Turbo Gssl help please..

[Svart]

hmm I'm not following..

Let me restate this:

This unit had been working fine for years before the turbo install. Now it's compressing all the time (after the turbo install) but the threshold knob still changes the amount of compression.

EDIT:

I figure I must've done sometihng wrong but the wiring looks correct. I also checked each resistor with a meter(to doublecheck the value) before placing so I'm very sure that I didn't populate anything incorrectly. Stranger things have happened though..

 

[SSLtech]

Ah. -I didn't get that bit, so thanks for restating.

-Unplug the turbo board. One side should still compress, the other should not compress no matter HOW you set it.

Then re-plug the turbo board.

Now each side should compress the same in both turbo and original modes, so long as the signal is sent to ONE side at a time, ONLY.

Note any differences in threshold/ratio sensitivity from one side to the other.

Keith

 

[Svart]

Heya Keith, do you remember what the mod was that changed the level range of the GSSL (+4/-10)? I think I might have done that to this unit but I can't remember what that mod was. Maybe it has something to do with this?

 

[SSLtech]

The through level gain is at the output/post-VCA stage so shouldn't affect this unit... it's actually +6dB/0dB rather than a +4dB/-10dB modification...

Keith

 

[Svart]

Hmm. I thought there was a threshold change too, not just an output level change. Maybe I can dig it up.

 

[flight]

Hello All ,

Im confused , I cant make the turbo mode working with the same amount of threshold on the Left side and Right Side !!
The Board Turbo seems to start compreesion 20 Db later than the other side .

I ve follow step procedure to find any problem , the board seems to work
When i mesure AC voltage on pin 14 from TL074 i have the same 0,35 V on both turbo and GSSL without compression , but the GSSL AC voltage increase as soon as i move the thershold until the Turbo board only start to increase after much more than half of thershold .

ANy help ??
THANKS

 

[flight]

For Info i ve done GSSL with THAT2181LA and have made all mod that need to be done with VcA 2181.
I didnt think it could be the problem , i ve interchange Vca between Gssl and turbo and did the same with TL074.

-Is it normal i can mesure 2,6 V DC on pin 8 of TL074 on Turbo Board and 0V AC on GSSL ??
-As i see on schematic GSSL The control Thershold should be back on Turbo with S/C C.V. connection controled by the TL072 ??
so It should be the same control for each board no ?? ... :?:

 

[SSLtech]

[quote author="flight"]-Is it normal i can mesure 2,6 V DC on pin 8 of TL074 on Turbo Board and 0V AC on GSSL ??
-As i see on schematic GSSL The control Thershold should be back on Turbo with S/C C.V. connection controled by the TL072 ??
so It should be the same control for each board no ?? ... :?:[/quote]

A full explanation is contained on page 1 of this thread.

Keith

 

[flight]

Hello Keith

I know , i ve been reading page 1 ten times before posting my problem .

Keith i ve search long time , and the difference i ve seen is on the Vca input , PIN 1

on GSSL i read DC 0,6V input and 1,5 V DC on Turbo board ! when i send 1K sinus for example :roll:

 

[SSLtech]

You shouldn't read ANY voltage on pin 1 of the VCA... nor on pin 8. -They're current input and current output devices, and the output feeds a current input on an op-amp. -YOu have to read the OUTPUT of the following op-amp.

Pin 8 of the TL074 is the threshold (gain voltage) buffer, and varies with threshold voltage. The voltage at the output should be equal to the voltage at the non-inverting input.

Keith

 

[flight]

Pin 8 of the TL074 is the threshold (gain voltage) buffer, and varies with threshold voltage. The voltage at the output should be equal to the voltage at the non-inverting input

Yes i read DC 5 V on pin 8 of TL074 decrease with threshold to 0 V .
I Read AC 2,5 V on pin 8 decrease to 0V
and yes its equal on the non inverting input which is PIN 10 .
Thats also what happen to the s/c c.v input of turbo board throught 100R .

 

[Harpo]

[quote author="flight"]...Turbo seems to start compreesion 20 Db later than the other side .[/quote]
Sounds like a factor 10 problem. Doublecheck the resistor values. You may have placed a 5k6 instead of a 56k or 10k instead of a 100k value.

 

[flight]

Triple check them ! ... something really strange so ...
Ive change a 100K near TL072 to 127 K because of THAT2181 but didnt think it could be the problem .
Keith im sorry to have a come back to this but is it normal than Vca input get DC 1,5 v on turbo and only 0,6 v DC on Gssl ?? couldnt it be the problem ???

Thanks for your help !!! Im sorry 3 days looking why that happen until the turbo mode should be so easy to add !!
Flight

 

[SSLtech]

Measuring voltage at the signal input to the VCA is a red herring... you'll get random readings which are component-dependant. In either case, a DC variation there CANNOT cause a "shift" in AC signal threshold, so definitely look elsewhere. -If there's no DC anomaly at the OUTPUT of the follower op-amp, then FORGET it, and move on. You CANNOT make meaningful measurements at a current node using a voltmeter... it'll lie to you.

