SSL Clone compressor ratio measurements

[Greg]

I would definitely recommend doing this calibration to verify that you're actually getting the correct ratios... and c'mon, this is DIY, if you want to cut corners, just buy something of the shelf. :grin:

 

[Purusha]

Got'ya :thumb: :grin:

 

[mathflan]

I used 2181LB on my SSL so I remove 68 ohm resistors replace the 1 Mega resistors by 220K ang keep the trimmers as sugges by THAT corp.

But How Could I set tht distortion trimmer, is there a method?

 

[Greg]

You need a distortion analyzer... measures THD. I don't have one... wish I did.

 

[mathflan]

a distortion analyser :shock:

Do you think that there's a plugin which analyse that?

 

[synthetic]

Ehh, just run tones into it and tweak by ear. Rock and roll.

 

[Purusha]

[quote author="mathflan"]I used 2181LB on my SSL so I remove 68 ohm resistors replace the 1 Mega resistors by 220K ang keep the trimmers as sugges by THAT corp. [/quote]

Hello Mathflan.

How does your threshold and ratio work with your changes? Have you done any tests before and now?

BTW I thought that the Amsterdam was the only place in Europe where pot was legal :shock: :wink:

 

[mathflan]

sorry Purusha but I did the change before test the orignal value :?

I will test my ratio but I don't how.

I have only a yamaha MG12/4 Mixer, a mia midi soundcard, I have also a software Tone generator.
Any idea HOw I can set my ratios...

 

[Purusha]

Find this two thread titles in the Lab:

Taming the SSL's threshold sensitivity &
SSL Clone compressor ratio measurements

I just noticed that one of them is this one :shock: :green: just read from the beginning.

it's all in there :thumb:

 

[mathflan]

Hi,

I'll try to Set the gain trimmer with a WAVE Frequency plugin.
In fact I put a 0 dB 1KHz sinus ocillation into my SSL and I see on the spectrum that I have the 1Khz and another 2KHZ oscillation that I can remove by the Gain trimmer so I think my method is not bad.

I turn the Gain trimmer until this oscillation was at there minimum Amplitude.

I saw also that My Right Output had 0.4 dB more than LEft Outputs, I'll try to correct that with a TRimmer...

 

[Greg]

hi mathflan, are you still having your problems with the clicks and pops and has and stuff? If so, the I wouldn't start any type of calibrations for the "audio path" because the hash is getting into the audio path and that's why you're hearing it. First things first work on the grounding stuff :thumb: .

 

[mathflan]

HI greg

Yes I have "POP" when I power on and power off the SSL, perhaps because I use Relay circuit :roll:

I rewire entirely me SSL with a good star grounding...
Just have this Background noise but Inaudible when I use 0dB Source...

BUt it's not this thread....

Therefor, I test my RAtio and with the resistor 120K instead of 100K I Have :

2:1

4.5:1

10:1

I have just 4.5:1 instead of 4:1

 

[mathflan]

I'am trying to calibrate the ratio and Meter on my SSL, BUt many things that I don't understand on my SSL, if you can help me..

1 - What attack and Release Time I have to set for Calibrate ratio?is it important.

2 - Why I don't have the same results on my differents ratio when I set first the 2:1 after the 4:1...

For example when I test 2:1 It's looks good for 2:1 but I don't have the good ratio when I pass to 4:1 and 10:1.
And when I test after the 4:1 ratio it's looks good for 4:1 and 10:1 ratio but isn't good for the 2:1, Is it normal?


3 - Why threshold go from 0 to +20, Threshold isn't neagative usually.. :roll:

When I Use my SSL with a 4:1 ratio my Threshold pot is at + 10? for a - 2dB reduction.
Normally 0 is the Setting to have no compression, whereas on my ssl at 0 I have compression.

4 - Is my method to calibrate my Meter is good :

I put a 0 db in My SSL, I set the threshold at +20, and Put the make up to have 0dB.
After I set the threshold to have 5dB of reduction and I see if my meter read 5.

