GSSL HELP THREAD!!!

[spudstyle]

Ok, now my compressor is working but on my left channel, I got a ground noise. The right channel is ok, very low noise. My kit is from PCBGrinder and a capacitor was missing in the package (cause the BOM say 9x100pf and really need 10). I find another capacitor at home that is 100pf but not the same size cause it's a 500v (see attached picture). So this capacitor can be the problem ? In this case, what type of capacitor I need ? 50v, 100v ? I don't have the reference of PCBgrinder kit capacitor.
Thanks for your help.

Your 100pF cap is OK. You won't find a cap with this dialectric where voltage rating in this spot will be your concern.
Some other parts in the blurry area of your pic are at least questionable, IE without trimmer fitted, ment for a different type of VCA, some resistors are one side connected only, doing nothing. The pretrimmed THAT2180 VCAs prefer pin4 unconnected, so you might pull out the 47R and 68Rs connecting to THAT2180 pin4. Other members snipped pin 4 off or bent this pin sideways, so it didn't make connection to pcb (just leaving the 47R or 68R out seems easier/cheaper, but YMMV). You might pull out the 10Ks between VCA pins3/5 as well, once ment for a different type of VCA.
Whatever your 'noise' might be, this will more likely be either hum at double mains frequency, caused by ground loop(s), hum at mains frequency, induced by your mains transformer or hiss, caused by a missing ground connection. From your pic, seeing the molex center pin connected, this might be caused by the 1st case. XLRs pin1 connect to chassis in the shortest possible way and using seperate wires instead of a mic cable (with shield only one side connected), you want the wires connecting between XLR-pin2/3 and pcb twisted together, so the differential receiver has a better chance to cancel out induced garbage. Using metal/conducting standoffs in the wrong spot might be another reason.
Just my 2ct.

Thank you very much ! I will remove 47k, 68R and 10k.
For the noise, I will follow your advices. Thanks

 

[phancak]

Hi Harpo.

Can you help me with GSSL threshold sensitivity?
Treshold potenciometer is active only 75%

Voltage on TL 072/pin1 ( without 47K resistor) is

Treshold -20dB = -0.53V (is OK?)
Treshold +20dB = +2.97V


TL 074/pin7
Tr -20dB = -0.83
Tr +20dB = -0.05



Connect 47K resistor on pot. CCW - no change.

Thank you for the help.

 

[phancak]

People help me.
Any idea?
Thank

 

[straypacket]

Do you know the taper on the potentiometer?  Does it say A50K or B50K or some other such marking on it?

Both 50k pots should be Linear taper.

 

[MeToo2]

People help me.
Any idea?
Thank

The threshold pot is a simple voltage divider, followed by an inverting DC amp.

Check your +12V and -12V supplies.

Measure at point F. It should move from -12V with the pot fully CW to 50/(50+47)*24 -12 fully CCW = 0.37V [ignoring for now any effect of the current through the 220K]

When moving the Threshold pot, this should in turn alter the voltage at pin 1 by -56/220 * the change at point F

= 3.05V to 0.094V from whatever DC offset it would be without any threshold pot connected to point F.
What effect this has on your signal is rather dependent on the sensitivity of which VCA you're using.

If it does change voltages at pin 1, then the Threshold pot is working OK.

If the threshold doesn't scale like you want it to, or to what is marked on your particular front panel, then change the voltage divider by adding additional resistance or reducing resistance between the +12V supply and the pot top leg, and/or adding additional resistance between the -12V supply and the pot bottom leg to change the max and min points of the threshold, and/or change the scaling ratio [220K resistor] until it has the correct range of 40dB when sweeping over the max - min settings. This is group DIY.

