Don't think my preamp likes feeding signal to two seperate places.
I have read in another thread that the multiple outputs on ARC preamps are just additional outputs that are all wired directly to the single analog stage in the ARC. In other words, this is no better than using a Y-splitter cable to feed both the X30 and the main amp. In this situation, you could have a scenario where the combined impedance of the X30 and main amp is dropping the impedance average so low that the ARC can't drive them properly. I don't know if this will affect the highs, but I suspect that it is possible (others on this forum will have to confirm this). The only preamp I have found to actually have multiple output audio stages is the Classe CP-800. You can actually use multiple outputs on that preamp at the same time without an impedance problem. Alternative is to get something higher end like a Bryston 10B crossover. Use the balanced outputs on the ARC to drive the Bryston crossover, and then use BOTH the low-pass and high-pass outputs on the Bryston to drive the sub/main amps. |
Looks like this person ran into the same issue! LOL https://forum.audiogon.com/discussions/arc-ref-3-main-output-impedance-question?highlight=paradigm%2... |
Georgelofi, I am not directly connecting the 555 to the ARC, I'm using a paradigm crossover in line between it. Apparently it has an input impedance of 20kohms. According to the thread I referenced, this is a not optimal, as well as using single ended and balanced simultaneously from the arcs output. thanks for the suggestion, but I don't have quality interconnects to go all single ended. I might pursue having a buffer made as per the thread I referenced. Seems he was in a very similar situation, with the same crossover unit as I. |
Erik, note in the initial post that he is connecting the LS17 to the DS450 power amp directly, via XLR. Treble gets a little less extended.If the cable length from the LS17 to the crossover is particularly long, and/or if the cable has high capacitance per unit length, that could be a contributing factor in addition to the impedance issue that has been cited. The capacitance of the cable to the sub crossover will affect the signal received by the DS450 essentially the same as if the only cable present on each channel was the one connecting the LS17 to the DS450, and if the capacitance of that cable equaled the total of the capacitances of the two cables you are using. In either case, given that all of the preamp’s output connectors are driven by a single output stage, a low pass filter would be formed by the interaction of the preamp’s output impedance with the total of the cable capacitances that are present. If either cable is particularly long and/or has high capacitance per unit length the high frequency rolloff and/or phase shifts introduced by that filter could occur at frequencies that are low enough to be audible . Would the preamps up the range not have this phenomenon?While I don’t have specific knowledge of all of the recent high end models, just about every one of the many spec sheets I have seen for ARC line stages and preamps at www.arcdb.ws indicates a recommended minimum load of 20K. And just about every one of the many schematics I have seen shows the output connectors that are provided for each channel all being driven from a single output stage, with the RCA connector connected directly to XLR pin 2, and with the two XLR connectors (if provided) connected directly together. Regards, -- Al |
Almarg and atmosphere, you have it correct. I believe the paradigm crossover unit is 20k, SE, as per my referenced thread. (That user had the exact same crossover, but with a ref 3. It seems I would need to have a balanced crossover, as the ARC doesn't like to have both the SE and the balanced outputs running together. Imho, equipment costing this much should be built with more robust or better implemented output stages. Many of us will utilize two seperate amplifiers or in my case an amplifier and a sub crossover. We shouldn't have to worry about the output stage "choking". The difference in sound quality once the crossover unit is disconnected is amazing. I had no idea how much I had been missing before. I will not connect the sub until I can figure out what I will do to remedy this shortcoming, because the bloom and air is too good to give up just to extend the bass. From Preamp to crossover, I'm using a set of 1 meter silver interconnects that were made by a gentleman for me that I no longer have contact with. I do not know it's capacitance. The signal from the crossover is fed mono to the 555se with a no frills radio shack gold single cable which is two meters. I would assume the capacitance of the radio shack cable, and the he input impedance of the 555se doesn't matter because the paradigm crossover is acting as a buffer itself, and that the issue is from the paradigm to ARC relationship. |
