2. amps-preamps
  3. 1407646817

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
pakwong OP
38 posts
 
My appreciation to everyone for their serious advices.

Answer to Lloydedee21:
"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 do have dampers from Herbie's Audio Lab on all tubes so I assume no issue with microphonic effect.
pakwong OP
38 posts
 
Answer to Mrderrick:
"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."

In my case I do agree the Maggies need to be driven at moderate levels to sound best as the distortion were less obvious or even disappeared with lower volume. Perhaps I need a more powerful amp but this would be my last resources to solve this. In the mean time I will try all output taps to hear the difference. No harm trying!
pakwong OP
38 posts
 
Answer to Jfrech:
"Do you have the Bob's devices SUT into the MC or the MM input on your CAT pre?"

CAT SL1 Ultimate MK2's phono stage are thought to be MM only. Is doesn't comes with MM/MC switch.
pakwong OP
38 posts
 
Answer to Brownsfan: "There are plenty of people that drive Maggies with tube amps. I agree that tube microphonics would explain what you are hearing, and it is pretty easy to address. Also, the fact that you tried two other speakers, one of which gave you the same result, probably means it is not the Maggies per se. However, because they are dipoles, they may direct more energy back to the tubes. Just wondering, the other speakers you tried--- were they both rear ported? If the one that didn't give you distortion is front or bottom ported, or sealed, that could also be a clue."

Please refer to my answer to mrderrick about tubes's microphonic. Both pair of speakers I used for testing were box speakers. One pair was KEF Ref 201/2 which has the same distortion while the other Focus Audio FC9 pairs sounded okay. The KEF is upright ported while the FC is back ported at medium height. Any clue?

I did swapped ICs and speaker cables but nothing change.
pakwong OP
38 posts
 
Answer to Smoffatt:
"Can you borrow a digital source (CD player) and play the same recording to see if you can identify the same distortion as with your analog source. If no apparent distortion, the problem may be with your tonearm/cartridge alignment.
Somewhat odd that only some recordings and/or passages of same are sound distorted. Could very well be your SUT or cartridge or alignment."

I do have a CD player but don't have CD version of distorted recordings on LP as my CD collection was very limited. It's definitely not the SUT. I bypassed the SUT and the CAT preamp by connected phono cable of tonearm directly to a phono preamp with volume control and feed the signal directly to Ref 150 with the same distortion.
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