Nice. We have been discussing about the psichoacoustics approach and now we have genetics in the debate.
It could be worse .....
Components Specifications use and the Truth
- Thread starter FrantzM
- Start date
It could be worse .....
We use specs too but there is always the issue of what spec is important to the ear and which is not?
So it really becomes a study of how we perceive sound. Its become my theory that the closer we can get the gear to follow human perceptual rules, the more we can get it to sound real.
For example, the human ear uses odd ordered harmonics to figure out how loud a sound is. How loud a sound is is pretty important- IMO one of the fundamental perceptual rules. So we can't add odd-ordered harmonics. Not only does the ear find them objectionable, but it will cause the system to sound louder and brighter to the ear. This is why two amps can measure flat on the bench but one can be bright while the other not.
Loop negative feedback is known to increase odd ordered harmonics while decreaing THD overall. But since the ear is so sensitive to the odd orders, the use of loop feedback becomes dodgy. So our amps and preamps are designed to not make distortion without feedback. That is one of the reasons they are fully differential thoughout.
Bandwidth is another issue. If you don't have wide bandwidth, you have phase issues. For example in the bass, to reproduce a 20Hz signal correctly, you need bandwidth to 2 Hz (1/10th the freqeuncy to be amplified). The measure is squarewave tilt- the tilt on top of the squarewave allows one to see a low frequency problem. If you can deliver 20Hz waveforms without phase problems, you will have greater impact. The ear does not hear phase in a sine wave, but it certainly hears phase issues in frequency bands and also it is used to create a proper soundstage.
Because many of the specs were created decades ago, they frequently don't have a lot to do with the human perceptual rules, as most of that information has only began to show up since our measurement standards were put in place. This has given rise to the objectivist/subjectivist debate, as the specs simply don't reflect anything meaningful in many cases. This is why an amp that measures poorly can sound good and vice versa. IOW the specs (these days at least) represent a sort of Emperor's New Clothes- they are there to make the product look good on paper rather than make it sound better. Another way of putting this is that we frequently measure things that are not important to the human ear and we don't meausre things that are. I am hoping we will change this as time goes by. We certainly have the computing power to do it now.
Due to the human perceptual rules and the use of feedback, I had to take a good look at what is important- make the amp work with a lot of speakers, or only make it work with speakers that have a chance of sounding like real music? The measure of that of course is 'does the speaker require the amp to need feedback in order to work?' If yes, then the speaker will never sound like music due to the problems outlined above. There is more at this link:http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php
So it really becomes a study of how we perceive sound. Its become my theory that the closer we can get the gear to follow human perceptual rules, the more we can get it to sound real.
For example, the human ear uses odd ordered harmonics to figure out how loud a sound is. How loud a sound is is pretty important- IMO one of the fundamental perceptual rules. So we can't add odd-ordered harmonics. Not only does the ear find them objectionable, but it will cause the system to sound louder and brighter to the ear. This is why two amps can measure flat on the bench but one can be bright while the other not.
Loop negative feedback is known to increase odd ordered harmonics while decreaing THD overall. But since the ear is so sensitive to the odd orders, the use of loop feedback becomes dodgy. So our amps and preamps are designed to not make distortion without feedback. That is one of the reasons they are fully differential thoughout.
Bandwidth is another issue. If you don't have wide bandwidth, you have phase issues. For example in the bass, to reproduce a 20Hz signal correctly, you need bandwidth to 2 Hz (1/10th the freqeuncy to be amplified). The measure is squarewave tilt- the tilt on top of the squarewave allows one to see a low frequency problem. If you can deliver 20Hz waveforms without phase problems, you will have greater impact. The ear does not hear phase in a sine wave, but it certainly hears phase issues in frequency bands and also it is used to create a proper soundstage.