 

[Harpo]

Can you help me with GSSL threshold sensitivity?

not with these input condition missing numbers.
Would be the same as asking, 'will distance 20m be enough to stop my car' without giving the initial speed (and speed without dimension MPH or km/h will say as much as dB without the following u or V for reference).
With your TL074 pin7 at -0.05V? (this is audio AC before it gets rectified and timed, your signed number might be a DC offset) and TL072 pin1 at 2.97V? (this is DC control voltage), the 6.1mV/dB law sidechain-VCA already has dropped signal by 38dB. SC-VCA with following I2V stage drops signal by 33K/47K=another factor 0.7, so you might be feeding the GSSL with a 5.75VAC or +15.2dBV=+19.6dBu signal. Sounds to me like a 0dBFS feed from your D/A converter. Your 'Connect 47K resistor on pot. CCW - no change' indicates, your signal is already above threshold. Could be totaly different though.

 

[phancak]

People help me.
Any idea?
Thank

The threshold pot is a simple voltage divider, followed by an inverting DC amp.

Check your +12V and -12V supplies.

Measure at point F. It should move from -12V with the pot fully CW to 50/(50+47)*24 -12 fully CCW = 0.37V [ignoring for now any effect of the current through the 220K]

When moving the Threshold pot, this should in turn alter the voltage at pin 1 by -56/220 * the change at point F

= 3.05V to 0.094V from whatever DC offset it would be without any threshold pot connected to point F.
What effect this has on your signal is rather dependent on the sensitivity of which VCA you're using.

If it does change voltages at pin 1, then the Threshold pot is working OK.

If the threshold doesn't scale like you want it to, or to what is marked on your particular front panel, then change the voltage divider by adding additional resistance or reducing resistance between the +12V supply and the pot top leg, and/or adding additional resistance between the -12V supply and the pot bottom leg to change the max and min points of the threshold, and/or change the scaling ratio [220K resistor] until it has the correct range of 40dB when sweeping over the max - min settings. This is group DIY.

Thank you for your reply.
The front panel is written Threshold-20dB, 0,  + 20 db

(no 47K)
This is-20dB, =-3V 0dB = 0V (center potentiometer) and +20 dB = +3 V??

Why not in the original scheme 47K to +12 V?

or
(with 47K)
  -20dB, = 0 xxV, 0dB = 1.5 V, +20 dB = 3V?


What is right?

Thank

 

[MeToo2]

People help me.
Any idea?
Thank

The threshold pot is a simple voltage divider, followed by an inverting DC amp.

Check your +12V and -12V supplies.

Measure at point F. It should move from -12V with the pot fully CW to 50/(50+47)*24 -12 fully CCW = 0.37V [ignoring for now any effect of the current through the 220K]

When moving the Threshold pot, this should in turn alter the voltage at pin 1 by -56/220 * the change at point F

= 3.05V to 0.094V from whatever DC offset it would be without any threshold pot connected to point F.
What effect this has on your signal is rather dependent on the sensitivity of which VCA you're using.

If it does change voltages at pin 1, then the Threshold pot is working OK.

If the threshold doesn't scale like you want it to, or to what is marked on your particular front panel, then change the voltage divider by adding additional resistance or reducing resistance between the +12V supply and the pot top leg, and/or adding additional resistance between the -12V supply and the pot bottom leg to change the max and min points of the threshold, and/or change the scaling ratio [220K resistor] until it has the correct range of 40dB when sweeping over the max - min settings. This is group DIY.

Thank you for your reply.
The front panel is written Threshold-20dB, 0,  + 20 db

(no 47K)
This is-20dB, =-3V 0dB = 0V (center potentiometer) and +20 dB = +3 V??

Why not in the original scheme 47K to +12 V?

or
(with 47K)
  -20dB, = 0 xxV, 0dB = 1.5 V, +20 dB = 3V?


What is right?

Thank

Nothing is "right." This is DIY. People build stuff how they like it. This is not a kit. We have no idea who made your case. We have no idea what VCA's you've built.

