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 |
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 |
ZD, the comment you were responding to was from the OP, Pakwong, not from Martykl (who is not the OP).
Best regards,
-- Al |
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 |
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 |
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 |
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
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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 |
Outstanding! And a great suggestion by ZD. Can you explain to a guy like me with almost zero electronic knowledge about how the transformer from Jensen or SMc can actually convert unbalanced signal to true balanced signal? My Maggie dealer also talked about something like pin 1 or pin 2 "hot" in the RCA to XLR cable and he suspected that the termination of my RCA to XLR cable was not done correctly hence the distortion. How true is it? Taking your second question first, the problem you have been dealing with cannot be avoided with an adapter cable, no matter how it is wired. To work properly, your amplifier (and other ARC and other amplifiers that are similarly designed in the relevant respects), must be provided with a balanced pair of signals at its inputs. That means two signals that are essentially identical except that one is inverted relative to the other (i.e., when the voltage of one signal moves in a positive direction, the voltage of the other signal moves in a negative direction, and vice versa). An adapter cable cannot produce those two signals, when it is only being provided with one of them. A transformer can do that, however. A voltage will appear between the terminals that are connected to the two ends of the secondary (output) winding of a transformer, that in the absence of any external connections to that secondary winding would be electrically isolated (i.e., unconnected, or "floating" in EE terminology) relative to the ground of the signal source, and relative to all other voltages or grounds or other reference points that may exist in the system. If the input circuit of the amplifier is designed as a balanced receiver, it will process the voltage that exists between those two ends of the transformer secondary in a manner that is symmetrical relative to the amplifier's circuit ground, which means that it will "see" that voltage no differently than if a balanced source (providing two equal voltages of opposite polarity) were being used. This Jensen white paper, although somewhat technical, goes into further detail that may be of interest. BTW, regarding the transformers I suggested, be sure to note that (as indicated in the manual I linked to for the particular Jensen model I suggested) that particular Jensen model would have to be placed close to the amplifier, and connected to the amplifier with a very short (less than 2 foot) length of XLR cable. The RCA cable from the preamp could be any reasonable length. I believe that no such constraint would exist with the SMc transformer (or with some other Jensen models, although those other Jensen models may not perform quite as well as the one I suggested). Best regards, -- Al |
Stringreen, if you read through ALL of the above posts beginning with mine on 8-12-14, I think you'll conclude that there is nothing wrong with the amp.
Regards,
-- Al |
Good answer from ARC. As I indicated earlier, though, a number of other A'goners have reported using the particular Jensen transformer I suggested with extremely good results, in very high quality systems. Although that opinion, as might expected, has not been 100% unanimous. Personally, I suspect it will work out fine.
Best regards,
-- Al |
Great!
I don't doubt their statements about the RX vs. XX. And actually when I suggested the RX I hadn't thought of the possibility of using the XX with your existing adapter cable.
I'd expect that either approach will work well, and will solve the initial problem, but there may be some sonic differences resulting mainly from differences between the cables themselves. Which would be preferable, if in fact there is any difference, is probably unpredictable.
Regarding the slots and screws you asked about, I believe those are to provide the option of connecting via bare wire, which is sometimes done in pro applications. So you can ignore them.
Best regards,
-- Al |
Sorry to hear of this development, Pakwong.
However, I feel quite certain that a problem involving the AC power relay not closing within a few seconds after turn-on has nothing to do with the use of the Jensen signal transformer.
Also, the instructions you quoted from the CAT manual, while being applicable to most balanced amps, are not applicable to yours. As you had found when using the adapter cable, and as has been explained earlier in the thread, using the adapter cable (without the Jensen transformer) sacrifices approximately 75% of the amp's power capability, as well as having various sonic disadvantages.
In fact, although it is probably unlikely, and I'm not specifically familiar with the design, I wouldn't completely rule out the possibility that the amp became susceptible to this problem as a result of having frequently been driven into clipping (i.e., being required to exceed its greatly reduced power capability) when the adapter cable was being used for a prolonged period of time.
In any event, it sounds like either the relay or something in its associated circuit needs to be replaced.
