, Amplifier choice

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Mitchell2004-02-25 22:43

I am currently using CJ Premier tube monoblocks, Classe dr5l preamp, Krell kps30i player. I would like to biamp my Logans with a stereo amp preferably solid state since they have a ohm dip! Can anybody recommend which stereo amp will give me the control and extension I miss with the CJs but still have a liquid midrange and accurate musical timbre that tubes have. Lamm mono\'s too expensive The Ayre amps look promising any suggestions??


Barry Waldron2004-02-25 22:44

Hello Mitchell, In the 1970\'s and \'80\'s products from Acoustat and Beveridge used High Voltage Direct Drive amplifiers integrated into selected models. Several DIY ESL projects also incorporated Direct Drive; the most popular were projects by David Hermeyer, Roger Sanders (”Audio Amateur Loudspeaker Projects” book.) , and, Alan Kimmel (c/o David Lucas.)

The rationale was to circumvent the output transformer and deliver the required high voltage directly to the panels. This technique resulted in tremendous transient attacks and greater headroom. Direct Drive fell out of favor because of cost, complexity, and the increasing scarcity of specialized electrical components.

In the years since, solid state amplifiers have become more powerful; however, the product of volts and amperes that make up ”power” has been tailored toward conventional magnetic speakers. Specifically, the ratio of volts and amps favors power supplies having a very high current capability. While also required for electrostatic loudspeakers, even more so is having the ability to supply the panels with a very high voltage.

As a rule of thumb, most commercial electrostats (Quads being the exception) require a minimum of 100 w/p/c. in order to be energized adequately. 150 or more is even better and can often provide greater headroom. A major shortcoming of many of today\'s amplifiers is that their respective power supplies do not operate at very high voltages.

Although present day solid state amplifiers are being introduced with outputs well in excess of 200 w/p/c, their operating voltages are still relatively low. Here are two extreme examples--both rated at 100 watts: The first amplifier swings +/- 50 volts at 2 amps. The second example swings 5 volts at 20 amps. When connected to an electrostat, the first example will play much louder because it is delivering much more voltage to the panel(s) through the impedance matching transformer. When shopping for a suitable amplifier, logic dictates trying to find a high wattage amplifier and with the highest voltage swing.

One incredible amplifier, available on the used market, is the Hafler DH-500. These range in price from about $350 to $600.

A new design, specifically engineered to energize electrostatic loudspeakers is the InnerSound ”ESL Amplifier”. Of conventional design, this product does operate at a much higher voltage, and it can also supply prodigious amounts of current. Its very high operating voltage gives these speakers exceptional headroom and the potential for tremendous SPLs. The high current delivery improves transient response to a point that seems to make a speaker\'s matching transformer transparent. It is well suited for full range and hybrid electrostatic speakers. I invite you to visit the InnerSound website at: http://www.innersound.net and read more about this tremendous amplifier.

Barry Waldron from ESL Information eXchange

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