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
Hmmmm, I am no techie. But when you get a problem at only presents itself during certain passages of music...it seems less like an electric problem (which you would think would occur all the time or at least randomly)...and more like a mechanical problem. Something reacting to those treble frequencies or something?

Is it possible the tubes are slightly microphonic, and your speakers are picking it up? Have you tried tube dampers? Borrow some if you can before going out and buying. Sometimes when a tube is microphonic it will pick up certain noises either internal to the tube due to vibration or due to vibration in the room outside the tube...and translate it as distortion thru the systems signal.

I once had a tube so microphonic if I clapped or whistled you could hear it thru my speakers. A tube damper from EAT solved it...and so did replacing the tube! Again, I am no techie, just a thought. Good luck.
I suspect that your problem lies with your amplifier.

If I recall correctly, the Maggies prior to the ".7's" had rather ruler flat impedance curves.
The crossovers have changed and this is no longer the case.

I owned MGII B's, 3.6's and still have a pair of early MMG's.
The MGII B's (6 ohm load ) could be driven with a 40 watt PP tube amp quite nicely and sounded beautiful, at low to moderate levels.
The 3.6's I drove with a Classe CA400 SS amp which pumped out 800 watts into a 4 ohm load.

You tried a second tube amp and still had the same issue.
I would try all of the output taps on the Ref150 and see if there is a difference. ( without the auto formers first )

I would then try the auto formers with the best performing tap if you still need them.

My experience is that Maggies need to be driven at moderate levels at the very least to sound best.

More power was always better for me with Maggies.
The Ref 150s may not be up to the task, even with the auto formers.

If you have not visited the Planar Forum at the Audio Asylum, you should and ask for assistance there.
Do you have the Bob's devices SUT into the MC or the MM input on your CAT pre?
There are plenty of people that drive Maggies with tube amps. I agree that tube microphonics would explain what you are hearing, and it is pretty easy to address. Also, the fact that you tried two other speakers, one of which gave you the same result, probably means it is not the Maggies per se. However, because they are dipoles, they may direct more energy back to the tubes. Just wondering, the other speakers you tried--- were they both rear ported? If the one that didn't give you distortion is front or bottom ported, or sealed, that could also be a clue.

On the other hand, I had no such problem with my 3.7s with my Coincident Line stage preamp, which uses highly microphonic 101D tubes, and had no problems, although I do use tube dampeners.

It might also be worth switching out the speaker wires and ICs if you have spares. A weak connection at the terminal can give intermittent distortion problems.
Can you borrow a digital source (CD player) and play the same recording to see if you can identify the same distortion as with your analog source. If no apparent distortion, the problem may be with your tonearm/cartridge alignment.
Somewhat odd that only some recordings and/or passages of same are sound distorted. Could very well be your SUT or cartridge or alignment.
Good luck!!
I own a pair of Maggie 3.7's but I run them with a SS amp.
I have no idea what the problem is but was just wondering if you ever tried using the resistors with the Maggies and if that would correct any of your issues?
You have described the distortion problem I have been working on for some time now, although yours sounds more severe. Mine was with high pitched, high amplitude vocal "air", mostly female, but piano was ok. I have the DV XX2 MK2 and also use the Mint tractor. The problem turned out to be the distance from the spindle to the tonearm pivot was off a little. A very tiny little. Because of that the Mint Tractor made me align, very precisely, to the wrong arc and overhang. I used the VPI jig that came with the arm to reset the distance. After realigning the cart with the Mint the distortion was eliminated and replaced by incredible detail. Double wow! I had tried everything I could think of for months on end. The DV carts have a well deserved reputation of being sensitive to setup error. Good luck!

Bill
From what you describe, I think that maybe you are overloading the phono input. Make sure you are using the MM input and not the MC. If you are using the MC along with the SUT, it could very well indeed be too much gain.
I agree on the overloading. If its louder musical peaks, its a higher output voltage at those peaks and its just about exceeding somethings limit.
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
"08-10-14: Smoffatt
Can you borrow a digital source (CD player) and play the same recording to see if you can identify the same distortion as with your analog source. If no apparent distortion, the problem may be with your tonearm/cartridge alignment.
Somewhat odd that only some recordings and/or passages of same are sound distorted. Could very well be your SUT or cartridge or alignment."

