Which power amps (or all of them) have their own sound signatures, and why, by design, or just happened to be?

[<eargiant]

That amp is a current dumper feed forward amp. So it is using Peter Walker's invention. It states in the reviews it is 1980 technology, but actually Peter Walker's landmark paper was in 1975.

Since his patents have long expired, I have never understood why his invention has not become the most common amp design of all. To me it is absolutely a no brainer,
It is reliable, reduces part count and is resilient, resulting in long term reliability along with consistent performance.

To me this design does sound superior to other output designs, especially the ubiquitous AB amps. My favorite amps are a short list. The AR Sugden/Richard Allen class A amps from that era and the current dumpers. Those class amps were 10 watts per channel. Unusually for class A amps they were reliable. My sister has had one in continuous use for over 50 years and ir has never seen a service tech or had the case opened. They now fetch very high prices on eBay.

I did do a carefully matched double blind study between a Perreaux amp and factory Quad 405-2 200 amp mono blocks years ago and listeners picked the Quads consistently as the superior amps.

I'm convinced that Peter Walker's invention not only produces better sounding amps, but also more robust and reliable amps. In my view it should be the standard amp topology.

I have used current dumpers since the mid 70s and also tinkered with them in conjunction with Peter Walker in the early days. I use current dumping amps exclusively in my systems and feel they make a significant contribution to their superior sound.

I bet those Benchmark amps do sound very good indeed.

This is the current Quad top of the line current dumper.

Peter Walker used a current dumper design (some debated if it was actually feedforward) but he did NOT invent Feedforward. That distinction goes to Harold Black way back in 1928.

In 1980 Sansui used a variation of Black's invention (giving him credit) and called it Super Feedforward. They claimed to be the first to use NFB & FF simultaneously in an audio amp, which is what Benchmark is also doing now.

https://secure.aes.org/forum/pubs/journal/?elib=3934

https://www.hifiengine.com/manual_library/sansui/super-feedforward-system.shtml

 

[R.Elder]

I’ve owned a bunch of AVRs with internal power amps and never really noticed a difference without the receivers sound processing. It might be that the processing is what people notice but don’t realize and think it’s the amp. I noticed a different sound for audessey versus pioneers mcaa and YPAO.

What I don’t notice is a difference in pure direct mode regardless of manufacturer which turns off all processing.

 

[mtrycrafts]

...
What I don’t notice is a difference in pure direct mode regardless of manufacturer which turns off all processing.

That is how amps should be compared, not with processing in the circuit operating. The latter would be comparing an apple and some other fruit. but certainly not another apple.

 

[PENG]

Absolutely I do. I have stated that here on many occasions. I agree with Peter Walker that testing an amp on a bench with a purely resistive load does not provide the totality of the information you need. Testing with extreme reactive and inductive loads is crucial. That is he only way to produce an amp that will perform well into the plethora of loads an amp will face. Apart from Maggies I can think of no real world speaker loads that are in any way comparable to a 8, 6 or 4 ohm resistor. That brings us to the next problem that amps will perform better with some speakers than others. Yes, they really do as you would expect. So amps do need to perform well and an array of varying inductive and reactive loads, and to make matters worse these loads can be inductive or reactive at different frequencies. That is the real world, so no wonder results may vary. So the key to a good amp, is not only must it do well into a resistive load, but also loads way outside that parameter. Testing an amp with a resistor is like testing a car only on a long straight flat road.

I don't disagree as long we don't generalize. For example, it is not a factor if the amps being compared are used within their power limits into "extreme reactive loads (difficult to drive speakers),a 200 W into 8 ohm resistor load rated amp should have no issue driving any conventional speakers that have extreme phase angles of even 60 degrees at some frequencies, if it has sensitivity of say 85 dB/2.83V/1m and if the seating distance is 2 meters, at average spl of 75 dB. Likewise, if the average spl for the same test is 85 dB and seating distance is 4 meters, then we have to look into the power limits of the same amp(s) when driving highly reactive loads.

 

[PENG]

Did someone notice that this AHB2 works indeed in class AB at low to moderate output levels and uses a second voltage rail to operate in class H at high outputs?

We normally see that topology in high power pro audio amps, not on 100 watts or so amps.

Yes, it is class H "tracking" power supply so the rail voltage is variable. Emotiva gen 3 does that too.

 

[PENG]

That amp is a current dumper feed forward amp. So it is using Peter Walker's invention. It states in the reviews it is 1980 technology, but actually Peter Walker's landmark paper was in 1975.

Since his patents have long expired, I have never understood why his invention has not become the most common amp design of all. To me it is absolutely a no brainer,
It is reliable, reduces part count and is resilient, resulting in long term reliability along with consistent performance.

