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 6 responses by bifwynne

bifwynne
2,206 posts
 
As an fellow owner of an ARC Ref 150, I have a sense of what your Ref 150 can do. You cam confirm what I am advising with Kal at Audio Research.

Although I am not speaking to whether the rest of you rig has issues, I have serious doubts that the Ref 150 has enough power to properly drive the Maggie 3.7s. The consequence of over-driving the amp is ... distortion.

Btw, if the Maggie's have a nominal impedance of 4 ohms, especially in the bass/lower midrange frequency spectrum, I suggest trying the 4 ohms taps. While many tout the virtues of the Zeros, to me, they are just another artifact.

The Ref 150 is designed to produce clean power up to its rated spec (150 wpc) if the speaker's impedance (4 ohms) matches the amp's output impedance off the 4 ohm tap ... at least if tasked to produce in the power spectrum (bass/midrange). Impedance matching is less critical at higher frequencies because power demands are less.

Btw, btw, output voltage regulation is tighter off the 4 ohms taps. As a consequence, if the Maggie's impedance function rises in the mid/tweeter range, using the 4 ohm taps will result in the Maggies sounding less bright.

Let us know how you make out.

BIF
bifwynne
2,206 posts
 
Pakwong, using zeros will not help, and could possibly hurt. Tube amps like the ARC Ref 150 work best if the speakers impedance is perfectly flat as a function of frequency response.

Take a look at John Atkinson's bench test results of the Ref 150 and look at his measurements of output power and distortion as a function of speaker impedance. The amp's ability to produce clean power is attenuated if the load impedance deviates from the amp's nominal impedance at the relevant output tap.

This is not a big issue because as Al (Almarg) recently remarked, a rough rule of thumb is that an amp's power output demand is roughly 50/50 at the 300 Hz frequency. Stated differently, one would do better to match the speaker impedance in the low bass/midrange frequencies to the amp's nominal impedance at the relevant output tap.

An example might help. If your Maggies present a flat 4 ohm impedance load as a function of frequency response, then I surmise that the Ref 150 will deliver close to its rated 150 wpc channel with the least distortion ... if the 4 ohm taps are used. By contrast, if the Maggies impedance is between 3 and 5 ohms between 20 Hz and 500 Hz power region, then rises to 8 ohms thereafter, I surmise that the Ref will still do a pretty good job delivering clean power into that load if the 4 ohm taps are used.

OTOH, if the Maggies impedance is between 3 and 5 ohms between 20 Hz and 500 Hz, then rises to 8 and 15 ohms thereafter, I surmise that the Ref ability to deliver clean power may be a tad attenuated if the 8 ohm taps are used. The reason is the amp is being asked to drive a low impedance load in the power range when speaker and amp impedance is not well matched.

Hope this helps. In the end, most tubies like me say, go with what sounds best. Nevertheless, I am a little concerned as to whether the Ref 150 can bring out the best in the Maggies.
bifwynne
2,206 posts
 
Pakwong ... I still think the Ref 150 is a marginally powered amp for your Maggies. But the most recent posts which speak to the Ref 150 using balanced inputs is extremely important. I cannot overstate how critical it is that you use a linestage/pre with balanced outputs.

Don't know what your budget is. But let me suggest that from time to time, I have seen ARC Ref 3s going for the low $5000s. Even an LS 27 linestage/pre would be a great match.

Last comment. I own a Ref 5 SE/Ref 150 combo. I love my ARC gear. The sound is great. It's built like a tank. ARC provides great customer support. I hope you can figure out a way to keep your Ref 150. IMO, it's a classic piece of kit that will keep its value for a long tim.
bifwynne
2,206 posts
 
Just read the last 5 or 6 posts. I posted a few comments a while back. Two points.

First -- Yes ... it is true. The ARC Ref 150, and presumably Ref 250, are designed to accept only a balanced (XLR) inputs. Not an SE (RCA) type. If you can rig some contraption to somehow do an end-run ... all the power to you. I own an ARC Ref 150. The last thought that would come to my mind would be to jury-rig (sp?) that type (or any type) of similar gizmo.

Second -- I've said this before and I'll repeat it once again. Maggies are power hogs.

I think Maggie 3.7s deserve a lot more juice than the Ref 150 can deliver. I'm sure the Ref 150 can drive the Maggies to an "ok" SPL, but not to the point where the 3.7s will open up and sound their best. I seem to recall that many years back, I had a similar conversation with either Len or Kal at ARC. They expressed similar views.
bifwynne
2,206 posts
 
Thanks Al. I take your point about using a transformer to connect an SE output to an XLR input. As I have admitted many times, I am not a EE-type, so the theory and application is way north of my pay grade. I suppose I am just biased (pun) about inserting artifacts into the signal path.

You may properly ask why, if I really feel that way, did I insert a DEQX digital time and EQ correction device in between my linestage and amp? My response: perceived sonic cost versus perceived sonic benefit. So far, I believe the latter significantly outweighs the former, ... I hope and think?????

Thanks for the electronics lesson. :)
bifwynne
2,206 posts
 
Knghifi ... your comment applies not just to amp/preamp combos but to other system components as well, such as speaker and tube amp matches.

Believe me, just read some of my posts where Al (Almarg) and Ralph (Atmasphere) had to walk me through electrical compatibility issues involving my Ref 150 tube amp and my Paradigm Sig 8s (v3). The issue being electrical consequences of matching my tube amp's somewhat high'ish output impedance and the rock and roll impedance and phase angle plots of my S8s.

I'm ok now ... but only after lots of on line conversations with Al and Ralph, off-line learning, and ultimately putting together a combo that makes a lot of sense in terms of integrating my Ref 150 amp, my speakers, my self-powered sub woofer via a new gizmo I just bought ... the DEQX PreMate.
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