The xover as you say is 20kohm input, this combined with the se input 150kohm of the DS450 is a total loading of 17.6kohm. The owners manual states of the LS17 regarding the minimum load for it. "20K ohms minimum load and 2000pF maximum capacitance." It would be nice if that LS17 was around 100ohms output impedance or less. The next best is to get the input impedance of the xover changed from 20k to say 100k, it’s just a small resistor and usually doable (1/2hr work) if the first active stage of the xover is fet input, if bi-polar there maybe offset problems. The capacitance you can measure if you have a capacitance meter, but I dare say your interconnects will be under the 2000pf max, unless your running cheap high capacitance very long lengths. Cheers George |
Regarding the SMS-1, the one concern I would have about connecting it to the DS450 outputs relates to the fact that the DS450 is a differentially balanced amp. So presumably its negative output terminals as well as its positive output terminals have full amplitude signals on them. The concern would be that depending on the internal grounding configuration of the SMS-1 and the design of the external 12VDC power supply it apparently uses, that a low impedance path might be created from the amp’s negative output terminals to the circuit ground of the SMS-1, then through some unknown but possibly low impedance to the AC safety ground of the SMS-1’s power supply, then via the AC wiring to the amp’s AC safety ground, then probably through a low value resistor within the amp to it’s circuit ground. In effect possibly putting a near short circuit on the amp’s negative output terminals, and applying a much higher voltage across that resistor than it was designed to handle. If the SMS-1’s power supply had a two-prong AC plug (i.e., a plug that doesn’t have a safety ground connection) I would be confident that wouldn’t be an issue, but photos I found online appear to indicate that it has a three-prong power plug, which leaves me uncertain. So if you decide to go that way it I’d suggest asking Velodyne what the impedance is between the SMS-1’s negative speaker-level input terminals and the AC safety ground pin of its power supply. If it is high, or if those points are electrically isolated from each other, there won’t be a problem. Regards, -- Al |
So many considerations just to add a subwoofer without comprimising my signal for the main amp!!! Sheesh! almarg, thanks for your insights. Another idea- what if I used balanced to SE converters and used the other currently unused balanced output on the preamp. Would that put me where I need to be to not have the low pass phenomenon, or would this be a continuing problem. Not keen with the math formulas. I appreciate your help. |
P.S. to my previous post: Now that I think of it, even if the SMS-1 wouldn’t create the problematic circuit path I described above, a similar path might be created via the SMS-1’s connections to the Adcom amp, and then via the Adcom amp’s safety ground connection (assuming it has a three prong power plug). Sheesh indeed :-) what if I used balanced to SE converters and used the other currently unused balanced output on the preamp.That should work ok provided that the chosen converter has a relatively high input impedance, so that the parallel combination of that impedance and the input impedance of the DS450 is not too low for the preamp to handle comfortably. (Keep in mind that the preamp’s two XLR output connectors for each channel are undoubtedly wired directly together, and driven by the same output stage). It’s never been clear to me if ARC’s 20K minimum load recommendation applies to the balanced outputs or the unbalanced outputs or both. But to be safe in this case I think it would be preferable to look for a converter having an input impedance of 47K or more. Good luck. Regards, -- Al |
Fundsgon, I see no indication in the manual or the datasheet for your amp that it has balanced (or bridged) outputs. So as would be the case with most amps I don’t see any problem using the SMS-1 with it. And I would expect that even in some and perhaps most cases involving amps having balanced or bridged outputs there would not be a problem; as I mentioned earlier it would depend on the internal grounding configuration of the SMS-1 and the other components that are involved. But in the absence of specific information to the contrary I would not rule out the possibility of a problem arising if it is connected at speaker-level to amps having balanced or bridged outputs. Regards, -- Al |
Does the crossover have outputs for the mids and highs? If so, even if they are single-ended, this would be worth trying. Some of the ARC amplifiers that have allegedly balanced differential inputs really don't do well with single-ended inputs (which indicates a radically poor Common Mode Rejection Ratio spec). This is so profound with some of them that if operated single ended they have lower power and much higher distortion. But if your amp is not one of those types this would be worth trying. (FWIW our amps behave the same whether the balanced or single-ended input is used.) |
