Amplifiers perform audibly differently under different speaker loads?

[Phelonious Ponk]

The actual frequency response and distortion spectrum at least.

Which should be easily demonstrable and...well, I'm a bit shocked, frankly, that some of you guys just seem to just accept this as if it is no biggie. It strikes me as extremely problematic. Manufacturers have worked for decades to reduce distortion, drop noise floors, etc., knowing that once you actually hook their amps up to speakers all bets are off? I would think the best amp builders would be busting their patooties to solve this problem and tooting their horns, complete with charts and graphs and paragraphs on the back explaining each (forgive the 60s hippie reference) every time they made an improvement. One thing is for sure -- if it's frequency response and distortion spectrum, at least, and it's audible? It's measurable. Why would the better magazines not be doing these measurements when they review amps, across a range of speakers representing a range of loads, so they could make informed recommendations regarding how to best use the amps they rave about? If the XYZ Extraordinaire is clean, quiet and linear driving Magicos but struggles with the upper midrange, generating a fatiguing harshness when wired up to Revels, wouldn't that be critical information that would be part and parcel of reviewing? And wouldn't measuring, at least the basics of noise, FR, distortion spectra, across multiple loads be the very heart of creating system synergy?

You're painting a picture of a loyal hobbyist market spending tens of thousands of dollars on their gear, and being very poorly served by their experts, their press and their suppliers.

I'm not sure I believe it. I know I don't want to. Something is terribly wrong with this picture.

Tim

 

[treitz3]

If the XYZ Extraordinaire is clean, quiet and linear driving Magicos but struggles with the upper midrange, generating a fatiguing harshness when wired up to Revels, wouldn't that be critical information that would be part and parcel of reviewing?

One would think even though I don't recall ever seeing this in a review before. Just think about how many separate reviews would have to happen with just one amplifier if this were to be the case. Besides, what would you choose as a load. A 2 ohm nominal load or 4? Or 4, 6 and 8? Then after that was decided, what would the requirement or expectation be for how low that nominal load dips down too? Even though you present a good point and it would be nice to include such observations in a review, I don't think this will ever happen.

Tom

 

[Phelonious Ponk]

OK, this is better. From Don's post on the technical forum...thanks Don --

The first amp is SS with 0.1 ohm output (damping factor of 80) rising to about 1 ohm (DF=12.5) at 20 kHz. This mimics the way a lot of amplifiers behave with rising output impedance with frequency. The second amp is a tube amp with 0.8-ohm output (DF=10) rising to about 4 ohms at 20 kHz (DF=2; this is about as bad as I have measured in the primordial past).

Radically different amplifiers, very subtle variations under speaker load. Correct me if I got this wrong, Don, but I think I read that the most dramatic result was a 3 dB peak at 20khz? I know I'm not going to hear that.

Don -- Can you hear this? I don’t know, but in a careful side-by-side test you might.

Indeed, someone might. The young daughter of an audiophile perhaps. This sounded really bad for a bit there. It appears that it may just have been a bit of a tempest in a teapot.

Tim

 

[Phelonious Ponk]

One would think even though I don't recall ever seeing this in a review before. Just think about how many separate reviews would have to happen with just one amplifier if this were to be the case. Besides, what would you choose as a load. A 2 ohm nominal load or 4? Or 4, 6 and 8? Then after that was decided, what would the requirement or expectation be for how low that nominal load dips down too? Even though you present a good point and it would be nice to include such observations in a review, I don't think this will ever happen.

Tom

Yeah, it would be cumbersome to do it comprehensively, but if it were the kind of ubiquitous problem, creating the kinds of dramatic distortions that I thought I heard people reporting, I'd at least expect a pub like stereo review to test each amp against 3 - 4 pairs of popular, broadly representative models, as in "The XYZ Extraordinaire proved clean, quiet and linear driving our Magicos but showed a 6 dB hump from 1khz to 2.5khz driving our Revels and performed significantly below spec for IMD when we hooked it up to our Wilsons." Too much to ask? If this were the problem I thought I was reading about a couple of hours ago, no, we should expect no less. Fortunately, it appears to be a very small, if audible, issue.

Tim

 

[treitz3]

Eh, with certain combos perhaps. With others, not so much.

Tom

 

[ack]

Don, thanks, nothing surprising here - all as expected. It would be interesting to repeat with SS amplifiers with much higher damping factor, >1000; and also with an impedance dip in the midrange, or a bass rise which is pretty common in some speakers

 

[DonH50]

Don, neat work. And thank you for your time.

However, what were you plotting in db on amplifier output? Voltage?

Transfer function from the ideal input (a perfect amplifier, in this case an ideal voltage source) to the amplifier's output terminals. A perfect amplifier would be a flat line at 0 dB across all frequencies; anything else is less than perfect.

An interesting aside (at least to me and perhaps no one else) is that listening tests must use an amplifier. Thus any such tests may be influenced by amp/speaker interaction. That is one reason major manufacturers usually have a plethora of gear around; speaker designers try numerous amps, amp designers numerous speakers...

