G1176 Strange Output-Gain Drop

[basementmedia]

Hi,

i've finished a G1176 Unit and in principle it seems to work, but one thing is very strange:
When i feed the input with an -1db 1000Hz sinus and select the +4, +8 or GR option
i get -15db at output with Q-Bias already turned fully CCW. if i turn Q-Bias CW the drop increases).

And when i push the bypassknob i get the opposite: Distortion (over 0 db) at the output (with input and output at 12 o clock).

Any suggestions?
I have checked all cable connections more than one time and also the solder work seems to be ok (no bridges) and the function of the compression is ok (attack and release work as they should do).
So it seems to be a pure gain problem...

Every help is appreciated!
I hope you understand my bad english...

Greetings

Daniel

 

[W DeMarco]

Id try re calibrating it. 

 

[doubleroger]

Hi Daniel,
I think it probably means there is a problem into he sidechain part of your compressor (gr control amp part of this schematic ). Q1 is working all the time, even with Qbias CCW. The bypass switch actually cuts signal from going into the control amp. You maybe have your 1176 cranked all the way up to make up for the 15-20dB Q1 sucks up, and when you go in bypass mode, those 15-20 dBs come back (as there is no signal on the base of Q1).
If you take out Q1, you should have the same thing as in bypass mode.
I'd recheck traces, solder joints, and voltages in this area.
Sorry that's not much help I'm afraid.





(I might have said something stupid here, as I'm still learning. Please if you read something stupid above, explain.

 

[doubleroger]

Just a quick question: are you doing it with -1dBFS?
If we're talking dBFS, you should be around -18 or -20dBFS. around nominal level.

 

[gyraf]

..please use the giant 1176 thread (to keep related q&a together in one place)

Jakob E.

 

[basementmedia]

Hi,

thanx for your answers.

@W DeMarco: The problem occured WHILE i tried to calibrate the unit for the first time (It never worked before...)
@doubleroger: I will check the area around Q1 for faults.
I created an 1000Hz -1db with Wavelab (is this dbf? i don't think so but i'm not sure, there is no info in wavelab about this) and supplied the input of the G1176.

@Gyraf: Sorry, i promise that i will put the next thread were it has to be. Do you have also suggestions, what could be the solution for my problem. Did you have similar behaviours in one of your clones/prototypes.

Greetings

Daniel

 

[doubleroger]

I created an 1000Hz -1db with Wavelab (is this dbf? i don't think so but i'm not sure, there is no info in wavelab about this) and supplied the input of the G1176.

I don't know wavelab, but I'm quite sure that might be be your problem.
You should try to generate a -18dB (as in dBfull scale ) signal for your calibration. If you're doing it at -1dBFS, it is way too high.
There is a lot of infos on different dBs, you should check that in the metas.

 

[basementmedia]

Hi again,

I have put another PCB (from another second clone) into the unit and get the same result.

A -1db signal at the input with

- Meter switched to +4/+8 or GR
- Q-Bias turned fully CCW
- InputPot/OutputPot/Release/Attack at 12 o clock

... gives me an -12.9db Signal at the output.

I have also tested this with another signal generator so the signal should be ok (-1dbFs).

Any other suggestions?

Can the problem be also located at the ratio board?

Greetings

Daniel

 

[doubleroger]

sorry to quote myself, but:

You should try to generate a -18dB (as in dBfull scale ) signal for your calibration. If you're doing it at -1dBFS, it is way too high.

-18dBFS equals 0dBVU. You feed the 1176 with it, turn Qbias clockwise. When you see a 1dB drop at the output, you're set for the Qbias.

 

[basementmedia]

Hi again,

me is such a fool. Seems that i can't read ...
Youre suggestion was right, the little "FS" behind the dB WAS the fault.
Now the unit seems to behave as it should.
I made the Q-Bias and all the other adjustments (which was not easy for diy-beginner).

But i think theres still something wrong with the ratio.
If i change feed the input with a snaredrum signal starting with ratio 4 and then switch to 20 the two or three snare-hits are more compressed but then the compression seems to decrease and the signal becomes louder again (like at the ratio 4 setting).

