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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
randy-11
1,913 posts
 
The First Watts are the best watts.
atmasphere's avatar
atmasphere
7,068 posts
 
However, transformers do have drawbacks. Many speakers don't expect the low damping factor transformers provide and they drive a lot of speaker hot in the highs. There's a reason DC coupling is the standard in solid state amps. It gives the output stage maximum control over the load.
We direct-couple our amps and they are vacuum-tube. An output transformer does not mean that you get a low damping factor. Its far more complicated than that!

Tube amps, including OTLs, can operate at voltage sources much like solid state. It all depends on the design and intention.

The thing is, with tube amps you get linearity, but usually not a low output impedance. So you add loop feedback and then you have the low output impedance. With solid state, you don't (usually) get linearity but you usually have a low output impedance. So you add loop feedback to obtain linearity.

The problem is that loop feedback, while suppressing distortion, adds some of its own in the process (this fact has been known for decades- see the writings of Norman Crowhurst). Some of it is IM distortion (which is highly audible) and some is higher ordered harmonic distortion (which is also audible). This is why amps with feedback tend to sound brighter (and also harsher) than amps without.

To this end, loop negative feedback is eschewed by many designers as they don't want coloration. Contrary to what has been stated elsewhere on this thread, its possible to design a speaker for an amplifier that has a higher output impedance (which it will have if it has no feedback). Such a speaker does not have to have a flat impedance curve either! Its also possible to find speakers that will obtain flat frequency response even though the amp has a high output impedance, despite the fact that the speaker was not designed for such an amp.

Its easy to see in the specs of the speaker when it will work with amps of higher output impedance. We've stayed in business for over 40 years doing just that. But there are also speakers that are designed with this expectation- Audiokinesis, Coincident Technology, Merlin, Altec, JBL, Tannoy...and many more. Intention also plays a big role.

So there is more than one way to obtain flat frequency response. The thing is, higher ordered harmonics are very audible to the human ear as the ear/brain system uses them to sense sound pressure. So if the system has more higher ordered harmonics than it should, it will sound bright and harsh despite the actual distortion being quite low. This is why amps with a high output impedance exist; its not because somehow we designers can't make them low impedance- we can! - its because we are trying avoid not just some colorations but **all** colorations, and a higher output impedance is a result of that. But no worries- if you want accurate reproduction that sounds like real music, look at it this way:

If the speaker requires that the amp employ feedback to sound right (regardless of why the amp has the feedback), **with today's technology** that speaker can't ever sound like real music- it might sound like a really good stereo, but it won't have the feeling of real music.


willemj
1,036 posts
 
Well, my Harbeths are easy to drive and nobody will deny that they are very good sounding speakers. So it can be done.
stfoth
435 posts
 
I still can't say I understand all of this, even as very knowledgeable and helpful folks are doing their best to dumb it down.  I get it that, oftentimes, a speaker with a high, flat impedance and high sensitivity tend to work well with high output impedance tube amps, SETs and such.  I also get it that a big, low-sensitivity speaker with wild impedance and phase angle fluctuations tend to work well with powerful solid state amps.  Some of this seems somewhat easy to discern when graphs like what Stereophile often puts out are available.

Under the assumption that I'm not going to blow stuff up, sometimes I try things that seem like mismatches.  Sometimes, it's obvious.  Sound is goofy and the woofer cones are all over the place.  But, other times, the sound is really, really nice, even if it may not measure well.

Or a low-power SET with a "mismatch" low-sensitivity speaker, but restricted to low-volume.

But, what about a common middle ground...speakers that generally vary from 4-8 ohms with moderate phase angles.  Mid-high power push-pull tube amps or SETs with huge transformers (e.g. Cary 805).

I get it that the frequency response may not be flat, but what else might be happening--good or bad?  Are we just making bloomy bass and hilly frequency responses?  Are we just making a personal decision on whether that is better than some of the nasties Ralph describes--high-order harmonic distortion, IM distortion, etc.?
mapman's avatar
mapman
15,679 posts
 
slfoth I think it is important to distinguish between good "performance" versus just "sounding good".

Carefully matching amp and speakers along the lines you spoke of is key to getting good performance, which can be measured. Good performance matters a lot but alone does not mean one will like the sound or even that it sounds better. But you cannot accurately reproduce all forms of music similar to the original without it.

Good sound is totally subjective and is a judgement call. Good performance is not required. It may sound lovely in some cases to some people but cannot compete with good performance any more than a nice driving Toyota Camry (very nice car!) can compete with a state of the art luxury vehicle.

My recommended strategy is get the good performance first using specifications to match components (as opposed to pure luck or just hope) then tweak from there as needed to get the sound just right.

Its not a black and white thing. There is a match between a low power SET amp and high impedance high sensitivity speakers (optimized performance) as well as a match between high power high current SS amps and smaller and harder to drive, lower efficiency speakers still with good bass extension. There is also everything in between (less optimal at least on paper). Both done right should perform fairly optimally though each will still likely sound different for various reasons and the choice will come down more to personal preference based on a myriad of factors in the end.

Of course one can always just choose to roll the dice and pick each component you like for whatever reason. Most any amp and speakers are "compatible" to the extent that you can connect the two with no issue and hear what you got. You might get lucky but chances are if you want it all then it will take much longer to get anywhere near that goal than otherwise.

Cheers!


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