Because many of the specs were created decades ago, they frequently don't have a lot to do with the human perceptual rules, as most of that information has only began to show up since our measurement standards were put in place. This has given rise to the objectivist/subjectivist debate, as the specs simply don't reflect anything meaningful in many cases. This is why an amp that measures poorly can sound good and vice versa. IOW the specs (these days at least) represent a sort of Emperor's New Clothes- they are there to make the product look good on paper rather than make it sound better. Another way of putting this is that we frequently measure things that are not important to the human ear and we don't meausre things that are. I am hoping we will change this as time goes by. We certainly have the computing power to do it now.
Due to the human perceptual rules and the use of feedback, I had to take a good look at what is important- make the amp work with a lot of speakers, or only make it work with speakers that have a chance of sounding like real music? The measure of that of course is 'does the speaker require the amp to need feedback in order to work?' If yes, then the speaker will never sound like music due to the problems outlined above. There is more at this link:http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php
Hello Atmasphere,
No feedback or very little ..? i'm not aware of any amplifier being able to have "low"distortion without some sort of feedback ......
Regards,
No feedback or very little ..? i'm not aware of any amplifier being able to have "low"distortion without some sort of feedback ......
Regards,
Distortion spectra, which starts out low , in the miliwatt range and then go high as power increases seems to fair better than those which starts out high then lowers as power is increased, when in subjective listening test ..this is believed to happen because sounds in Mother Nature ,reflected, or transferred, by any medium, are more distorted the louder they get , as such this distortions are then heard as cues to the media, not as distortions, Like when you hear a hammer striking wood, or a jet engine roaring , They are not heard as distortions, for this reason it is believed by some, That distortions by electronic media, which follow this similar pattern are not recognized as distortions, but is perceived as being more natural sounding.
Pictured below are test graphs showing thd vs power output , you will notice a trend as to those amplifiers people find natural sounding (tubes) and those they don't, you will also notice there will be both SS and tubes with out this type of spectra that still sound good to us and do not follow the measured vs perceived mantra, so there are other things going ( there are) on and as we progress a picture will emerge, starting with that first microwatt , forward thru PSU design, bias class, noise floor, load demand and last not least topology .
Hopefully and the idea , is that we will all get a better understanding via measurements as to what is relevant to us in recognizing what it is we find pleasant sounding and why in a specific amplifier's sonic signature .
Regards,
Pictured below are test graphs showing thd vs power output , you will notice a trend as to those amplifiers people find natural sounding (tubes) and those they don't, you will also notice there will be both SS and tubes with out this type of spectra that still sound good to us and do not follow the measured vs perceived mantra, so there are other things going ( there are) on and as we progress a picture will emerge, starting with that first microwatt , forward thru PSU design, bias class, noise floor, load demand and last not least topology .
Hopefully and the idea , is that we will all get a better understanding via measurements as to what is relevant to us in recognizing what it is we find pleasant sounding and why in a specific amplifier's sonic signature .
Regards,
Attachments
Definitely, you can have low or acceptably low distortion with zero feedback, and it's hard to argue there are not perks to doing this, but more to Atmasphere's point, there are many measurements that correlate to what we hear and everyone’s design criteria is different. Square wave response and bandwidth is a perfect example that he brings up, that many don't discuss and is a valuable tool in seeing how circuits behave and seldom used as a comparative spec... I hope to listen to an Atmashere amplifier in a well setup system soon~
A.wayne, Thanks for sharing the plots.. Boy it would be interesting to get these and about 100 more products to do a real analysis and break that down into groups.
Atma-sphere, excellent post. But this begs a question: how are, we as consumers, to know which amps will pair well with what speakers. For example, it is a well known fact that your amps paired with notoriously tough-to-drive Soundlabs make SUBLIME MUSIC. Your 150 wpc or 200 wpc, or whatever the specs of your amps are, seem to be more true than claims of other amp manufacturers for some reason.
How can we know if your amp can drive other notoriously difficult to drive speakers such as MBL 101 or Magico Q5? Is it only through trial and error?
Look at output impedance vs speaker impedance, historically ESL'S tend to have fairly high impedance in the bass/ midrange area , only dipping low in the extreme high frequencies .