The original SSL mix bus compressor had a threshold control spanning ±15dB. You can see that on the schematic here http://www.gyraf.dk/gy_pd/ssl/ssl_82e27.gif in the bottom left
It uses 3K9 to each of ±12V and a 360K scaling resistor.

The schematic for the GSSL here http://www.gyraf.dk/gy_pd/ssl/ssl_sch.gif has a threshold control of ±20dB (without the 47K)

Some people wanted a less sensitive threshold pot, because they are using prosumer gear running at -10dBV rather than +4dBu (see http://www.kompoz.com/compose-collaborate/messages.forum.minisite?siteId=1050&topicId=9410) so they inserted a 47K resistor to have finer control of the threshold at lower levels. "Note that, for use with modern-day levels, the threshold potentiometer can seem to be too sensitive; in this case, mount a 47K resistor between the control PCB and the +side of the threshold potentiometer" - http://www.gyraf.dk/gy_pd/ssl/thresh_red.jpg.

You choose. But I'm guessing from your front panel that you should not fit the 47K.

 

[phancak]

People help me.
Any idea?
Thank

The threshold pot is a simple voltage divider, followed by an inverting DC amp.

Check your +12V and -12V supplies.

Measure at point F. It should move from -12V with the pot fully CW to 50/(50+47)*24 -12 fully CCW = 0.37V [ignoring for now any effect of the current through the 220K]

When moving the Threshold pot, this should in turn alter the voltage at pin 1 by -56/220 * the change at point F

= 3.05V to 0.094V from whatever DC offset it would be without any threshold pot connected to point F.
What effect this has on your signal is rather dependent on the sensitivity of which VCA you're using.

If it does change voltages at pin 1, then the Threshold pot is working OK.

If the threshold doesn't scale like you want it to, or to what is marked on your particular front panel, then change the voltage divider by adding additional resistance or reducing resistance between the +12V supply and the pot top leg, and/or adding additional resistance between the -12V supply and the pot bottom leg to change the max and min points of the threshold, and/or change the scaling ratio [220K resistor] until it has the correct range of 40dB when sweeping over the max - min settings. This is group DIY.

Thank you for your reply.
The front panel is written Threshold-20dB, 0,  + 20 db

(no 47K)
This is-20dB, =-3V 0dB = 0V (center potentiometer) and +20 dB = +3 V??

Why not in the original scheme 47K to +12 V?

or
(with 47K)
  -20dB, = 0 xxV, 0dB = 1.5 V, +20 dB = 3V?


What is right?

Thank

Nothing is "right." This is DIY. People build stuff how they like it. This is not a kit. We have no idea who made your case. We have no idea what VCA's you've built.

The original SSL mix bus compressor had a threshold control spanning ±15dB. You can see that on the schematic here http://www.gyraf.dk/gy_pd/ssl/ssl_82e27.gif in the bottom left
It uses 3K9 to each of ±12V and a 360K scaling resistor.

The schematic for the GSSL here http://www.gyraf.dk/gy_pd/ssl/ssl_sch.gif has a threshold control of ±20dB (without the 47K)

Some people wanted a less sensitive threshold pot, because they are using prosumer gear running at -10dBV rather than +4dBu (see http://www.kompoz.com/compose-collaborate/messages.forum.minisite?siteId=1050&topicId=9410) so they inserted a 47K resistor to have finer control of the threshold at lower levels. "Note that, for use with modern-day levels, the threshold potentiometer can seem to be too sensitive; in this case, mount a 47K resistor between the control PCB and the +side of the threshold potentiometer" - http://www.gyraf.dk/gy_pd/ssl/thresh_red.jpg.

You choose. But I'm guessing from your front panel that you should not fit the 47K.

Thank you. So if you want to use-20dB +20 dB = no 47K?


New measurements are:

point F-12V +12 V

TL 072/pin1

-3V to +3 V

Is this correct?
I'm sorry for the stupid question

 

[phancak]

I have a small problem with the Ratio.