 

[DonH50]

A speaker is not linear, in fact it is an impedance, what that means simply is that although you may be providing one volt, the speaker is not asking for one amp at that particular point in time.

Clarification: Impedances they are, and in fact nonlinear, but those two are independent. Case in point, my model is linear, using impedances; there is no nonlinear element in it. And, a resistor is an impedance, one that has only real and no imaginary part. Speakers operating well within their power range can be fairly linear devices.

Impedance X = R + jI where R is the real part and I the imaginary part (mathematically) of the impedance. j = sqrt(-1); Google complex numbers and linear systems or just look up in Wikipedia.

Linear impedances can still cause trouble, obviously, and perhaps less obviously linear functions operating on each other can produce non-linear results.

 

[JackD201]

Amps don't sound. Speakers do. In my opinion, an amplifier's performance is intertwined with the speaker or driver it is used with. An amp may be very linear with one speaker and be all over the place with another. If linearity is the goal find an amp that allows the speaker to behave linearly. It really is no biggie. It may or may not be easy but really, if that's the goal, that's all there is to it. Whether you actually like the result given that linearity is only a small part of qualitative assessment, is another matter altogether.

 

[bretdago]

Well Tim, a good question, and I hope our Amplifier manufacturer will shed some light on the subject. Just to warm things up, a resistor is a linear load, that means, say, one volt in equals one amp in too.

A speaker is not linear, in fact it is an impedance, what that means simply is that although you may be providing one volt, the speaker is not asking for one amp at that particular point in time.

Actually, your original question about what have amplifier manufactures been doing is simply pumping watts into linear resistors because the speaker manufacturers are using their voltage source (solid stage voltage feedback amps) to "drive" their speakers with the wildly varying impedances at each instant in time.

And, it happens as well in your active units, although, as you have surmized in the past, a better "harmony" can be brought forth if the amplifier and speaker are known to be working with each other only.

In that linear resistor load, if you envision a sinewave, of voltage, there will also be an identical sinewave (in time relationship) of current.

In an impedance, the sinewave of voltage and the sinewave of current can be happening 20 or 40 or 60 degrees different from each other in time. This can also happen due to the crossover fighting the amp (hence active crossovers before the amp are so much cleaner in real audio replication.)

I defer to anyone else who wants to spill the beans...dont hold your breath though...

Tom, This is definitely an interesting twist. I can say in my opinion and I am oversimplifying it, amplifiers on a whole are stupid devices and most I believe try to block feedback from the speaker with lower output impedances or perhaps some type of shunt. Amps that don’t address this are the ones that don’t do as well with difficult speakers. In doing this as you state, the amp just delivers power regardless of where the speaker’s power cycle may require it. The speaker uses what it needs and dumps the rest of the current into the various components as heat. Not really a perfect solution either.
Ideally, measuring points on the crossover and adding a measuring device like an accelerometer to each driver and somehow sending all that information back to the amp which could in turn interpret and adjust to the dynamic parameters of the loud speaker would be very cool. You would have to have a circuit that sees what the input is getting in, get feedback from the speaker, and then adjust the amp’s output to deal with it. Or something like that
Certainly easier to do with a powered speaker, I have seen subwoofers that use driver feedback to control excursion, but not a full feedback system… Could be an interesting project. To much thought before I have finished my coffee… Great group of folks on this forum.

 

[Phelonious Ponk]

This?

Amps don't sound. Speakers do. In my opinion, an amplifier's performance is intertwined with the speaker or driver it is used with. An amp may be very linear with one speaker and be all over the place with another. If linearity is the goal find an amp that allows the speaker to behave linearly. It really is no biggie. It may or may not be easy but really, if that's the goal, that's all there is to it. Whether you actually like the result given that linearity is only a small part of qualitative assessment, is another matter altogether.

Or this?

Bretdago;
Tom, This is definitely an interesting twist. I can say in my opinion and I am oversimplifying it, amplifiers on a whole are stupid devices and most I believe try to block feedback from the speaker with lower output impedances or perhaps some type of shunt. Amps that don’t address this are the ones that don’t do as well with difficult speakers. In doing this as you state, the amp just delivers power regardless of where the speaker’s power cycle may require it. The speaker uses what it needs and dumps the rest of the current into the various components as heat. Not really a perfect solution either.

I'm not technically astute enough to be sure, but they seem to be a bit at odds. One sees it as a widespread problem without a clear solution, the other sees it as a problem mostly with designs with higher output impedances?

As most of you know, I use integrated actives and have no skin in this game, but it seems like it would be something very fundamental, something needed to be understood and addressed by those using passive systems. Besides, I just thought it was a lot more interesting than vinyl pressings of digital masters .