To me this design does sound superior to other output designs, especially the ubiquitous AB amps. My favorite amps are a short list. The AR Sugden/Richard Allen class A amps from that era and the current dumpers. Those class amps were 10 watts per channel. Unusually for class A amps they were reliable. My sister has had one in continuous use for over 50 years and ir has never seen a service tech or had the case opened. They now fetch very high prices on eBay.

I did do a carefully matched double blind study between a Perreaux amp and factory Quad 405-2 200 amp mono blocks years ago and listeners picked the Quads consistently as the superior amps.

I'm convinced that Peter Walker's invention not only produces better sounding amps, but also more robust and reliable amps. In my view it should be the standard amp topology.

I have used current dumpers since the mid 70s and also tinkered with them in conjunction with Peter Walker in the early days. I use current dumping amps exclusively in my systems and feel they make a significant contribution to their superior sound.

I bet those Benchmark amps do sound very good indeed.

This is the current Quad top of the line current dumper.

Miller audio/Avtech bench tested many amps including a Quad 909. Surprisingly the 909 did not perform as good as the AVR-3805 (sorry, I know you hate AVRs) in most of the important categories.

It failed the 2 ohm and 1 ohm test while the AVR passed. The AVR even beats it in the distortions vs frequency as well from 125 Hz to 20,000 Hz but the Quad did a little better in the freq below 125 Hz. The AVR's distortions were lower in almost all tests.

Based on such available bench test results, they may be of similar design, but the Benchmark amp has much better numbers than the Quad 909 for sure.

For those interested:
http://www.milleraudioresearch.com/avtech/
http://www.milleraudioresearch.com/download2007/reports/yb07/quad_909.html
http://www.milleraudioresearch.com/download/reports/aug04/denonavr3805.html

 

[Verdinut]

Yes, it is class H "tracking" power supply so the rail voltage is variable. Emotiva gen 3 does that too.

So do QSC DCA 3022 (550w/ch) and DCA 3422 (700w/ch): Class AB complementary linear output with Class H 2-step high efficiency circuit

 

[TLS Guy]

I don't disagree as long we don't generalize. For example, it is not a factor if the amps being compared are used within their power limits into "extreme reactive loads (difficult to drive speakers),a 200 W into 8 ohm resistor load rated amp should have no issue driving any conventional speakers that have extreme phase angles of even 60 degrees at some frequencies, if it has sensitivity of say 85 dB/2.83V/1m and if the seating distance is 2 meters, at average spl of 75 dB. Likewise, if the average spl for the same test is 85 dB and seating distance is 4 meters, then we have to look into the power limits of the same amp(s) when driving highly reactive loads.

That's all very well. A speaker impedance should not drop to the 1 to 2 Ohm range. If they do then it it is usually a speaker with a passive crossover far too low that has has resonance in the crossover network. This is more common then you think, especially incompetently designed exotics.

A key parameter that is not specified and should be is the output impedance which can be derived from the damping factor. It can be measured. Neither are usually specified. However if the output impedance is greater than about 0.1 of the load then the frequency response will tend to follow the impedance curve of the speaker. This is a particular problem for tube amps which commonly have output an output impedance in the 2 to 5 ohm range.

The Quad 909 has an output impedance of 0.05 ohms. The fact is that these amps have a very relaxed non fatiguing sound to them.

 

[PENG]

That's all very well. A speaker impedance should not drop to the 1 to 2 Ohm range. If they do then it it is usually a speaker with a passive crossover far too low that has has resonance in the crossover network. This is more common then you think, especially incompetently designed exotics.

A key parameter that is not specified and should be is the output impedance which can be derived from the damping factor. It can be measured. Neither are usually specified. However if the output impedance is greater than about 0.1 of the load then the frequency response will tend to follow the impedance curve of the speaker. This is a particular problem for tube amps which commonly have output an output impedance in the 2 to 5 ohm range.

The Quad 909 has an output impedance of 0.05 ohms. The fact is that these amps have a very relaxed non fatiguing sound to them.

I did notice that the 909's output impedance was vanishingly low.

 

[Irvrobinson]

That's all very well. A speaker impedance should not drop to the 1 to 2 Ohm range. If they do then it it is usually a speaker with a passive crossover far too low that has has resonance in the crossover network. This is more common then you think, especially incompetently designed exotics.

