Atmasphere, technically there is no such thing as no feedback in an electrical circuit and hence a zero feedback amplifier, can you quantify your statement ? Loop negative feedback is what I was referring to. I have no issues with degenerative feedback as it occurs in real time. Foster_9, with traditional SS amplifiers using feedback and operating class AB, you are not going to find a lot of difference in the sound. So older amplifiers are indeed an option, but making sure the electrolytic caps that occur in the circuitry are actually good will be important. In this regard the HK Citation 11 and 16 were decent amplifiers- sounding very much like many modern amps for a fraction of the cost. But you had better know a technician that can service them out, as their filter caps will be shot by now. Another amp that seems to stand out is the BEL amplifier. It was a well-made amplifier whose designer died too soon. |
Weseixas: Luxman B-1000F monos Price: $55,000/pair- well yes, they are high current and new... I'll give you that. |
Luxman:
http://www.stereophile.com/content/luxman-b-1000f-monoblock-power-amplifier |
There's a Marantz SM-11 power amp in the listings right now for $2K even (original list $4600). 110W into 8 ohms, 220W into 4 ohms, 101dB S/N ref 1W into 8 ohms. This seems to meet the OP's requirements. I recently acquired one of these myself, along with the matching preamp, and am very happy with it.
No knowledge of or connection with seller, etc |
I admired your effort. I do wish you a speedy and pain free recovery. |
@Unsound... That's because I've been laid up and bored to tears after knee arthroscopy. |
I'm not that familiar with your speakers and didn't take the extra time Ngjockey took took to consider system compatibility. My suggestion was merely based upon your posted request. |
That seems like quite an impedance swing from the Cary. I'm not sure I would want to be married to it. |
Thanks Unsound and Ngjockey. Unsound, at the time you referenced the Threshold it had a Sale Pending- I saw it before and it was Sale Pending for quite a while. I would likely have jumped on it.
Ngjockey:
From Stereophile's mearsurements of the SLP 05:
"The SLP 05's output impedance is specified as a usefully low 400 ohms. However, I got significantly higher values for the unbalanced output of 1500–1600 ohms in the midrange and treble, rising to 3400 ohms at 20Hz, with similar if slightly lower figures for the balanced output." |
Assumed you had some kind of passive. The 400 ohm Zout of the Cary should not be a concern even for an amp with 10Kohm Zin.
The 3.5 ohm minimum (4.25 - ultimateavmag) of the speakers isn't that critical either, unless it's coincides with a big phase angle, which it doesn't on those. In fact, they tend to be a little midbass heavy, peaking with the minimum impedance at about 90 Hz. Yes, they benefit from the bass control of a strong amp but, along with the titanium tweeter and some high frequency fluctuations (sibilance?), I think you're going the wrong way. Although, you could do much worse than the ones mentioned. |
I hate to repeat myself, but a Threshold S500 with new caps and a re bias appears to be just what your looking for. Though Threshold made very well received pres, many used them with tubed Audio Research and some used tube c-j pres. If memory serves me correctly the input impedance was 75 KOhms. 250 Watts per channel 8 Ohms, 500 Watts per channel 4 Ohms. 20% Class A bias into 8 Ohms. Class A bias halving as power doubles into 4 Ohms. |
I appreciate the discussion of amplifier topology and performance. It's informative for electronics novices (like me).
An amp with high input impedance is important
not "dry" or "lean"
lively with bass weight and clarity.
An issue is my Cary SLP 05 preamp has fairly high output impedance into the lower frequencies. My speakers are Mirage OMD 28 /Impedance 6 Ohms nominal /3.5 Ohms minimum 87db efficient /Crossover Point 550 Hz and 2.5 kHz |
Irv,
We have taken Krell's and re-biased them to 10% of their original class-a bias after service and recapping and the difference is astronomical.
Anyone with an older Krell KSa 200/300 et al series should give it a try, no more 1400 watts being pulled at Idle .
regards |
Unsound ,
I won't disagree, i can only express my involvement at many levels and again iterate that I find high Class-A Bias amplifiers not to sound like live music IMO, tending to be soft and laid back ( gentle) and nothing like the recording or live music, of course there are exceptions, but for the most part, , yes, this has been my observation.
