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

Showing 8 responses by atmasphere

atmasphere's avatar
atmasphere
12,128 posts
 
Dbarger, I spoke to both Kalvin and Warren at ARC and they told me the same thing: if the amp is used with a single-ended source it will have lower output power and will make distortion.

This is because the drive to the power tubes will become unbalanced. IOW, the amplifier is not compatible with single-ended sources and if one is employed, a transformer should be used to balance the input to the amp.
atmasphere's avatar
atmasphere
12,128 posts
 
Pakwong, I would not take this particular event as somehow being a problem with balanced operation. I've been working with balanced line equipment for decades; this sort of problem that you experienced says more about Audio Research than anything to do with balanced operation.

We've been building balanced line equipment for high end audio longer than anyone else- all I can tell you is this should not have been a problem and is something unique to ARC.
atmasphere's avatar
atmasphere
12,128 posts
 
As you may have surmised by this time, the ARC amplifier cannot be used with a single-ended source! If you do so, the amp **will not make anywhere near full power** and it will be distorted.

This is because the amplifier has a very poor Common Mode Rejection Ratio figure, on account of its input circuit (which apparently is differential) is not in fact very differential. IOW, IMO/IME, ARC missed a bet here.

At any rate, the only way to use this amplifier with a single-ended source such as the CAT is to use a transformer like you are doing (The Wadia worked of course because it has a balanced output).

There are several problems with this. The Jensen, while excellent, does not load the CAT ideally nor does it have the bandwidth of the CAT, so you are not hearing everything it does. However, unless you sell the CAT and get a balanced preamp, this is the only game in town.

I have to admit I am puzzled why the amplifier is designed in this fashion, but in conversations with the good people at ARC (a good number of whom I have known for decades) this is very much the case (As a manufacturer of balanced line products, we had to sort out compatibility with single-ended equipment many years ago). If I were you I would be seeking a balanced line tube preamp, but that's me: I don't like transformers. Plan B: Sell the amp and get something that works with your CAT. Both units are capable of excellent performance; its really a matter of which you like more. Good Luck- keep us informed.
atmasphere's avatar
atmasphere
12,128 posts
 
Davef, this quote is incorrect:

single ended gear sounds better than balanced gear; IMO,unless one is using their gear in a VERY highly corrupted noise environment or with VERY long runs of cable, balanced is nothing but a joke in high-end.

If you have ever heard a difference in audio interconnect cables, then you now know why balanced lines are not a joke- because they solve that problem if used properly! Further, it does not matter the length, 6 inches is easily enough to hear a difference, especially if there is a noisy environment. Further, the proper use of balanced lines and balanced operation offers lower distortion.

Tubes are often docked for having that ever-lovin 2nd harmonic, which is nice and rich sounding, but not neutral as it is distortion. That can be eliminated by employing balanced operation, resulting in more transparency and no loss of smoothness.

By running balanced lines, I can put my amps much closer to my speakers, allowing me to run shorter (thus better sounding) speaker cables, plus I can put my front end where I want it, rather than in between the speakers. The first thing I noticed in doing this was greater ability to make out vocals. It was not subtle.

Al, what I was describing in my post above is not a malfunction. The OP did have a malfunction, but it was coincidental and unrelated to the basic problem: distortion when driven by the CAT directly.
atmasphere's avatar
atmasphere
12,128 posts
 
Daveyf, anytime you put current through the shield of the cable, you are subject to the construction issues of that cable. So this is a big issue with single-ended, even if its only 6 inches. In a balanced system (caveat: if the balanced standard is being properly supported...) the shield sees no signal current at all.

FWIW there does not have to be any 'loss potential' caused the additional circuity when going balanced (a common myth is that there is twice as much circuitry, which is not true, especially if the circuit is fully differential). For example, a fully differential circuit can have up to 6 db less noise per stage of gain as opposed to the same topology running single-ended. So in two stages of gain you could have up to 12db less noise! This has real benefits in preamps working with low output moving coil (which is a balanced source BTW), as you might only need two stages of gain for a functional tube phono section! That is **less** stages for the signal to go through than single ended.

In our amps because of this we only have one stage of gain. So you can actually have a simpler signal path than an SET might have.

On top of that, balanced operation in the preamp or amp means that the unit is more impervious to noise that gets into the power supply. So the potential is for lower noise and not from just the cables.
atmasphere's avatar
atmasphere
12,128 posts
 
^^ This.
atmasphere's avatar
atmasphere
12,128 posts
 
Agreed! Our amps are also fully balanced and differential; we made sure that it was no worries or loss of performance to use them with a single-ended preamp or source.
atmasphere's avatar
atmasphere
12,128 posts
 
**Most of the time** you can expect an amplifier with a balanced input to work just fine with a single-ended source.

However, balanced line and single-ended operation are not normally considered to be compatible (by the pro audio industry). As a result, you usually have to jump through some hoops to make the two work together. In our equipment, that means joining pin 3 to pin 1 on the XLR and its all good. With the ARC amplifiers, the *only* way to do it is to use a transformer; Jensen makes some of the best transformers world-wide for this application.
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