Tim

 

[MylesBAstor]

Tom, This is definitely an interesting twist. I can say in my opinion and I am oversimplifying it, amplifiers on a whole are stupid devices and most I believe try to block feedback from the speaker with lower output impedances or perhaps some type of shunt. Amps that don’t address this are the ones that don’t do as well with difficult speakers. In doing this as you state, the amp just delivers power regardless of where the speaker’s power cycle may require it. The speaker uses what it needs and dumps the rest of the current into the various components as heat. Not really a perfect solution either.
Ideally, measuring points on the crossover and adding a measuring device like an accelerometer to each driver and somehow sending all that information back to the amp which could in turn interpret and adjust to the dynamic parameters of the loud speaker would be very cool. You would have to have a circuit that sees what the input is getting in, get feedback from the speaker, and then adjust the amp’s output to deal with it. Or something like that
Certainly easier to do with a powered speaker, I have seen subwoofers that use driver feedback to control excursion, but not a full feedback system… Could be an interesting project. To much thought before I have finished my coffee… Great group of folks on this forum.

Isn't that essentially what the Infinity servo tried to do? With mixed results, at least in the stock form.

 

[bretdago]

Isn't that essentially what the Infinity servo tried to do? With mixed results, at least in the stock form.

Yes Myles or similiar... It is an interesting discussion. I think it requires some pretty serious microprocessing power to get it right. Imagine all the extra stuff How are you? Hope to see you at RMAF!

 

[bretdago]

This?



Or this?



I'm not technically astute enough to be sure, but they seem to be a bit at odds. One sees it as a widespread problem without a clear solution, the other sees it as a problem mostly with designs with higher output impedances?

As most of you know, I use integrated actives and have no skin in this game, but it seems like it would be something very fundamental, something needed to be understood and addressed by those using passive systems. Besides, I just thought it was a lot more interesting than vinyl pressings of digital masters .

Tim

Come on Tim, vinyl pressings of digital masters is the best.... ever. Teasing of course.

 

[LL21]

From a Marc Michelson tour of CJ in 2003:

I asked Lew Johnson the question that so many tubeophiles have had on their minds: Why hasn't Conrad-Johnson produced a single-ended amp? Lew admitted that some SET amps have a "beguiling charm," but as he sees it, their high output impedance will affect how they drive different speakers. "They sound different with every speaker and won't sound right with any," was Lew's assessment.

 

[FrantzM]

Tom, This is definitely an interesting twist. I can say in my opinion and I am oversimplifying it, amplifiers on a whole are stupid devices and most I believe try to block feedback from the speaker with lower output impedances or perhaps some type of shunt. Amps that don’t address this are the ones that don’t do as well with difficult speakers. In doing this as you state, the amp just delivers power regardless of where the speaker’s power cycle may require it. The speaker uses what it needs and dumps the rest of the current into the various components as heat. Not really a perfect solution either.
Ideally, measuring points on the crossover and adding a measuring device like an accelerometer to each driver and somehow sending all that information back to the amp which could in turn interpret and adjust to the dynamic parameters of the loud speaker would be very cool. You would have to have a circuit that sees what the input is getting in, get feedback from the speaker, and then adjust the amp’s output to deal with it. Or something like that
Certainly easier to do with a powered speaker, I have seen subwoofers that use driver feedback to control excursion, but not a full feedback system… Could be an interesting project. To much thought before I have finished my coffee… Great group of folks on this forum.

Seems to be making the case to something audiophiles (myself, at times, included) have fought fiercely: Active Speakers

 

[bretdago]

Seems to be making the case to something audiophiles (myself, at times, included) have fought fiercely: Active Speakers

Indeed.

 

[JackD201]

This?



Or this?



I'm not technically astute enough to be sure, but they seem to be a bit at odds. One sees it as a widespread problem without a clear solution, the other sees it as a problem mostly with designs with higher output impedances?

As most of you know, I use integrated actives and have no skin in this game, but it seems like it would be something very fundamental, something needed to be understood and addressed by those using passive systems. Besides, I just thought it was a lot more interesting than vinyl pressings of digital masters .

Tim

I don't see anything at odds. It applies to the selection of amplifiers in actives as well. Remember I said speaker or driver.

 

[mep]

Tim,

The difference in cost/size/weight in just the power supply between a 800va transformer based vs a 1600 or 2600 is pretty steep, but certainly well within the budget of some of these mega buck products.

Bret-Isn't the power transformer in the Krell KSA-250 4.5kVA?

 

[bretdago]

Bret-Isn't the power transformer in the Krell KSA-250 4.5kVA?

Yeah its like 4.5 or 5 it is among one of the most powerful amplifiers ever made period. It also had i believe 16-24 250v 30a custom Motorola metal-can output devices per channel. It could double its power to .5 ohms. We did all the jack hammer comparison propoganda around those amps, it was a fun time in the audio biz. It sounded pretty damn good, was fairly high bias class A 100-150 watts I believe. It started a trend for sure. Sonically I was a fan of the earlier amps which is what inspired me to form BSC.