OTL's tend to have high output impedance unless tons of parallel output tubes , IMO would not be a good match for MBL's or MQ5, but you may like it , no one can predict such .
Regards,
OTL's tend to have high output impedance unless tons of parallel output tubes , IMO would not be a good match for MBL's or MQ5, but you may like it , no one can predict such .
Regards,
Well easier with tubes not so with SS , the distortion spectra of tubes will allow for higher levels of acceptability before reaching for the volume knob. Regardless hard to believe 0db feedback (global/nested) with acceptable levels of distortion (below 1%) ...
Regards,
Thanks. I wonder if Atma-sphere would agree with you... Many would also avoid mating tubes and stats, though, without even trying.
I would disagree , stats are pretty good with tubes , well those that have good stability ...
Regards ,
Frantz
Power amps that "start in Class A but slide into Class B" are called "Class A/B" - anything else would simply be a lie. It is not unreasonable to spec a Class A/B amp as "being Class A for the first 30 watts" if it is biased such that both sides of the output stage are carrying current up to the 30 watt level, but that needs to be made clear. The benefits of Class A operation are dubious to begin with, so it's probably more a matter of hyped marketing than a deliberate attempt to mislead in most cases... but who can say. Anything with a single-ended output (say a SET tube amp or a headphone amp with a single power FET on each channel, HAS to run Class A in order to deliver a listenable output. Unfortunately, "Class A" has pretty much devolved into an audiophile buzzword anyway. There are many products running in Class A/B that far outclass others running in Class A - co Class A operation is NOT a good indicator of sound quality. The only thing Class A operation guarantees you in a power amp is a lot of heat, a lot of weight, and a high price tag (or, in the case of those itty bitty SET tube amps, not enough power).
Solid state preamps that use discrete transistors usually run Class A; they don't use much power so there's not much downside. Preamps with ICs in them may have the ICs running Class A or Class A/B; whether it matters depends on the particular chip - they should be run in whatever mode the manufacturer specifies for best performance (the difference is about ten cents worth of parts). Tube preamps pretty much HAVE to run Class A; it would be very difficult to design one that ran differently, and there isn't much reason to.
None of this has anything to do with the term "doubling down" - which means that an amplifier delivers twice as much output into 4 Ohms as it does into 8 Ohms. Most well designed Class A/B solid state amps do that; it's simply a matter of whether the power supply can deliver enough current (same voltage, half the load, twice the power). The only significance is that an amplifier that CAN "double down" has proven that it has a nice hefty power supply, and so will probably have little trouble running low impedance speakers like Magneplanars (notorious for having a VERY low impedance at some frequencies). An amp that can't double down WILL have trouble driving Maggies and other difficult speakers.
DACMan
unless their power supply simply can't supply enough current.
Power amps that "start in Class A but slide into Class B" are called "Class A/B" - anything else would simply be a lie. It is not unreasonable to spec a Class A/B amp as "being Class A for the first 30 watts" if it is biased such that both sides of the output stage are carrying current up to the 30 watt level, but that needs to be made clear. The benefits of Class A operation are dubious to begin with, so it's probably more a matter of hyped marketing than a deliberate attempt to mislead in most cases... but who can say. Anything with a single-ended output (say a SET tube amp or a headphone amp with a single power FET on each channel, HAS to run Class A in order to deliver a listenable output. Unfortunately, "Class A" has pretty much devolved into an audiophile buzzword anyway. There are many products running in Class A/B that far outclass others running in Class A - co Class A operation is NOT a good indicator of sound quality. The only thing Class A operation guarantees you in a power amp is a lot of heat, a lot of weight, and a high price tag (or, in the case of those itty bitty SET tube amps, not enough power).
