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
pakwong OP
38 posts
 
Thanks for valuable input from all!

Yes, trouble shooting procedures which I've been carried out also includes bypassing the SUT and CAT SL1 in the system, by using a EAR 834P phono preamp that comes with volume control and MM/MC function connected directly between the tonearm and Ref 150. Same thing happens! So I assumed there is no issue with overloading from the SUT and preamp.

Last night I did a final test by listening again to digital sources from a Wadia 381i CD player connected to line stage of the CAT SL1. To my surprise, the same distortion also happens on the digital source which I thought didn't exist! I'm not a big fan of digital hence very seldom listen to it. The last time I listened to it were kind of background listening with lower volume. This time I crank up the volume control to about the same level while listening to LPs and the same distortion shows off immediately!

In the mean time, I also tried listening closely to the speakers and found that the distortion appears almost on all frequency including bass while cranking up the volume.

With these latest discovery I began to suspect that the true problem might be coming form either the Ref 150 or the Maggies.

Any thought?

Thanks again!
pakwong OP
38 posts
 
BTW, I do agree that my system sounds more linear and faithful to the source by connecting the 4 ohms tap directly to the Maggie.

Thinking about the beginning when I first bought the Ref 150, it was used to drive my previous KEF 201/2 speakers and from that time on I started to experienced distortion on certain recording. Only not as severe as with the Maggie. Perhaps the Maggie's higher resolution and the recently purchased XV-1S which replaced the XX2 has made the issue worst.

If both KEF and Maggie suffer the same distortion from the Ref 150, and no sign of anomalies from other components, is it possible that I've purchased a defected Ref 150? Or simply because the Ref 150 did not match the Maggie perfectly?
almarg's avatar
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almarg
8,673 posts
 
If I've followed all of this correctly, you've perceived the problem with two different speakers, two different tube amps, two different preamps (one of them being a phono stage used as a preamp), two different sources (one vinyl, one CD), and a variety of different cables.

If so, it seems to me that there are likely to be two different problems that have been present, which are causing somewhat similar symptoms.
I also tried listening closely to the speakers and found that the distortion appears almost on all frequency including bass while cranking up the volume.
I would infer from this that the distortion at low frequencies is more subtle than the distortion you described earlier which was evident mainly on high volume high frequency content. And my guess is that the distortion that is evident at low frequencies is the result of amplifier clipping, while the other problem (evident especially on female vocals and piano) is due to something else. At this point I'm as mystified as you are as to what the "something else" may be.

What may be an important point regarding the possibility of clipping the amp: Depending on how the Ref 150 is designed, by providing it with a single-ended signal you MIGHT in effect be using only one-half of its balanced signal path, which would reduce its 150 watt power capability to possibly as little as 1/4 of that amount (37.5 watts). I'd suggest contacting ARC and asking them if providing the amp with a single-ended signal would affect its power capability, or have other adverse consequences.

If that turns out to be an issue, converting single-ended to balanced with a suitably chosen transformer from Jensen Transformers or (at a higher price point) SMc Audio (Steve McCormack) would be a solution.

Mofi, thanks very much for the nice words. Coming from someone with your extremely extensive experience, that's a meaningful compliment indeed.

Best regards,
-- Al
syntax's avatar
syntax
2,033 posts
 
If both KEF and Maggie suffer the same distortion from the Ref 150, and no sign of anomalies from other components, is it possible that I've purchased a defected Ref 150? Or simply because the Ref 150 did not match the Maggie perfectly?

I think you narrowed it to the Ref 150.
This problem has nothing to do with a "mismatch" with a speaker, when your Phono Input is ok and based on your own comparisons, the Ref 150 has a defect part inside.
mrderrick
291 posts
 
If the issue is related to driving the REF 150 SE instead of balanced, perhaps one of the early Audio Research single ended to balanced converters would solve the problem?
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