Discovering pure Class A - It's true, not all Watts are created equal

[ChemMan]

Pass Labs amps, but also interested in the Colin Wonfer designs being sold under 'EWA' (from ABC Audio). Any others to consider at maybe a maximum price of £3 or £4k?

(I'm planning on SS rather than valves at the minute, but I can always be convinced).

I thought the Sugden ANV 50 was luxurious in class A warm and wonderful sound. The Pass Labs INT-60 might be the best amp I've ever heard. It's technically A/B but biased in the A for normal volume levels. (It's possible you could find one second hand)

I have the VTL IT-85. All valves with 4 x KT77 output tubes. You can read about how it compares to NAD's flagship elsewhere here in 2 Channel.

 

[Rayymondo]

I was led to believe that the first few watts in class A/B were class A anyway? But happy to be corrected if I got that wrong?

 

[TLS]

Would that equate more to maximum current availability in your amp, subject to any limiters coming into play? Or, in effect, the amp’s ability to continue to double its output with each halving of impedance.

Yes, I think it does have something to do with current availability. Of the few amplifiers I had over the years I noticed that the heavier ones (even with low power rating) never had any problem driving loudspeakers.

 

[TheFlash]

I've heard some good class A and some bad some valve and some SS. Like a lot of things, depends what your preferences are.

I still prefer my MOSFET AB power amps over pure class A for my taste in sound and music.

And scientifically, at least, Watts most definitely are Watts, assuming you are using the same standard to measure them thing is, at modest listening levels most of the time a lot of people are using <10w so really don't need all that much power.

yes, but haven't you heard it said Marshall watts are twice as loud as anyone else's ... like you, I know the definition of a Watt, also that various speakers have varying efficiency, but if a guitarist is playing through a Marshall he is more likely to be heard (or asked to turn it down)

There's more than 1x 100W valve guitar amp head here that have seen their share of big gigs

It down to the design of the amp and not the power they are capable of delivering.

I don’t think anyone here is suggesting a measured watt is not a measured watt. What heavy, energy-hungry Class A usually does at one end of the scale and light, energy-efficient Class D ysually does not do at the other is to deliver current. It seems to suit many manufacturers to quote large numbers of watts whereas most of the loudspeakers I’ve had have been more appreciative of amps than of watts.
I’m not saying this is a rule - note my careful insertion of the word “usually” and I remember being wowed by a ridiculously small Class D amp at a show once. It’s merely that in the absence of published current figures by most manufacturers I’ve found amplifier weight - yes, in pounds or kg - to give me the strongest indication of sound quality.
For completeness, I believe/presume the amps in my active ATC’s are Class AB… and would be very keen indeed to hear the aforementioned Mosfet amps as they appear to have a faithful following from those who’ve heard and/or own them.

 

[TheFlash]

Yes, I think it does have something to do with current availability. Of the few amplifiers I had over the years I noticed that the heavier ones (even with low power rating) never had any problem driving loudspeakers.

You beat me to it!

 

[TheFlash]

I thought the Sugden ANV 50 was luxurious in class A warm and wonderful sound. The Pass Labs INT-60 might be the best amp I've ever heard. It's technically A/B but biased in the A for normal volume levels. (It's possible you could find one second hand)

I have the VTL IT-85. All valves with 4 x KT77 output tubes. You can read about how it compares to NAD's flagship elsewhere here in 2 Channel.

Whereas I was blown away the first time I heard A21, owned and loved IA-4, and was excited by the prospect of the ANV-50 based on a handful of enthusiastic reviews… but was left completely cold by its performance and quickly returned the demo model.

 

[flak monkey]

I don’t think anyone here is suggesting a measured watt is not a measured watt. What heavy, energy-hungry Class A usually does at one end of the scale and light, energy-efficient Class D ysually does not do at the other is to deliver current. It seems to suit many manufacturers to quote large numbers of watts whereas most of the loudspeakers I’ve had have been more appreciative of amps than of watts.
I’m not saying this is a rule - note my careful insertion of the word “usually” and I remember being wowed by a ridiculously small Class D amp at a show once. It’s merely that in the absence of published current figures by most manufacturers I’ve found amplifier weight - yes, in pounds or kg - to give me the strongest indication of sound quality.
For completeness, I believe/presume the amps in my active ATC’s are Class AB… and would be very keen indeed to hear the aforementioned Mosfet amps as they appear to have a faithful following from those who’ve heard and/or own them.

A good indication of power supply capability in terms of current supply is the ability of the amp to double its power into halved impedence.

My DIY lateral MOSFET amps are capable of 150W RMS into 8 ohms, and 250W into 4 ohms. Using +/-56VDC supplies from a 40-0-40 500VA transformer and a big bank (60,000uF) of smoothing caps.

More power than I need? Yes. Have I ever been tempted by a low power full Class A amp? No, while they can sound great, they just don't do it for me for some reason.

Regardless watts are still watts. Everything that goes with them in terms of amps specifications is what makes the difference in my experience.

BTW If you're ever up this way, you'd be more than welcome to have a listen to the MOSFET amps

 

[karlsushi]

I do wonder why current rating isn't something that is quoted more within manufacturer specs.

It is a frustration I experienced when researching headphone amps for my LCD2's, which, along with most other planars, require lots of current, not merely power, to drive them properly.

I understand why the mass market players just quote the same specs, but in a world of ever-increasing 'boutique' and 'one-man-band' products, you would think that they would want to put out as much (relevant) information as possible.