Again speaker topology play's a big role here and of course there are those that prefer soft and gentle to
"real " and if you have a speaker which is forward sounding or "bright" it will have an issue on anything but Class-A.
Class- D have what i speak of in spades, unfortunately other issues with that topology leaves it a bit dry making ClassA/AB still the best output stage topology IMO.
regards, |
Unsound says: Well Weseixas, I think we part ways on your appraisal of Class A. More often than not (but not always), I've found the more Class A the better the sound. The only problem is many so called pure Class A amps either don't have enough power for the the speakers I prefer, or the cost is beyond my budget. ...And of course, the issues of size heat, efficiency, etc..
-----------------------
Is predictive bias-level adjustment a la Krell and Levinson enough, or must it be pure, brute-force Class A operation only? |
Well Weseixas, I think we part ways on your appraisal of Class A. More often than not (but not always), I've found the more Class A the better the sound. The only problem is many so called pure Class A amps either don't have enough power for the the speakers I prefer, or the cost is beyond my budget. ...And of course, the issues of size heat, efficiency, etc.. |
Not a fan of the VK500 or The Belles, Threshold S500 .. Yes! |
Irvrobinson, he wants something that doubles power as you cut the load impedance in half. But I don't like feedback (human hearing perceptual rules meow meow...)
-03-18-11: Atmasphere
Atmasphere, technically there is no such thing as no feedback in an electrical circuit and hence a zero feedback amplifier, can you quantify your statement ?
regards,
|
Looking down the list for my interpretation of your electronic/price/weight criteria:
Sale pending: BAT VK500 (105 lbs), Threshold S500
Used: Belles 350A Reference
New: W4S ST-1000 |
Irvrobinson, he wants something that doubles power as you cut the load impedance in half. But I don't like feedback (human hearing perceptual rules meow meow...)... |
Because it shows a deficiency in the power supply and hence topology being used IMO, nothing to do with speakers.
Why spend thousands on an amplfier that has a mediocre PSU and Amplifiers that do so always sound unmusical IMO, same with high bias Class-A ( SS) amplifiers, they give up life for smoothness and is usually preferred by those not familiar with recordings of live music and or poor speakers.
Regards, |
Weseixas, If some have speakers that don't operate within those impedances, why would it matter to them? |
Atmasphere threw me off with that Ayre recommendation. :-) |
Unsound, I did miss the $2K limit. That makes it difficult... and my previous post useless. ;-) |
I can't for the life of me understand those that spend thousands on an amplifier that shows current limiting and power supply issues going from 8-4 ohms.
Ahhhh bwoy ... |
Irv, I guess you didn't see his $2K budget limit? |
Accuphase, is often overlooked, very good amplifiers...
regards, |
Foster-9, if you're looking for used amps there's a lot of selection:
Any Krell amp. There are several Evolution 302s available, as the 302e just came out. The older FBPs are great too. Any higher power than a 300-series amp just seems like overkill to me.
Any Levinson 33x or 43x-series amp, or any later models. My one caveat with Levinson is that service can be complex and expensive. My 334s have been bullet-proof, but in current dollars remember that even the low-end 334s would likely be $10K each.
The Parasound JC-2. These have always tempted me, and they are occasionally available used. They were $3K each when they were introduced in 2003, but now they retail for $4500 each.
Bryston, Ayre, Pass Labs, Classe, Coda, Boulder... mostly North American stuff, since high current amps seem to be a largely western hemisphere thing. Of course, these are all very expensive amplifiers. For used equipment there's a good economic argument for Krell & Levinson, simply because there's an active market and these amps retain high resale values. Any of them will be costly to service.
New high-current amps that claim to double power with halved impedance seem to start in the $5K range and go up. Way up. Krell and Levinson seem to think $20K amps are mid-range nowadays. Mostly I think what we're paying for is fancy aluminum casing work and Swiss-watch-class build-quality in a North American factory. (Most of the components will be imported.)
