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Old Yesterday, 12:11 AM   #1
diyAudio Member
Join Date: Jun 2014
Default Parasound Zamp 120Hz hum

I recently acquired a Parasound Zamp V1 used, and it has a constant loud hum at what sounds like 120 Hz to me. The hum is in both channels and is there even when only a speaker(s) on either or both channels is connected in addition to AC power (no input is required for the hum). The hum is reduced when I connect an input via the pre-out on my NAD C372 (which I've never had this issue through and still don't using its amplifier stage instead of the Zamp), and I can increase/decrease the volume of the hum by adjusting the level for each channel with the knob on the back of the unit. I tried plugging it in in a totally different room that is on a different circuit as well, but that did not make any difference.

I noticed that immediately when I plug the amp in with speakers connected, the hum starts quiet and then gets louder over the course of a few seconds -- this leads me to wonder if this might be caused by bad capacitors since this is about the same time period that, based on labs in the physics class I had a few years ago, a larger capacitor seems to take to reach capacity/equilibrium.

Any thoughts on how I could fix this? Does my theory about the caps make sense, or are there any other ideas anyone has?

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Old Yesterday, 01:44 AM   #2
rayma is online now rayma  United States
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Join Date: Apr 2011
Location: Upper midwest
Originally Posted by ILikeFoodz View Post
I recently acquired a Parasound Zamp V1 used, and it has a constant loud hum at what sounds like 120 Hz to me.
Check the input sockets and level controls carefully, because the ground connection(s) may be loose,
have a bad solder joint, etc. If these are good, then the main filter capacitors may be bad.
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Old Yesterday, 09:03 AM   #3
Enzo is offline Enzo  United States
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Join Date: Sep 2004
Location: Lansing, Michigan
Main filter cap could be bad, or simply cracked free of its solder.

120Hz points to power supply ripple. grounding hum and induced hum tends to be 60Hz.
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Old Yesterday, 01:00 PM   #4
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Join Date: Jun 2014
The ground connections and all solder joints look good, so I've ordered Nichicon replacement caps for all of the electrolytics on the board. Thank you guys for the suggestions, I'll let you know how it goes when they get here in a few days!
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