SSG, when you say you hear hiss at “above 70db”, are you talking Soind Pressure Level (SPL) or voltage? If SPL, bow are you measuring that? 70 db SPL at the listener position is not very loud. Anyway, hiss when you crank the volume control on a solid state preamplifier is usually a sign it’s gain is inadequate for the input signal voltage OR RFI.
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I think SSG is saying he hears a big difference between 47K ohms load and any value equal to or less than 1000 ohms, where 47K sounds bad to his ears. I didn’t see where he talked about gain per se. So Karl, how do your Pass phono stages sound when you load LOMC cartridges at 47K ohms? And which cartridges have you tried?
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I am not suggesting you should continue to beat your head against the wall in order to make the 47K option sound "good" to your ears in your system. Just enjoy what works best for you. But your result does not illustrate a principle (47K sounds bad with Hana ML, for example) that others might use as a guide in their own systems.
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SSG, I think we established that your experience with loading your MC at 47K ohms, namely that it sounds BAD, is so unusual as to be considered "unique". So I would not warn others against loading at 47K ohms. John Curl and Audible Illusions knew what they were doing. 47K ohms should work just fine. Lower R loads work fine too and are subtly different from SQ at 47K ohms, in all my 40 years of experience. Therefore it is also legit to find that you prefer a lower resistance load; many others do. Laginz, you are most assuredly not "SOL".
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Again, you’re relatively happy with load resistance other than 47K ohms, so a mismatch between cartridge and tonearm is not high on my list.
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I don’t quite understand your last post, except it seems you’ve checked the cartridge and speaker wires and the two channels are NOT out of phase. Do you understand that point?
the rest of your last post eludes my grasp. The issue I focused on is why the 47K ohm setting sounds so uniquely awful. There shouldn’t be much if any difference between 500, 825, and 1000 ohms load with your cartridge and either phono stage. Which is to say they should all sound fine and not much different from 47K ohms.
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Also check the leads at the cartridge as Atmasphere suggested and even though you say you’re relatively happy when load R is 1K or less. So this is a real shot in the dark. Color code as follows:
red= right channel hot
green = R channel ground
white = left channel hot
blue = L channel ground
Also check that your speakers and any subwoofers are wired in phase with each other, meaning left vs right.
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Until now, you never revealed that both the XP 15 and the XP 17 had this sonic character when you set the load to 47K ohms. Since you used the term “amps”, is it correct to assume that you mean both phono stages? If so, I am stumped, because it is highly unlikely that both phono stages were miswired at the factory. So by all means call Pass labs. I would be interested in what they say.
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Which is what I said, too. But it can’t be at the cartridge because he reports relatively good results with all other choices of load R. Which is why I suggested there may be a phase error incurred in relation to wiring of the load selector switch, when he sets load to 47K. Or something like that is reversing phase in one channel, only when 47K is selected.
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One remote possibility: when you set load at 47K, the two channels are out of phase with each other. That would have to be due to a glitch in the internal wiring of that resistor, since other loads are at least functional. I would consider sending the XP17 to Pass for inspection. If there’s some other problem, they’ll find that, too. Because believe me, there is a problem somewhere.
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Have you tried a 47K ohm load with any other typical LOMC cartridge, ever, with either of the two Pass phono stages? What was the result? Thx. Also, can you define "terrible"? Do you mean that the treble was rolled off or missing, as you mentioned earlier?
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You are not the only one who reports the result that changing the load resistance by 20,30, 40 ohms in the already low resistance region (say, below 1000 ohms) makes a critical difference, with a LOMC cartridge. All I can say is, I never have understood such reports. It runs completely contrary to my experience. in my experience, yes, there is a very slight difference between very low load resistances and 47K ohms. However, the differences are mostly that the highest resistance sounds a little more lively to me. I certainly have never heard a difference between say 200 ohms and 250 ohms With any low output moving coil that I have ever owned. This is certainly not to say that you are wrong or misguided. It probably has something to do with the design of the phono stage, although I confess my experiences are the same with any of three or four phono stages that I own, some of which are solid state and some of which are tube Types.
There is one exception: As you may know, it is optimal for the ratio between the internal resistance of the cartridge and the input impedance of the phono stage (which is largely determined by the phono load resistor) to be related by a factor of 1:10 or better. For example, for an LOMC with an internal R of 10 ohms, you want to load it with at least 100 ohms or higher resistance (which is why even 47K ohms is fine). The reason is as that ratio gets lower than 1:10, you begin losing more and more of the cartridge output (signal voltage) to ground. So the coupling becomes less and less efficient. But if your phono stage has an excess of gain, that wouldn't matter so much. What also happens however is that as the ratio gets lower, you begin to preferentially lose treble, because of any capacitance at the phono input stage. (All gain stages, both tube and solid state, present a tiny capacitance at their inputs, unless the input is a cascode. There is also cable capacitance.) And the sound gets dull. (Which is why I was so surprised that you say you lose treble when R goes to 47K ohms. Should be the other way around.)
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There’s absolutely no way that loading an MC with 47K should eradicate treble. That’s very odd.
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Ok. Then play with the values. You can’t damage anything.
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As Atmasphere is fond of reminding us, the phono load resistor is for the phono stage. Anyway, in my personal experience of playing with load resistors, the value makes very little difference. Of course, there are others who have had contrary results. So try it and let us know.
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Of course, try 47K; nothing is going to blow up. But it’s most likely that the difference in sonic character between 15 and 17 is due to circuit differences, not load.
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