IMHO, the most important spec for a properly design solid state amp these days (well, at least the one I look at first) is signal-to-noise ratio. Almost everyone has low distortion and high power, but noise is a different story. Most amps are rated at something like -100db below full power, and since they usually have 25-30db of gain we're talking in the range of -70db of noise, sometimes worse, below 1 watt of output, which can be audible with some speakers, especially if the frequency distribution of the noise amplitudes include a good bit of output below 20KHz. Maybe it's just me, but I find a dead-quiet background attractive. The latest Krells are very low noise, for example, the older Levinsons less so. |
Here's my vote: a zero-feedback transistor amp that behaves as a voltage source, from Ayre. http://www.ayre.com/mxr_details.htmInput impedance is very high- any preamp will work with it. |
Fitting your criteria, I really liked the Moon W5 in sound, build quality, and bench performance when I had one on loan. The Bryston 3BSST is also a nice amp.
The McIntosh MC7200 might also work, but their input impedances are usually like 22k. BTW it's a high current amp with a low output impedance, which can't be inferred from it's specs that don't "double down". It's continuous power output into lower impedances is limited by the power supply . . . but that's not really a criticism, as there's still a ton of power available, and lots of dynamic headroom. |
Yes Atmasphere that was a typo. I meant an amplifier input impedance of 50k Ohms - 100k Ohms. |
If you decide to go for an inegrated, the Krell 300i or 400i if you can squeeze it could be an interesting choice.
I have heard these and was quite impressed running both full range Martin Logan and Focal Profile speakers.
Krell is known for providing a nice full low end and having excellent clarity and resolution. That is what I recall hearing as well. Extremely transparent with holographic like imaging as well, at least in the big, open and airy display room that I heard it in. |
Audio research has some SS amps that come up in that price range that meet the criteria as I recall.
I strongly considered these when looking in a similar price range because AR is primarily known for its tube gear and their SS amps are seemingly designed to match well with higher impedance tube pre-amps and were generally well received.
If I had not decided to splurge as I did on the BCs, one of the ARC SS amps was probably next in line for me especially in that I already owned an ARC tube pre-amp. |
Foster_9, I think there was a typo in your last question- the input impedance you are looking for is 50K ohms (50,000 ohms) or 100K ohms.
Most transistor amps, FWIW, seem to be closer to 10,000 ohms input. |
Caveat: I know nothing about the seller:
http://www.audiogon.com/cgi-bin/cls.pl?ampstran&1304255043&/Threshold-S500-Jon-Soderberg-U |
Well, I suppose the original answer from my thread was answered. Can any of you electronics experts recommend a high current amp? That
doubles down
100 watts minimum (200 watts or more preferable)
input impedance- highish 50-100 ohms (for a tube preamp)
quality sonics (known for clarity, powerful bass, neutral, transparent, without leanness)
$2k or less on the used market |
The first is simply the lack of citation of any historical or scholarly references, or measurement data. This need not be . . . I think that Atmasphere could actually support his design choices much better by a properly researched, documented, and peer-reviewed paper on the subject. Kirkus, thanks for your comments. I can produce a lot of data on this, but FWIW the paper I have often linked to is designed to be easy to read, and also easily understood by someone who does not want to go through mathematical proofs that they may well not care about. However I take your point so perhaps a second document that is a bit more in-depth? The second is the interchangability of pespectives on amplifier output power ratings, output impedance, and circuit design, specifically the use of negative feedback. Obviously, Atmasphere prefers Class A OTL designs with little loop feedback . . . and the consequences are very poor power efficiency and a high output impedance, both of which are key factors in the rated power outputs of Atmasphere amplifiers. I should clear something up here. Yes, this paper is on our site but it does not specifically point to our gear as the solution. I see this as a bigger issue! I have had a few people accuse me of making this stuff up- what I suggest to them is use Google to look for older Fisher amplifiers with the variable damping control (it has a spot on the dial labeled 'constant power'). I don't go for feedback simply because I've never seen it sound right (I use master recordings as a reference FWIW). Audiophiles are always looking for that 'difference' in gear that is responsible for it sounding like music rather than electronics. I have run into plenty of info on the subject, from such luminaries in the industry as Norman Crowhurst and Nelson Pass and it seems redundant on my part to restate that which has been part of the lexicon now