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Speaker hiss from power amp

I have a Mark Levinson 532H amp that is connected to a Levinson 390S CD processor only (no preamp).  Recently, I switched from single-ended to balanced interconnects (Cardas Neutral Reference) because it's a pretty long run (~12 feet) between the components.  The 532H has switches on the back for selecting balanced or unbalanced interconnects.  The switches had always been set for the RCA single ended inputs, so I just noticed that when the switches are set to balanced, there is a very slight hiss coming from my tweeters.  When unbalanced are selected, the hiss is substantially reduced, nearly but not quite silent.  Both speakers have an equal amount of hiss.  In balanced mode, the hiss is only audible when my ear is 3 or 4 inches from the tweeters so it doesn't in any way detract from my overall musical experience.  I should note that the hiss is evident whether or not anything is actually connected to the amp (other than the speakers, obviously), and there's no difference with gain when I have the 390s connected.  Also, the addition of a power conditioner has made no difference at all.  Two other things: there is a very slight hum coming from the amp (again, only audible if I'm very close to the amp) and the A/C power from my outlets seems pretty inadequate (probably less than 5 amps according to the Parasound).  Appreciate any ideas on why the hiss increases when the switches are set to balanced inputs and how it could possibly be eliminated.  
rwatson

Showing 2 responses by georgehifi

georgehifi's avatar
georgehifi
10,312 posts
 


Ok then same noise if the dac is not connected to the amp just the speakers,
Then when it’s switched to XLR input (which is .5db lower gain than SE) as Stereophile measured, it has more noise to you from the speakers, it must be a Balanced to SE summing opamp giving the extra noise, and therefore should not only be quieter using the SE as you found, but also sound better because the summing opamp is not used.
I found exactly the same but other way around using Belcanto Ref600 monoblocks, the RCA input used a se to balanced opamp into the Hypex NC500 balanced input buffer module, the XLR input input did not use it and had the same gain, and not only had less noise but sounded better as well (less hifi’ish), because the opamp was not used.

Cheers George
georgehifi's avatar
georgehifi
10,312 posts
 
Att rwatson OP


cleeds I’m pretty sure that your amp is a true balanced ("differential") amplifier, so you will get 6dB more gain using the balanced connections than you will from unbalanced.
Levinson 532H it’s +0.4db difference in favor of the RCA!!!.
What "could" be is that the balanced input is a balanced summing opamp feeding the single ended discrete input circuit. If so less noise and better sound if you go direct with rca, as this cuts out that balanced opamp with it’s added noise.

Stereophile measured Levinson 532H .
The voltage gain into 8 ohms was to specifications: at 26.8dB using the balanced inputs, and slightly higher, 27.2dB, using the unbalanced inputs.

Or it could be the same but to do with the dac, it’s se output is one less opamp compared to it’s bal output.

PS Here’s the answer, similar to what cleeds said but from the dac not the poweramp.
The Levinson’s 390S DAC maximum output level was 2.18V from the unbalanced RCA jacks, this doubling to 4.36V from the balanced XLRs



Cheers George
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