Solid state preamps that use discrete transistors usually run Class A; they don't use much power so there's not much downside. Preamps with ICs in them may have the ICs running Class A or Class A/B; whether it matters depends on the particular chip - they should be run in whatever mode the manufacturer specifies for best performance (the difference is about ten cents worth of parts). Tube preamps pretty much HAVE to run Class A; it would be very difficult to design one that ran differently, and there isn't much reason to.
None of this has anything to do with the term "doubling down" - which means that an amplifier delivers twice as much output into 4 Ohms as it does into 8 Ohms. Most well designed Class A/B solid state amps do that; it's simply a matter of whether the power supply can deliver enough current (same voltage, half the load, twice the power). The only significance is that an amplifier that CAN "double down" has proven that it has a nice hefty power supply, and so will probably have little trouble running low impedance speakers like Magneplanars (notorious for having a VERY low impedance at some frequencies). An amp that can't double down WILL have trouble driving Maggies and other difficult speakers.
DACMan
unless their power supply simply can't supply enough current.
i beg to differ, magnepans are an EASY load* even for tubes which is partly why if you were a ARC dealer back in the day you also carried Magnepan and they were distributed together almost since day one. its more like a constant load @ 4ohms regardless of frequency. i had to dig deep to find a review with JA's measurements on any magnepan that indicated otherwise. the MG3.6 barely dips to 3.3 ohms:
"The speaker's impedance (fig.1) approximates a resistive load of around 4 ohms over much of the audioband. However, there is a slight magnitude peak centered at 1.6kHz, due to the crossover between the ribbon and the midrange diaphragm. The minimum value is 3.3 ohms at 10kHz, which is not going to be problem for any good amplifier to drive..."
*pure ribbons and electrostats are another matter, original quads go down to 1 ohm and the apogee scintilla a 1/2 ohm
An oscilloscope doesn't help much; you can't see anything below about 5% THD anyway
It's really not safe to infer things from the design either - unless you understand the engineering quite thoroughly.
(Contrary to folklore, for example, feedback provides huge benefits and almost no downside - unless the rest of your design is poor.
And ten poor output devices, or ten good devices used improperly, will perform much worse than one good one,
or even one mediocre one - if the engineer understands its limitations and they don't matter in that particular application.)
The measurements are useful, but only if you understand them... and what they imply.
Unfortunately, a lot of what you get to see is marketing...
and there is an awful lot of plain old bad information out there these days.
For example, MOST solid state amps make very low distortion at anything below full power.
The THD graph is a low, almost flat line near zero until some point, where it zooms up.
The company where I work (Emotiva) makes power amps (we even usually publish the test reports if you want to see what they look like).
A particular one of our amps could be specified as
"350 watts per channel at 1% THD";
it could ALSO be specified as
"300 watts per channel at 0.02% THD".
Same amp, same graph; it's just a matter of whether marketing would rather see a higher power rating or
a lower THD rating.... which would you consider "better"?
Output impedance is one of those specs that is very misunderstood.
Having a LOW output impedance is important for two reasons:
First, it means that the frequency response of the amp won't be much affected by changes in the impedance of the load.
Since most speakers have impedances that vary widely at different frequencies, this means that an amp with a lower
output impedance will be flatter, be less affected by differences between speakers, and will in general measure the same
into a speaker as it does into a resistive load. In short, you'll be able to trust it to do what the measurements suggest it will into
real world loads. (A typical speaker may range from one or two Ohms to 50 Ohms at different frequencies.
For modelling purposes, you draw the output impedance of the amp as a resistor between the amp and the speaker.)
Second, there's this little thing called "back EMF". What that means is that a typical speaker (with a coil and magnet)
acts as both a motor and a generator. When you drive it, the current you send through it interacts with the magnet
and "drives" the cone like a motor. When the sound (a pulse for visualization purposes) stops, the cone wants to keep
moving, and the voice coil acts as a generator. The amplifier stops the speaker by shorting the output of the voice coil
(which, like if you short a generator, makes it want to stop). It does this by "sending out 0 volts".