Try that first. Use any CD/DVD player you can find. It doesn't have to be expensive. If that doesn't work, I would try a different pair of IC's between your amp and preamp. I don't think you can switch your amp to run in SE or Balanced operation. I think it just runs in Balanced. I've seen several times where you can get a noise because of it. The solution, in the cases I've seen at least, was to use a good quality shielded IC. Any Audioquest with the DBS system always worked (providing that was the problem). Most ARC dealers have AQ. See if they will lend you a balanced and a SE IC to try in your system. You'll also need 2 adapters. If your dealer doesn't have them, you can get them at any music store. You need male xlr/male rca adapters for the balanced cable and male xlr/female rca adapters for the SE cable.

You've probably already did this, but you may want to try some different taps on you amp, both with and without the autoformer. Now that I think about it, is it OK to use the autoformer with an amp that already has an output transformer? Hopefully, someone that knows will comment on that. I'm not sure.
I once had a similar problem and it was cart alignment issue as several others have suggested.
Try increasing the tracking force to the maximum recommended for your cartridge
Alan
My appreciation to everyone for their serious advices.

Answer to Lloydedee21:
"Is it possible the tubes are slightly microphonic, and your speakers are picking it up? Have you tried tube dampers? Borrow some if you can before going out and buying. Sometimes when a tube is microphonic it will pick up certain noises either internal to the tube due to vibration or due to vibration in the room outside the tube...and translate it as distortion thru the systems signal."

I do have dampers from Herbie's Audio Lab on all tubes so I assume no issue with microphonic effect.
Answer to Mrderrick:
"You tried a second tube amp and still had the same issue.
I would try all of the output taps on the Ref150 and see if there is a difference. ( without the auto formers first )

I would then try the auto formers with the best performing tap if you still need them.

My experience is that Maggies need to be driven at moderate levels at the very least to sound best."

In my case I do agree the Maggies need to be driven at moderate levels to sound best as the distortion were less obvious or even disappeared with lower volume. Perhaps I need a more powerful amp but this would be my last resources to solve this. In the mean time I will try all output taps to hear the difference. No harm trying!
Answer to Jfrech:
"Do you have the Bob's devices SUT into the MC or the MM input on your CAT pre?"

CAT SL1 Ultimate MK2's phono stage are thought to be MM only. Is doesn't comes with MM/MC switch.
Answer to Brownsfan: "There are plenty of people that drive Maggies with tube amps. I agree that tube microphonics would explain what you are hearing, and it is pretty easy to address. Also, the fact that you tried two other speakers, one of which gave you the same result, probably means it is not the Maggies per se. However, because they are dipoles, they may direct more energy back to the tubes. Just wondering, the other speakers you tried--- were they both rear ported? If the one that didn't give you distortion is front or bottom ported, or sealed, that could also be a clue."

Please refer to my answer to mrderrick about tubes's microphonic. Both pair of speakers I used for testing were box speakers. One pair was KEF Ref 201/2 which has the same distortion while the other Focus Audio FC9 pairs sounded okay. The KEF is upright ported while the FC is back ported at medium height. Any clue?

I did swapped ICs and speaker cables but nothing change.
Answer to Smoffatt:
"Can you borrow a digital source (CD player) and play the same recording to see if you can identify the same distortion as with your analog source. If no apparent distortion, the problem may be with your tonearm/cartridge alignment.
Somewhat odd that only some recordings and/or passages of same are sound distorted. Could very well be your SUT or cartridge or alignment."

I do have a CD player but don't have CD version of distorted recordings on LP as my CD collection was very limited. It's definitely not the SUT. I bypassed the SUT and the CAT preamp by connected phono cable of tonearm directly to a phono preamp with volume control and feed the signal directly to Ref 150 with the same distortion.
Answer to Lack:
"I own a pair of Maggie 3.7's but I run them with a SS amp.
I have no idea what the problem is but was just wondering if you ever tried using the resistors with the Maggies and if that would correct any of your issues?"

Tried that. Nothing change.
Answer to Mofimadness:
"From what you describe, I think that maybe you are overloading the phono input. Make sure you are using the MM input and not the MC. If you are using the MC along with the SUT, it could very well indeed be too much gain."

Please refer to my answer to Jfrech.
Answer to Bifwynne:
"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. "

I do speculate perhaps Ref 150 not powerful enough to drive the Maggie properly. Remember I said Maggie dealer used a transistor amp to test and it sounded okay without distortion? That Class D Esoteric can output 400 watts into 4 ohms. So probably power is the issue.

