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
martykl
3,578 posts
 
I haven't read thru this long thread so I apologize if this has already been posted:

Some ARC amps cannot take a single need output into their XLR input without major issues. Per ARC, They lack a phase splitter and require true balanced signal in. I know this was true of my VT 130 SE and I suspect that it's the case here.

I posted a thread on this issue some years back that got good responses from some of the techier types here and you should try to find it if only for educational value.

Im not sure, but I believe that the Bottom line is : Find a preamp with true balanced out via XLR if you ant to use you 150.

Contact ARC to be sure.

Good luck
almarg's avatar
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almarg
9,670 posts
 
Marty, thanks very much for that input, which together with Pakwong's experiments seems to confirm the suspicion I mentioned in my post dated 8-12-14. Probably by inputting a single-ended signal into the Ref 150's balanced input the power capability of the amp is being reduced to not much more than 1/4 of its rating.

Pakwong, your preamp, amp, and speakers are all very fine pieces. I see no reason why they can't be made to work together, at relatively modest cost.

The SMc transformer I mentioned lists at $1895 and is described here. I can recall at least one other A'gon member saying that he has used it with excellent results. Besides converting the single-ended signal to balanced, it would also lower your system gain somewhat, which as alluded to earlier would be a good thing with your particular components.

At a lower price point, the Jensen PI2-RX transformer is used in very high quality systems by at least several A'goners that I am aware of. All but one of them reports no perceptible sonic compromise with it. It looks like its price has been recently raised to $345. It is identical to the model PI2-XX, described in this datasheet and this manual, with the exception that it has RCA input connectors. The relevant top-level Jensen page is here.

Before ordering either of those devices, it would probably be a good idea to contact the manufacturer and ask him to confirm that the specific model is suitable for use between your particular preamp and power amp, although I'm highly confident that it will be.

Good luck as you proceed. Regards,
-- Al
czarivey
5,946 posts
 
How many hours in your Dynavector? Have you tried different cartridge/needle?
Did you get your cartridge new/used?
martykl
3,578 posts
 
Al,

IIRC, that is exactly the result ARC described. In my post above I suggested that the OP try to find an earlier thread on the subject of ARC amps that behave this way. In that thread, there was a long, technical debate as to how power output could be quartered in this circumstance. I don't recall specifics, but after much debate, one 'Goner who is a service tech confirmed the phenomenon by putting a unit on a test bench.

The OP apparently tried to troubleshoot this problem by switching preamps, but my guess is that his alternative preamp didn't output true balanced, either.

I'm speculating, but having been down this road myself, my guess is that the OP needs a true balanced output to fix this problem.
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almarg
9,670 posts
 
Thanks Marty. Yes, the other "preamp" the OP tried was an EAR 834P phono stage, which includes a level control but provides only unbalanced outputs.
I'm speculating, but having been down this road myself, my guess is that the OP needs a true balanced output to fix this problem.
... or he can convert the single-ended output of the preamp to a balanced signal pair using one of the high quality transformers I referred to. That should work fine; possibly even better than if he were to change to a single-ended amp, as the transformer will eliminate any ground loop-related effects that might otherwise occur.

Best regards,
-- Al
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