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

[Purusha]

[quote author="RogerFoote"]MartenSo, it is safe to say that if you use THAT 21xx VCAs of any flavor, not removing the 10K and keeping the 3.9K in there is just wrong.

I doubt it will change sonic performance much, but in the case of the 3.9k vs 5.1K, the Iset function will be set to the wrong current. That can't be that good.

Cheers[/quote]

It all makes sense. But your last statement confused me a little. Which Iset will set the wrong current, 3.9K or 5.1K?

 

[Greg]

Amen! And I'll also throw in the schematic and PCB layout ! Put it under your pillow and maybe the Gyraf fairy will bring you something...


... like a working G-SSL.

 

[fucanay]

[quote author="RogerFoote"]Purusha

Are you looking at the datasheets?

3.9K is wrong, and will allow too much current to flow out of Iset.

If you, or anyone is building a GSSL, you should have, and study the datasheets. It is the only way to see what is going on here.[/quote]

Would you say that this value was estimated at 3k9 in gyrafs original design? The datasheet shows the 5k1 for all of the chips, not just 218x.

Also, I'm not the worlds best schematic reader, but can I assume that the the 51R resistor for R2 on the datasheet is the same as the 68R we are removing?

Thanks

Matt

 

[Greg]

Couldn't agree more :thumb: !

I've got a few FCs hanging around, but I can't see myself ordering anymore. On the other hand, 21 channels of my mixer re-capped with PWs, 3 to go. That should speak for itself.

 

[Purusha]

[quote author="RogerFoote"]Purusha

Are you looking at the datasheets?

3.9K is wrong, and will allow too much current to flow out of Iset.

If you, or anyone is building a GSSL, you should have, and study the datasheets. It is the only way to see what is going on here.[/quote]

I wish I would really know how this unit works in details but sorry I am miles away from such understanding. I can follow some more gross things about the whole design but the subtleties are unknown to me. I have no idea what the VCAs actually does... and I am happy about it as long as I know which resistors to change at the end so I can go back to my studio work :green:

Don't worry, I am learning slowly :thumb: This is my first DIY project of 8 G-SSLs with all possible mods but with your help I've been very successful so far :wink:

 

[martthie_08]

Marten

These resistor changes are not mods.

yes, I am fully aware of this, though it is a matter of point of view - if you are just about to build your unit consider this as NOT doing things wrong. But in my case, there are two units in daily use in the studio, so I will have to "modify" those :grin:

cheers, Marten

 

[fucanay]

[quote author="Greg"]I'm not sure what you're saying...

But 120mV is the max input the VCAs can have before saturating... or I guess becomming non-linear. But in my max range of operation, I'm getting from 50-75mV, so in my operating range everything should be linear. And my ratios are good so everything is peachy as I see it. Does that makes sense to you?

I actually had to disconnect the meter to get the 200 to 400mV because I didn't want to peg it out.

Also, I actually tweaked the 1K going to the CV to adjust ratios. My summing resistors are 47K.[/quote]

I just want to ask a question regarding your reasons for not changing this other than it being a hassle. If you did make this change wouldn't you get a your range of operation at a finer scale and therefor be able to fine tune the settings better? My threshold kicks the compression in to fast as well and I think I'd rather have it ONLY be in a range I would use, does that make sense?

Matt

 

[fucanay]

[quote author="RogerFoote"]
Matt

I would agree that you would have more resolution to play with if you scale the response closely, but I can see where Greg is going too. His sounds the way he wants it to. I might be hesitant to change it too.

[/quote]

Yeah, I can see that. I probably wouldn't be taking apart one of my favorite pieces of gear either. I'll try to not get too used to the ones I've built so I can get that resolution set right. :grin:

Matt

 

[Purusha]

1.) Roger, can you explain why would my G-SSL add 0.3 dB (when it's not compressing and makeup at 0) after I changed the 3.9K to 5.1K and deleted the 10K in the VCA section? Before I had zero dB output, the same as input.

2.) Next strange thing is that I have to use the 2.8K resistance instead of 1K for the 10dB meter scale to get 98% accuracy from 0 - 6dB of GR. After 6dB of GR my meter goes off, at real 13dB of GR my meter shows only 10dB of GR. Can someone explain this or maybe give some idea how to fix it?

What I noticed also is that if I reduce my summing resistor I have to increase the meter resistors for meter accuracy.

So far I used or changed:

- replaced the two 47K summing to 340K (more here, less resistance for the meter)

- took out the 68R next to VCAs

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

- deleted the 10K resistor between pins 3 and 5 of the VCAs

- replaced the 3.9K resistor with the 5.1K next to the VCAs

- replaced the 1M resistor with the 220K

- replaced the 100K to 122K on the right of the TL074

- soldered the 47K to the +leg of the threshold pot

 

[Greg]

[quote author="Purusha"]Next strange thing is that I have to use the 2.8K resistance instead of 1K for the 10dB meter scale to get 98% accuracy from 0 - 6dB of GR. After 6dB of GR my meter goes off, at real 13dB of GR my meter shows only 10dB of GR. Can someone explain this or maybe give some idea how to fix it?[/quote]
If you used a cheap meter, it might not be perfectly linear. Regardless, you're in the ballpark. When it comes to compression, you really have to use your ears in the end anyway.

