SSL Clone compressor ratio measurements

[Steffen]

I did it another way by increasing the 100k resistor feeding the gain-make-up-mixer, rsulting in less audio VCA tracking
127k was the perfect value but I used 120K...was close enough for me....

steff

 

[SSLtech]

[quote author="matthias"]I have an idea :grin:

if I would set the ratio switch to 10

and connect a pot with the 1k's in series then I would have full sweepable ratio control, from 1:1 - 10:1 :?:

mat[/quote]Well yes.... but your release times and attack times also vary by a factor of ten in terms of dB/mSec... and your GR meter will still show 10dB reduction while you're compressing by only 1dB...

But otherwise, yes.

Keith

 

[matthias]

@ steff: does this improvement make the comp more like the real
ssl mixbuss comp or is it just for better control ... > ratio switch and the displayed gr on the meter...
:?:

mat

 

[Steffen]

[quote author="matthias"]@ steff: does this improvement make the comp more like the real
ssl mixbuss comp or is it just for better control ... > ratio switch and the displayed gr on the meter...
:?:

mat[/quote]


it´s for matching the "real" compression ratio to the ratioknob setting.

without the mod the 2:1 ratio was something like 3.5:1 and 10:1 was inverse!!! 10 dB input level boost was resulting in 0.5dB level drop on the output! (ratio = 10: -0.5 ???)

steff

 

[Greg]

I think I put the cover on my GSSL for the last time. I adjusted my ratios by putting a 220R in series with the 1k resistors. They're not perfect, but really close. I'm at 2:1, 4.5:1, and about 12:1. Not too bad.

Thanks for the help !!!

 

[matthias]

what about the threshold ??

In Jakob's ssl.pdf the threshold goes from -20 to +20 ... on the original it's from-15 to +15 .. ??

 

[eugene]

Zwoef

I'm doing my first diy project ... and already fully adicted !

My SSL clone is doing well ... execpt when changing the ratio no big changes are happening to the output signal ... . I checked the circiut about a million times ... and no missing parts !

Probably got to know I am using the That 2180 VCA ... .

What do I have to do ? What should I test ? Or is this just a drawback of the 2180 VCA in this circuit ?

 

[ChuckD]

I think I am seeing the same result on the ratio button thing but I haven't had time to take measurements.

I too am using the 2180's

I will take some measurements tommorow and get back to you.


-ChuckD

 

[Ian MacGregor]

[quote author="ChuckD"]I think I am seeing the same result on the ratio button thing but I haven't had time to take measurements.
[/quote]

Good! This is how the ratio is supposed to work. The threshold value changes depending on what ratio you are set on, so that no matter what ratio you have chosen, you should have the same amount of GR. I actually like this feature. It allows me to compare say, a 2:1 and a 10:1 ratio while compressing the same amount.

Ian

 

[eugene]

A kind of interesting !

The SSL compressor isn't working as any other compressor ... .
No matter what ratio you are chosing the compressor is always giving the same amout of gain reduction ... . Having a fixed tresholf ... this means that the compressor makes no difference between a 2:1 or a 10:1 ratio ? Or do I miss the clue ?

 

[eugene]

Conclusion: this compressor got an varibale treshold depending an the treshold fixation and on the ratio one is chosing ?

 

[Ian MacGregor]

Yes, I believe so. The threshold changes (depending on ratio) so that the amount of GR stays the same depending on ratio. Think of it this way: you get more range out of the threshold the higher the ratio.

 

[eugene]

Can Somebody confirm this ratio thing ?

 

[gyraf]

Yep - just take a look at the schematic.

The ratio switch both sets different gains at the rectifier AND adds different DC levels to the rectified signal in order to change threshold.

The "actual" threshold is the diode at point "C", leading to the A/R timing circuits. A simple 0.6V threshold..

Jakob E.

 

[matthias]

I just made some tests for ratio with my ssl comp and I found out there's a 5,7db drop when I change the 2180 to the 2150

is this normal and does it affect the ratio thing ??

I wanted to measure the actual ratios of my comp, but as someone said the thresold range depends on the atio setting I don't know where I have the 0db threshold setting,...

any suggestions ??

mat

 

[mesmer]

Which that vca has the closest ratios to the ssl design right off the bat?
Peter

 

[matthias]

@ mesmer: that's a good question

I think the 2150 was declared as a "spare part" for the original vca..

but I prefer the 2180 because of the higher dynamic range and the better specs, the compression sounds exactly the same...

but I want that the ratio settings on the frontpanel are equal with the compressor!! so how can i measure/compare them when theb "zero point" of the threshold is "moving" when changing ratio...

 

[radiance]

I tried to meassure my ratio values and this is what I got:

2 : 1 = 2.2 : 1
4 : 1 = 4.5 : 1
10 : 1 = 12.5 : 1

I used THAT 2180 lb and my method of meassuring was not really precise.
I guess using carbon 20% tolerance resistors can make quite a difference here....

 

[hitchhiker]

I've got 2180LA's in both of my units. The ratio's tested to be performing very close to correct on all settings.

cheers,
Lance

 

[matthias]

thanks,

can you give some details how you measured the ratios??

mat