Btw, before adding the Zeros, I run Maggie with 4 ohms tap with the same distortion.
Answer to Zd542:
"Try that first. Use any CD/DVD player you can find. It doesn't have to be expensive. If that doesn't work, I would try a different pair of IC's between your amp and preamp. I don't think you can switch your amp to run in SE or Balanced operation. I think it just runs in Balanced. I've seen several times where you can get a noise because of it. The solution, in the cases I've seen at least, was to use a good quality shielded IC. Any Audioquest with the DBS system always worked (providing that was the problem). Most ARC dealers have AQ. See if they will lend you a balanced and a SE IC to try in your system. You'll also need 2 adapters. If your dealer doesn't have them, you can get them at any music store. You need male xlr/male rca adapters for the balanced cable and male xlr/female rca adapters for the SE cable.

You've probably already did this, but you may want to try some different taps on you amp, both with and without the autoformer. "

It so happens that I have some AQ Columbia ICs with DBS but it just didn't work after I tried them this afternoon. I also tried with different taps with and without the autoformer and it didn't work either.
Answer to Wlutke:
You have described the distortion problem I have been working on for some time now, although yours sounds more severe. Mine was with high pitched, high amplitude vocal "air", mostly female, but piano was ok. I have the DV XX2 MK2 and also use the Mint tractor. The problem turned out to be the distance from the spindle to the tonearm pivot was off a little. A very tiny little. Because of that the Mint Tractor made me align, very precisely, to the wrong arc and overhang. I used the VPI jig that came with the arm to reset the distance. After realigning the cart with the Mint the distortion was eliminated and replaced by incredible detail. Double wow! I had tried everything I could think of for months on end. The DV carts have a well deserved reputation of being sensitive to setup error. Good luck!

This is something I never think of. Well worth a try.
Answer to Skinzy:
"I once had a similar problem and it was cart alignment issue as several others have suggested."

Although I have done this many time but I will surely do it all over again as suggested by Wlutke.
Answer to Alan:
"Try increasing the tracking force to the maximum recommended for your cartridge."

Another good suggestion. Will try out.
I agree with many of the others that the likeliest cause of the problem is related to cartridge installation and adjustment, including VTF. One thing that hasn't been mentioned is anti-skating. Take a look at the cartridge from the front, while a record is playing, and see if the cantilever is pointed approximately straight ahead, or more precisely, that it is at the same angle as when it is lifted off of the record. If there is a significant deflection of the cantilever to the right or the left while the stylus is in the groove of a rotating record, relative to its rest position, it means (IMO, at least) that anti-skating is significantly misadjusted.

However if further work with the cartridge-related adjustments does not resolve the problem, overloading, as mentioned by others, is also a strong possibility IMO. I say that despite the fact that the SL1 appears to have unusually good overload margin.
08-11-14: Pakwong
Answer to Jfrech:
"Do you have the Bob's devices SUT into the MC or the MM input on your CAT pre?"

CAT SL1 Ultimate MK2's phono stage are thought to be MM only. Is doesn't comes with MM/MC switch.
According to the specs shown here for your particular version of the SL1, its phono stage gain is 47 db. The lowest gain setting of your SUT (which I assume is the setting you are using) is 26 db. The line section of the preamp will add up to another 26 db depending on the setting of the volume control. That all seems very high even for a cartridge rated at 0.3 mv.

So an experiment that would seem to be very much in order would be to see if the distortion still occurs with the SUT removed from the system, even if that results in unacceptable noise levels.

Susceptibility to overload will be further increased (especially when high frequency energy is present at high amplitudes, consistent with your description of the problem) if the cable between your SUT and the preamp is long and/or has high capacitance per unit length. The capacitance of that cable, as seen by the cartridge, will be multiplied (not divided) by the square of the voltage step-up ratio of the SUT. In other words, by 400 times (for the 26 db gain setting). That will raise the amplitude and lower the frequency of the ultrasonic resonant peak in frequency response formed by the interaction of the inductance of the cartridge and the capacitance it is loaded with.

In addition to keeping the cable length between SUT and preamp short, you might try putting a load resistor across either the input or the output of the SUT. I see that the recommended load resistance for your cartridge is specified as ">30 ohms," while the 26 db gain setting of your SUT together with the 47K input impedance of the preamp will result in a load of 118 ohms. You might try something like 50 to 100 ohms across the primary (input) side of the SUT, or 20K to 40K across the secondary (output) side.

One final point: You mentioned that the problem remained when you tried a single-ended tube amp. If that amp provided an XLR input even though its internal signal path is unbalanced, and if you connected the preamp to that amp with the same RCA-to-XLR cable used with your ARC amp, the cable is not ruled out as a suspect. If the unused signal pin on the cable's XLR connector (generally pin 3, although possibly pin 2 in some countries) is not grounded (i.e., connected to pin 1), it could account for the problem. Proper connections within the cable can be easily verified with a multimeter.

