GSSL HELP THREAD!!!

[Che_Guitarra]

Hi.  Keen to start accumulating parts for a G SSL MBC build.  It's a bit overwhelming searching this entire thread for the info i'm chasing, so hopefully this post can be a bit of a shortcut for me.

Is there a preferred PCB for this build?  Seems there's a few suppliers, but i'm finding a lot of old information and not sure if it's still relevant... and i'm not sure if there's a benefit in opting for one vendor over another.  And how to match a PCB with an available case?  Side-chains, turbo switches - it seems no two enclosures are the same... surely they're matched to specific PCBs though? 

 

[warpie]

I tend to use the "Good for searching within topics:" option in long threats.
Works pretty well for me.

 

[mokkinger]

hi guys,
having some problem with an older GSSL build here (with super sidechain and turbo board). the unit has different levels since some months, now that I wanted to calibrate it again I cant find the calibration procedure again that I used from marten thielges... his page is offline.

homepage.mac.com/marten.thielges/gssl/calibration.html

does anybody have the complete step by step procedure how to calibrate this unit again?
thanks & regards,
mark

 

[Sredna]

http://web.archive.org/web/20100523224841/http://homepage.mac.com/marten.thielges/gssl/calibration.html

 

[mokkinger]

okay, thanks!
though it seems that my different levels are due to some other fault; I checked the whole comp yesterday on the bench, and there are two strange things:
- the levels are different even in bypass mode, as well as in compression mode (gssl & oxford)
- when the unit is switched off there is no "true bypass" - shouldnt that be the case when the SSboards with the relais are installed?

maybe I am a little confused, but after reading quite a lot again about this build (was 3 years ago when I built this one), I couldnt find any reasonable option to tweak for the levels... any hint?

thanks,
mark

 

[gyraf]

There are no tweaks for levels in the GSSL, and not necessary - your levels should be within +/-0.5 dB if you build the unit with 5% resistors.

If they're not, there is something else mucked up.

Jakob E.

 

[Harpo]

- the levels are different even in bypass mode, as well as in compression mode (gssl & oxford)

level difference by what amount? If by 6dB, this might simply be a faulty XLR cable, connecting between your gear. Otherwise check the single stages to isolate the problem.

- when the unit is switched off there is no "true bypass" - shouldnt that be the case when the SSboards with the relais are installed?

Assuming barclaycons SSCF boards (I know of at least 4 other and different sidechain filter boards), the relais uses the same switching function as the bypass switch from Jakobs GSSL schematic (cutting sidechain control voltage before the timing section and forcing the VCA to current-in=current-out condition, so there is no "true bypass", that would require 4 additional DPDT relais).
Your previous posting said 'with super sidechain and turbo board' (singular) and now you said SSboards (plural), that would have a differing connection and different input resistors when made switchable between Aarhus/Oxford mode.

 

[mokkinger]

sorry to be so unprecise  :-\
I have two SuperSidechain-Boards and one turbo-Board in my GSSL, so switchable between Aarhuus / Oxford Mode (btw. like that Aarhuus Mode!!! should be written on my front panel instead of GSSL)
And yes, the SSCF boards are those from barclayon;
I cannot say exactly how much the levels differ, but you can see it clearly on a meter and I can clearly hear the difference. (as I didnt use the comp for quite a while I cant remember if this has been that way from the very beginning)
I will check the single stages to see where the problem pops up, and will report. Just to know where I should meassure: I check all voltages on the rails on the main board and the additional boards, then the VCAs and what else?

thank you guys! 

 

[Harpo]

Just to know where I should meassure: I check all voltages on the rails on the main board and the additional boards,

1st.step only takes some seconds to prove +/-15V and +/-12V in respect to 0V reference voltage are alife.
Without power supply working at all 4 rails, following steps wouldn't make much sense, so fixing a faulty supply would be 1st.priority.

then the VCAs and what else?