I owned an example of a speaker that had an impedance curve that dropped into the 1-2 ohm range: the original Legacy Focus, not that I knew it when I bought them. A friend who was trying to become a speaker manufacturer was fascinated by them and wanted to measure them. I agreed, and he hauled over a bunch of specialized HP measuring equipment. (This was the middle 1990s). When he measured impedance he exclaimed loudly something like "I don't believe it!". He found the Focus fell below 2 ohms in the bass and was consistently in the range of 2 ohms. He figured Legacy just wired the three 12" woofers in parallel, and that they must have been 8 ohm rated, meaning they were sometimes less than 8 ohms. I was driving the Foci with a powerful solid state amp, but I had complaints about rough highs. I thought it might be the Kevlar midrange drivers, since some pundits were saying they had break-up problems. But no, my friend said that Legacy did that right, and that the Kevlar drivers were used in such a narrow bandpass that he didn't think breakup was the problem. He thought the Foci were loading the amp in such a way that it caused distortion in the highs. He recommended I vertically bi-amp. I thought he was nuts, but got a duplicate amp from the dealer and tried it. The Foci became the only speaker I have ever encountered that audibly benefited from passive vertical bi-amping, and I bought the second amp. I was less than pleased. I actually didn't believe what he measured until John Atkinson measured the second generation, the Focus 20/20, and measured virtually the same impedance curve in the bass:

One key parameter that is not specified and should be is the output impedance which can be derived from the damping factor. It can be measured. Neither are usually specified. However if the output impedance is greater than about 0.1 of the load then the frequency response will tend to follow the impedance curve of the speaker. This is a particular problem for tube amps which commonly have output an output impedance in the 2 to 5 ohm range.

The Quad 909 has an output impedance of 0.05 ohms. The fact is that these amps have a very relaxed non fatiguing sound to them.

I agree. Output impedance is also sometimes used to "voice" amplifiers to pump up a speaker's bass response. I surmise that many boutique amp designers did this when dealer demos were very important. 0.05 ohms is about the highest I like to see.

 

[M Code]

Many years ago I was in Japan for 1 of the major audio brands and their chief amplifier and I were doing a major tour touting their new amplifier to some of the major Japanese audio critics. And we were told of another brand high-end Japanese designed amplifier that had an adjustable damping factor...
When researched further we found out that this amplifier actually had a variable resistor in the output stage that would alter the damping factor creating more Seeburg jukebox hanging bass..
To better understand the Japanese market one needs to realize the typical Japanese house is typically modular with metal walls with little absorption material but highly reflective. So the end effect was like the listening room was similar to a shipping container...
I think that's 1 of the reasons the Japanese had great difficulty in designing/delivering a loudspeaker with creditable low frequency response acceptable to the rest of the global markets. What the Japanese thought was the ideal loudspeaker was this large enclosure designed/built by Mitsubishi sold under the Diatone brand which was the NHK standard..

Just my $0.02...

 

[KEW]

Many years ago I was in Japan for 1 of the major audio brands and their chief amplifier and I were doing a major tour touting their new amplifier to some of the major Japanese audio critics. And we were told of another brand high-end Japanese designed amplifier that had an adjustable damping factor...
When researched further we found out that this amplifier actually had a variable resistor in the output stage that would alter the damping factor creating more Seeburg jukebox hanging bass..
To better understand the Japanese market one needs to realize the typical Japanese house is typically modular with metal walls with little absorption material but highly reflective. So the end effect was like the listening room was similar to a shipping container...
I think that's 1 of the reasons the Japanese had great difficulty in designing/delivering a loudspeaker with creditable low frequency response acceptable to the rest of the global markets. What the Japanese thought was the ideal loudspeaker was this large enclosure designed/built by Mitsubishi sold under the Diatone brand which was the NHK standard..

Just my $0.02...

That is really interesting, I always wondered why they seemed not to be able to make a very good speaker. Among the mainstream Japanese companies, Technics made what I thought were the best value oriented speakers, but they still fell well behind companies like Wharfdale, AR, EPI, KLH, etc!

 

[shadyJ]

I actually didn't believe what he measured until John Atkinson measured the second generation, the Focus 20/20, and measured virtually the same impedance curve in the bass:

View attachment 29617

Wow, that impedance/phase curve is nearly catastrophic, especially below 100 Hz. To have such low impedance at such a steep phase angle in the range that serves as the fundamental for so much content.. absolutely brutal for most amps.

 

[M Code]

That is really interesting, I always wondered why they seemed not to be able to make a very good speaker. Among the mainstream Japanese companies, Technics made what I thought were the best value oriented speakers, but they still fell well behind companies like Wharfdale, AR, EPI, KLH, etc!

Some years later...
Pioneer did design/deliver some excellent loudspeakers driven by then CTO Bart Locanthi who put significant emphasis on the Pioneer pro-audio TAD drivers. Also Locanthi developed 1 of the best MM phono cartridges sold by Pioneer as the PC1000/II, but Pioneer couldn't export it due to some patent conflicts with Benjamin/Miracord... During a similar period Yamaha was making some creditable inroads with their pro-audio loudspeakers known as the NS series, the Pioneer loudspeakers were known as the HPM series...

