Nuforce STA200

The Nuforce should be dead quiet with Just the sys. When I had my RP-5 in for warranty work, I used my Pro-Ject s2 Pre Dac as a preamp. Dead quiet. I mean dead quiet!!! My Zu's are rated at 101 db. Slight tube hiss is normal (ear against speaker) for the rp-5. The Nuforce has such high gain, along with my efficient speakers, I needed the SYS between the pre and amp to pull things back. 

Hi Mr. D, jetter, and aberyclark, and everybody on here! So tonight I went ahead and did an experiment. I bought a grounding adapter to isolate (disconnect) the ground from the 3 prong plug from Lowe's. That did not eliminate the problem. I also tried plugging in the amp straight to the wall outlet, but still the same problem. So, I went ahead and used a different speaker wire... problem still there. Then, I tried using my Sony TA-F500es just to see if it produced similar hum/hiss... they're still present but it is more quiet compared to the nuforce. Now, I'm not sure what's wrong with my system. 

I also tried connecting my nuforce to my NHT floorstanders and the noise is present, only louder. 

All these tests were with the sys connected to the nuforce, except the test with the Sony integrated. The hum is isolated to the mid-range driver and the hiss (sounds less of a hiss and sounds more like electricity buzzing) is isolated to the tweeter. I tried recording the noises on my phone but it is difficult to be discerned from ambient noise. 

I feel like I can live with the hum and hiss/buzz, but I also wouldn't want to be keeping a defective amp. Tough call.

Thanks again, guys!

Hi japol, if I understand your post above you have a hum with both the nuforce and with your sony integrated.  So you are not sure if you have two amps with a problem or the problem lies elsewhere in your system.  You have already determined that your speaker wires are ok. 

I only have a couple of thoughts.  One is are you using shielded interconnects and if shielded you are sure they are functioning properly?  The other is that I have the TV cable box connected to my preamp and this resulted in a hum through my speakers.  I had to purchase a cable tv ground loop isolator which eliminated it. 

The hiss with the Nuforce should be louder than the Sony due to higher than normal gain. Do you have a friend’s house you can take the amp to and try there? Also, light dimmers have caused noises with my systems in other homes. Even if the dimmer is not in same room. 

I have my STA200 paired with a Parasound Zpre2 and both have been left on for about a year+ virtually without being switched off, if so, then only briefly turned off then turned straight back on.
Is it scare mongering, or should I be worried about the STA200 going pop? I find the sound quality excellent. I actually bought two, the other is still in its box unopened. For the money $499 they are really nice sounding power amps. Don't know or care about the power rating, they sure do go loud when required. These findings are to my ears.