But i'm gonna test this again tomorrow and maybe you can "guide me" the last few steps to a really "as it should" working compressor ;-)

Greetings & many thanx

Daniel

 

[basementmedia]

Unfortunately after another test a new "problem" has arised (as written in my last thread):

Here's a short description (i hope it's understandable, cause my english is not that good...)
I feed the input with a signal (e.g. -6db) and start with e.g. ratio 4.
When i switch to higher ratio (e.g. 20) the gain reduction first increases (as it should!) but then falls back to the former value (of the ratio 4 setting).
In other words: it doesn't matter which ratio i choose, in the end i get the same gain reduction at all settings!

Do you have further tips/suggestions?
Still i am hopeful to bring this Compressor to an happy end.

Or i will go crazy...

 

[gswan]

Measure the gain reduction for the various ratio settings and come back with some numbers.

 

[basementmedia]

Hi gswan,

i have to correct myself.
The Gain reduction values (when switching between the ratio) fall back after a second but then are different to each other . Also the values seem to make sense. Only the fact that they are first higher and then fall back makes me think that theres something wrong. Or is this behaviour normal?

Here are some values:

At Input: -12 dbFS
--> At Output (20:1 setting): First -19.3 after fallback -14.3
--> At Output (12:1 setting): First -12.3 after fallback -15.7
--> At Output (8:1 setting): First -14.4 after fallback -16.4
--> At Output (4:1 setting): First -14.8 after fallback -17.8

At Input: -9 dbFS
--> At Output (20:1 setting): First -23.3 after fallback -14.1
--> At Output (12:1 setting): First -11.5 after fallback -15.4
--> At Output (8:1 setting): First -13.8 after fallback -16.0
--> At Output (4:1 setting): First -14.1 after fallback -17.2

Isn't it also strange that at the 20:1 setting the output gain decreases and at all other settings increases?

It would be great if someone could post his values (with -12dbFS and -9 dbFS) also.
Thanx and keep on compressing

Daniel

 

[toffifee]

..please use the giant 1176 thread (to keep related q&a together in one place)

Jakob E.

As Jakob said - I think all the answers to your questions are there...

 

[basementmedia]

Ok, sorry. I will search there.
Unfortunately i had already opened a new thread and got a few answers and so i thought that it would be ok to finish my "problem" in this thread.
But i will do a search in the existing threads now, i swear ;-)

 

[gswan]

Hi gswan,

i have to correct myself.
The Gain reduction values (when switching between the ratio) fall back after a second but then are different to each other . Also the values seem to make sense. Only the fact that they are first higher and then fall back makes me think that theres something wrong. Or is this behaviour normal?

Here are some values:

At Input: -12 dbFS
--> At Output (20:1 setting): First -19.3 after fallback -14.3
--> At Output (12:1 setting): First -12.3 after fallback -15.7
--> At Output (8:1 setting): First -14.4 after fallback -16.4
--> At Output (4:1 setting): First -14.8 after fallback -17.8

At Input: -9 dbFS
--> At Output (20:1 setting): First -23.3 after fallback -14.1
--> At Output (12:1 setting): First -11.5 after fallback -15.4
--> At Output (8:1 setting): First -13.8 after fallback -16.0
--> At Output (4:1 setting): First -14.1 after fallback -17.2

Isn't it also strange that at the 20:1 setting the output gain decreases and at all other settings increases?

It would be great if someone could post his values (with -12dbFS and -9 dbFS) also.
Thanx and keep on compressing

Daniel

It takes a while for the GR amp to settle after switching between settings. This is normal.
To measuer the actual ratios, you need to plot the input/output relationship for a number of input values.
See here:
http://www.axtsystems.com/index.php?view=article&catid=34%3A1176ln&id=54%3A1176lnratios&option=com_content&Itemid=62

You will then be able to see what the compression curve looks like for each ratio and where the threshold is.
Don't expect them to be accurate or the same between two units.