McIntosh amp help

[deepinton]

Level matched, double blind, change only one variable at a time.

 

[ski2xblack]

You think something else in the amp could be causing the input selection issue, or something else in the amp could be causing my perceived "low power" issue? Any idea where else I should look besides the selector switch?

Well, yeah, it's possible that something else in there is faulty. You did describe them as "well used" after all. I hope not, for your sake, but anything is possible. Cleaning the input switch with deoxit is a good idea, low hanging fruit and all that. But unless you really know what you're doing, I suggest you don't start probing around in there.

The input sensitivity difference is responsible for less percieved power. You said the Classe needs only 1.37v (seems more like an unbalanced input sensitivity?? Does the classe specify balanced input sensitivity?) to hit rated power, while the Mac needs 4.2v on it's balanced inputs, 2.1v unbalanced. (I am not sure if Gene bench tested your model Marantz, but it should be more than capable of swinging those voltages from it's preouts. You will have to crank the volume higher in order for it to reach those higher voltages.)

 

[highfigh]

Is the labeling for the switch for 'Balanced or Unbalanced mode?

 

[PENG]

So the expected function of that switch is to specifically cutoff the XLR input if it is set to unbalanced? Would a malfunctioning switch attenuate the input level? My power output suspicion is driven by ear - my old Classe CAV 180 (5x180 watts) sounds louder at the same pre-pro output level, all else in the chain being the same.

Maybe some amps would do what you expected, but some amps just don't, example: Parasound, Marantz, Bryston etc., based on the models that I had used in the past. So, the Mc501 probably would behave like those amps, that is, the input selector are not really a physical selector switch, but one that was designed to maximize SNR, so if you use balanced output from a preamp, and connect to the Mc's XLR input and you flip the switch to unbalanced, you would likely get louder sound at the same preamp volume setting.

In that case, if you want to keep the volume low, but still get loud enough sound for you then do that, but it would make no sense because you will get poorer signal to noise ratio. My suggestion is, just use that selector switch according to the instructions, and always use balanced except of course when you have use preamps that have only unbalanced outputs.

Note: If you read the manual, the Mc501 specified:

Sensitivity 2.1 Volts Unbalanced Input 4.2 Volts Balanced Input

That confirms what I thought, that if you use the switch properly, you will hear no difference in sound pressure level at any given preamp volume setting whether you connect your preamp RCA output to Mc501 RCA input, or preamp XLR output to Mc501 XLR input.

 

[highfigh]

Maybe some amps would do what you expected, but some amps just don't, example: Parasound, Marantz, Bryston etc., based on the models that I had used in the past. So, the Mc501 probably would behave like those amps, that is, the input selector are not really a physical selector switch, but one that was designed to maximize SNR, so if you use balanced output from a preamp, and connect to the Mc's XLR input and you flip the switch to unbalanced, you would likely get louder sound at the same preamp volume setting.

In that case, if you want to keep the volume low, but still get loud enough sound for you then do that, but it would make no sense because you will get poorer signal to noise ratio. My suggestion is, just use that selector switch according to the instructions, and always use balanced except of course when you have use preamps that have only unbalanced outputs.

Note: If you read the manual, the Mc501 specified:



That confirms what I thought, that if you use the switch properly, you will hear no difference in sound pressure level at any given preamp volume setting whether you connect your preamp RCA output to Mc501 RCA input, or preamp XLR output to Mc501 XLR input.

I installed a system with Krell AV preamp and 5 channel power amp- I had requested that the electrician wire the outlets across the wall behind the cabinet a specific way and they don't seem to hav done that because it hummed with XLR cables, quiet with unbalanced. I would really like consumer and prosumer equipment to be designed for function, not marketing.

 

[deepinton]

Is the labeling for the switch for 'Balanced or Unbalanced mode?

Yes, the switch label says "Balanced/Unbalanced"

 

[deepinton]

Maybe some amps would do what you expected, but some amps just don't, example: Parasound, Marantz, Bryston etc., based on the models that I had used in the past. So, the Mc501 probably would behave like those amps, that is, the input selector are not really a physical selector switch, but one that was designed to maximize SNR, so if you use balanced output from a preamp, and connect to the Mc's XLR input and you flip the switch to unbalanced, you would likely get louder sound at the same preamp volume setting.

Everything (AKA Gemini) seems to point to this -
"A properly functioning INPUT MODE selector switch on the McIntosh MC 501 would completely cut off the XLR balanced input when you move the switch to the "unbalanced" position." Since I can hear XLR input with switch on "unbalanced" position and with nothing connected to the unbalanced input, step 1 is to start with the switch. I'll keep the channel posted in case folks are curious.