5 - When I send a 1Khz at 0dB into my SSL I have + 1dB when my SSL is active with the settings ratio 10:1, the theshold at +20 and Make up at 0.
Is it bad. I don't think so...

 

[Greg]

1. Not important
2. I usually set my ratio to 10:1 to calibrate. The 2:1 has a very big "knee," so it's not a good idea to calibrate with that one. Also, when you're tweaking the ratios, make sure you have alot of compression... ie 10-15dB. You don't want to be in the knee of the compressor.
3. ? Don't understand ?
4. Yup. Calculate GR from voltages then make sure you're meter reads the same.
5. ? Don't understand ?

 

[mathflan]

Hi,

In fact On my SSL +20 is in fact 0 if you see what I mean.

WHen I put 0 on threshold I have compression, but I'am asking if If the SSL receive a good 0dB.

HOw I measure the voltage of the 0db sent on th SSL.? to see if I had good voltage.

I have to read 750mv between PIN 2 and pin 3 of XLR??

Thanks

 

[mathflan]

My meter is now calibrate but I'd like to know if My method for calibrate the ratio on my SSL is good .


I have a MIA midi soundcard with a generator software.

1 - I Send a 0 dB 1Khz signal to the inputs of my SSL.

2 - I measure + 1.0 VOLT AC on the inputs between GROUND and HOT pin.

3 - I connected the Outputs of my SSL into the inputs of my soundcard.

4 - I LOAD nuendo so as to see the Meters of my STEREO IN on my soundcard inputs.

5 - I check that I have 0dB with my SSL bypass.

6 - I set the RATIO at 10:1, ATTACK and RELEASE to 0.1 and THRESHOLD to 0.

7 - I active the compressor and Turn the makeup gain until I have 0dB.

8 - I turn the generator to -20 dB and check that I have -20 dB when SSL is bypass and unbypass.

9 - I turn the THRESHOLD untils I have a -10 dB defeats so I must see -30 dB on Nuendo Meter.
I turn the makeup gain until I have -20 DB as SSL bypass.

10 - I turn the generator to -10 DB instead of -20 dB and see what happen when I have +10 dB on the SSL.

11 - I check the Meter on NUENDO to see the dB defeats on the differents ratio.

My problems are :


1 - When I turn The THRESHOLD to have -12 dB or 15 dB defeats or more I can Arrive to Turn The makeup until I have the same as SSL unbypass.

FOR example ;

with -20dB signal
I turn the threshold to have -15 db but I can have only -21.5 with makup gain at MAX.

2 - I have differents results on ratio when I put -20 dB signal or -10dB.

3 - HOw I know that I have set My threshold at 0 ?

Thanks and sorry for all my questions, but I'd to have works with a Calibrate SSL.

 

[druedger]

Thought I'd throw in my two cents. I just finished my first SSL clone, and I encountered a number of issues that I was finally able to resolve with the help of many posts on this forum. Some of the information was very helpful, and some was just plain misleading. It took a while to sift through it all, but after some trial and error tweaking I was able to get pretty darned close to what I needed.

So...here's what I have in my unit. I put in That corp 2181LB for the VCAs and the Modutec edgewise panel meter for metering (Mouser part 541-me-dma-001). There was a lot to sift through on the necessary mods for the 2181LB, and I ended up looking at the datra sheet to see what needed to be changed. Based on info here and what was published on the That site, these are the mods I did to the unit:

1. In the 2150 emulation circuit I made the following changes:
- Remove the 10K resistor and replaced it with a jumper
- Replace the 3.9K resistor with a 4.99K resistor (That site says to use a 5.1K, but this is what I had on hand - close enough)
- Remove the 68 ohm resistor
- Replace the 1 Meg resistor with a 220K resistor

