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
Outstanding! And a great suggestion by ZD.
Can you explain to a guy like me with almost zero electronic knowledge about how the transformer from Jensen or SMc can actually convert unbalanced signal to true balanced signal? My Maggie dealer also talked about something like pin 1 or pin 2 "hot" in the RCA to XLR cable and he suspected that the termination of my RCA to XLR cable was not done correctly hence the distortion. How true is it?
Taking your second question first, the problem you have been dealing with cannot be avoided with an adapter cable, no matter how it is wired.

To work properly, your amplifier (and other ARC and other amplifiers that are similarly designed in the relevant respects), must be provided with a balanced pair of signals at its inputs. That means two signals that are essentially identical except that one is inverted relative to the other (i.e., when the voltage of one signal moves in a positive direction, the voltage of the other signal moves in a negative direction, and vice versa). An adapter cable cannot produce those two signals, when it is only being provided with one of them.

A transformer can do that, however. A voltage will appear between the terminals that are connected to the two ends of the secondary (output) winding of a transformer, that in the absence of any external connections to that secondary winding would be electrically isolated (i.e., unconnected, or "floating" in EE terminology) relative to the ground of the signal source, and relative to all other voltages or grounds or other reference points that may exist in the system.

If the input circuit of the amplifier is designed as a balanced receiver, it will process the voltage that exists between those two ends of the transformer secondary in a manner that is symmetrical relative to the amplifier's circuit ground, which means that it will "see" that voltage no differently than if a balanced source (providing two equal voltages of opposite polarity) were being used.

This Jensen white paper, although somewhat technical, goes into further detail that may be of interest.

BTW, regarding the transformers I suggested, be sure to note that (as indicated in the manual I linked to for the particular Jensen model I suggested) that particular Jensen model would have to be placed close to the amplifier, and connected to the amplifier with a very short (less than 2 foot) length of XLR cable. The RCA cable from the preamp could be any reasonable length. I believe that no such constraint would exist with the SMc transformer (or with some other Jensen models, although those other Jensen models may not perform quite as well as the one I suggested).

Best regards,
-- Al
Thanks. It looks like I finally did something right. It feels strange. I don't know what to make of it.
It's pretty rare when a real problem like that faced by the OP is posted and a straight up creative solution is offered by an Audiogon respondent. Congrats, ZD, you found a high quality, zero cost solution to a thorny problem.
Id send the amp back to Audio Research for a look-see. I think thats where your problem is..