At increase of the input signal by 10dB is:

Ratio 2:1 = 5 db
         4:1 = 3.5 dB (2.5dB is ok)
        10:1 = 2 db (1 db is ok)


It's okay, or where the problem may be?
Thank

 

[spudstyle]

After a long search my ssl is now less noisy. Hum is under the hiss but Cubase or wavelab tell me -56 db noise. It's too much. Do you think crc board could help me ? What is your S/N ?
I make a star grounding with pin 1 xlr's, middle pin of input and output and I had to wire one Ground point of the PCB to have less noise. I've seen on websites that I must wire the 0v transformer to the star ground but with this hum is very high.
I've made something wrong ?

 

[gyraf]

wavelab tell me -56 db noise. It's too much.

Does not compute. -56dB compared to what?

GSSL noise should be <80dB under the unit's maximum output level. But if you turn down makeup gain and send this into e.g. a mic-level input, you'll have excessive noise because you're not using the louder part of it's working area.

Noise is very a very rare problem in this build - check your setup.

phancak,

Are you sure there is a problem? Does the unit behave nicely?

Jakob E.

 

[spudstyle]

In my sound card (Steinberg mr816) I can't choose line or mic level. So I just plug and let the gain at 0db. The same with other line level gear. Noise is not excessive but with make at 0 or in bypass mode, without sound, cubase tell me -56db. I've no other Way to measure it.

 

[phancak]

wavelab tell me -56 db noise. It's too much.

Does not compute. -56dB compared to what?

GSSL noise should be <80dB under the unit's maximum output level. But if you turn down makeup gain and send this into e.g. a mic-level input, you'll have excessive noise because you're not using the louder part of it's working area.

Noise is very a very rare problem in this build - check your setup.

phancak,

Are you sure there is a problem? Does the unit behave nicely?

Jakob E.

Please????
I do not understand the question

 

[MeToo2]

In my sound card (Steinberg mr816) I can't choose line or mic level. So I just plug and let the gain at 0db. The same with other line level gear. Noise is not excessive but with make at 0 or in bypass mode, without sound, cubase tell me -56db. I've no other Way to measure it.

But what is 0dB on your cubase meter?

0dB = full scale? So your meter goes from say -90 to 0?
0dB = -10dBv consumer levels ?
0dB = +4dBu or 1mW into 600 ohms? And your meter goes from say -60 to 0 plus above 0 up to say +24

Unless you have some sort of a reference level, dB is totally meaningless.

Which inputs are you using on your MR816?
Inputs 1-2 can behave quite differently to 3-8.
Are you using the mic/line level inputs [3-8], or the mic/line/Hi Z inputs [1-2]?
Are they in Hi Z or mic/line mode? [mic mode is usually selected using XLR, Hi Z usually by using jack plug on inputs 1-2, but the Steinberg has a physical Hi Z switch on channel 1-2]

There's also a gain knob on the Steinberg channel too.
Input Channels 1 – 8 Gain knob 44 dB variable (-60 dB to -16 dB) with pad or -34dB – +10dB with pad off.
Is the pad turned off on these channels?
What have you got the input gain on the channel set to?

What signal are you putting in to your gssl when testing?
Have you connected the input XLR's pins 2 & 3 together with a 600 Ohm resistor or other properly terminated signal generator source when measuring the noise floor of your GSSL , or just left the inputs floating unconnected?

If it's -56dBFS and your input gain is set to 0 and your make up gain is 0 then indeed it looks like there's something wrong, because that would be pretty awful [noise floor somewhere around 56-10dBFS = 46dB.
But if you've got your input gain on the Steinberg channel set to 34dB gain then -56dBFS noise floor would be pretty fantastic....... [34+56 = 90dB EIN]

So you need to check your levels and create some sort of reference.

