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In Reply to: EAR/Yoshino 834T w/ Maggie 3.6’s posted by saltyflies on March 14, 2007 at 12:13:39:
Neither the referenced review not the EAR/Yoshino site give a clue about the output impedance. I expect it is low, but exactly how low and over what frequency spectrum are up to the skill of the designer.I like the idea of using a high rail voltage and transformer coupling. This will overcome the crossover distortion problems with complementary transistors direct-coupled to the speaker, but at the expense of limiting the audio resolution with the transformer core magnetization response at the zero magnetization crossing. Transformers can be made to perform very well within this limitation. It is not clear that transistors can.
Follow Ups:
Hi Al, hope all is well. I agree there’s more to it than the wpc ratings, but don’t recall reading your previous thoughts on the effects of output impedance or more than likely didn’t grasp it if I did. If you respond to Dr. Jazzs’ questions, can you do it in laymen terms.
ALIs there a relative range of output impedance to look for ? Or a ratio in relation to the amps power or the speaker's sensitivity or impedance ??
For example:
my amp : Out Imp = 0.005 ohmMG 20.1s: Sensitivity 2.828v., 500Hz, 86dB @ 1 Meter
Impedance 4 OhmsHow does cable length affect this output impedance seen by the speaker ?? Does the increased resistance also increase the impeadance seen by the amp.
thanks
Some amps have their damping factor specified, based on a measurement at some low frequency where the feedback loop is well-behaved. The "damping factor" (DF) is defined as the ratio of load impedance to output impedance.DF = Zload/Zout
It is incorrect to assume that a very low output impedance determined by this definition and the specified number for DF holds true for all frequencies where the speaker needs electrical damping, however. Amps that use feedback have a feedback time delay that modifies the effective output impedance at higher frequencies. If the speaker is a multi-way design that depends on amplifier damping at higher frequencies (such as my Magnepan MG-20s), then the specified numbers may not apply to the speaker requirements.
You can also calculate how much the speaker cable resistance degrades the specified damping factor as seen by the speaker, by just adding it to the amplifier output impedance in the above equation. The speaker cable resistance is small compared to the speaker, so the amp will not be affected by it.
What this means in practice is that we cannot depend on published specifications, either for power or output impedance (or damping factor) to determine the best amps for our speakers. We want the best sound possible within our budget, but we still have to try the amps with our own or similar speakers. IME, Maggies need amps with very low output impedance across the audible frequency range, not just at low frequencies. Such amps will have physically large power supplies in most cases, but not all amps with large power supplies will have low output impedances over frequency. It really is up to the skill of the designer to make an amp that works well with Maggies.
Thanks ALI guess I was trying to find a way to help me choose smaller power rated amps (cheaper usually) to audition that still produce enough current to control the big maggies.
I buy just about everything used, so I don't like to go and waste the dealors time - I have one dealor that lets me listen when he's not busy (he knows my intentions) but he only carries Audio Research, Accuphase, Sim Audio & Parasound.
I want to try Ayre, Pass, Mark Levinson, maybe VTL, so the only way is to buy and sell if I don't like it (which I try not to do).
So I have been reading up to help trying to make the first choice work. Planning to change to fully balanced and probably add Ayre 1xe for the top half and use my big Cal Audio for the bass. Eventually add DEQX as active crossover.
I asked about cables because I do have to use 25 ft runs right now due to young kids in house. I went with Synergistic Research Alpha X2 Active based on a live audition over Harmonic Tech, Kimber Cable, & Nordost at home.
Do you feel the "active" signal is all gimic, or will it truely help reduce RFI ??
I also wonder with the big maggies how much the longer run is making the amp work harder.
Thanks Again
AL
It will reduce the effective damping factor seen by the speakers, and, IME, take away some subtle palpability that the Maggies can deliver in the right setups. The amps will be relieved of some damping duties, so they will work less hard. This is likely to be a small change for any reasonable cable resistances, however.If you can't audition the amps in your setup, then this forum is one place to go for information about amp/speaker matching. You can also look at the raw weights of the amps: within a power and circuit class, the bigger the power transformer, the better. None of these are guaranteed methods to find the best amp for your setup, however.
I'm not clear on your question regarding "active." If you mean active crossovers, I don't have experience with them, but distrust them because of the extra gain stages, power supplies, and connection points they require. They will increase RF noise and susceptibility to RF noise degradation.
AlActually I was referring to Active Shielded speaker wires, but now you have two points I would ask about.
1) my speaker cables are both passive and Active Shielded speaker wires (http://www.synergisticresearch.com/index.php?PageID=70) -- do you think this "active" charge really helps reduce RFI introduction into the cables - or is this a gimic ?? Would not the transformer that plugs into the wall seperately near the origin of the wires from the amp end not create more RFI in the air around the system ??
2) "If you mean active crossovers, I don't have experience with them, but distrust them because of the extra gain stages, power supplies, and connection points they require. They will increase RF noise and susceptibility to RF noise degradation. "
Most seem to really disreguard the passive crossovers of all maggie lines and suggest adding the active crossover. One of my thoughts with this has also been what about the added wires to, inside, and out of the active system ... Are they as good of quality as the 20.1s passives ?? From what I have read, I guess getting the crossover "parts" in the system BEFORE the amp can improve the amp / speaker interaction ?? (in my layman's terms). Any thoughts ??
Also, the active crossover is needed to balance the gain if two different amps are used.
Thanks
Sorry I did not think about active shielded speaker cables. What I know about this is mostly second-hand, as a good friend of mine designs and makes his own active cables. My own speaker cables are damped with carbon fiber, which is a weak sort of shielding, and with dynamic loading. I do use actively-shielded power cords.The DC bias in active cables makes the wire insulation more linear as a dielectric, but also can make it microphonic. The shield electrode supports the DC bias as well as shields against external noise. The problem with the shield is that it supports RF resonance modes of its own and with the internal conductors. These resonances can make RF noise problems worse unless the cable design includes damping mechanisms. I don't know if Synergistic Research cables include damping mechanisms in their designs.
Shielding also increases the total capacitance of the cables. This might present a problem with some amps, where it could drive them into instability. The shielding is not likely to be effective against magnetic fields. Therefore, its main use in speaker cables appears to be to support DC bias to make the insulation behave more like a perfect dielectric. If you have ever compared PVC to Teflon insulation, you will know that this is not a small benefit.
You are correct that a wall-wart bias supply is a possible entry path for RF noise. I don't think you can use batteries with these cables. The power connection and feed wires for the bias supply have to be designed with care to suppress RF noise carried on the house power wiring.
As for active crossovers, the main benefit is to allow direct coupling of the amps to the speaker elements. The direct-coupled amps will damp the speaker elements outside their operating ranges, while some of the Magnepan passive crossover designs prevent adequate out-of-band damping. I modified my MG-20 passive crossovers to include R-C shunt elements at the outputs of the bass panel low-pass filters, and this made a definite improvement. The stock design has a series inductor at the output, so higher frequency resonances in the bass panel cannot be damped by the amplifier.
The main draw-back, as I said before, is the additional active electronics and cabling required to implement the crossover. Magnepans can be tweaked to be very revealing speakers, and would easily reveal the distortion and noise added by the active crossover, IMO. Proponents of active crossovers always wave this argument away. I simply don't know if an active setup can be made to be as natural-sounding as a teaked passive setup.
hello Al Sekela,thanks for your great work.
I need help about RC network and you are the expert.
can you mail me please (impossible for me with your optinal E-mail Preference )Thanks,best regards,
:)
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