Good luck. Regards,
-- Al
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P.S: To clarify my previous comment about what is stated in the CAT manual, the adapter cable you had been using resulted in the amp being operated in exactly the same manner as what would occur if you were to do what is described in the paragraph you quoted from that manual.
Regards,
-- Al
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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
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Ralph & Dbarger, you appear to be disagreeing simply because you are using the term "source" to mean different things. I believe that Ralph is referring to the "source" of the signals which are sent into the power amp, e.g., a preamp. Dbarger is referring to the "source component," e.g., a CD player.
As Dbarger appears to indicate, I would not expect there to be any problem if the power amp were driven by a balanced output of a preamp which in turn receives a single-ended input. Assuming, that is, that the preamp's output truly consists of a balanced pair of signals, rather than a single-ended signal provided on an XLR connector.
Regards,
-- Al |
As might be inferred from this post I made two days ago, I am in essential agreement with Minorl's comments. And especially with: My reading of the posts, indicates that the OP used the Jensen transformer and the resulting sound is wonderful. Problem solved. The old saying "if it ain't broke, don't fix it" comes to mind. (In this case, of course, the amp is broken and in need of repair, but that is unrelated to the question of whether or not to replace it). Certainly the JL5 will be a good match with Pakwong's preamp. But can anyone say with a high degree of confidence that it will be a better sonic match for the Maggie 3.7 speakers than the combination of the ARC amp and the Jensen transformer? Or that its 100 watt power capability will be adequate, considering that a VTL amp rated at 50W triode mode/100W tetrode mode into 5 ohms is not? Pakwong, hopefully you can audition the JL5 in your system prior to committing to a purchase. Otherwise, it seems to me that you would be bringing significant risks into play, in an effort to eliminate what may be from a subjective standpoint (as opposed to a theoretical standpoint) a non-issue. Good luck. Regards, -- Al |
Bruce (Bifwynne), I wouldn't consider the use of a Jensen transformer to be a jury rig/jerry rig/kludge (whichever terminology one prefers). It's a legitimate means of converting a single-ended signal to a true balanced signal pair. Consider also that some extremely highly regarded preamps have transformer-coupled outputs, and in some cases also utilize transformer coupling in their internal signal paths. Examples include the Coincident Statement line stage, and some ultra-expensive Audio Note models. Of course, all transformers are not created equal. But the Jensen transformers are well regarded, and as I've indicated multiple times in this thread, a number of highly experienced members here who have very high quality systems have reported excellent results with it. And the OP was quite happy with the results he was getting with it, until an unrelated problem he experienced caused the thread to be resurrected, and various subsequent responses unrelated to that problem caused him to become concerned about theoretical issues that may or may not be subjectively significant, or even perceptible, in his system. Regarding your other comment, I don't doubt that for some and perhaps many listeners the Ref 150's power capability may be marginal with the Maggie 3.7, and in fact that very issue is being discussed in another current thread you are participating in. Of course, the degree to which that may be a concern will depend on the particular listener's preferred volume levels, on the dynamic range of the recordings that are listened to (well recorded minimally compressed classical symphonic music perhaps being the worst case), and on listening distance and room size. My impression, however (derived in part from your comments in other threads), is that the power supply of the Ref 150 is robustly designed, including large amounts of energy storage. Which, together with your comments about its marginality with the particular speakers, reinforces the concern I expressed in my previous post about the adequacy of the lower power rating (100 watts) of the CAT JL5. Onhwy61, I'm surprised at your response to what I thought was a knowledgeable and entirely appropriate input from Knghifi. I would especially not have expected such a response from you in particular. Best regards, -- Al |
Thanks for the update, Pakwong. Sounds like a good plan, which will greatly reduce the risk I had been envisioning if the CAT doesn't work out.
BTW, although I could be wrong, I had been interpreting Knghifi's comment about doing homework before purchasing to be in reference to the CAT purchase, not to the ARC purchase. As you said, it's very unusual for a balanced amp to not be able to work in a reasonable manner when provided with an unbalanced input, so that "oversight" is certainly understandable. And since you have a fallback strategy which minimizes the risk I and perhaps he were envisioning regarding the CAT purchase, it seems like all the bases are covered (to use a baseball analogy).
Continued good luck as you proceed. Regards,
-- Al
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