Turbo Gssl help please..

[schrobbelbop]

Considering the turbo is just a copy of the gssl sidechain, I would recommend that when they are built, they are built with matched components so that both sides are identical.
You can buy just the pcb with no components from Expat Audio, that way you can put in your own components.  I personally would never use two different vca's for turbo/sidechain purposes.

Did you test each resistor before putting them into the turbo?  Could be you've got a wrong resistance value somewhere.  Unless you put the TL074 in backwards and powered on, it's unlikely that there's anything wrong with it. 

Hmm then it's strange the board is driving the sidchain way to hard. in first instance i connect the switch wrong to bypass or engage the board, i guess that can't destroy my board?

 

[artosaudio]

Okay, here's a basic troubleshooting run-through:

First print out the Schematic from here, and refer to it as you go through the troubleshooting.

First checks:

When switched to Turbo mode and with SILENCE at both inputs, the turbo TL074 outputs for pins 1 and 7 should all have 0Volts DC and 0 volts AC on them. Pin 14 should have a fixed DC voltage on it which varies as you switch through the three available ratios. This should match the same exact thing happening at pins 1, 7 and 14 respectively on the main board TL074. On the turbo board, pin 8 should have a DC voltage on it which varies as you adjust the "threshold" control.

This is what i read:
tl074 no input
pin 1 0.17
pin 2 0
pin 3 0
pin 4 -12.09
pin 5 -0.01
pin 6 0
pin 7 0.78
pin 8 0
pin 9 0.14
pin 10 0
pin 11 12.18
pin 12 0
pin 13 0
pin 14 0.19 (ratio 1:2) 0.34 (tatio 1:4) 0.38(tatio 1:10)

So step 1 all goes wrong!

Now, leave the compressor switched to 2:1 ratio, with the threshold set to LEAST sensitive... i.e. compressing the least. -Apply a steady tone at a decent signal level (about 0dBm: -In fact anywhere between a 0.5 -to- 1 Volt is perfect) to BOTH inputs. Verify that the outputs of BOTH of the input 5534s on the main boards have a similar AC voltage at pin 6.

All good!!

Next, leave the meter switched to AC, and measure the voltage at pin 7 of the main board TL074. -You should see that the signal voltage rises and falls as you vary the threshold control. -You see that? -Then make the same measurement at pin 7 of the Turbo board TL074, and you should see the same thing. -In fact you should see basically the SAME voltages for all settings of the threshold control.

Here is where it really goes wrong... What I read does indeed vary with the threshold, however the current jumps right back to zero (sometimes even after dipping below zero)

Now meter the signal at pin 1 of the Main board TL074. -It should now have BOTH and AC and a DC component, and how much of each you will measure depends on your meter.

Same story as above..

what should I do now! I've been troubleshooting for 2 days now! Thanx in advance

 

[schrobbelbop]

Ordered a new board, and it worked inmediatly

I think the 074 and 2180 fried first time...

Sound wayyyy better now

 

[Rochey]

wonderful news

 

[Dr_J]

Hi everybody!

Well my first post and i'm crying for help!! That's not what i thought off...

I'm now sitting for hours, days, month in front of these little black PCB and it's killing me....
I was right before throwing this thing out of the (closed) window 

When i switch to turbo mode the meter hits hard maximum....
I check the resistors 1,2, 3 times... change the TL074... I couldn't find an error...
so i decided to order a new board... some weeks of rest...

Put the new board together... ok one step forward the meter problem is gone... BUT...
it's still not working the right way (e.g. YouTube Video)...
Turbo OFF setting threshold to -9db (meter), when switching to Turbo ON it drops to -4db!!!

I've been through the troubleshoot run several time, i guess i'm stuck at step #3.
What i measure is:
TURBO
Pin#1      0.0 AC // 0.0 DC  (constant)
Pin#14    0.0 AC // 0.25 DC

I guess here ends the problem, but i have not idea what to check further...?!?
Maybe can't see the wood 'cause of the trees...!?

Any hints??
Thanxs!!

J

 

[Dr_J]

... ok i did some more and more checking!
I found out that the 3k9 resistor that feeds PIN#5 of the VAC was not getting -12V!??
PCB-Error?!?!
I put a wire link to it (same voltage at PIN#5 on both boards) and now i see 0.29VAC at PIN#14 on the TURBO TL074 and 0.12VAC on the MAIN...!? Switching to TURBO OFF i get 0.29VAC on the MAIN TL074?!? Grrrr...

