Originally Posted by chewynuts
Riding on your knowledge train here. Do you know how I can determine if my Yamaha aventage mx-a5000 amplifier has differential balanced XLR inputs? I'm running a Nad t777 v3 and using pre outs to the amp on RCA I get a very slight but irritating hum on all my speakers. That's all 11 of them. I can't hear it in the day with the background noise but close to midnight when it's quiet out, I can hear it seated 6 ft away from the center channel. Tried playing with plugging both the amp and receiver into the same wall socket, same power distributor, fancy audioquest Niagara 1000 power conditioner, the hum is still there. Really don't want to try a cheater plug for safety's sake since I'm in a rental apt. Any advice if common mode noise rejection with the htp-1 balanced xlr output is my magic pill? Thank you in advance.
The MX-A5000 does have balanced inputs. It also uses a nice, three opamp circuit for the balanced inputs, which should provide good noise results. There are different ways to design balanced inputs and of course different levels of quality in components such as opamps and resistors. Note that the XLR inputs reduce gain by 6dB. More on this below.
While these design questions are interesting, at least to me, measurements of the MX-A5000 are available, so it would be best to look at those since the results of design decisions are reflected in actual, measure performance.
To me, the MX-A5000 measures quite well. The drop off in output with 7 channels driven is unlikely to be encountered in actual use. It is unfortunate that Marantz didn't include power amplifier output stages (and heat sinks, transformer, capacitors - more cost) with higher output in the MX-A5000 since the surrounding circuitry, and the basic design of the output stages, is quite good. Much better than in a typical AVR for example.
The voltage sensitivity for clipping in the review for the MX-5000 is measured at 1.45V with RCA inputs, which means 2.9V with the XLR inputs since the sensitivity is 6dB less. Ignoring the review, these sensitivities are fine. 2V into the XLR's will give 100W. For the HTP-1 these voltage sensitivities should work well. Doubling the RCA input (to determine the voltage sensitivity setting for the HTP-1) gives 2.9V as well so a guess is that 3V would be a good setting.
From the above:
o The MX-A5000 is fundamentally a quiet amplifier
o The MX-A5000 has very good balance inputs.
o The HTP-1 should drive the MX-A5000 very well. The HTP-1 is quiet.
The hard question is hum. If the hum is resulting from a voltage drop in the return wires in the RCA connections then using balanced connections will reduce or more likely, eliminate the hum.
The cause of your problem is from another part of your system (cable TV ground, satellite TV ground, return wire in trigger circuit, who knows?). The resistance of the RCA return lines just causes the problem to be audible. Using balanced lines may eliminate the symptoms (hum), which is great. While you can try the HTP-1 and return it if it doesn't eliminate the hum, that of course takes your time and costs Monoprice money.
My guess is that if you get the HTP-1, and a set of balanced cables, it will either satisfactorily remediate the symptoms of your problem, or you'll soon determine the actual cause out of the remaining options. In the HTP-1 you'll of course have an excellent unit. Needless to say, it's your money and time.