 

[Purusha]

:? Yes, I bought the cheap ones from Fernell. I don't think I will be compressing more than 6dB anyway, and it's true that the ears are more important than the eyes in the process :thumb:

1.) What about the + 0.3 dB on the output? Is there a way to put some trimpots somewhere to reduce this. Otherwise I might just put back the 10K and 3.9K even if it is wrong as long as it helps getting the G-SSL back to the 0 dB output.

2.) I also noticed that left ch. adds +0.1dB compared to the other one. Is such tolerance normal for this unit?

3.) Back to my voltage on the 3rd leg of VCA:

- threshold pot fully CCW = 112,3mV
- 10dB Gain reduction = 88,2mV
- 6dB Gain reduction = 39,1mV
- 2dB Gain reduction = 14,7mV

Can some of you experts please confirm if my voltage is in the OK or acceptable range now so I can move on to the next 7 units... I would really like finish this project already. Sorry for bothering you all with all this questions but I need to clear this few things first.

 

[Greg]

I think Roger said max is 120mV, and you're obviously under that, so yea... it's fine.

 

[Purusha]

Thanks Greg, I need to hear everything twice to be 100% sure. :?

What about the IN/OUT and L/R differences? Should I be worried about it? Maybe I could add two trimpots to the 27K resistors for the unity gain to fine tune my outputs? Does it make any sense?

 

[Purusha]

Thanks for the tips Roger. I will wait and see how the other 7 units turn out regarding L / R levels.

You will soon see some nice pictures of the whole stack when all units are finished. :green:

 

[fucanay]

I just did the first "real" amount of testing on the SSL after doing some of the other changes and I realized that I'm getting about -5db per .2 marking on my meter. It's working right and I'm getting about -25db at the 1.0 mark. I've already changed the 2k resistor to a 1k and I thought that was supposed to change this. Am I doing something wrong or is this the way it's supposed to be? I'm pretty confused on this one and any help would be appreciated.

Thanks

Matt

 

[Purusha]

I don't know what meter are you using but I had to replace the 1K resistor with the 4.7K trimpot and adjust the pot to arround 2.8K to get my meter working right. I am using 0.1mA meter with 332R across the + / - legs. The meter resistance will change when you change your summing resistance. I have 340K instead of 47K at the moment.

Can you please name all your changes and benchmark results of your ratio at 10dB GR and also the voltage on the 3rd leg of VCA like I did. In this way we can compare mine and yours. You are using 2181LB like me, aren't you? When I come home later on today I'll post my ratio results from the last settings.

 

[fucanay]

I'm using the Modutec Edgewise 0-1MA meter from mouser. It's a bit slow while a drum track is going through it, but accurate with a 1k sine wave. It's just not at the scale I thought it should be (-25db at the 1.0 mark) with the 1k resistor in place of the 2k.

The changes I've made are the same as the ones you've made for the most part.

- took out the 68R next to VCAs

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

- deleted the 10K resistor between pins 3 and 5 of the VCAs

- replaced the 3.9K resistor with the 5.1K next to the VCAs

- replaced the 1M resistor with the 220K

- changed the 100K to 120K on the right of the TL074

- changed the 47k summing resistors to 120k (actually, reading your comment above, maybe this is my problem. Maybe I should try swapping these ones back to the 47k.)

Most of these changes make sense to me, but not so much this one. Where did this come from? The data sheet doesn't mention anything regarding feeding the sidechain VCA. I'm not sure this one is worth messing with.


I just don't want the meter scaled so small that a -2db GR would hardly move the meter. You know?

Matt

 

[Purusha]

You can try also the 47K or 27K on the + leg of the threshold pot and different values for summing, try more than 120K and see where it will take you.

I suggest the 5K trimpot instead of 1K resistor for the meter.

I just tried the overkill HP filter with the G-SSL and it works great. tomorrow I'll give some more info on the whole thing.

 

[fucanay]

I just checked my ratios and they are pretty close. It's right for 2:1 and 10:1, but a little off on the 4:1. no big deal to me.

I think I'm just going to leave this one as it is for now. I have some of Gregs HPF boards coming in a few weeks and I hardly see the point in messing with those resistors since they are getting pulled out to fit the HPF anyway. All of the other changes have been fine, so I think this one is done for now.

Matt

 

[Purusha]

Nice :thumb: mine are also very close, I have 4:1 perfect and the other two a little off, but no big deal.