VCAs are current devices (and these have a type number, so we're talking on the same subject). For now assuming, your audio-VCAs might be THAT2180 or THAT2181 in grade A, B or C.
Next step is checking the audio path for unity gain in bypass condition. Power down, pull your audio-VCAs out of their (hopefully fitted) socket and temporary jumper VCA sockets pin1/8 with a piece of wire, a paperclip or whatever else handy. Power on again, feed your left side Ch.input with a maybe +4dBu (1.228Vrms) sine signal at a frequency, your multimeter can handle (probably below 1kHz, 100Hz seems a safer bet), and measure voltage of your left Ch. audiosignal at input (between XLR-pins2/3). Same level should arrive at left side Ch.output between XLR-pins2/3 (but with inverted polarity because of the now missing audio-VCA).
If not, double check (22K) resistor values at input stage, (10K) at output inverter stage, the (27K) resistor in front of the audio-VCA and the (15K) feedback resistor in the I2V stage. With from schematic 15K/27K fitted, your output level will read a little (times 1.111 or +0.915dB) higher. If this buggers you, a 5K trimmer/rheostat in series with this 27K, trimmers initial value 3K, would give you the oportunity to tweak this for same i/o level. Keeping the 27K and substituting the 15K with 2* 27K in parallel (=13K5) would have the same effect without the trimming ability.
Repeat this procedure for the right side Ch. with same signal source (just switch the XLRs over) for same readout.
Power down, pull out the temporary jumpers and refit the pulled VCAs with their correct orientation and power on again.
This already might have fixed your level differences. If not, report back with a little more info (type of VCAs used, value of fitted SSCF input resistors, Aarhus/Oxford switch wiring, ...)

 

[orangerec]

Hello,
This is going to be an elementary question for some of you. I'm finishing a GSSL compressor build. I also have a pre-existing Five Fish Audio PSU-2448mk2 Kit providing the +-15V. My question is, where would I connect the +-15v DC to the gyraf ssl board? The board was previously stuffed by a friend and he offered it to me to finish. Would  it be the +- rails right next to the VCA's? Any help would be great. Thanks.

 

[damien]

Hello,

I am working with my GSSL for a few weeks and everything is perfect. The sound is good, compression ratio as well, no ground loops...
but I still experience some issue with Input/Output Gain loss.

I don't know if it's coming from the GSSL or my damn old soundcard, or both.

To get into the details I started adding an external insert connection in Cubase.
FX Send is set on Soundcard OUT 3&4 and Return on Soundcard IN 3&4.
CUBASE SEND GAIN 0dB / Return GAIN 0dB

1. I plug my FX Send to the Return directly with cables.
> I connect the SEND/Return bridge as an insert on my master bus
> I send 1KHz sine wave @ -18dBFS > I return -12.7dBFS  ???
> To reach 0dBFS return I must output 1KHz sine wave @ -5.35dBFS

2. I plug my FX Send(Out 3&4 of my soundcard) to the GSSL In and the GSSL Out to the FX Return (IN 3&4 of my Soundcard)
> I insert my GSSL compressor as an insert on my master bus / GSSL Comp is bypassed
> I send 1KHz sine wave @ -18dBFS > I return -23.9dBFS  ???

NB. there is no gain difference between comp Bypass/compressor ON
NB. I measured the output level in AC volt mode for 1KHz sinewave @ 0dBFS Soundcard Output : 1.4V on my multimeter.

ScreenCaps attached.

I definitely experience an In/Out Gain level issue. Does it mean that I lose -5.3dB -6.1dB=-11.4dB on the GSSL input?

Where the issue is coming from (soundcard, GSSL) and what can I do to fix that?
To me it sounds pretty normal to send 0dBFS and return 0dBFS if all is alright on the signal path.

thanks in advance for your help, I am about to buy a new soundcard with sharp calibrated In/Out...

