GSSL THD Problem
« on: November 02, 2018, 10:54:35 AM »
Hi guys  :)

Couple weeks ago I finish build my GSSL, everything working fine, but there is a problem I can not fix.
I add sidechain for the left and the right channel without HPF.
The problem is in the left channel, especially heard in the low frequency spectrum, there is a big THD,
and when Its going thru nice clean drum bus, its like some distortions in the left channel destroying that sound.

I start from changing components from left to the right channel, I changed everything, from caps, opamps, VCAs (2180), and nothing. Im not using pin 4 on 2180.
Cables and interface not the reason.
Its like some magic, I change all components, and its still a THD.

Right channel -  0.05% THD
Left channel - 2% THD

Has anyone have this type of problem?


Re: GSSL THD Problem
« Reply #1 on: November 02, 2018, 02:55:49 PM »
What do you mean by "add sidechain to the left and right"? do you mean "external sidechain" board?

Re: GSSL THD Problem
« Reply #2 on: November 02, 2018, 04:02:36 PM »
What do you mean by "add sidechain to the left and right"? do you mean "external sidechain" board?
I just meant about oxford mod

RuudNL

Re: GSSL THD Problem
« Reply #3 on: November 03, 2018, 08:44:01 AM »
At what frequency are you measuring 2% THD?
(It is normal that low frequencies produce more distortion, especially at fast release times.)

By the way: I modified the release circuit in my GSSL, but I don't think this is the cause of your THD problem.
https://groupdiy.com/index.php?topic=68871.msg877042#msg877042
There is a solution for every problem!

http://www.vansteenisaudio.nl

Re: GSSL THD Problem
« Reply #4 on: November 03, 2018, 12:44:06 PM »
The distortion is heard even in bypass.
In every frequency spectrum, but the most in the low.

RuudNL

Re: GSSL THD Problem
« Reply #5 on: November 03, 2018, 02:21:34 PM »
The audio signal path is pretty straightforward.
The steps  I would take are:

- Check the signal at pin 6 of the NE5534 at the input
- Check the signal at pin 1 of the NE5532 at the output
- Check the signal at pin 7 of the NE5532 at the output

This will give you a clear indication where things go wrong.
There is a solution for every problem!

http://www.vansteenisaudio.nl

Re: GSSL THD Problem
« Reply #6 on: November 03, 2018, 04:47:40 PM »
The audio signal path is pretty straightforward.
The steps  I would take are:

- Check the signal at pin 6 of the NE5534 at the input
- Check the signal at pin 1 of the NE5532 at the output
- Check the signal at pin 7 of the NE5532 at the output

This will give you a clear indication where things go wrong.

Thanks for trying help
I dont know what can be wrong if I changed every component, and the problem still exist

RuudNL

Re: GSSL THD Problem
« Reply #7 on: November 04, 2018, 09:41:51 AM »
The only way to find out what is wrong, is to eliminate things.
So, if you have for example a good signal on the input NE5534 on pin 6, but distortion on pin 1 of the NE5532, there could be something wrong with, or around the VCA chip or the NE5532.
(And if you have distortion on the NE5532, remove the VCA chip and bridge then input and output pins on the VCA socket.)
Just blindly exchanging components won't bring you a solution (as you already found).
What you should do is find the cause of the problem!
There is a solution for every problem!

http://www.vansteenisaudio.nl

Re: GSSL THD Problem
« Reply #8 on: November 04, 2018, 01:45:43 PM »
The only way to find out what is wrong, is to eliminate things.
So, if you have for example a good signal on the input NE5534 on pin 6, but distortion on pin 1 of the NE5532, there could be something wrong with, or around the VCA chip or the NE5532.
(And if you have distortion on the NE5532, remove the VCA chip and bridge then input and output pins on the VCA socket.)
Just blindly exchanging components won't bring you a solution (as you already found).
What you should do is find the cause of the problem!
Thanks
I know what you mean, I just dont have oscilloscope to measure in that details :(
And about bridging input to output, there is 2 inputs and one outputs in each opamp, inverting and noninverting, what input to output i should connect to check that?
Thanks

RuudNL

Re: GSSL THD Problem
« Reply #9 on: November 05, 2018, 03:06:57 AM »
You should bridge the input and output of the VCA (that is in a socket anyway, of course with the chip removed).
By doing this, you bypass the VCA and can eliminate if this might be the cause of the distortion.
And if you don't have an oscilloscope, you can just 'listen' on the points I mentioned.
You wrote that you got 2% THD on the wrong channel. How did you measure that without equipment?
There is a solution for every problem!

http://www.vansteenisaudio.nl


Re: GSSL THD Problem
« Reply #10 on: November 05, 2018, 05:20:31 AM »
You should bridge the input and output of the VCA (that is in a socket anyway, of course with the chip removed).
By doing this, you bypass the VCA and can eliminate if this might be the cause of the distortion.
And if you don't have an oscilloscope, you can just 'listen' on the points I mentioned.
You wrote that you got 2% THD on the wrong channel. How did you measure that without equipment?
I dont have oscilloscope, Im using signalscope software, its not profesional tool, but audio signals I can measure
Ok, I will try that on VCA
Thanks

Re: GSSL THD Problem
« Reply #11 on: November 06, 2018, 09:07:16 AM »
You should bridge the input and output of the VCA (that is in a socket anyway, of course with the chip removed).
By doing this, you bypass the VCA and can eliminate if this might be the cause of the distortion.
And if you don't have an oscilloscope, you can just 'listen' on the points I mentioned.
You wrote that you got 2% THD on the wrong channel. How did you measure that without equipment?

Hi Ruud
I did what you said, I connected input to the output on VCA and distortion gone :)
After I put different 2180, big THD back again
So what can that be ?

RuudNL

Re: GSSL THD Problem
« Reply #12 on: December 02, 2018, 04:01:30 AM »
Sorry for the delay, but I just found your reaction.
The good news is that you have eliminated the problem: the VCA stage.
Now, what could cause the distortion?
It is unlikely that the VCA chip itself causes the problem, especially because you have exchanged the chip.
But if there is a strange signal on the control voltage of the VCA (oscillation?), this could be the cause of the distortion.
So: if you connect the control voltage input of the VCA's to ground (the junction of the two 1K resistors), the gain of the VCA chip chip will be 0 dB.
If the distortion is gone with the CV grounded, the distortion is coming from the sidechain.
There is a solution for every problem!

http://www.vansteenisaudio.nl


 

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