Does anyone care to ask an amplifier designer a technical question? My door is open.

I am getting some ground loop noise from my Classé 5300 amp.

I wired studios with 1000's of interconnections. We never used cheater plugs. E V E R !!  Solve the problem, don't bandaid it. Sometimes it involved fixing the gear's internal wiring.

Are you using balanced or unbalanced inputs? If balanced, remove the screen connection on the amp end. In a balanced system, the screen should be lifted on all the driven ends.

Get some shorting plug and start with just the amp connected to the speakers. Add in each component back from the amp. When the hum starts, solve the problem there and continue.

@almarg Many Thanks!

In your case, both your VAC and Pass amps are capable of producing 32w I presume. What gave XA25 an edge over the VAC amp with your speakers? Does XA25 have less distortion due to its class A operation in the first 25 watt?

@ieales.  

Hum is coming from the center and surround speakers and am using unbalanced cables.  

I apologize for my lack of knowledge, but could you explain what shorting plugs are?

@ffzz, you’re welcome!

My former VAC Renaissance 70/70 MkIII amp is a class A amp employing four 300B power tubes per channel, in a push-pull parallel configuration, and is rated at 70 watts per channel. It is a 100+ pound beast, which I believe consumes something like 700 watts of AC at all times, converting most of that power into heat that is injected into the room.

The Pass XA25, as you realize, is rated at 25 watts into 8 ohms and 50 watts into 4 ohms, operating in class A, and it is specified as consuming 240 watts of AC. John Atkinson’s measurements that were provided in conjunction with Stereophile’s review, though, indicated that it is capable of providing 80 and 130 watts into those impedances, respectively. He stated that some of that disparity is due to the fact that Pass bases its power ratings for the amp on much lower distortion percentages than JA uses, and presumably a lot of that disparity reflects the XA25 transitioning to class AB when outputting more than a certain amount of power.

As I mentioned in my earlier posts that you saw my speakers are nominally 6 ohms, and have an unusually flat impedance curve as well as relatively high sensitivity, which makes them very versatile with respect to amplifier selection. Since like most solid state amps the XA25 is designed to provide an essentially constant output voltage into varying load impedances, for a given input voltage, (as long as the amp is operated within the limits of its maximum voltage, current, power, and thermal capabilities), even if we assume the very conservative 25 and 50 watt numbers it can be calculated that it is capable of providing at least 33.3 watts into 6 ohms.

I wouldn’t say that the XA25 has "an edge over the VAC amp." They are both wonderful amps, in their own ways, and some non-sonic reasons factored into my decision to change. See the comment I left two days ago near the end of the following thread, as well as a subsequent comment by member "1markr":

https://forum.audiogon.com/discussions/pass-labs-xa25-amp-and-bw-804-d3

Best regards,
-- Al