If the amplifier's output impedance is high, it doesn't do a good job of shorting the speaker, so the speaker gets to rattle
around a bit before it stops. This is what we call "loose bass" or "sloppy bass". The number that defines how well the amplifier can
do this is called "damping factor" - which is the ratio of the output impedance of the amp to the impedance of the speaker.
Lower output impedance equals higher damping factor equals tighter bass.
Most modern speakers sound best when they are controlled tightly by the amplifier (higher damping factor).
With some really old speakers, they actually sounded better when the speaker was allowed to handle that part of things mechanically.
They sound a bit dead when you control them TOO well. Tube amps tend to have high output impedance and LOW damping factor
(a damping factor of 4 of 5 would be normal for a tube amp, 500 would be normal for a solid state amp.)
This is why speakers made when tubes rules tend to sound good with tube amps, and why tube amps tend to have
poorly controlled bass when you connect them to modern speakers.
The last piece of the puzzle is the speaker wire - ALL of it.
Damping factor is defined as "the ratio of the impedance of the speaker over the output impedance of the amplifier".
So, if your speaker was really 8 Ohms, and your amplifier had an output impedance of 0.08 Ohms, the damping factor would be 100.
But (guess what), it's a bit more complicated.
When that amplifier is trying to control the speaker, it has to "push" current through the speaker wire between it and the speaker,
AND the wire inside the speaker. (A typical 8 Ohm woofer has a VOICE COIL resistance of about 3 Ohms.)
This means that, even if the amp had a zero output impedance, and the speaker wire the same,
the resistance of that voice coil is still in series with everything (for purposes of calculating how well the
amp can control the speaker by "shorting it").
In the end, this limits the highest possible "useful damping" you can get.
The reality is this:
On a modern speaker, not designed specifically for use with tube amps, you will definitely hear big differences as the
damping factor varies between none and about 10 (where most tube amps are); you will probably hear SOME difference
up to about 50 (depending on other things); over 50, damping factor doesn't really matter.
(Remember that most tube amps range between about 2 and about 10, while most solid states are 500+.)
So the tube amp doesn't control the speaker well, and the bass sounds flabby or muddy.
Speakers designed for use with tube amps usually have more internal mechanical damping.... since they expect to NOT
be tightly controlled by the amplifier. Thus, connecting them to a solid state amp, which does control them, tends to
reduce their bass output, because they are "overcontrolled", and make them sound "dead" or "overdamped".
On solid state amps, the output impedance does indeed vary throughout the frequency band,
but it's usually high enough throughout that it doesn't really matter.
[Incidentally, with Class-D amps like the Hypex's, it's a whole lot more complicated.
As far as I know they have a pretty good damping factor, they just don't sound as good as one might hope... ]
And, a "pretty low" output impedance for a solid state amp would be around 0.01 Ohms,
not that it especially matters at numbers that high, although anything below a few Ohms would be low for a TUBE amp -
(Remember that the speaker itself is about 3 Ohms, and the speaker wire is a few tenths anyway.)
Sadly, most dealers just aren't especially knowledgeable these days.
DACMan
It's really not safe to infer things from the design either - unless you understand the engineering quite thoroughly.
(Contrary to folklore, for example, feedback provides huge benefits and almost no downside - unless the rest of your design is poor.
And ten poor output devices, or ten good devices used improperly, will perform much worse than one good one,
or even one mediocre one - if the engineer understands its limitations and they don't matter in that particular application.)
The measurements are useful, but only if you understand them... and what they imply.
Unfortunately, a lot of what you get to see is marketing...
and there is an awful lot of plain old bad information out there these days.
For example, MOST solid state amps make very low distortion at anything below full power.
The THD graph is a low, almost flat line near zero until some point, where it zooms up.
The company where I work (Emotiva) makes power amps (we even usually publish the test reports if you want to see what they look like).
A particular one of our amps could be specified as
"350 watts per channel at 1% THD";
it could ALSO be specified as
"300 watts per channel at 0.02% THD".
