possible. There could be other threads started to address other issues. That will make all of the information easier to obtain for the particular need, I think.

If somebody more knowledgeable than me could tell me which value on the board are supposed to be changed, I'll try to wade through all of the GSSL posts to find the values. Then everyone will have the opportunity to tell me they are wrong. :green:

Right now I know that the 100k, 68R, 10K, 1M and possibly the 3K9 need to be changed depending on which VCA used. Is there any more?

Matt

here are the mods i have done with the 2181LB..Will power up in the next few days, waiting on the power trannie:
removed 68R's
removed 10K's (still confused about whether to jumper or not)
replaced 1M with 220's
replaced 2 47k's with 120k's
replaced 100k with 120k

Thanks for that. Were the two 47k's for threshold range adjustment or part of the vca adjustment? I'll throw that on the list for now, but I hope for some clarification from the masses.

Matt

Link Updated.

http://fucanay.fischerworks.com/diy/gssl/gssl_vca.html

Matt

if i'm not mistaken they are summing resistors

If I remember someone said that the 100K next to the TL074 should be replaced by 122K although 120K would be very close also.

You can take away the ? next to your jumper word. 10K should be replaced with a jumper in the VCA section.

[quote author="Purusha"]If I remember someone said that he 100K next to the TL074 should be replaced by 122K although 120K would be very close also.

You can take away the ? next to your jumper word. 10K should be replaced with a jumper in the VCA section.[/quote]

I'm not so sure. In this post, Roger said you remove it and leave nothing in it's place. I take that to mean the jumper as well.
Thoughts?

Matt

Roger,

For the 1M when using 2180 VCAs, it would it be correct to remove it all together, right? No Jumper. It seems like it is coming from the 10k and going to the 50k trimmer, which is not in use with the 2180.

I think this list is coming along, I'll make some updates.

Matt

[quote author="RogerFoote"][quote author="Purusha"]
You can take away the ? next to your jumper word. 10K should be replaced with a jumper in the VCA section.[/quote]

Huh? The 10K should be eliminated and NO jumper used! If you put in a jumper there, you are shorting the EC pin to the Iset pin. Not good.[/quote]

Nice! I did run my G-SSL with the jumper in. I hope it didn't demaged the VCAs or something else :roll: I was following the instructions found here http://groupdiy.silentarts.net/martthie_08/gssl/calibration.html

2. replace the 10k resistor from pin4 to distortion trim pot with a piece of wire

Ok, just to make things clearer, because it seems that 2180 and 2181 are being used interchangeably.

2180 = remove 68R, 10k, 1M, and 50k trim.

2181 = remove 68R, jumper 10k, change 1M to correct value based on THAT datasheet, and install 50k trimmer

By looking at both the board and the datasheet, that is what I'm getting.

On this section of the board, , if the 10K is not jumpered the 1M value won't be connected to anything, right? So we do need the jumper for 2181.

Matt

Hmm, I have another question and maybe Jakob can comment if he sees this. On the THAT datasheet it shows the 1M should be 470k for 2151, 390k for 2150A, and 300k for 2155.

Is this something I should add to my list?

MAtt

Great Idea for a site...


maybe its just me, but i have been having strange values for the mods


in 2 units with Gregs filter PCBs..

a 2K on the pos leg of the threshold


the trimmer on the filter all the way down (ccw)

a 91R across the pole of the meter (instead of 330R) exactly spot on meter readings across the whole scale (using a 100mA Sifam AL19B)

[quote author="RogerFoote"]

The 10K I was talking about is the one that goes from pin 3 to pin 5...[/quote]

Doh, now I see. I didn't even think about that one. I'll add that to my list as well. Thanks Roger.

Matt

It's coming along good now. Maybe somebody would be willing to double check for correctness.

I would also welcome information for the places with question marks if anyone has it available.

http://fucanay.fischerworks.com/diy/gssl/gssl_vca.html

Matt

what exactly does replacing the 3k9 with a 5k1 achive?

i seem to be having no problems (unless there is an underlying one)


the second of the 2 units I just built only needed the 330R changed to 91R and that was it.

oh, well, and the 100 to 120 of course

[quote author="quadwould"]what exactly does replacing the 3k9 with a 5k1 achive?

[/quote]

I think this is just complying with the THAT datasheet mentioned earlier in this thread. THAT took the time to give that information so people who used the older 2150 could use the 218x in it's place. So what it achieves is making the circuit perform the same as the 2150 did.

Matt