Solid State Amps for Quad ESL 57?

ct0517 (Chris) uses a Music Reference RM10 with his Quad 57's, and he will tell you how well that particular amp works with the speaker. Roger Modjeski designed the amp with the Quad as it's load! Though a tube amp, Roger designs his amps with reliability as a high priority, and for low maintenance requirements and considerations. His amps provide very long tube life, unlike many of the more well-known and owned contemporary tube amps.

The Quad 57's are an anomaly. Both physically and electronically. 

Electronically and on the subject of this thread - I am not familiar with any SS amplifier design, that is able to concentrate its energies for bass, which sucks up the most power - at 30 ohms+, which the 57's need. And why should they be designed this way if the Quad 57's are an anomaly?  There are no business reasons that I can see for a manufacturer to build an amp this way.  

@Atmasphere,  (other amp manufacturers)
 
if you are still following this thread - does such a SS Amp beast exist, and or can a SS amp be built that is like the Quad II, ......I mean if someone really wanted to ?  

I believe.... and its theory only, because I am not an EE, but, I think that SS amps get smoked and dizzy, start oscillating (what's the technical word I am looking for?) by the 30+ ohms bass requirement. Many Class A seem to be designed from 8 ohms, to double down in watts and half up in watts. If designed for the Quad 57, from 8 ohms they should be doubling up to allow the amp to cruise and not be taxed.  

had to find this on my hard drive. imo - the reason Acoustat will work with good Solid State. very different requirements from the 57 graph that Ajant posted.

https://photos.google.com/search/_tra_/photo/AF1QipPLvcWgX83WAzSfmba9hKxw7vtl2Jx0HOEOzS4G

@Atmasphere, (other amp manufacturers)

if you are still following this thread - does such a SS Amp beast exist, and or can a SS amp be built that is like the Quad II, ......I mean if someone really wanted to ?

I believe.... and its theory only, because I am not an EE, but, I think that SS amps get smoked and dizzy, start oscillating (what’s the technical word I am looking for?) by the 30+ ohms bass requirement. Many Class A seem to be designed from 8 ohms, to double down in watts and half up in watts. If designed for the Quad 57, from 8 ohms they should be doubling up to allow the amp to cruise and not be taxed.

Actually a solid state amp isn’t ’taxed’ at least not in the way that it would be working hard. The problem is that the impedance is high so the amp can’t make the required power. This is not a matter of debate, its simple physics.

Put another way- if a solid state amp makes 100 watts into 8 ohms its likely to only make about 25 watts in the bass region. Contrast that with the possibility of the same amp making over 200 watts in the upper treble and you start to see what the problem is!

The problem here is that generally speaking, most solid state amps are intended to be a ’voltage source’, which means that regardless of the speaker load they can make the same voltage. This works great on a lot of box speakers where the impedance often represents the speaker efficiency as well- for example if there is a bass resonance (which will have a higher impedance) in a box speaker the amp won’t make much power and so does not exacerbate the resonance.

But the Quad does not have a high impedance in the bass due to resonance- it is there as a function of it basically being a capacitor (that being the ’electrostatic’ part of the way the speaker works). IOW, its impedance curve is not an efficiency curve like it is with many box speakers!! I can’t emphasize that enough- ESLs are fundamentally different in this regard.

What is needed is an amp that can make about the same power regardless of impedance, rather than the same voltage. This is so simply because the efficiency of the speaker is fairly constant over its range. Obviously this is not served by most transistor amps (although many owners that use solid state tend to back the speaker up against the rear wall in order to get it to play bass; that works in a way but you get a ’one-note’ bass because what you are really doing is reinforcing the bass at one frequency only). Quads need to be out in the room a bit in order to play properly and not be disturbed by the wall behind them- 5-6 feet is about the minimum (this is true of any panel speaker).

The only amps I know of that can produce anything like a constant power characteristic are all tube amps. However, if you **do** use solid state, its quite evident that loop feedback should not be used in the amp’s design!! The lack of feedback will steer the amplifier’s voltage response to be more like that of a ’power source’ and although it will fall short of that, it will be much better than an amp that does use feedback. Obviously this severely limits the field!

This is why tubes and ESLs have really had a liking for each other going back to the day ESLs were invented. If you want to know more about this see
http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php

The article at the link defines the differences between what is called the "Voltage Paradigm’ (the rules required if the amp is to be a ’voltage source’) as opposed to the ’Power Paradigm’ (where the investment in the speaker is best served by an amplifier that behaves as a ’power source’).

The Quad, and any ESL for that matter, are Power Paradigm devices; its the rather simple physics of the matter which is why they don’t fit into the voltage model (which was first proposed and championed by MacIntosh and ElectroVoice back in the late 1950s).

Most of us have grown up in the age where the Voltage Paradigm is the dominant model of amplifier and speaker interface (so we may have trouble understanding how there could be any other way to drive a speaker); that is why threads like this exist where people are trying to sort out how to work with the outliers like a Quad. The fact is that if you attempt to make solid state (Voltage Paradigm) work with a Quad (Power Paradigm) you will wind up with a tonal anomaly (which is what the Voltage Paradigm was supposed to eliminate FWIW...): brightness and a lack of bass.

BTW this is easily measured as well as heard. I’ve had it suggested to me in the past that the extra bass tubes have on Quads is not correct but the measurements don’t confirm that. What they **do** confirm is that Quads can play bass quite nicely if you have the right amp on them!

An extremely educational thread, even for non-Quad ESL owners like me. So based on the facts presented earlier, it appears that the ESL speakers do not follow the same amplifier requirements when compared to  "dynamic" or cone design speakers. In other words, even though almost ALL speakers can have significant fluctuations in impedance over the frequency response curve, the demands on the partnering amplifiers are significantly different based on the speaker design. As another example, I've posted a picture of the impedance curve for my (ESL) speakers - Martin Logan Aerious i, and according to the preceeding discussion, my "voltage source" amplifier is not handling the the peaks - midbass and midrange, properly. So by extension, this begs the question that every ESL speaker manufacturer should either develop and sell a matching amplifier or almost all ESL speaker owners out there will not be able to take full potential of their investments. The latter would be a sad compromise.

http://www.stereophile.com/images/archivesart/MLAFIG1.jpg