Follow the step-by-step description begun on the first page. -The circuit is the same as the GSSL TL074 sidechain for three of the four parts, and the fourth part (pins 6, 7 and 8) is a buffer for the threshold control.

All you need to do is find out where the two begin to behave differently. 20dB difference in threshold sensitivity suggests a gain error of ten in either the signal or DC rectification stages, but most likely the signal. -did you check to make sure that all of the component values are correct? -once again, measure to see where the two begin to differ, then look in THAT area. The first poster in this thread -Sinestar- had apparently swapped the two capacitor values, which made the sidechain VERY low level, although frequency-dependent. -I believe that he only ever tested at one frequency, so he never saw that things were working better at low frequencies, which would have clued us in sooner... but Pete (Sinestar) would have to confirm that supposition before I propose it as fact.

Keith

 

[user 10827]

yes Keith is spot on, Im still not sure how to read those little blue ceramics. I also should have checked one input at a time.

you will get there, it's probably staring you in the face, take a little break and come back to it.

Best
Pete

 

[flight]

HI all
As i didnt find myself why my threshold still lower , i ll post my test result .

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.

GSSL/ AC1 : 0v DC1: -0.10v PIN 14 DC vary with Ratio change
AC7 : 0v DC7 : 0v
TURBO/ AC1: 0V DC1: 0.19v Pin 14 DC vary with ratio change
AC7: 0v DC2: 0v
DC8: 2,5 v to 0v with threshold change.

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.

AC PIN 6 on 5534 is the Same .

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.

NO i cant see anything in turbo board or GSSL board .

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. -Basicallty, for each setting of the threshold control, BOTH TL074s should have the same sort of shape waveform at pin 1, and whether your AC voltmeter meter is averaging, true RMS, or just making a guess at the waveform, -so long as the readings for each meter setting (AC and DC) are similar for each position that you set the threshold control to, then all is good.

Now meter the signal at pin 14 of the Main board TL074. -It should now have BOTH and AC and a DC component, and once again it shoudl agree with the same numbered pin on the Turbo board TL074. This time there will be a DC offset (this is the threshold).

 

[SSLtech]

Dude...

NONE of your readings look anywhere NEAR right.

Pin 14 should be something between two and four Volts depending on ratio... -you're showing a tenth of a volt.

The threshold on pin 14 should be swinging by about twelve volts... -you're showing 2.5 volts.

If you're not reading ANY AC at pin 7 with a constant sinewave input, then something is DESPERATELY wrong with your build.

-There's definitely something enormously wrong... whatever it is, it's so fundamental that I can't even take a guess at it...

...Are your DC supply voltages right? -Let's start there.

Keith

 

[flight]

Hi keith
First thanks for your help .

Ok lets start all again so ...

Yes all my Dc power are ok
NE5532 / pin 4 -15,16 pin 8 14,97

NE5534/ PIN 4 -15,15 PIN 7 14,97

TL072 / PIN 4 -12,04 PIN 8 12,12

TL074/ PIN4 12,12 PIN10 - 12,04

VCA / PIN 5 and PIN 7


Ok here is what i can said , in fact when i am on GSSL mode , sending sinuswave ONLY to left compress 5 db sending ONLY to right compress 5 db and then sending to Both input it compress much more .
But it should be normal on GssL mode , So all seems ok there .

When going Turbo mode

Only Left : compress 5 db
only right : Do not compress until i move down the threshold

Send sinuswave to Both input , it Still Compres 5db ( as the left side )
The compresseur compress Left and right side the Same thing
There is no difference level compression between Left and Right .

BUT when i send only to Right normaly IT should Compress the SAME Thing no ??? 5 db , no less ??? :?: :?: :?:


Keith are you sure on pin 14 of TL074 when moving the ratio i should read something 2V and 4 V ?
Ive build 3 units and cant read than on any of them !

TL074 PIN 14
0,18v ratio 2
0,35v ratio 4
0,38v ratio 10
there is 0,01 difference betwenn GSSL and turbo board .

 

[flight]

Also for Threshold on Pin 1 of TL072 , you told me about Twelve volt ...
But i can read that , i m only 3V to 0 V But it should be good if i read this post from Jakob ...

Use logic: you feed the IC +/-12V (from the threshold pot) into the inverting input through a 220K resistor. You have 56K feedback resistor. The gain should be 56/220=0.25x - giving you some +/-2-3V at opamp output when the unit is in bypass. If it's not bypassed, there will probably be a lot of interaction due to feedback through the control circuit.

Check that you have -12 to +12V at one end of the 220K resistor when varying threshold. Check that you have approx. 0V at the other end of said resistor (as it's a virtual-ground coupling).

Jakob E.

So are you sure i should read 12 v on pin 8 of TL074 on turbo board ??
This is incoming from 100R and cant be 12 V ! :!: :?:

 

[flight]

Anyone know the correct voltage ??

Thanks