[ricardojoa]

Hi guys,

so i finally got a power amp, from nuforce, a small one indeed to pair with my tube preamp that i initially have it pair with an AVR with not so good results. At that time, there was not hum issue when the tube and avr connected. Now, with SS amp, there is a hum when i connect the RCA output  to the amps. So i guess the hum are from the RCA. I have blue jeans RCA, i have tried some cheaper RCA, the problem still the same. Either way, there wasnt any improvement or worsening. I have tried having the same power source and different power source and the problem reamin the same.
The power socket is grounded.

Any suggestions?

[Austin08]

If hum heard through speakers then Look like it is a ground loop hum. Try to unplug all your connected equipment and re-insert one by one back. That is the only way to find out which equipment is causing the hum.

[avahifi]

Try this to identify your hum source.

First turn the system off and disconnect the interconnect cables from the preamp to the power amp at the power amp end.  This leaves the power amp connected only to the speakers.

Now turn the power amp back on.  Do you now hear hum from the speakers?  If you do, then the hum is being generated by the power amplifier itself.

If not, turn the amp back off and reconnect the interconnect cables to the power amp and disconnect all interconnect cables connected to the preamp except the outputs to the power amp.  Turn both units back on.  Hum there again?  The issue is either your preamp or the cables between them.  Are you using unshielded interconnect cables?  You should not be as these will hum more often then not.

You can call me at 651-330-9871 for more help if you desire.

Frank Van Alstine

[Wayner]

Does your amp have a 3-prong plug? If more then one component has a 3-prong plug, you are asking for a ground loop. The shield side of the RCA interconnects are usually connected to the chassis, so when you connect your RCA cables, you have completed another circuit.

If so, a cheater plug is required somewhere in the chain.

[ricardojoa]

Hi guys,

thank you for the suggestions. I actually tried all those suggestions prior to posting because i have read quiet few times about this type of issue. Unfortunetely none really work. What puzzle me is that prior, the tube preamp was connected to an Avr, and there was no hum. I have even tried to reconnect that set up just to make sure it wasnt a mistake or my mishearing, and sure enough there is no hum.
I do believe it has to with either the preamp or the power amp. There is no hum when the amp is connected to another processor. So is more likely the tube preamp, which i also noticed, as i turn the volume up, the hum gets louder. What really become a mystety is that with an AVR connnected, there was no hum.

[Wayner]

There are many folks that are getting hum into the system via their cable system. Have you tried removing the cable from it? Some older systems that connect to the cable box via a coax cable are the problem makers. At my house, I am wireless and enter my AV system via HDMI, so there really isn't any way to get a ground loop from the cable guys.

Wayner

[mboxler]

Sorry, but just to clarify...does your AVR have a two or three prong plug?  How about the new amp?

[Austin08]

There are many folks that are getting hum into the system via their cable system. Have you tried removing the cable from it? Some older systems that connect to the cable box via a coax cable are the problem makers. At my house, I am wireless and enter my AV system via HDMI, so there really isn't any way to get a ground loop from the cable guys.

Wayner

100% agree. There was a "cable guy" in my system and I had to get rid of him couple years ago.

[pjnad]

I had a similar issue awhile back between a Modwright preamp and my Krell amp; I tried all of the suggestions as outlined above and nothing worked. I even had the pre back to Dan at Modwright to check to see if there was any issue with it, none found. someone suggested running a simple wire between one of the output jacks on the back of the pre to one the amp...I unscrewed the connector on the pre, wrapped some wire and screwed it back down then connected the other end underneath a screw on top of the amp. Voila! no more hum...it didn't look pretty but it worked.
Last summer I had the amp over to Krell for a complete recap etc. whne it came back I decided to try it without reconnecting the wire...no hum! Now, I believe that I had also replaced some of my interconnects as well but I can't say for sure...
Anyway, you could give the wire trick a try to see if that helps.

[ricardojoa]

Thanks guys.

I sent an email to the desingner of the preamp and he explained that high gain amps can cause this from the output stage of the preamp. Something of that sort.
I will follow up and see what can be done.

Thank you again

[ricardojoa]

My tube preamp designer suggested me a volume control before the amp to lower the gain. With no volume control at home, i did a quick test using the AVR as volume control, using 7.1 in's and the preouts . The hum is gone. I then paused the CD, and turn up the volume one the AVR to really high and sure enough, the hum appears. So im guessing my desingner is right.

[Ericus Rex]

There are many folks that are getting hum into the system via their cable system. Have you tried removing the cable from it? Some older systems that connect to the cable box via a coax cable are the problem makers. At my house, I am wireless and enter my AV system via HDMI, so there really isn't any way to get a ground loop from the cable guys.

Wayner

I had a cable hum problem once too.  Went to my local and hifi shop to talk it over and this was suggested:  go to Rat Shack and buy one of those adaptors that converts coax to double spades.  Then buy an adaptor that converts spades to coax and install both between cable line and preamp.  Seemed awfully crazy but that stuff was cheap so I tried it and it worked!