[andow]

I recently finished racking a pair of NTP 179-400 limiters. Basically they're working, but I get some strange clicks that don't sound right...

Here is a recording of a bass drum running through the limiter. In the beginning the click is present for a few seconds then disappears. Then the tempo is getting slower and the clicks are back. I then mute the right channel input and the click is still present on both outputs!

https://www.dropbox.com/s/ej9bwvacvdcjnfc/ntp_179-400_clicks.wav?dl=0

Any idea what might be the problem here?

[andow]

Here is a pic of the wiring...

[mjrippe]

When a unit has noises on both channels, I usually suspect the power supply.  You are using a linear supply so it isn't switching noise.  Is the voltage at the input of the regulators at least 3v higher than the output?  If not you may be going in and out of regulation.

[andow]

When a unit has noises on both channels, I usually suspect the power supply.  You are using a linear supply so it isn't switching noise.  Is the voltage at the input of the regulators at least 3v higher than the output?  If not you may be going in and out of regulation.

Thanks for your help!
I also suspect the power supply. The voltage difference between input and output of the regulators is more than enough, so they should work.
I measured the supply voltages with my oscilloscope and noticed that the negative voltage fluctuates about 20mV up and down, the positive voltage is constant. Also, when an sending a signal through the unit, both voltages decrease (I can't recall how much) when the limiter kicks in.
Maybe this helps to identify the fault...

[thomasdf]

what voltage are you feeding them? is the psu powerful enough ?

unrelated, but I have a pair that I love but wasn't able to find a proper calibration procedure, and to have them stereo linked ? do you have informations regarding this ?

[thomasdf]

also, did you toy with the time constants? sounds like a very fast attack / bug thingie going on, and if the channels are linked, both the sidechains are working and both unit compressing..

[RuudNL]

Sounds like the control voltage is leaking into the audio.

[andow]

Sorry for the late reply! I was on vacation and then forgot to check...

what voltage are you feeding them? is the psu powerful enough ?

unrelated, but I have a pair that I love but wasn't able to find a proper calibration procedure, and to have them stereo linked ? do you have informations regarding this ?

I have +/- 10V output from the power supply (it's the same with 9V btw). I use LM337 and LM317, so theses should be able to supply more than enough current for the two modules.
I couldn't find any information on calibration of the limiter module (it does have trim pots), the only thing I have done is set the limiting threshold with P4. To link the two modules I just connected the two control voltages on pin 28.

also, did you toy with the time constants? sounds like a very fast attack / bug thingie going on, and if the channels are linked, both the sidechains are working and both unit compressing..

Only the release time is adjustable and it doesn't seem to have an effect on the clicking. I forgot to mention: in the sample I posted, the units were NOT linked! So the only connection between them is through the power supply.

Sounds like the control voltage is leaking into the audio.

I don't know how this would happen....

The next thing I will do is to use another power supply and see if the problem is still existent.

[ToBSn]

I have +/- 10V output from the power supply

Did you changed the onboard virtual ground single rail supply?

From the tech specs:
recommend supply voltage is 22 - 32 V dc with a max ripple of 300 mV.
Current consumption 55-80mA per module

[andow]

Did you changed the onboard virtual ground single rail supply?

From the tech specs:
recommend supply voltage is 22 - 32 V dc with a max ripple of 300 mV.
Current consumption 55-80mA per module

Yes, I have converted the power supply section on the boards to accept +/- 9V and have ground at 0V.

[andow]

Today I put in a new power supply and the clicks are gone!   

[andow]

The front panel is from a fellow GDIY member...   

[mjrippe]

That looks really good!  Such nice limiters deserve a proper home.

[ToBSn]

Cool, nice build!

PSU from Volker!  Top!

[timtom]

Which switches and vu meters did you use?

[andow]

Which switches and vu meters did you use?

I bought the front panel with meters installed from another GDIY member, so I have no idea about them...
The switches are binary coded rotaries from Lorlin.

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