Which watts are the right watts in SS amps?


Hello Sports Fans!

More than a few people over the years on these pages have said only those SS amps which double down in output power as impedance drops are truly special or worthy amps. Eg., 200 @ 8ohms; 400 @ 4 ohms; 800 @ 2 ohms; etc.

Not every SS amp made does this trick. Some very expensive ones don’t quite get to twice their 8 ohm rated power when impedance halves to four ohms. BAT, darTZeel, Wells, and Ypsalon to name just a few.

An amps ‘‘soul’’ or it’s ‘voice’ is the main reason why I would opt in on choosing an amp initially and keeping it. Simultaneously , I’d consider its power and the demands of what ever speakers may be intended to be run with it or them.

I’ve heard, 80% of the music we are listening to is made in the first 20wpc! I’m sure there’s some wisdom in there somewhere as many SS amps running AB, are biased to class A Only for a small portion of the total output EX. 10 – 60 wpc of 150 or 250 wpc.

After all, any amps true output levels are a complete mystery when anyone is listening to music anyhow.

I suspect, not being able to actually measure true power consumption, the vast majority of listening sessions revolve around 60wpc or so being at hand with traditional modern reasonably efficient speakers.

Sure, there are those speakers which don’t fit into the traditional loudspeaker power needs mold such as panels or electrostats, and this ain’t about them.

The possibility of clipping a driver is about the only facet in amp to speaker matching which gives a person pause while pondering this or that amplifier.

I feel there is more to how good an amp is than its ability tou double output power with 50% drops in speaker impedance.

However, speakers are demanding more power lately. Many are coming out of the gates with 4 ohm ‘nominal’ IMPs which lower with fluctuations in frequency. Add in larger motors on larger drivers, multiple driver arrays, and on paper these SOTA speakers appear to need more power.

IMHO It is this note which introduces great concern.

I’ve read every article I can find on Vienna Acoustics Music. Each one says give them lots of watts for them to excel.

Many times good sounding speakers I’ve owned sounded better with more power, albeit from arguably a better amp.

I tend to believe having more than an adequate amount of cap power is indeed integral. … naturally the size and type of transformers in play possess a strong vote for an amps ability to successfully mate with speakers.

Controlling a driver’s ability to stop and restart is as well a key to great sound and only strong amplifiers can manage this feat. Usually this gets attributed to ‘damping’ factor, but damping as I read it is more a shadow than a tangible real world figure as it depends on numerous factors. Speaker cable length alone can alter damping factors.

A very good argument exists about those mega watt amps voices. Each 500 or 600 wpc amp or amps, I’ve heard have had stellar voices too, not merely more watts.

So is it predominately these mega watt power house amps souls or their capacities that fuels the speakers presentation?

Would you buy an ‘uber expensive’ amp based more on its voice or soul, than on its ability to output loads of watts, even if you feel the amp may be somewhat under powered for the application?

Choosing this latter option also saves one money as the more powerful amps do cost more than their lower outputting siblings.

Please, share your experiences if possible.

Tanks muchly!

blindjim
I'm not sure I've ever seen any transformer coupled amp show damping over 100 into 8 ohm. I'm also not convinced that the drawbacks of feedback are so bad it should be completely avoided. I feel like thats a knee jerk reaction like many people have about guns. It's just a tool to be used.
The thing about feedback is there are more variables than the formula taught in school! You have to deal with RFI being injected into the amp via the speaker cables (and most designs don't...) and the amp has to have sufficient phase margins prior to application of the feedback... here is a great article about how to apply feedback properly:
http://www.normankoren.com/Audio/FeedbackFidelity.html

Since feedback is rarely applied with this sort of care, its incorrect to say that eschewing it is a 'knee jerk' reaction. Its misapplication is audible!

With regards to speakers, there is never a need for 100:1 (or more) damping; almost any speaker made is overdamped with a damping factor that high. Here is another great article that despite its age has stood the test of time, written by the head engineer of Electro Voice:
http://www.dissident-audio.com/Loudspeakers/CriticalLSDamping.pdf

Note that at the time of this article, there were speakers that needed far less damping than even 5:1, and there are still speakers around today that barely need that or even less (as an example, Nelson Pass demonstrated a small yet very impressive open baffle speaker at RMAF about 10 years ago that was driven by a current source amplifier, so the damping factor in that system was less than 1:10 and you did read 1:10 correctly, yet it played bass quite well).

It was Electro Voice and MacIntosh that led the way in championing the idea that the amplifier should be a voltage source and the speaker voltage-driven, back in the late 1950s and into the 1960s. But the simple fact is that this model simply did not and does not encompass all speakers and speaker technologies (any speaker that does not employ a cabinet would be an example, as well as many speakers that do have cabinets..). In addition, all amplifiers that are capable of acting as a voltage source are push-pull, and such amps (with rare exception) have distortion characteristics wherein the distortion actually **increases** below a certain minimum power level, typically about 5-7% of full power. So if you use a speaker that is too efficient for the amp, you will not be getting the best sound out of it.

The voltage model is intended to eliminate equipment matching issues, and if you are only interested in box store mid fi, none of this is a problem. But in high end audio there is quite a bit of diversity such as planar speakers, horns, full range devices as well as more conventional designs, SETs, OTLs, class A, class D, etc. because everyone is approaching the goal of electronics sounding like real music in a different way. So if you apply a generalization such as 'all amps should be voltage sources' right away it is belied by very notable exceptions!

The bottom line is that equipment matching is still very much with us and won't be going away anytime soon.
I’m also not convinced that the drawbacks of feedback are so bad it should be completely avoided.


A little story about feedback.

An output transformer "GOD" wound up some very nice massive cores for a friend of mine who was his buddy cost no object, interleaved to the hilt. I ended up with these cores when he passed away.
The transformer "GOD" I got in touch with and he got me to get some special C-Cores from Egypt where apparently is the best silicon. These transformers could be changed via the separate interleaved winding tabs for 16,8,4,2,and even 1ohm.

They sounded magnificent on a big pair of 150w tube monos I had, and I decided that maybe because the transformer were that good that there was maybe no need for feed back to help them have a lower output impedance. So I put on a variable feedback pot that could be changed from 30db down to zero. Adjusting the volume for the change in gain, it was clear as a bell that zero feed back was by far the best and because the transformers were that good the bass remained tight and dry.

So that proved to me, feedback is good in tubes to get better bass with lower output impedance, but it does have a negative effect on the rest of the music.

Cheers George 
Go ahead and spend gobs of money on those pure class A amps that burnout after 7-10 years
Any truth to this? (i.e. is a class A amps life span known to be less than other designs)

If so, is there anything that can/should be done from a practical perspective to prolong the longevity of a class A amp?

Thanks.
If so, is there anything that can/should be done from a practical perspective to prolong the longevity of a class A amp?

Thanks.

Keep them biased right, Pass recommends palm hand test on the hottest part of the heatsinks being able to keep them pressed for at least 6 seconds (no brickies hands) any shorter and it’s running too much Class-A, and also keep them in a well ventilated spot.

Cheers George