Define high current amp?

This may be a very rudimentary question, I'm just trying to learn:

I've fallen in love with electrostats, and am contemplating Magnepans or Soundlabs. The Martin Logan's I've heard are dark and ill defined to me (just my ears' opinion).

In selecting upstream equipment, I keep reading on these forums about planars requiring an amp with high current output to do their best.

In what specification for an amp would I be looking to select a high current amp? Is there a particular threshold of this spec which defines high current vs. low? I'm a little confused, as I have an old Yamaha integrated, and have been told a couple of times it puts out high current, but would like to know how to definitively compare this characteristic of different amplifiers.

Thanks in advance.
Magnepans are planar magnetic speakers, not elestrostatics and present a relatively benign resistive impedance curve as far as I know. They are somewhat inefficient and are said to benefit from a high-current amp design. On the other hand, purely electrostatic planar speakers, e.g. large Soundlabs, require amps that can produce proportionately more voltage than amperes. Theoretically it may be beneficial to drive a hybrid ESL with a high-current amp powering the dynamic driver(s) and a high-voltage amp to power the ESL panel.

If you divide the amp's power output in Watts (voltamps) by the voltage it will give you the amperes; and if you divide the Watts by amperes it will tell you the voltage.

I don't know if this clears anything up for you, but I think it is important to know the load characteristics of the speaker you intend to drive -- before you buy a high-current amp to drive an electrostatic speaker that may be better served using an amp that can produce proportionately high voltage. Since many electrostatic speakers dip to very low impedance in the high frequencies, you also need to find an amp that is stable into low impedance loads. As far as I know Magnepan's do not exhibit a low-impedance dip.
High current output has become nothing more than an advertising buzzword. There is NO "official" guideline or spec that says "this one is high current and this one is not". Even published specs for such things can EASILY be manipulated to make the biggest piece of junk look "killer". The FTC test procedure does not cover this area, so it is a VERY "grey area" at best.

While this is a VERY rudimentary method, one way to tell if an amp is relatively "high current" is to look at the power output at 8 ohms and then compare that to the power output rating at 4 ohms. The power should increase VERY noticeably as impedance is lowered, sometimes to the point of doubling as impedance is cut in half ( commonly called "doubling down").

This can be deceiving though as some manufacturers play games with the power figures. Some tend to stretch the rating at 8 ohms to the max ( as that is what most people look at ). The figure at 4 ohms will not look as impressive in cases like this since the 8 ohm figure and 4 ohm figure may not differ as much as you would think. On the other hand, some manufacturers will purposely LOWER output ratings at 8 ohms. This will typically let them get away with showing that the amp "doubles down", making it a theoretical "perfect voltage source". On top of that, de-rating the amp also makes it seem "built like a tank" for the lower wattage rating and allows a greater dynamic headroom rating. This can give the appearance of a "very punchy" or "very powerful" amp for the rating or "wattage class". Kind of like stuffing a high performance V8 engine into a Chevette and calling it an "economy car" simply because it is small. Appearances ( and ratings ) can be QUITE deceiving.

The bottom line is this: Can a specific amplifier drive a specific set of speakers to the required volume levels that you would like to attain in a specific sized room and do it cleanly ? Regardless of all of the "hoopla" and "press" that specific models get, the only way to tell is to try them and see. Different types of acoustic environments, listening styles and types of music will produce varying results in each situation.

Besides this, some people have different ideas about what "loud" is, have different ideas about what "good control" in an amp / speaker interface is and have different ideas / levels of experience as to what is a "good match". For instance, some people think that 100 dB's is absolutely cranking and others find this to be "the starting point" for lifelike concert level reproduction. Others think that "high volume" equates with "high performance". Only you know what you want and expect out of a system. While finding someone ( a "regular" that posts on various audio forums, a reviewer, a local dealer, an internet friend, etc... ) that shares common likes and dislikes can be a great way to compare notes, there is only one set of ears that hears EXACTLY what you hear. Those are YOURS.

Regardless of brands, look for something that sounds good to you and will EASILY run at the SPL that you want it to. This means both the amplifier AND the speakers. They may or may not be "audiophile approved" or "high current", but so long as it makes you happy when listening to music, that is all that counts. Sean
The two postings above are excellent, and I just want to bring an amp to your attention that would do very well with planars, ESLs, ribbons, or dynamic speakers. I own the Innersound "ESL" amplifier, and currently use it with Martin-Logan CLS IIz speakers. It is purpose-built to drive electrostatics, and is rock stable into the low impedances typically seen at high frequencies with ESLs. I have also used this amp to drive Acoustats, Innersound Eros, Gallo Nucleus Ref. speakers, and Apogee Duetta Signatures, all with ease. It is able to provide the large voltage swings that ESL speakers need, and also sufficient current for speakers that require it. Sound Lab owners have commented very favorably about the ESL amp when used with these speakers.
It is rated at 300 w/ch into 8 ohms, and 600 w/ch into 4 ohm loads, (and stable at 1 ohm.) Balanced & RCA inputs, 45 lbs. in a compact package, runs cool in operation with no protection circuitry needed, due to its (18!) bipolar transistors per channel, each rated at 250 watts. All this and it sounds great, with no distortion, very extended high frequency response, and world class dynamics (even with ESLs.) If you get the amplifier / speaker combination cooking, the rest of the system will perform to its maximum.
For more detail go to "", and check recent reviews in "The Absolute Sound" Good luck!
Electrostats are the most demanding speakers to drive.
It's not just the current in your amp but also it's
stability. In the last few years most high powered solid state amps have also become "high current" amps, but a lot
of these still have trouble with 'stat loads. The classic
amp to drive them with would be an OTL tube amp such as
a Futterman or Sans Pariel. The modern choice is a
Wolcott Presence.
I am no expert, but from all I have heard, Tubofun is right. ... OTL tube amps are fantastic for ESL's; especially Soundlabs. I have heard the big Soundlabs driven by OTL's and it was a match made in heaven!

I think I would add the Graaf amps to your search.

Also, this info is coming to you from a Krell lover.
OTL's are an outstanding match with Soundlabs, I can attest to this personally. Currently, I am using a single David Berning ZH-270 with full-range Soundlab Pristine II's with very good results. The 270 outputs 70W @ 8 ohm and steadily increases power output as impedance curve drops. It is boasts both high current and voltage.

Good luck,


Thank you all for the wealth of information. I've got some more listening and research to do, and really do appreciate the insight and recommendations.
In 'Theory' a High current amp is an amp that is capable of delivering significantly "higher" current than standard design practices would dictate. For example a 'typical 100 watt amp would produce 28.5 volts at ~9 amp into a fixed 8 ohm load, and a 'high current amp' might do the same but be capable of delivering 11 amps.
THe discussion, as noted very well above is somewhat specious, as the current draw will be different from the current capacity, and you don't really want to see full current via a dead short, which may lead to a dead amp.
Tube amps are current limited by the output transformer [ OTL amps by the circuit]. Most of the "high-current" designs are Solid State, and are either (as mentioned above) down-rated amps, or amps with abnormally oversized power supplies; either way unless your speaker wants it, the amp won't deliver it, irrespective of the MFG claims.
Try an amp that sounds good - to you!- and that you can afford.
Happy listening