Same amp, same graph; it's just a matter of whether marketing would rather see a higher power rating or
a lower THD rating.... which would you consider "better"?
Output impedance is one of those specs that is very misunderstood.
Having a LOW output impedance is important for two reasons:
First, it means that the frequency response of the amp won't be much affected by changes in the impedance of the load.
Since most speakers have impedances that vary widely at different frequencies, this means that an amp with a lower
output impedance will be flatter, be less affected by differences between speakers, and will in general measure the same
into a speaker as it does into a resistive load. In short, you'll be able to trust it to do what the measurements suggest it will into
real world loads. (A typical speaker may range from one or two Ohms to 50 Ohms at different frequencies.
For modelling purposes, you draw the output impedance of the amp as a resistor between the amp and the speaker.)
Second, there's this little thing called "back EMF". What that means is that a typical speaker (with a coil and magnet)
acts as both a motor and a generator. When you drive it, the current you send through it interacts with the magnet
and "drives" the cone like a motor. When the sound (a pulse for visualization purposes) stops, the cone wants to keep
moving, and the voice coil acts as a generator. The amplifier stops the speaker by shorting the output of the voice coil
(which, like if you short a generator, makes it want to stop). It does this by "sending out 0 volts".
If the amplifier's output impedance is high, it doesn't do a good job of shorting the speaker, so the speaker gets to rattle
around a bit before it stops. This is what we call "loose bass" or "sloppy bass". The number that defines how well the amplifier can
do this is called "damping factor" - which is the ratio of the output impedance of the amp to the impedance of the speaker.
Lower output impedance equals higher damping factor equals tighter bass.
Most modern speakers sound best when they are controlled tightly by the amplifier (higher damping factor).
With some really old speakers, they actually sounded better when the speaker was allowed to handle that part of things mechanically.
They sound a bit dead when you control them TOO well. Tube amps tend to have high output impedance and LOW damping factor
(a damping factor of 4 of 5 would be normal for a tube amp, 500 would be normal for a solid state amp.)
This is why speakers made when tubes rules tend to sound good with tube amps, and why tube amps tend to have
poorly controlled bass when you connect them to modern speakers.
The last piece of the puzzle is the speaker wire - ALL of it.
Damping factor is defined as "the ratio of the impedance of the speaker over the output impedance of the amplifier".
So, if your speaker was really 8 Ohms, and your amplifier had an output impedance of 0.08 Ohms, the damping factor would be 100.
But (guess what), it's a bit more complicated.
When that amplifier is trying to control the speaker, it has to "push" current through the speaker wire between it and the speaker,
AND the wire inside the speaker. (A typical 8 Ohm woofer has a VOICE COIL resistance of about 3 Ohms.)
This means that, even if the amp had a zero output impedance, and the speaker wire the same,
the resistance of that voice coil is still in series with everything (for purposes of calculating how well the
amp can control the speaker by "shorting it").
In the end, this limits the highest possible "useful damping" you can get.
The reality is this:
On a modern speaker, not designed specifically for use with tube amps, you will definitely hear big differences as the
damping factor varies between none and about 10 (where most tube amps are); you will probably hear SOME difference
up to about 50 (depending on other things); over 50, damping factor doesn't really matter.
(Remember that most tube amps range between about 2 and about 10, while most solid states are 500+.)
So the tube amp doesn't control the speaker well, and the bass sounds flabby or muddy.
Speakers designed for use with tube amps usually have more internal mechanical damping.... since they expect to NOT
be tightly controlled by the amplifier. Thus, connecting them to a solid state amp, which does control them, tends to
reduce their bass output, because they are "overcontrolled", and make them sound "dead" or "overdamped".
On solid state amps, the output impedance does indeed vary throughout the frequency band,
but it's usually high enough throughout that it doesn't really matter.
[Incidentally, with Class-D amps like the Hypex's, it's a whole lot more complicated.