Damien

 

[Harpo]

Hello,
This is going to be an elementary question for some of you. I'm finishing a GSSL compressor build. I also have a pre-existing Five Fish Audio PSU-2448mk2 Kit providing the +-15V. My question is, where would I connect the +-15v DC to the gyraf ssl board? The board was previously stuffed by a friend and he offered it to me to finish. Would  it be the +- rails right next to the VCA's? Any help would be great. Thanks.

No. With Owels 2448mk2 (for simplicitys sake lets call it 5F for now) set for +/-15VDC, on GSSL-board leave out the bridge rectifier, both 1000uF/35V caps and the 7815 and 7915 voltage regulators. Connect the 5F +15V to the GSSL bridge rectifiers + solder lug, the 5F -15V to the bridge rectifiers - solder lug and the 5F 0V to the center pin of the external AC in solder lug. Jumper not fitted 7815 pins 1/3 and jumper not fitted 7915 pins 2/3. You still need the 78L12 and 79L12 for the +/-12V supply part of the sidechain section.

 

[orangerec]

Harpo!!!
...makes complete sense! Thank you. 

 

[MeToo2]

To me it sounds pretty normal to send 0dBFS and return 0dBFS if all is alright on the signal path.

Absolutely not! Read a few posts back in this thread about how to calibrate your sound card. dBFS is relative to the _maximum_ possible signal on an interface before clipping, not relative to a reference level like +4dBu.
Maximum input signal is generally quite different to maximum output signal on computer sound cards (largely due to low voltage computer power supplies compared to those used in classic pro audio gear)

The other 23.9dBFS -12.7dFS = 11.2dB difference (round off to 12dB) between a straight patch cable and a GSSL sounds very much like your sound card is an unbalanced interface, whereas the GSSL is electrically balanced, so you'll probably lose 6dB at each unbalance point. Check your cables and your interface specification first.

 

[damien]

Hello MeToo2,

I checked the specs of my soundcard. It's unbalanced -10dBv on inputs & outputs and cannot switch to +4dBu range.

6dB is missing from send to return in the DAW.
so I set up an FX return gain of +6dB which is big I must admit, but when I bypass the insert loop in cubase, I can now compare the clean and processed sound on the same level which is mandatory for a good A/B

1. Is +6dB gain on the DAW return FX settings ok; or may I go for +3dB send and +3dB return or...???

2. Is there something I can do inside the GSSL to use the -10dBv in/out level range?

I am thinking about purchasing a new card like the UAD appolo in few weeks, it has full pro +4dBu/-10dBv switches amongst cool other features

 

[Harpo]

2. Is there something I can do inside the GSSL to use the -10dBv in/out level range?

sure, change 6 resistors and 6 4 caps.
You want the GSSL operate at +4dBu [power(10;4/20)*0.7748V=1.2277Vrms].
Your soundcard operates at -10dBV [power(10;-10/20)*1.0000V=0.3162Vrms].
To get there, the GSSL input stage needs a voltage gain of 1.2277/0.3162=factor 3.882 or +11.78dB.

For each L/R Channel
substitute 22K feedback resistor between NE5534 pins2/3 and 22K shuntarm resistor between NE5534 pin3/gnd with [22K * factor 3.882]=85K408. Closest standard part is 85K7.
Substitute both 33pF caps across prementioned resistors with 8.2nF 10pF caps.
After operation, the GSSL needs a level drop to your -10dBV operating level again. This is factor 1/3.882 or -11.78dB.
Substitute 15K feedback resistor between NE5532 pins6/7 (pins1/2 from schematic) with [27K / factor 3.882]=6K955. Closest standard part is 6K98.
Leave XLR-pin3 on GSSL-out unconnected for your unbalanced interface.

I am thinking about purchasing a new card like the UAD appolo in few weeks, it has full pro +4dBu/-10dBv switches amongst cool other features

Seems the safer bet. If you modded your GSSL for -10dBV operation, you have to undo the mod when operating at +4dBu.

