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Discussion Starter · #1 ·
Hello all, I used this forum quite a bit years ago when purchasing my HT setup, and have a new issue I thought the experts could help me on. I did searches for similar problems, but haven't found a solution yet. Hopefully you guys can help.


Here's the situation. I bought (for practically nothing) two monoblock PA amps. They're Bogen HTA-250A's, rated at 250watts rms each. My thought was to use one to power a subwoofer, or maybe party speakers at some date. I wasn't concerned about super clean power, but that they'd have some decent power. I had heard of a few people doing this online, and they were surprised at how clean they DID sound, so I thought I'd try it.


The issue was inputs, and it has RCA unbalanced Hi-Z (52k ohm), and low-z balanced (600ohm) inputs. I wanted to use the low-z preamp outputs from my receiver. I asked Bogen if they had some sort of module to add to connect these correctly and they said plug the RCA from your receiver to the Hi-z inputs". That's it.


Now here's the problem; plugging into the hi-z only creates a loud ground loop hum, and very little music. Just to test to see if it was the input creating the noise, I disconnected the preamp and plugged an ipod directly into the RCA, figuring there's no ground issue with a battery powered source, and the hum/buzz is completely gone, replaced by music. However, even at its max (the source output and the amps input knob. I was able to turn it up that loud, if that gives you any idea how NOT loud it was), it certainly wasn't delivering full power.


What can I do? Convert the RCA unbalanced to a balanced input? I've read online that a low-z output to high-z input is common, and it's usually on the magnitude of a 1/10 ratio of impedance. I'm not sure what a typical rca preout is rated at, but this imbalance in impedance seems to be too great and then there's the issue of the ground loop. Any advice is appreciated
 

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Discussion Starter · #3 ·
I did some testing and found a bad ground on the coax connection to the adjacent TV, and this minimized the hum, although there is still some. The issue is now still the lack of power. Should I be trying to sync preamp output and amp input impedance, or would my best bet be to convert to a balanced low-z from RCA?
 
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