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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
crustycoot
644 posts
 
Another point is that 12’ is not a worrisome length for unbalanced cables. In pro audio applications there can be 50 to 100’ of cable as in the mic drops in a big concert hall. Unless you have a proven source of RFI/EMI nearby, like a broadcast tower, you’re better off with the RCA connects. 
mammothguy54's avatar
mammothguy54
949 posts
 
georgehifi has it right, in my opinion.  I would also suggest that you contact Levinson and inquire on the design of the amp on weather or not it uses an op-amp for the XLR inputs.  My guess is that is probably the case; that they do use op-amps to convert the incoming single-ended signal to a balanced design.  And if so, then simply revert to using RCA connections for the best signal integrity to the amps primary design.  In my own system the components are expressly designed for use with XLR cables.  Hence, they pulled that into the name of the brand, Balanced Audio Technology (BAT).  

I also have to question MC comment about Balanced XLR cables being more costly than RCA cables.  The cables I use are by Audioquest.  They can be purchased with RCA terminations or XLR terminations for the exact same price.  I imagine it is possible that some cable vendors have a difference in price based on the terminations, but obviously not all.  And indeed, there are a lot of quality cable vendors on the market by which you can choose from.  Just my two cents on this particular comment.
jb1
97 posts
 
Nothing to worry about. I am not an engineer but I have owned amps from Adcom, Aragon, Proceed, 2 Mark Levinson 300 series and McIntosh, speakers from Martin-Logan, Sonus Faber Guarneri Homage & B&W 803 d3. Every system combo had low level hiss when my ear is 6" away and every amp has a low hum from the transformers when standing a few inches away. From listening distance 9 to 10' away, I hear nothing. If you can hear the noises from the listening distance, there may be a ground issue somewhere that is causing the hum or a part starting to fail  in the amp. The final conclusion is that amps are not silent creatures and you will drive yourself crazy trying to fix what is normal. If you feel that the noises are too loud, then contact the manufactures Technical support and they will, most likely, tell you that what you are experiencing is normal. I am sure they would be happy to give you an RA and  charge you $100.00 an hour + shipping to tell you there is nothing wrong with the Amp.Given the weight of the amp shipping cost can be prohibitive. Unfortunately, unless you live in Texas or California, there are no local service people for Mark Levinson. Try to enjoy the music and don't listen from 6" away and you will be fine.
68pete
1,001 posts
 
Just because you have XLR connections, does not mean you are true balanced. Lots of company put the XLR connectors on their equipment, but they are not balanced from input to out put.
atmasphere's avatar
atmasphere
11,807 posts
 
Interesting since I thought the point of using balanced interconnects was to reduce noise.  
Reducing artifact from the cables and reduction of ground loops are why.
I suspect George is right; that this amp uses an additional circuit for the balanced input which is an additional opamp circuit. If true this suggests that internally the amp is not fully balanced. A schematic would sort that out...


At any rate if you have to be within 3 inches from the tweeter to hear this, than you have no worries!
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