Richard Clark $10,000 Amplifier Challenge - Why Couldn't Anyone Pass this Test??

Hi Al,

There are flat impedance speakers out there, which is often accomplished with additional impedance normalizing circuits in the crossover. Certainly a niche.

In these cases it is rightfully argued that the output impedance of amplifiers will have negligible effect on the frequency response.

If this was Atma’s argument I would leave it alone. His repeated disinformation that the high output impedance is BETTER because it has constant power output regardless of impedance is nonsense. In no measurable case is it ever better. The measurements by SoundState and Stereophile are consistent. With "normal" speakers high impedance causes significant deviation from ideal.

Of course, buy what you like.

Best,


E

What Al said, plus

You know, it is a real shame that you take this tack, because I actually think you have a lot of fans, and built good products, but I've gotten really tired of you constantly hammering the superiority of high output impedance amps as a feature based on false and misleading (that's your own phrase) statements you repeat over and over again.

What is it that you're saying here? That I build good products, but - ? they aren't real or something? I'm sensing a contradiction here.

IMO you've been misreading what I've been writing.

I have qualms about **feedback**, not output impedance, as long as the low output impedance does not come with added higher ordered harmonics. And I can back my qualms up easily enough without going into the weeds. If you are not familiar with Norman Crowhurst, he is a well-known authority in the field of amplifier design. His books are likely a bit rare but the important ones are a free download from Pete Millet's site:
http://www.tubebooks.org/technical_books_online.htm

In fact I would love it if I could make the output impedance of our amps lower. The problem I have with solid state is that many semiconductors have a non-linear aspect about them that causes them to have higher ordered harmonics (at low levels, but as I pointed out earlier, the ear is very sensitive to that sort of thing) and hard clipping. The only devices that I have found that don't are the static induction transistors made by Sony. IMO They had a chance to really set the audio world forward, but in true Sony fashion (which is to come up with an innovation and then shoot themselves in the foot) failed to make a full complement of driver and voltage amplifier devices to go with their rather amazing output devices.

With such technology we could have had low distortion, zero feedback and low output impedance all at the same time!

For the most part, what I'm really hammering on is the simple fact that you can't seem to get low distortion **and** low output impedance at the same time. Now I do this in the face of the fact that many solid state amps **appear** to have very low distortion, but what research in the last 40 years has shown is that the ear has distortion on a curve of sorts; the lower ordered harmonics being unimportant to the ear and the higher ordered harmonics are really really important. I freely acknowledge that this flies in the face of the test and measurement regime, which I feel is outdated by research of the last 40-50 years.

Can you describe the sound of an amplifier by looking at its spec sheet? Most audiophiles can't; so why is there a spec sheet? The fact is most spec sheets are there to make the product look good on paper and have nothing to do with how the ear hears. That's a pretty good example of the Emperor's New Clothes...

Now if one is to say that the specs are the final arbiter, great, no worries. Have at it. But I feel that the ear, not the specs, is why we buy audio equipment and that equipment will sound better if the gear follows the rules of human hearing. 

Did you mention what your speaker brand is? I missed that bit.



 

I don't understand the comment re Melcher.  He is a neuropharmacologist.  Can you provide a citation to which of his publications you are thinking of??

Ampilfers need to have a low output impedance preferably far less than < 1ohm, otherwise they start to act like a tone control instead of being flat.

If an amplifier with high output impedance (>1ohm) were to drive these speakers there would be very little bass!! All you would get is upper-mids and highs that would fry your ears.
http://www.stereophile.com/images/1213Walexfig01.jpg

Cheers George

@georgehifi , that's correct! As I pointed out in the article, any time you mix equipment from the two technologies, the result is likely to have a tonal aberration.

The example you give is a good one, although 'fry your ears' is likely not what would happen on account of the higher impedance would result in low distortion from the amplifier. It just would not make the bass energy since designer is expecting 3 db more power output out of the amp in the bass region.

Another example is solid state driving an ESL- with the reduced impedance at high frequencies and the tendency for the load impedance to vary about 10:1 (IOW, if 10ohms at 50Hz, could be about 1 ohm at 20KHz) over its range, the result will also be too bright with not enough bass. The reason is that the impedance curve of the speaker is based on a capacitor and not a driver in a box, so the impedance curve is not also an efficiency curve.  This is quite unlike a driver in a box, where the resonance of the driver is represented by a peak in the impedance curve (IOW the impedance and efficiency curves are the same thing).

This is why the equipment matching conversation is still very much with us 5 decades on! Its also why of two amps on the bench that might measure perfectly flat to 100KHz, one might sound bright while the other does not. 

Its worth pointing out that if the designer of the speaker is expecting the amp to have a higher output impedance that the crossover will be designed differently as well. The fact that the source impedance of the amp can affect how the crossover works means that drivers might be operating outside of the area for which the designer intended! This is one of the reasons that horns got the reputation for being 'honky'.