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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
lloydelee21
1,202 posts
 
Hmmmm, I am no techie. But when you get a problem at only presents itself during certain passages of music...it seems less like an electric problem (which you would think would occur all the time or at least randomly)...and more like a mechanical problem. Something reacting to those treble frequencies or something?

Is it possible the tubes are slightly microphonic, and your speakers are picking it up? Have you tried tube dampers? Borrow some if you can before going out and buying. Sometimes when a tube is microphonic it will pick up certain noises either internal to the tube due to vibration or due to vibration in the room outside the tube...and translate it as distortion thru the systems signal.

I once had a tube so microphonic if I clapped or whistled you could hear it thru my speakers. A tube damper from EAT solved it...and so did replacing the tube! Again, I am no techie, just a thought. Good luck.
mrderrick
292 posts
 
I suspect that your problem lies with your amplifier.

If I recall correctly, the Maggies prior to the ".7's" had rather ruler flat impedance curves.
The crossovers have changed and this is no longer the case.

I owned MGII B's, 3.6's and still have a pair of early MMG's.
The MGII B's (6 ohm load ) could be driven with a 40 watt PP tube amp quite nicely and sounded beautiful, at low to moderate levels.
The 3.6's I drove with a Classe CA400 SS amp which pumped out 800 watts into a 4 ohm load.

You tried a second tube amp and still had the same issue.
I would try all of the output taps on the Ref150 and see if there is a difference. ( without the auto formers first )

I would then try the auto formers with the best performing tap if you still need them.

My experience is that Maggies need to be driven at moderate levels at the very least to sound best.

More power was always better for me with Maggies.
The Ref 150s may not be up to the task, even with the auto formers.

If you have not visited the Planar Forum at the Audio Asylum, you should and ask for assistance there.
jfrech's avatar
jfrech
1,816 posts
 
Do you have the Bob's devices SUT into the MC or the MM input on your CAT pre?
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