But now i have an other strange behavior...
0.0 to 0.42VAC PIN#8 MAIN (TURBO OFF)
0.0 to 0.22VAC PIN#8 MAIN (TURBO ON)
0.0 to 0.24VAC PIN#8 TURBO (TURBO ON)

Any hints?? Please?!

 

[Rochey]

Hello Dr_J,

let me see if I can get Keith (SSLTech) in this thread to help out. He's the brains behind the board.

Let me check one thing: Have you read page 3 of the manual?:
http://www.expataudio.com/diy/Turbo/TurboInstallationManual.pdf

Some people have missed this one in the past.

/Rochey

 

[Dr_J]

Hi Rochey,

first: thanks, both PCBs arrived well!
But still both are not working... grrr...

And Yes of course i read page 3 (and the others as well  ), i only use the inner holes!

More or less now i understand what's happening on the PCB / side-chain, but the F*** i can't
find an error.... grrrr it's killing me....

Cheers,
Jxrg

 

[Dr_J]

fprintf: H E L L O  W O R L D!
anybody out the in the universe...??

Ok, then i use this to discus things with my self... and as a kind of documentary..

well, i found out the PIN#7 TL074 seems to have a problem...
Sinus input Mono both channels
TURBO OFF
PIN#7 MAIN 0.045VAC (0.016 to 0.455)
TURBO ON
PIN#7 MAIN 0.022VAC (0.006 to 0.260)
PIN#7 TURBO 0.038VAC (0.015 to 0.322)

as PIN#7 is the output and PIN#6 is input with PIN#5 to 0V the problem leads to PIN#8 of the VAC... mmm or the feedback loop... but why does the MAIN board change it's behavior when switching to TURBO?? That makes me wonder...?! The S/C C.V is up to PIN#3 of both VACs the same... 0.22 to 0.05VDC MAIN and TURBO.

... i have to think about that...

any hints out there...??

 

[Dr_J]

Keeeeeeeeiiiiiiiiith!!!!!!!!!!!

 

[Harpo]

well, i found out the PIN#7 TL074 seems to have a problem...
Sinus input Mono both channels
TURBO OFF
PIN#7 MAIN 0.045VAC (0.016 to 0.455)
TURBO ON
PIN#7 MAIN 0.022VAC (0.006 to 0.260)

not Keith, but
0.0005VAC difference looks close to spot on, so both 47K resistors seem to match.
With Turbo ON, the VCA on main board now receives only half of the signal current of your correlated signal source.

PIN#7 TURBO 0.038VAC (0.015 to 0.322)

You use the same type of sidechain-VCA (they are all different) with same surrounding components? (schematics show parts values for DBX2150 VCAs. THAT2180 or 2181 differ from 2150s).
From a previous post you might have connected the -12V supply to VCA-pin5 directly. If so and with a little luck the VCA might have survived this abuse. The 3K9, connecting to VCA-pin5 is setting the VCAs bias current for this +/-12V supply voltage.
With more commonly used THAT2180s here, you probably leave out the 10K between VCA-pins3/5 and leave out the 47R, connecting to pin4 as well.
As both Turbo/mainboard EC- control ports read the same mV, both 470R/47R voltage dividers in front of pin3 seem to match, so if there is still a TL074-pin7 voltage discrepancy after maybe needed previously described fixes, you might decrease the 33K feedback resistor between Turbo-TL074-pins6/7.
Good luck.

 

[Dr_J]

Hi Harpo,

thanks a lot for the reply!!!

Well, yes of course I use the same VAC on the turbo board as on the main board, they are THAT2180.
The surrounding components are more or less the same, but not 100% identical.
And of course I did not connect the -12VDC direct to PIN#5, i did a wire link to the 3K9, because no -12VDC was arriving there... PCB failure!?! (My other turbo board is ok for that, focusing on that point) An now I have exactly the same voltage on all of PIN#5!

I have already read (i guess it was a post from you?) about leaving out the 10k and 47R around the VAC, but i still have them.
I will think of it, but for me it seems not to be an issue for the problem i'm facing...?!