If you output a -20dBFS 1KHz tone from your DAW out via channel 1 output Jack 1 and pass this through a straight patch cord back into your DAW, what level does that show back into your DAW input? [to check if there's really 0dB gain in the whole path]

If you output a -20dBFS 1KHz tone from your DAW out via channel 1 output Jack 1 and pass this through your GSSL left channel and then back into your DAW, what level does that show back into your DAW input? [to check if there's really 0dB gain in the whole path including GSSL make up gain]

How much lower is the noise floor than this test tone [without compression]?

 

[phancak]

Problem with threshold senstivity is solved - bad input cable
Thank you HARPO and MeToo2.

Please is OK when threshold sensitivity is dependent on the input signal and ratio settings?
When the input signal is 0dB and ratio 2:1  threshold is active 100% to CW.
When but ratio 4:1, 10:1 is active  about 90% to CW.
It's OK???
Thanks

 

[spudstyle]

In my sound card (Steinberg mr816) I can't choose line or mic level. So I just plug and let the gain at 0db. The same with other line level gear. Noise is not excessive but with make at 0 or in bypass mode, without sound, cubase tell me -56db. I've no other Way to measure it.

But what is 0dB on your cubase meter?

0dB = full scale? So your meter goes from say -90 to 0?
0dB = -10dBv consumer levels ?
0dB = +4dBu or 1mW into 600 ohms? And your meter goes from say -60 to 0 plus above 0 up to say +24

Unless you have some sort of a reference level, dB is totally meaningless.

Which inputs are you using on your MR816?
Inputs 1-2 can behave quite differently to 3-8.
Are you using the mic/line level inputs [3-8], or the mic/line/Hi Z inputs [1-2]?
Are they in Hi Z or mic/line mode? [mic mode is usually selected using XLR, Hi Z usually by using jack plug on inputs 1-2, but the Steinberg has a physical Hi Z switch on channel 1-2]

There's also a gain knob on the Steinberg channel too.
Input Channels 1 – 8 Gain knob 44 dB variable (-60 dB to -16 dB) with pad or -34dB – +10dB with pad off.
Is the pad turned off on these channels?
What have you got the input gain on the channel set to?

What signal are you putting in to your gssl when testing?
Have you connected the input XLR's pins 2 & 3 together with a 600 Ohm resistor or other properly terminated signal generator source when measuring the noise floor of your GSSL , or just left the inputs floating unconnected?

If it's -56dBFS and your input gain is set to 0 and your make up gain is 0 then indeed it looks like there's something wrong, because that would be pretty awful [noise floor somewhere around 56-10dBFS = 46dB.
But if you've got your input gain on the Steinberg channel set to 34dB gain then -56dBFS noise floor would be pretty fantastic....... [34+56 = 90dB EIN]

So you need to check your levels and create some sort of reference.

If you output a -20dBFS 1KHz tone from your DAW out via channel 1 output Jack 1 and pass this through a straight patch cord back into your DAW, what level does that show back into your DAW input? [to check if there's really 0dB gain in the whole path]

If you output a -20dBFS 1KHz tone from your DAW out via channel 1 output Jack 1 and pass this through your GSSL left channel and then back into your DAW, what level does that show back into your DAW input? [to check if there's really 0dB gain in the whole path including GSSL make up gain]

How much lower is the noise floor than this test tone [without compression]?

I love this forum

Thanks for your complete and detailed answer ! (and a big thanks to Jacob too !!!)

I use input 7/8 without pad so I think noise level is ok. But I will make some tests tomorrow to be sure. I'm not at home.
Db with digital interface and daw are boring to understand ! 0db vu = -14dbfs ?

You can listen a short test of my gssl here: http://www.soundcloud.com/justforyourears and choose the set called test gssl (files are downloadable in 96k)

 

[MeToo2]

I love this forum

Thanks for your complete and detailed answer ! (and a big thanks to Jacob too !!!)

I use input 7/8 without pad so I think noise level is ok. But I will make some tests tomorrow to be sure. I'm not at home.
Db with digital interface and daw are boring to understand ! 0db vu = -14dbfs ?

