Current amp vs Voltage amp

Powered speakers are like an albatross around your neck.

If you want more power, you can't. You have to sell the amps *and* the speakers to upgrade.

I have to agree with Bombaywalla. Some manufacturers of ESL's specifically made/make ss amps for use with their speakers, Acustat and Sanders come to mind. Many ESL manufactures use ss amps when demonstrating their speakers. I remember a particularly fine demonstration of Martin Logan's with Threshold amps.

'Many ESL manufacturers'. A bit cumbersome to be a real oxymoron, but nevertheless it is an oxymoronic phrase. And a bit of a red herring, there are not 'many' ESL manufacturers :)...

There is more going on here than meets the eye. ML and Sanders (the Acoustat powered speaker used a tube amp) are both trying to make their speakers work better with transistors by reducing the impedance of their speakers (unfortunately, Quad has been treading this path in recent years too). To this end you encounter some very low impedances (0.5 ohms to 4 ohms) with them. However if you can get around the impedance problem (with a set of ZEROs or the old Atma-Sphere Z Music autoformer) what you find is that the tubes sound better even on those speakers. Sure, such and such a speaker might have sounded 'fine' with a transistor amp, did you then compare it with a tube amp in such a way that that the tube amp was not having a problem with the load? Just because a speaker sounded 'fine' is not the same as it sounding its best.

The old Quad 57s and 63s, as well as most Sound Labs and some Acoustats, have impedance curves that vary from about 2 to 30 ohms or more. Usually if someone with such a speaker and a transistor amp claims that it makes bass, its because the speaker is too close to the wall. They are not winnowing out the performance of the speaker in that fashion.

Paul Speltz, who make the ZEROs, has a letter from Steve McCormick, who makes (or made) the McCormick amplifiers like the DNA1. In the letter, Steve states that while the amp can easily double power into 4 ohms, it actually sounds better driving the 4 ohm load through the ZEROs (meaning that it is seeing 16 ohms).

If you interview solid state amp manufacturers, you will find that they will pretty much agree on this point- just because they can double power into 4 ohms does not mean that they are sounding their best, and you can see that in the specs on any solid state amp- the distortion is higher as the load impedance is decreased.

Essentially, if the goal is the audio *quality*, there is no argument for four ohms or less. If sound *pressure* is the goal, then 4 ohms has a weak argument. Looked at another way, a simple means of making your speaker sound smoother and more detailed is to increase its impedance, not because the speaker will work any differently, but because the amplifier will.

It might interest you to know that the Quad 405 current dumping solid state amp which was designed for use with the Quad 57 and later the Quad 63 actually damaged the speaker because is lacked a limiter. The amp was capable of producing to much output for either speaker. A limiter add on circuit board was designed for the 405-2 to stop the damage. Ten different iterations of clamp circuit boards were designed for the Quad 63 speaker so that when the clamp engaged, it didn't blow up the amp powering it. Quad had it right with their original QuadII amps which were tube. Quads prefer voltage amps not current amps. The Quad 57 wanted to see no more than 40 Vp-p or about 25Wrms across 8 ohms.

I don't mean to sound picayune, but I would once again call attention to the first of my posts dated 5-5-13 in this thread, dealing with terminology. IMO the terms "voltage amp" and "current amp" are incorrect and misleading.

A "voltage amp" would be one that amplifies voltage. A "current amp" would be one that amplifies current. But all or nearly all amplifiers amplify both. What is really being referred to are amps that act as voltage sources, and amps that act as current sources. But that isn't right either, in most cases, because most of the amps that are being referred to as acting as current sources only act in that manner to an extremely loose approximation.

What would be better, IMO, is to refer to amps that have negligibly small output impedance (i.e., most solid state amps) and amps having significant output impedance (i.e., most tube amps and a few solid state amps). Or, alternatively, using Atmasphere's terminology, amps conforming to the "voltage paradigm" and amps conforming to the "power paradigm."

Regards,
-- Al

Al, that is why I came up with the 'Paradigm' part of it. In investigating this topic years ago what I found was just as you pose in your last post, that the terms are slung loosely and freely, resulting in a lot of confusion.

On top of that, I used the word 'paradigm' since a paradigm is a platform of thought, outside of which exists only blasphemy. This is why you see such staunch argument on this topic!

I also saw failure. I say this because whenever a new technology comes along, if it is really better it will supplant the prior art. In the case of audio, the Voltage Paradigm and all that it entails failed to supplant the Power Paradigm which was the only game in town before 1956 or so. The proof of that? Tubes are still in production 60 years on, audiophiles still can't tell how an amp sounds by looking at the spec sheet. The tubes/transistor debate and the objectivist/subjectivist debate have raged on the internet as long as the internet has existed.

If you look at internal combustion, the overhead valve supplanted the side valve in the early 1950s with no-one looking back except collectors. That should have happened in audio too, but it didn't, for the simple reason that the Voltage Paradigm was not in fact better. It was just different.

05-14-13: Hifigeek1
It might interest you to know that the Quad 405 current dumping solid state amp which was designed for use with the Quad 57 and later the Quad 63 actually damaged the speaker because is lacked a limiter. The amp was capable of producing to much output for either speaker. A limiter add on circuit board was designed for the 405-2 to stop the damage. Ten different iterations of clamp circuit boards were designed for the Quad 63 speaker so that when the clamp engaged, it didn't blow up the amp powering it. Quad had it right with their original QuadII amps which were tube. Quads prefer voltage amps not current amps. The Quad 57 wanted to see no more than 40 Vp-p or about 25Wrms across 8 ohms.

fwiw

I used the 405-2 with the limiter with my WPK Quad 57’s. It sounded ok. The 405 was bettered by the Music Reference RM10 which was also designed for the Quad 57’s and no fear of damaging them. Sold the 405.

Cheers.