I have although though about the feedback loop, too.
Ok, decreasing the 33k could be a way, but could it be the origin of the problem??

Ok, I will now catch a beer and then error searching a again this night....

Cheers,
Jxrg

 

[Dr_J]

As both Turbo/mainboard EC- control ports read the same mV, both 470R/47R voltage dividers in front of pin3 seem to match, so if there is still a TL074-pin7 voltage discrepancy after maybe needed previously described fixes, you might decrease the 33K feedback resistor between Turbo-TL074-pins6/7.
Good luck.

Ok!

- both VAC PIN#3 are having the same voltage (3.5mV).
- both feedback resistors of the TL074 between PIN36 & PIN#7 are 33.0R!
- resistance between TL074 PIN#6 & PIN#7 is 33.0R for both.
- I swapping the VACs (what i've done several times before...)

Now heaven has heard me  ;D, it looks quite ok... wired...?!
TURBO ON:
TL074 PIN#7 MAIN  0.063VAC
TL074 PIN#7 TURBO 0.055VAC

TL074 PIN#14 MAIN  0.299VAC
TL074 PIN#14 TURBO 0.319VAC

Ok, still a slide difference (for that a won't trust my old meter  ), but I think i can live with that.
Is tweaking the feedback loop resistor a appropriate way?
The result is: setting the meter to 6db as reference now the TURBO is 5db in single mode.
Well, it's changing due to release, attack and ratio settings, mmmmm....
Ok, put a fresh TL074 in and BANG here we go...  ;D

Maybe it was just a not proper fitted VAC in the end....

So, and now I have my second Turbo board waiting to be fixed!   

Thanks Harpo!!
Your few hints that the values were ok and i was seeing things right help a lot!! Cool! Big thumb up!!

Cheers,
Jxrg

 

[deadTalash]

Hello guys, sorry for a noob question :-[ How does the 4th part of TL074 (pins 8 9 10) influence the threshold?  At the first page Keith wrote that it reduces threshold voltage load, but as far as I see at the pictures of the pcb, pins 8 and 9 are shorted and control voltage comes to the pin 10 from the main board. What is the magic?

 

[Harpo]

Hello guys, sorry for a noob question :-[ How does the 4th part of TL074 (pins 8 9 10) influence the threshold?  At the first page Keith wrote that it reduces threshold voltage load, but as far as I see at the pictures of the pcb, pins 8 and 9 are shorted and control voltage comes to the pin 10 from the main board. What is the magic?

Welcome.
No magic. It is a simple non-inverting voltage follower. Without this buffer, the TL072 on main board that generates the sidechain-VCAs pin3 control voltage for the logging would have two 470R/47R voltage dividers in parallel and this type of opamp doesn't like heavy load (would be 100R+1/(2/(470R+47R))=358.5R instead of now 617R).

 

[deadTalash]

Thank you a lot! I just finished my "turbo mod" I did it slighly other way. I just duplicated "sidechain" part of the schematic from the 47k's to point "c" to a separate PCB, than added a buffer as Harpo said. I connected ratio switch according to the turbo manual.  Everything is good and measures exactly like at Keith's "troubleshooting guide" at the page 1.  When I feed the compressor with a signal on the left channel, it compresses say at 5 db. The same thing with the right channel. When I feed both channels, it still compresses at 5 db. Just like at the video. But what's strange - when I pan the signal, IT STILL COMPRESSES AT 5 db))) I use Cubase test generator.

 

[Harpo]

Why strange? With the Turbo circuit the higher of L/R rectified control voltages get timed by the attack and release circuit and set the amount of compression for both audio VCAs of this stereo compressor, so stereo imaging keeps in place.

 

[deadTalash]

As far as I understand, this guy pans the signal from the left - center - right, and the unit compresses less at the middle. How can this happen? :-[
http://youtu.be/EQD8GPhFGYE?t=2m45s

 

[Harpo]

Look up panning law that set the pan center in range between -3dB and -6dB or anything in between (most analoge consoles operate with a -4.5dB center law, some DAWs can be set for 0dB loss centered or for a constant power panning law). The higher of both L/R signals has level decreased by this amount when panned at the center position.

 

[deadTalash]

Oh thank you very much for your help! Wish you all the best from Minsk!)