Maybe some do and maybe you can just ask.

 

[audio_PHIL_e]

P=IV, so you need either lots of I or lots of V (or both) if you want lots of P. My (admittedly limited) understanding is that valves are voltage amplifiers rather than current amplifiers, whereas transistors are current amplifiers rather than voltage amplifiers. Valves (AFAIK) need a transformer to match their high voltage swing (with little current delivery) to the lower voltage/higher current requirements of the speaker, but ultimately it is the power supply that limits (or enables) the o/p stage to shove current through the speaker. IIRC Morgan Jones said the most important part of an amplifier is its PSU.

 

[TheFlash]

A good indication of power supply capability in terms of current supply is the ability of the amp to double its power into halved impedence.

My DIY lateral MOSFET amps are capable of 150W RMS into 8 ohms, and 250W into 4 ohms. Using +/-56VDC supplies from a 40-0-40 500VA transformer and a big bank (60,000uF) of smoothing caps.

More power than I need? Yes. Have I ever been tempted by a low power full Class A amp? No, while they can sound great, they just don't do it for me for some reason.

Regardless watts are still watts. Everything that goes with them in terms of amps specifications is what makes the difference in my experience.

BTW If you're ever up this way, you'd be more than welcome to have a listen to the MOSFET amps

Re your offer, thanks... will check out where you are and be in touch!

Re watts: yep, wats is indeed watts but I think we're converging here on a view that (in general terms with caveats exceptions etc etc) there is a poor correlation between power output expressed in watts and sound quality expressed in toe-tapping...

 

[flak monkey]

Re your offer, thanks... will check out where you are and be in touch!

Re watts: yep, wats is indeed watts but I think we're converging here on a view that (in general terms with caveats exceptions etc etc) there is a poor correlation between power output expressed in watts and sound quality expressed in toe-tapping...

I'm near Littleport in Cambridgeshire

Agreed - watts doesn't equate to all the subjective stuff by any means.

 

[Bodgit]

All watts are not created equal. As watts = voltage x current, you can get 100W using either 100V and 1 amp or 10V and 10 amps.

Amps is akin to torque and voltage akin to engine rpm. Power might be the same but a high torque engine (high current amp) is by far the more enjoyable to drive.

 

[Nopiano]

I do wonder why current rating isn't something that is quoted more within manufacturer specs.

It is a frustration I experienced when researching headphone amps for my LCD2's, which, along with most other planars, require lots of current, not merely power, to drive them properly.

I understand why the mass market players just quote the same specs, but in a world of ever-increasing 'boutique' and 'one-man-band' products, you would think that they would want to put out as much (relevant) information as possible.

Maybe some do and maybe you can just ask.

One reliable source of current is the HiFi News reviews, where their Lab Report tests power into 8, 4, 2, and 1 ohms. They always calculate the maximum current.

Some power supplies are tightly regulated so that power increases significantly into 4 ohms, but hardly at all into 2 or 1 ohms. In practice that wouldn’t matter much, unless you had exceptionally demanding speakers.

This was a good example recently of a super quality British amplifier that doesn’t weigh a ton, or cost a bomb, but with a chunky >25amp current capability.
https://www.hifinews.com/content/exposure-3510-integrated-amplifier-lab-report

 

[karlsushi]

Perhaps I should amend the thread title to "Amp power ratings aren't always the best indication for speaker matching"...or something along those lines...

 

[Rothwell Audio]

It seems to suit many manufacturers to quote large numbers of watts whereas most of the loudspeakers I’ve had have been more appreciative of amps than of watts.

I do wonder why current rating isn't something that is quoted more within manufacturer specs.

For a given impedance (ie, for a given pair of loudspeakers) and a given voltage, the current that flows is determined solely by the impedance and voltage. An amplifier "capable of more current" won't deliver any more current.

 

[ChemMan]

but was left completely cold by its performance and quickly returned the demo model.

WOW. Shocking eh? I was using ATC SCM40. You? IF anything I thought it might be TOO warm.

 

[rabski]

For a given impedance (ie, for a given pair of loudspeakers) and a given voltage, the current that flows is determined solely by the impedance and voltage. An amplifier "capable of more current" won't deliver any more current.

Absolutely. I was beginning to wonder whether audio had mysteriously managed to circumvent Ohm's law.

As a bynote here, quoting 'amps' is no better than quoting watts, for numerous reasons. Mostly though, in rough terms 'RMS watts output' is at least vaguely comparable.

As a second bynote, you can't actually directly measure watts, so it is always derived from a calculation under test conditions. And as a final bynote, a watt may always equal a watt, but the method of calculation does give manufacturers a little leeway. It may be urban myth, but at least one manufacturer apparently 'measures' the output of their amplifiers based on measuring the power consumption from the mains and multiplying it by the average efficiency of the type of output stage.

 

[andrew s]

Glad physics rules still even here. However, the speakers are a complex load so we need their impedance in the generalisations of Ohms law.

I tend to think it is the ability to deliver the dynamic out of phase current/voltage with varying distortion that gives rise to differences between amps when all else is equal.

Unfortunately, only resistive loads are measured as no one can agree on a more realistic standard.

Regards Andrew

 

[MotherSky]

I tend to think it is the ability to deliver the dynamic out of phase current/voltage with varying distortion that gives rise to differences between amps when all else is equal.

Could this be influenced in any way by having "standing" current in class A?

 

[ACS]

Amps is akin to torque and voltage akin to engine rpm.

It's the other way round, but please do check for yourself.