for over 50 years. The wholly illogical part is the inherent value judgement against amplifiers that have clipping-power-versus-impedance characteristics that are different from Atmaspheres'. Because an examination of this data gives ZERO information about how much current an amplifier will produce, what its output impedance is, or the amplitude of any distortion products in its output. Again, this is not just about the amplifiers with which I am associated. You will find similar characteristics in SETs and P-P tube amps that feature little or no feedback. Contrast that against the Wolcott, a tube amplifier that behaves as a Voltage source, and the point is made in better contrast. But there are SS examples of zero feedback designs which I have often mentioned and admire. With regards to why I eschew loop negative feedback, which I regard as a crucial issue, to restate myself: feedback adds odd-ordered harmonic distortion to nearly any (traditional) tube or transistor design and it is very easy to prove that our ears use odd orders to determine the volume of a sound (I can provide a simple test scenario that almost anyone with test equipment can perform to prove this). Essentially, a fundamental rule of human hearing is being violated in order to reduce (apparent) distortion on paper and to reduce output impedance. Its not coincidence that feedback affects distortion the way its does and we are able to hear its effects the way we do. Regarding distortion, FWIW our gear makes primarily the 3rd harmonic and is absent of the even orders on account of cancellation throughout the circuit, due to its fully differential topology. Now I think it is understood that I prefer tubes, but the truth of the matter is I would rather work with transistors. They are a lot less work to build than a good tube amp! So far I've not got transistors to sound right, and I have yet to hear a transistor amp that does. Being in the industry, I've had plenty of opportunity to hear a lot of amps- it comes with the territory. We can write that off to preferences, but there is enough standing evidence and literature to the contrary (IOW, that there is more to it than preferences) without *my* input. |
When I was looking at these kinds of amps for my rig, I looked at power ratings into various loads and specs indicating current delivery capability explicitly. In general, the higher current capable amps seemed to correlate pretty well though not exactly with the ability to at least mostly double down. I recall amps with higher current delivery capabilities almost always did this better at least than those indicating low current in general.
I also tending to look for higher damping factor to go along with this for my particular speakers.
This approach has worked out well for me.
I had a low current, high power 360 w/ch (to 8 ohm) carver m4.ot amp prior to a Musical Fidelity A3CR that delivered 120w/ch. The MF sounded more balanced with my "current hungry" speakers than the Carver, though the Carver could go usably louder.
The BC monoblocks I have currently raised the power level level to 500w/ch and also promised good current delivery, doubling down as well based on specs.
The results were exactly as expected. Good tonal balance plus ability to go louder and clearer. Mission accomplished! |
Ooops, Al, you're correct. Didn't see the 4-ohm bit . . . blasted eyes! |
But to comment on the thread . . . this is some REALLY well-trodden ground. Please see: http://forum.audiogon.com/cgi-bin/fr.pl?aamps&1258580057I have two main points of contention with Atmasphere's "white paper" to which he frequently links. The first is simply the lack of citation of any historical or scholarly references, or measurement data. This need not be . . . I think that Atmasphere could actually support his design choices much better by a properly researched, documented, and peer-reviewed paper on the subject. The second is the interchangability of pespectives on amplifier output power ratings, output impedance, and circuit design, specifically the use of negative feedback. Obviously, Atmasphere prefers Class A OTL designs with little loop feedback . . . and the consequences are very poor power efficiency and a high output impedance, both of which are key factors in the rated power outputs of Atmasphere amplifiers. The wholly illogical part is the inherent value judgement against amplifiers that have clipping-power-versus-impedance characteristics that are different from Atmaspheres'. Because an examination of this data gives ZERO information about how much current an amplifier will produce, what its output impedance is, or the amplitude of any distortion products in its output. So to answer the original poster's question . . . there are plenty of high-current amplifiers on the market. However, you can't tell which ones they are by examining the clipping-power ratings into various load impedances. |
|
I was listening to a nuclear "expert" from a well recognized American University explain on CNN a few days ago early on in the Japan nuclear fiasco why theoretically there was nothing to really be worried about with the troubled reactors in Japan.