Hope that helps. Regards,
-- Al
I think, you overload your phonsection. Distortion has nothing to do with Antiskate, Azimuth or wrong alignment when you only can hear it in the upper frequencies when the dynamics start to rise. "This" kind of distortion in Phono is normally the result when the SUT is too strong( or the cartridge is too strong for the SUT, you can see it this ways or the other way). 0.3mV MC run normally easy with 60-63dB, sometimes a bit more but not much. Try to loan a SUT with 10dB less, just for a check or when one of your friends owns a cartridge with 0.20mV, try to loan it. Next is the output power from your Preamp to your power amp. When the Pre drives the amp easily, this kind of distortion becomes much more present even at lower volume.
"It so happens that I have some AQ Columbia ICs with DBS but it just didn't work after I tried them this afternoon. I also tried with different taps with and without the autoformer and it didn't work either."

Is your Columbia balanced or single ended? I know I said to try both if you can, but a balanced cable with an adapter for the preamp connection will most likely be the fix (if the problem is actually cable related.).
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.
Sorry that I was lazy in my response above. I should have
stated what Al, (as usual, very highly detailed and correct.
We are really lucky to have Al on here. Yeah, I'm a fanboy)
did about the gain(s).

I did look up all the gain stages, but didn't really get
into it before. If you have 26 + 26 + 47 that's 99db of
gain which is WAY TOO HIGH! That really leads me to
determine that the distortion is coming from overloading. I
can almost guarantee that's your problem.

Try taking out the SUT and see what happens.
Thanks for valuable input from all!

Yes, trouble shooting procedures which I've been carried out also includes bypassing the SUT and CAT SL1 in the system, by using a EAR 834P phono preamp that comes with volume control and MM/MC function connected directly between the tonearm and Ref 150. Same thing happens! So I assumed there is no issue with overloading from the SUT and preamp.

Last night I did a final test by listening again to digital sources from a Wadia 381i CD player connected to line stage of the CAT SL1. To my surprise, the same distortion also happens on the digital source which I thought didn't exist! I'm not a big fan of digital hence very seldom listen to it. The last time I listened to it were kind of background listening with lower volume. This time I crank up the volume control to about the same level while listening to LPs and the same distortion shows off immediately!

In the mean time, I also tried listening closely to the speakers and found that the distortion appears almost on all frequency including bass while cranking up the volume.

With these latest discovery I began to suspect that the true problem might be coming form either the Ref 150 or the Maggies.

Any thought?

Thanks again!
BTW, I do agree that my system sounds more linear and faithful to the source by connecting the 4 ohms tap directly to the Maggie.

Thinking about the beginning when I first bought the Ref 150, it was used to drive my previous KEF 201/2 speakers and from that time on I started to experienced distortion on certain recording. Only not as severe as with the Maggie. Perhaps the Maggie's higher resolution and the recently purchased XV-1S which replaced the XX2 has made the issue worst.

If both KEF and Maggie suffer the same distortion from the Ref 150, and no sign of anomalies from other components, is it possible that I've purchased a defected Ref 150? Or simply because the Ref 150 did not match the Maggie perfectly?
If both KEF and Maggie suffer the same distortion from the Ref 150, and no sign of anomalies from other components, is it possible that I've purchased a defected Ref 150? Or simply because the Ref 150 did not match the Maggie perfectly?

I think you narrowed it to the Ref 150.
This problem has nothing to do with a "mismatch" with a speaker, when your Phono Input is ok and based on your own comparisons, the Ref 150 has a defect part inside.
If I've followed all of this correctly, you've perceived the problem with two different speakers, two different tube amps, two different preamps (one of them being a phono stage used as a preamp), two different sources (one vinyl, one CD), and a variety of different cables.

If so, it seems to me that there are likely to be two different problems that have been present, which are causing somewhat similar symptoms.
I also tried listening closely to the speakers and found that the distortion appears almost on all frequency including bass while cranking up the volume.
I would infer from this that the distortion at low frequencies is more subtle than the distortion you described earlier which was evident mainly on high volume high frequency content. And my guess is that the distortion that is evident at low frequencies is the result of amplifier clipping, while the other problem (evident especially on female vocals and piano) is due to something else. At this point I'm as mystified as you are as to what the "something else" may be.

What may be an important point regarding the possibility of clipping the amp: Depending on how the Ref 150 is designed, by providing it with a single-ended signal you MIGHT in effect be using only one-half of its balanced signal path, which would reduce its 150 watt power capability to possibly as little as 1/4 of that amount (37.5 watts). I'd suggest contacting ARC and asking them if providing the amp with a single-ended signal would affect its power capability, or have other adverse consequences.