2. Replaced the 15K resistors with 27K resistors (unity gain mod)
3. Removed 47K resistors and added High Pass filter sidechain (mod)
4. Replaced 100K resistor connected to TL072 (pin 6 on PCB, pin 2 on schematic) with 120K
5. Replaced 2K meter resistor with a 250 ohm resistor (I custom made by soldering two 499 ohms in parallel and adding heatshrink tubing)

With this configuration, the ratios clocked in as follows:

On 2:1, 10 db of gain resulted in an increase of 5.5 db
On 4:1, 10 db of gain resulted in an increase of 2.5 db
On 10:1, 10 db of gain resulted in an increase of 0.92 db

This put my effective ratios at 1.82:1, 4.44:1 and 10.96:1. They weren't exactly matched to the ratios on the schematic, but for my tastes these were close enough. I especially like the 1.82:1 because it yields some nice results when doing judicious compression for mastering level compression, which I do on occasion.

It took me a long time to dial in the meter movement because at first it was not tracking very well at all. It was roughyly showing half of what was compressing when the resistor was a 1K meter resistor. After experimenting with a pot replacing the resistor, I found the ideal tracking at 275 ohms. I had two 499 ohms that I wired in parallel to yield about 250 ohms. The tracking is really close and is only off +/- .3 db. Close enough for my tastes.

To calibrate the unit I sent a test tone of 1K sine wave at -10db using TRA spectrum analyzer. This went into the unit from my MOTU firewire interface, and the outputs from the unit fed another set of inputs on the MOTU. I monitored the incoming signal with Adobe Audition (Cool Edit Pro) so I could get really granular on the VU meters. With the -10 db signal I set the threshold so that it was compressing 10 db so that my signal was reading -20 on the VU meters. With the threshold set I now adjusted the test tone so that it was output at 0 db, giving an increase of 10 db. I would then check the VU meters to see how much additional gain I got, and that allowed me to verify my ratio. By dividing the additional input gain by the increase in gain post compression, you get the effective ratio. This allowed me to tweak the 100K resistor to get the ratios dialed in better. When I first started I was getting 1.73:1, 4:1 and 6.66:1. After tweaking I got pretty close.

Once you get your ratio figured out, you can now adjust the meter. Since you know exactly the amount of gain reduction that is occuring, you can change the meter resistor to get the meter needle to read the same amount of reduction that is occurring with the compressor output. Using a pot here saves a lot of guesswork and unnecessary desoldering and soldeirng to change parts out. You just adjust the pot till the meter reads right. Then use the multimeter to get the pot's resistance reading and VOILA! Instant resistor replacement.

Now here's what I noticed that I could not figure out. I wanted to get my meter to track 0 to 10 db instead of 0 to 20. No matter what I tried, I just couldn't get the meter reading low enough for the gain reduction that was occuring. When there is no resistance at all, i.e. the meter resistor is just jumpered, the meter tracks just slightly more than what it is supposed to for a 0 to 20 reading. I suspect there are other components that I'd need to tweak on the IC circuit that feeds the meter, but I didn't have time to do some more tweaking here to figure it out. Maybe I'll tackle that for the next one I'm putting together.

In any case, it's finally done, and it sounds great! I ran RightMark on it and got a THD reading of .003% and a noise threshold of 91 db. Not bad at all. There are pictures of it posted elsewhere. I used Purusha's case, and it came out really nice.

 

[matthias]

what type of meter are you using??? 1ma for full scale ?

 

[martthie_08]

that modutec is a 1mA meter, I will be using it on my next GSSL. Very strange value with that 275 ohms resistor.

 

[Greg]

I used the Modutec meter in one of my GSSLs, and I didn't like it all. I don't do heavy compression with the GSSL often, so I usually set up my meter to read about 1-6dB of compression. To acheive that, I removed the 2K resistor entirely. The Modutec has very slow ballistics IMO. I'd recommend trying to get the Behringer meter. I bought one of there tube preamps for $110 and got 4 meters out of it.