These reactors had containment structures, no problem!
So much for that theory....... |
Thanks Kirk. But note that Irv specified a 40Hz impedance of 4 ohms, so I believe that my indication of 50W (rms of course) at 40Hz was correct.
Also, I think that when you referred to 40V and 20V "peak-to-peak," you meant to say "peak." The 100W figure, presumably rms, corresponds to 28.28Vrms into 8 ohms, which would be 40V peak, or 80V peak-to-peak.
Dividing by two, to reflect each of the two frequency components of equal amplitude, whose peaks will add in phase at some instants of time, we have 14.14Vrms (equivalent to 20Vpeak or 40Vpeak-to-peak), which equates to the 12.5Wrms into 16 ohms and 50W into 4 ohms that I stated.
Best regards, and thanks for spotting the "summons." :-)
-- Al |
interesting, but unfortunately, simplified theoretical scenarios are not very enlightening regarding what really matters playing real music.
Having a well made amp that is in no risk of breaking a sweat in practice is simply one of the best and simplest strategies to pursue in putting together a system. The actual benefits may vary, but it is an insurance policy at worst.
Few other decisions in audio can be made this easily, so doing it provides a firm playing field for mucking with all the rest as needed. |
Ooooo . . . I've been summoned, like Notorious B.I.G.! http://www.southparkstudios.com/clips/155324/the-ghost-of-biggieActually Al, you're correct save a small arithmetic error. A "pure voltage source" amplifier that clips at 100W into 8 ohms of course puts out a maximum of approximately 40 volts peak-to-peak before clipping, regardless of the input waveform or load impedance. So for the combination of two equal-amplitude sine waves at 4KC and 40C, that's 20V peak-to-peak for each before clipping, or 14.14VRMS each . . . corresponding to about 12.5 watts RMS at 16 ohms, and 25 watts RMS at 8 ohms, or each at 1/4 the rated power like you said. To some, these numbers might seem like a large amount of "loss", but this waveform into even a low-sensitivity domestic loudspeaker would be absolutely ear-splitting (and probably tweeter-frying in short order). |
there are more manufacturers here in the US of vacuum tube audio products than there was in 1958! - Atmasphere
Yeah, but i wouldn't hold it against them, it's their use of carburetors that gets me... :)
regards, |
03-15-11: Atmasphere
Why not ask what the relationship is between doubling power and how your ear/brain system hears? The short answer is that you get flatter frequency response, but only with certain speakers. This comes with a price- distortions that the ear is extremely sensitive to. The ear hears these distortions as a variation (coloration) in frequency response! So in a way, you can't win with the explanation of flat frequency response.
- Atmasphere
LOL .. Deja vu Ralph ? |
You can get the exact same current delivery for a given load without the expense of an amp that doubles its power when the impedance is halved. It's true that such an amp, depending on its power capabilities, could accomodate a wider range of speakers, but in general it's unnecessary.
Which would you prefer, a 250 watt amp into 8 ohms that doubles into 4 ohms or a 600 watt amp into 8 ohms that produces 900 watts into 4 ohms? -03-14-11: Bob_reynolds
Errr ...ahhhh.... Hmmm.. the one that doubles thank you ...
regards,
|
So, are you saying here that you have a tube amp in your future?? :)
-------------
I can't imagine it. ;-) But after reading your website and reading so many of your posts I wish it wasn't such a PITA to listen to what your amps, which have a design I wouldn't normally consider, would sound like compared to my Levinson amps. Unlike properly designed speaker cables, power cords, and the like, I suspect there could be audible differences, though I more strongly suspect that these differences would be coloration, not greater accuracy. Nonetheless, even a curmudgeon like me occasionally succumbs to curiosity. |
Yes, factor in the ability to handle transients as well as the more macro dynamic/loudness aspects and the case for making sure your amp does not break a sweat doing it's job one way or another goes way up.
I'm not an expert on amp design by any stretch, but what I do know based on experience and reading tells me in my gut that this is the right approach. |