As far as I know they have a pretty good damping factor, they just don't sound as good as one might hope... ]
And, a "pretty low" output impedance for a solid state amp would be around 0.01 Ohms,
not that it especially matters at numbers that high, although anything below a few Ohms would be low for a TUBE amp -
(Remember that the speaker itself is about 3 Ohms, and the speaker wire is a few tenths anyway.)
Sadly, most dealers just aren't especially knowledgeable these days.
DACMan
I am no guru, so I'm not sure whether you want my opinion.
If I knew how to use an oscilloscope, I would probably do so when testing amplifiers. Unfortunately, I can only go by the specs provided and JA's measurements. I've tried a lot of different amps and I keep score of the measurements and compare with what I hear. In my case and with my speakers, output impedance is one of the most relevant specs. Unfortunately, there's no standardization. Is output impedance measured using standard size speaker cable or at the amp's binding posts? Is output impedance the same throughout the frequency spectrum? Does it vary with load or power output? At the end of the day, I can only decide based on listening. Having said that, specs CAN be useful in winnowing down choices.
I don't think output impedance is the ONLY spec that matters. But, it really can help to narrow things down. I have yet to hear an amp that sounds remotely good in the mid-bass with my speakers with an output impedance more than .2 ohm. However, I've heard Hypex class D which has ultra low output impedance and it sounded mediocre in the HF. Some of these things can be inferred from the amp's design; How many output devices? How much feedback?
I was recently looking at a solid state amp where the dealer website claimed a super low output impedance (significantly less than .1 ohm). I then went to the manufacturer's website which claimed a super high output impedance (.4 ohm). The dealer admitted that the manufacturer's website spec WAS correct, not his. The dealer tried to convince me that a .4 ohm output impedance was very low for a solid state amp. That's absurd and I told him so.
It seems no Devialet owner is reading this thread.
AFAIK this amplifier has state of the art specifications - if I was going to buy an amplifier just by specifications or measurements I would get a Devialet. I hosted one for a few days. It sounded impressive, but unhappily not my preference for my system.
Dacman,
The benifits of class-a is dubious .. or did you mean to state the amount of class -a as oppose to class - a itself ..
Regards ,
The benifits of class-a is dubious ..
or did you mean to state the amount of class -a as oppose to class - a itself ..Regards ,
i beg to differ, magnepans are an EASY load* even for tubes which is partly why if you were a ARC dealer back in the day you also carried Magnepan and they were distributed together almost since day one. its more like a constant load @ 4ohms regardless of frequency. i had to dig deep to find a review with JA's measurements on any magnepan that indicated otherwise. the MG3.6 barely dips to 3.3 ohms:
"The speaker's impedance (fig.1) approximates a resistive load of around 4 ohms over much of the audioband. However, there is a slight magnitude peak centered at 1.6kHz, due to the crossover between the ribbon and the midrange diaphragm. The minimum value is 3.3 ohms at 10kHz, which is not going to be problem for any good amplifier to drive..."
*pure ribbons and electrostats are another matter, original quads go down to 1 ohm and the apogee scintilla a 1/2 ohm
Correct in the world of ribbons , Maggie's are easy peasey ....
Regards
Dacman,
The benifits of class-a is dubious ..
Regards ,
DacMan clearly stated that the benefits of Class A operation are dubious which I find to be an interesting comment. Maybe we should take his statement about Magnapan speakers being a very difficult load for an amplifier to drive in the same light as the Class A statement.
I also don’t believe his statement that “most” well designed Class A/B amps double down their power as the impedance is cut in half. Many amps come close, but they don’t actually double their power output because the power supply just can’t supply the necessary juice. Take a look at the specs of “most” well designed Class A/B amps again and tell me that most of them truly double down in power output. They don’t. And close doesn’t count except in horseshoes and hand grenades.
Similar threads
 | Steve Williams Site Founder | Site Owner | Administrator |  | Ron Resnick Site Owner | Administrator |  | Julian (The Fixer) Website Build | Marketing Managersing |