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
atmasphere's avatar
atmasphere
11,807 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.
mapman's avatar
mapman
22,205 posts
 
If it were me, I would only run an amp like that designed for balanced input with a well matched balanced output device feeding it, like Atmasphere suggests.

If you can establish that a proper balanced output device works as it should, I would agree with Atmasphere that that is the way to go, assuming the ARC is working as it should mated to the right input. If it does not, then there is some defect at play that would have to be addressed, but hopefully that is not the case.
daveyf's avatar
daveyf
2,871 posts
 
I think the real problem here is as stated by several other posters...that is the incompatibility between the CAT and the ARC. I think ARC is simply trying to cater to fashion in regards to their seeming insistence on only using balanced inputs on their current gear. This fact has made me stay away from their gear and will continue to do so until they get the picture. I can see no reason why the extra electronics needed with the balanced option is at all necessary, except to add cost and to cater to as I stated earlier....'fashion'. Personally, I feel that 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.
My advice, dump the ARC Ref 150 and get a more suitable amp for the CAT...like maybe a CAT amp!
almarg's avatar
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almarg
9,670 posts
 
Gentlemen, keep in mind that the problem at hand is simply that the amp has broken down.

Also keep in mind that Pakwong was quite happy with the sound he was getting using the Jensen transformer, prior to the recent breakdown of the amp. And some other highly experienced A'goners having very high quality systems have reported in the past being similarly pleased, using the same Jensen transformer.

I have no doubt that Ralph's/Atmasphere's statements about the compromises the transformer introduces are correct, but it seems based on these anecdotal reports that the degree of those compromises is small enough that for many users it would not warrant replacement of either the amp or the preamp.

Best regards,
-- Al
dbarger
215 posts
 
Atmasphere mentioned using only a balanced source. This I assume is only referring to the preamp. It is very possible to use single-ended sources into a balanced ARC preamp, going into a Ref150. They work great, it is only the preamp which needs to be balanced. ARC even makes a few of the single ended sources...
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