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
 
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
syntax's avatar
syntax
2,193 posts
 
I have to believe that single ended and balanced components does have mating problem. It seems like many balanced only component were designed to match with other similar or same manufacturer component only.

No, even when some will say, balanced needs balanced ...it is blubber. What you have is a different output or input rating, that's all. And that you can hear when the preamp output is too weak for a balanced amp input for example. But it will not create a distortion.
XLR adaptors are very simple, probably a problematic soldering can produce such a distortion but you can check it easily, you can buy these everywhere.

The Maggie is something I cannot live without. So do the CAT SL1...

Yes, true. But forget SE amps with Mags...these speakers run with nearly everything BUT they love high powered amps. The more power you give them the better they sound. The problem is, high power + good sound is nearly impossible to find. It is the way it is.
When I would run the 3.7 today, I would choose the Lamm Hybrid amps. They bite the bullet.
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almarg
9,670 posts
 
08-14-14: Syntax
No, even when some will say, balanced needs balanced ...it is blubber. What you have is a different output or input rating, that's all. And that you can hear when the preamp output is too weak for a balanced amp input for example. But it will not create a distortion.
Syntax, I suspect that you submitted this comment before seeing the preceding several responses. It is not blubber. Apparently this and some other ARC balanced amps are designed such that when fed a single-ended signal no signal voltage will be processed through "half" of the balanced signal path. That will cause the maximum output voltage of the amp to approach being only 1/2 of the output voltage corresponding to its maximum rated output. (Probably a bit more than that due to the reduced demand on its power supply). Everything else being equal, power is proportional to the square of voltage. Therefore 1/2 voltage = 1/4 power.

As I said earlier, and as the comments by Marty confirm, by providing the amp's balanced (and only) input with a single-ended signal (via an adapter, rather than via a transformer which would convert it to balanced), its 150 watt rating has most likely been reduced to not much more than 37.5 watts. Way too little for the Maggies, and an invitation to clipping distortion at typical volume levels.

Regards,
-- Al
martykl
3,578 posts
 
It's funny, because this thread is starting to feel like it will spin off much like the old thread I referenced above. Several people posting that a power amp cannot be forced to produce less output because it receives a single ended signal rather than a balanced signal. I undrstand that this result is unusual, but.....

For the record, a single ended signal via XLR adapter will cause a particular set of ARC power amps tp distort horribly at relatively low output levels. Per ARC. Per my own experience. Period.

Whether he replaces his preamp or inserts a transformer (as Al recommends) the OP needs to feed a balanced signal to his ARC amp. It's a design quirk, but once my VT 130 SE was appropriately fed, performance went from IMHO unusable (much as the OP describes) to outstanding.

My advice to the OP, don't screw around with any other fixes. ARC told you what to do about this problem. Either do it, or ditch the amp. Trust me, I've been in this precise situation and the solution is a balanced signal.
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