If that turns out to be an issue, converting single-ended to balanced with a suitably chosen transformer from Jensen Transformers or (at a higher price point) SMc Audio (Steve McCormack) would be a solution.

Mofi, thanks very much for the nice words. Coming from someone with your extremely extensive experience, that's a meaningful compliment indeed.

Best regards,
-- Al
If the issue is related to driving the REF 150 SE instead of balanced, perhaps one of the early Audio Research single ended to balanced converters would solve the problem?
If you don't have a pair, see if someone will lend you a fully balanced IC. Be careful not to get a SE cable terminated with xlr connectors. You need a cable that's really balanced. Use it to connect your Wadia directly to your amp. If you do that, the noise will probably go away. Also, you may have to go inside the Wadia and adjust the overall gain settings using the dip switches. If the gain is too high on the Wadia, that can also create some background noise.
Referring to the Audio Research BL-1 and BL-2.
After many painful and time consuming experiments,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. Thus, I think I better trade in my preamp or power amp to set up a balanced or unbalanced only system.

The Maggie is something I cannot live without. So do the CAT SL1. And the Ref 150 seems doesn't up to the task to tamed the Maggie. So a more powerful single ended tubes or solid state amps would be a sensible replacement. Of course, before buying, I will have the dealer brings them to my house for audition to make sure there are no more distortion with the new set up.

Hopefully someone have good single ended amp in mind which could drive the Maggie efficiently and match well with the CAT can offer some suggestion.

BTW thanks Almarg, Syntax, MrDerrick, Zd542 and others for your kind assistant on this issue.
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
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
How many hours in your Dynavector? Have you tried different cartridge/needle?
Did you get your cartridge new/used?
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.
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
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.
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
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.
"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....."

I'm not sure I understand what you are talking about here. Wouldn't the preamp determine if the amp can be driven properly? If you had a preamp with enough gain to compensate for the difference between balanced and SE operation, it shouldn't make a difference. Or, is there something else that I'm missing?
ZD, yes, very uncharacteristically you are missing something :-)

Yes, there will be a gain difference. But that is not the problem. The problem is that the **output stage** of the amp will not be able to deliver much more than 1/2 of the voltage that it must deliver to reach its maximum rated output power without clipping, and therefore the amp won't be able to deliver much more than 1/4 of its rated power. The reason being that it is designed to be driven by a balanced pair of signals, having equal amplitudes but opposite polarities, but the design of the amp apparently is such that when a single-ended signal is provided to its balanced input, one of those polarities ends up being MIA (missing in action) at the output stage.

BTW, given all of that some may wonder why the OP reported that the problem remained when he substituted a single-ended tube amp for the Ref 150. There are two possibilities that occur to me. Either a second problem has been present which resulted in similar symptoms (as I speculated in my 8-12-14 post), or the substitute tube amp was clipping simply because it was not powerful enough for the particular speakers at the particular volume level.

Best regards,
-- Al
P.S. to my previous post. Think of it this way: As you (ZD) are certainly aware, a fully balanced amp puts out signal voltages on both its + and - output terminals, relative to the amp's ground, those voltages being of equal amplitude and opposite polarity. (In saying that, and in saying what follows, I'm oversimplifying a bit by not addressing the fact that an output transformer is present in the case of this and most other tube amps). The design of the amp in question is apparently such that when it is provided with a single-ended input, one of those two output terminals will be at zero volts relative to the amp's ground (reflecting the fact that zero volts has been substituted for one of the two input signals that would normally be present in the balanced input signal pair). Resulting in the voltage difference between those output terminals being half of what it should be. Resulting in the maximum possible voltage difference between those output terminals (i.e., the clipping point) being half of what it should be, or perhaps a bit more than that due to the lessened amount of current being demanded of its power supply.

Put simply, half of the output stage for each channel isn't being used. Visualize it (conceptually) as two amplifiers for each channel, one for the + and one for the -, with one of them receiving no input, and therefore providing no output.

Best regards,
-- Al
To rephrase my post:

The OP may or may not have several issues with his system. However, if he's trying to feed a single ended signal into an ARC amp designed for balanced inputs he WILL have an issue very much like the one he describes. Per ARC, he should not drive his amp with anything but a balanced signal.

As a less technical type, I can only gather that the ARC design is unusual. However, I can assure everyone that the relevant ARC amps do, in fact, behave in precisely this fashion.