We've had a number of customers running stacked Quad 57s. They used our M-60 amplifiers, and the Quads were wired in series. David Magnan of Magnan Cable fame ran this combo for years prior to his retirement.
Showing 10 responses by atmasphere
@Atmasphere, (other amp manufacturers)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! |
Bass is hard to get with transistors and Quads. The problem is that the speaker does not run according to the rules that a lot of box speakers use- it seems to work best with amplifiers that can make constant power regardless of load- which is usually a tube amp. Many transistor amps will double power as you cut the load impedance in half. The Quad has high impedances in the bass and low impedances in the treble/HF region. Most transistor amps will play the speaker with weak bass and too much highs. |
Sarcher30, Innersounds are built with lower impedances in an effort to make the speaker more compatible with transistors. The Quad ESL 57 has a peak of more than 50 ohms in the bass; there simply are not a lot of transistor amplifiers that can drive a load like that with any power. To give you an example, let's try a 200 watt SS amp, which does 400 watts into 4 ohms. Into the Quad, it will be limited to about 30 watts in the bass. OTOH, it will be able to make 500 watts at high frequencies! Its easy to see why people perceive such amplifiers as very bright and no bass when used on the ESL 57. |
Hi Sarcher30, in the case of transistor amps, the ideal is to be able to deliver the same output voltage regardless of the load impedance. That being the case, then a 100 watt amplifier driving 8 ohms will make 200 watts into 4 ohms and 400 watts into 2 ohms until the current limits of the power supply or output section are reached. They thing they don't tell you is what happens when driving higher impedances, like you see in the Quad ESL 57. Into 16 ohms you get 50 watts, into 32 ohms you get 25 and the ESL 57 has impedances in the bass well in excess of 45 ohms. So transistor amplifiers cannot make power in the bass, while at the same time they make too much in the highs, where the impedance of the speaker is down to 4 ohms. This is what I was trying to explain earlier. The Quad's impedance curve has nothing to do with box resonance in fact it has nothing to do with resonance at all. So it does not use the rules where the constant voltage characteristic is useful. It expects constant power out of the amplifier, or at least the attempt at it, for best results. It is what I call a Power Paradigm device, which is why transistors for the most part are tricky at best to get even mediocre results. IOW its an equipment mismatch. see http://www.atma-sphere.com/papers/paradigm_paper2.html |
^^Thanks! If you were planning to use an SET on the 57, you would likely use the 16 ohm tap. You would get a similar proportionate spread in total output power. However, the total output power does not represent what you would actually hear in practice. This is because there is less energy in music at higher frequencies. So the amp does not need to make as much power at those frequencies. In practice it seems to work well- we have a lot of Quad customers. Since the M-60 can make far more power than the 57 can handle, many of our customers run the amp with less than the full complement of power tubes (which is easy to do with our amps). This would further limit the 4 ohm power but this does not seem to be a problem. Alternatively the 57s can be outfitted with a modern protection circuit which shuts down the amplifier power if it senses too much output voltage. FWIW, Quads and OTLs have a long history together going back to the 1950s. |
with a much higher DF-that is, with a relatively high impedance, like many tube amps have.Damping factor has little to do with how much bass you get! - but it has a lot to do with how much distortion you get with that bass. IOW low damping factor does not translate to lack of bass! Nelson Pass has an interesting article on one of his sites regarding this fact and demonstrated it at the RMAF using a set of open baffle loudspeakers and his amps a few years ago. In the case of a Quad 57, the S-30 has a much higher damping factor in the bass simply due to the impedance of the speaker. Its far more likely that your friend simply hooked the S-30 up out of phase. The problem you run into with tube amps on ESLs in general is not that they don't make bass, its whether or not the amp can make highs on the speaker due to the low impedance at high frequencies. The J2 does look like an amp that might do the job. When using a solid state amp on the Quad 57s, due to the impedance curve an amplifier that does not use loop negative feedback is likely able to do a better job than one that does use feedback. |