You can listen a short test of my gssl here: http://www.soundcloud.com/justforyourears and choose the set called test gssl (files are downloadable in 96k)

No, not always. It's interface/equipment dependent.

dBFS = dB relative to Full Scale = 0dBFS the point at which an interface will start clipping, which is very relevant in digital recording, as digital clipping is awful.

The lower case 'u' in dBu normally stands for relative to 0.774596669V AC rms = 1mW of power into 600 ohms (V^2 / R).

If you want to convert to volts check out http://www.sengpielaudio.com/calculator-db-volt.htm
You can normally directly measure V RMS on your outputs with a high quality digital volt meter, but not cheap ones, as they can't cope with higher frequencies.

I checked the manual for your soundcard and it stated on page 48 that the input on the insert jack was was nominally 0 dBu with a maximum of +14 dBu. The other inputs are nominally up to +10dBu with a max of +24dBu, but whether that includes the pad or not in the +24dBu is ambiguous. I suspect it does because the sound cards do not normally have direct access to ±17V supplies which you need for the peaks of a sine wave at +24dBu. +24dBu would correspond to a good old professional standard input of nominal signal level of +4dBu with 20dB of overhead before clipping.

Outputs jacks 1-8 are apparently nominally +4dBu 600 Ohm (professional standard) but with only +18 dBu max before clipping. Again pretty normal for modern sound cards.

So round trip output to input via a straight patch cable you might easily have +4dBu out but 0dBu sensitivity in = 4dB gain, even with all controls set at '0'.

I've been caught out like this before with "hidden gain" on my own audio interface, which is why I normally use an external voltmeter or scope to calibrate levels/ sanity check all meters before I start trying to measure anything. You may find it boring, but it's well worth understanding the gain staging in detail in order to get the best out of your sound card.

 

[killjoy]

Quick question that i cannot find the answer too on this thread (probably because its such a simple, beginner question)

I got my GSSL kit from PCBgrinder. I only had 1 issue, it was missing one of the 100P capacitors ( marked 101). i had an old DOD mixer, and found the exact part, and mounted it on the right output stage above the opamp, no biggie... or so I thought.

I followed the component layout off the website to the T. used the digi-key transformer TE62063-ND, found ALL the info I needed off this thread (thanks) to get it plugged up, no VU meter yet, checked and rechecked for solder bridges or cold-joints, none.
and.......

no audio

on to my question: I need to know how to test this PCB with a Multi -meter (which i have).

I'm sorry to ask such a simple question, but this is crucial and i can only get basic or vague instructions on how to actually test this board.

put Negative probe on point A, and Positive on B ect.

here are some general pics, taken at different times, its all grounded (one off the board to input pin 1, jumped over, then to ground where IEC ground is at) now :

 

[georgeeasterbrook]

Hi all

Forgive me if I am interrupting any discussions. Here goes:

I am a complete noob when it comes to DIY electronics. I literally haven't tried anything even basic. I suppose my real question is, would it be possible to build an SSL Clone using the Gyraf schematics as a complete beginner? I'm pretty handy and reckon I could learn quickly.

I understand compressors, how they work, what they sound like etc. I make mostly electronic music in a small studio set up. I have soft comps 'The Glue' etc and have tried out hardware such as the SSL G Series and Alan Smart C2. I would really like to own one of these hardware pieces but my wallet wont stretch to that kind of asking price!

Although I could probably pick up the PCBs and components relatively cheaply I am obviously concerned that once I get started or even finish, it won't work correctly. I suppose another question would be, is there a way to make sure the clone is working as I go? e.g once i've soldered the components onto the PCB can i check that the circuitry is correct and if not, how would I know what was wrong ? ( I wouldn't know where to begin if the thing didn't work once i'd put it all together)

My apologies in advance if there are already questions/ threads about this, if so would anyone please paste a link.

Thank you all in advance!