2. amps-preamps
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Distortion with ARC Ref 150 and Maggie 3.7

I have this problem that drive me nuts for quite a while. I purchased a like new fully balanced ARC Ref 150 tubes amp through Audiogon for my single ended only CAT SL1 Ultimate preamp and connected both with a RCA to XLR interconnect. It sounded okay with most recording but has awful distortion with certain recording specifically piano and vocal. Some of this recording happens almost on entire record but some only on certain musical passage. Most of the time with higher pitch or peak of music or higher volume.

For your information I listen to vinyl only most of the time and more on Jazz music. Other component listed as follow:

Turntable: Sota Nova, Tonearm: Origin Live Illustrious, Cartridge: Dynavector XV1-S, Step up transformer: Bob's Device CineMag 1131 (Blue) feeding directly to CAT's own phonostage, Speaker: Magneplanar Magnepan 3.7. Power cords, ICs, Speaker cable, Autoformer: Paul Speltz Anti-Cable.

Trouble shooting which has been done includes: checking preamp tubes condition and checking power amp bias. Since ARC claims their Ref 150 was design for balanced preamp only so I also tested by replacing it with single ended tubes amp but the distortion remain. As for the cartridge I believe I have done the alignment pretty accurate with the Mint's Best Tractor but not very sure with the azimuth.

While tested with my other 2 pair of speakers, one which has higher spec show the same problem while the lower spec one seems get rid of distortion. So I suspected the issue probably was with the new Maggie. Called the dealer and he performed a test with his transistor amp with no distortion at all. So he assumed my Maggie is okay. Is it true that the Maggie only good with transistor amps?

By now it leaves me with total confusion! Sincerely hope fellow audiophile here could give me some advice and save me from this endless misery !

Thanks very much in advance!
pakwong
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atmasphere
11,807 posts
 
Dbarger, I spoke to both Kalvin and Warren at ARC and they told me the same thing: if the amp is used with a single-ended source it will have lower output power and will make distortion.

This is because the drive to the power tubes will become unbalanced. IOW, the amplifier is not compatible with single-ended sources and if one is employed, a transformer should be used to balance the input to the amp.
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atmasphere
11,807 posts
 
Daveyf, anytime you put current through the shield of the cable, you are subject to the construction issues of that cable. So this is a big issue with single-ended, even if its only 6 inches. In a balanced system (caveat: if the balanced standard is being properly supported...) the shield sees no signal current at all.

FWIW there does not have to be any 'loss potential' caused the additional circuity when going balanced (a common myth is that there is twice as much circuitry, which is not true, especially if the circuit is fully differential). For example, a fully differential circuit can have up to 6 db less noise per stage of gain as opposed to the same topology running single-ended. So in two stages of gain you could have up to 12db less noise! This has real benefits in preamps working with low output moving coil (which is a balanced source BTW), as you might only need two stages of gain for a functional tube phono section! That is **less** stages for the signal to go through than single ended.

In our amps because of this we only have one stage of gain. So you can actually have a simpler signal path than an SET might have.

On top of that, balanced operation in the preamp or amp means that the unit is more impervious to noise that gets into the power supply. So the potential is for lower noise and not from just the cables.
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almarg
9,670 posts
 
Ralph & Dbarger, you appear to be disagreeing simply because you are using the term "source" to mean different things. I believe that Ralph is referring to the "source" of the signals which are sent into the power amp, e.g., a preamp. Dbarger is referring to the "source component," e.g., a CD player.

As Dbarger appears to indicate, I would not expect there to be any problem if the power amp were driven by a balanced output of a preamp which in turn receives a single-ended input. Assuming, that is, that the preamp's output truly consists of a balanced pair of signals, rather than a single-ended signal provided on an XLR connector.

Regards,
-- Al
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atmasphere
11,807 posts
 
^^ This.
stickman451
553 posts
 
Guys, I read this entire thread and got lost a couple of times but here is my thought. The Ref 150 is NOT a good amp for any of the Maggies. Sell the 150 and try a pair of Carver Cherry 180's or even better a pair of his Black Beauty 305's. The Black Beauty's use six KT-120's per side and can drive anything. They sound fantastic on my 20.7's and I have tried many different amps.
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