andow

NTP 179-400 clicks
« on: September 02, 2019, 11:30:09 AM »
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

Re: NTP 179-400 clicks
« Reply #1 on: September 02, 2019, 11:33:07 AM »
Here is a pic of the wiring...


mjrippe

Re: NTP 179-400 clicks
« Reply #2 on: September 02, 2019, 12:07:40 PM »
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

Re: NTP 179-400 clicks
« Reply #3 on: September 04, 2019, 03:29:21 AM »
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...


 

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