1. I plug my FX Send to the Return directly with cables.
> I connect the SEND/Return bridge as an insert on my master bus
> I send 1KHz sine wave @ -18dBFS > I return -12.7dBFS

Just found the holy grail? Where can I buy these wires with +5.3dB gain?

edit: f...ed up cap value

 

[mokkinger]

VCAs are current devices (and these have a type number, so we're talking on the same subject). For now assuming, your audio-VCAs might be THAT2180 or THAT2181 in grade A, B or C.
Next step is checking the audio path for unity gain in bypass condition. Power down, pull your audio-VCAs out of their (hopefully fitted) socket and temporary jumper VCA sockets pin1/8 with a piece of wire, a paperclip or whatever else handy. Power on again, feed your left side Ch.input with a maybe +4dBu (1.228Vrms) sine signal at a frequency, your multimeter can handle (probably below 1kHz, 100Hz seems a safer bet), and measure voltage of your left Ch. audiosignal at input (between XLR-pins2/3). Same level should arrive at left side Ch.output between XLR-pins2/3 (but with inverted polarity because of the now missing audio-VCA).
If not, double check (22K) resistor values at input stage, (10K) at output inverter stage, the (27K) resistor in front of the audio-VCA and the (15K) feedback resistor in the I2V stage. With from schematic 15K/27K fitted, your output level will read a little (times 1.111 or +0.915dB) higher. If this buggers you, a 5K trimmer/rheostat in series with this 27K, trimmers initial value 3K, would give you the oportunity to tweak this for same i/o level. Keeping the 27K and substituting the 15K with 2* 27K in parallel (=13K5) would have the same effect without the trimming ability.
Repeat this procedure for the right side Ch. with same signal source (just switch the XLRs over) for same readout.
Power down, pull out the temporary jumpers and refit the pulled VCAs with their correct orientation and power on again.
This already might have fixed your level differences. If not, report back with a little more info (type of VCAs used, value of fitted SSCF input resistors, Aarhus/Oxford switch wiring, ...)

Hi Harpo, many thanks for this detailed guide to check my comp. - I will do so asap and report back, hope to get to the studio this week once more to do that. thats great help and already big thank you!
Mark

 

[damien]

Just found the holy grail? Where can I buy these wires with +5.3dB gain?

not a joke.check my screencapture  ???
this means my soundcard is not providing equal -10dBv power input and output.
> I send 1KHz sine wave @ -18dBFS > I return -12.7dBFS

And thanks Harpo for your explanation. I am going to mod it this way for -10dBv this weekend!

 

[MeToo2]

Just found the holy grail? Where can I buy these wires with +5.3dB gain?

not a joke.check my screencapture  ???
this means my soundcard is not providing equal -10dBv power input and output.

You are comparing apples and oranges.

dBV is an _absolute_ analogue level, referenced to 1V RMS = 0dB. -10dBV = 0.316V RMS
Same on all analogue interfaces. Same everywhere in the World.

dBFS is a _relative_ digital measurement referenced to an individual interface's maximum value before clipping digitally, and is in no way directly comparable to anything else in the analogue world:
dBFS only has meaning on one particular interface, such that 0dBFS corresponds to a digital PCM value of all 1's (just before digital clipping).
To hammer it home: the output voltage corresponding to -18dBFS on my sound card is nothing like the output voltage corresponding to -18dBFS on your sound card.
The output voltage corresponding to -18dBFS on an output interface is generally in no directly way related to the input voltage corresponding to -18dBFS on an input interface.
When/if you buy your new Apollo interface -18dBFS will very likely be a completely different analogue voltage level than your current interface.

If you can't get this straight, you're likely going to have a lot of problems debugging your gain staging, and wondering why your DAW signals get louder/quieter/distort as you pass them through various outboard effects units.

See http://www.jimprice.com/prosound/db.htm & http://www.digido.com/articles-and-demos12/13-bob-katz/22-level-practices-part-1.html

 

[damien]

Ok I understand everything now.
thanks for all the tips. (it's more a lesson than tips )

I'll purchase a pro card with pro signals in a while, mine is old and I need to change computer, and my PCI soundcard rig is no longer supported since 1967