Just my $0.02...

 

[M Code]

That is really interesting, I always wondered why they seemed not to be able to make a very good speaker. Among the mainstream Japanese companies, Technics made what I thought were the best value oriented speakers, but they still fell well behind companies like Wharfdale, AR, EPI, KLH, etc!

I recall Technics/Panasonic did deliver some reasonable mid-range loudspeakers mostly for their component rack systems, I think their assembly factory was in Puerto Rico.. With the drivers designed/assembled especially mids & tweeters in Japan...


Just my $0.02...

 

[Irvrobinson]

Wow, that impedance/phase curve is nearly catastrophic, especially below 100 Hz. To have such low impedance at such a steep phase angle in the range that serves as the fundamental for so much content.. absolutely brutal for most amps.

Like I said, the only instance I've ever heard of a distinct audible improvement from passive vertical bi-amping with a capable amplifier. The Salon2s don't get any benefit at all.

 

[Verdinut]

I owned an example of a speaker that had an impedance curve that dropped into the 1-2 ohm range: the original Legacy Focus, not that I knew it when I bought them. A friend who was trying to become a speaker manufacturer was fascinated by them and wanted to measure them. I agreed, and he hauled over a bunch of specialized HP measuring equipment. (This was the middle 1990s). When he measured impedance he exclaimed loudly something like "I don't believe it!". He found the Focus fell below 2 ohms in the bass and was consistently in the range of 2 ohms. He figured Legacy just wired the three 12" woofers in parallel, and that they must have been 8 ohm rated, meaning they were sometimes less than 8 ohms. I was driving the Foci with a powerful solid state amp, but I had complaints about rough highs. I thought it might be the Kevlar midrange drivers, since some pundits were saying they had break-up problems. But no, my friend said that Legacy did that right, and that the Kevlar drivers were used in such a narrow bandpass that he didn't think breakup was the problem. He thought the Foci were loading the amp in such a way that it caused distortion in the highs. He recommended I vertically bi-amp. I thought he was nuts, but got a duplicate amp from the dealer and tried it. The Foci became the only speaker I have ever encountered that audibly benefited from passive vertical bi-amping, and I bought the second amp. I was less than pleased. I actually didn't believe what he measured until John Atkinson measured the second generation, the Focus 20/20, and measured virtually the same impedance curve in the bass:

View attachment 29617


I agree. Output impedance is also sometimes used to "voice" amplifiers to pump up a speaker's bass response. I surmise that many boutique amp designers did this when dealer demos were very important. 0.05 ohms is about the highest I like to see.

I agree with you. And several members here say that damping factor is not important. It is of utmost importance with high Qts speakers!

Drive an old Tannoy Dual Concentric speaker with a McIntosh amp using a transformer in the output stage, and the speaker won't have any good transients! Some McIntoshes used to have a DF of only 8 for a 16 ohm load (= output impedance of 2 ohms).

 

[PENG]

Some years later...
Pioneer did design/deliver some excellent loudspeakers driven by then CTO Bart Locanthi who put significant emphasis on the Pioneer pro-audio TAD drivers. Also Locanthi developed 1 of the best MM phono cartridges sold by Pioneer as the PC1000/II, but Pioneer couldn't export it due to some patent conflicts with Benjamin/Miracord... During a similar period Yamaha was making some creditable inroads with their pro-audio loudspeakers known as the NS series, the Pioneer loudspeakers were known as the HPM series...

Just my $0.02...

Sony's SS-AR2 seemed good enough for JA to compared it to the Salon2. They don't make their own drivers though.

 

[mtrycrafts]

I agree with you. And several members here say that damping factor is not important. It is of utmost importance with high Qts speakers!
...

Yes, but I would posit that most speakers don't drop to 2 Ohms or less.

 

[TLS Guy]

Yes, but I would posit that most speakers don't drop to 2 Ohms or less.

The trouble is that output impedance is usually not specified. It can be calculated from the damping factor, but that is usually not specified.

It seems power amp output impedances vary from 0.01 to 1 ohm. There seems to be a cluster between 0.1 and 0.5 ohm. Now for the frequency response not to be driven by the impedance curve at all, then the speaker must have a minimal impedance 10 times the output impedance of the amp. So if an amp has an output impedance of 0.5 ohm then the minimum impedance of the speaker must not be less than 5 ohms, otherwise the frequency response will not be flat.

This is actually a major reason why an amp driving a speaker can vary from the response driving a resistor. Also the impedance must be corrected for phase angle. The impedance an amp actually sees is actually often lower than the impedance on the impedance curve.

This is not a simple issue and a real life problem.