What wattage amps should I be buying?

[David Ketley]

I have the prospect of buying new amplifiers for my 4 way system or 3 way plus a cap to a JBL 2405.

The set up is JBL 2245s 260tz JBL 2123 up to 1600htz JBL 2450s up to 8000 cap to JBL 2405s

I do have a Musical Fidelity KW 500 which controlled the bass just fine till it went faulty and intend to reinsert when mended.

What power would you recommend for the 2123 and 2450s + 2405s I think that using the same power would be an advantage.

Are there any pure class A amps out there, most seem to run class A few watts then B?

[grumpy]

If it were me wishing, I'd look for 40-100w with the first 5-10w or so in class A. Pick your poison re output devices.
For -me-, more would be wasted, less wouldn't leave me with a comfortable headroom margin.
Have you ever seen a real 25+W Class A amplifier?

[fpitas]

My 25W class-A amp (a First Watt J2) puts out 200W of heat continuously. Higher wattage class-A amps put out proportionately more heat, so be careful what you wish for. I agree that a high bias class AB amp is a good choice for general purpose use.

[grumpy]

yes... my "eek" face was in regard to heat and typical massiveness if the
unit is to behave like a voltage source into lowish impedance loads.

Most are somewhat surprised at what it takes in traditional form.

[more10]

Active crossover? I would use class-D for bass and midbass, and class A tube amps for the horns.

[martin2395]

I have yet to find an amp that couldn't cope with 2123+2450+2405....those things are very efficient.
The basic model 12W Audio Note EL84 did the job without breaking a sweat.
I suspect that even a 300B SET could drive those unit to reasonable sound levels.

For the bass - an old PA amp like the K2 from Crown or JBL MPA (QSC EX) sound marvellous.
Class D should do it too but I prefer models with conventional PSU instead of an SMPS.

If you want pure class A gear - old Krells, Pass Aleph and I think that Threshold did some pure class A amps too.
Krells have that legendary bass slam but they're not the last word in case of woofer control.

Of course, like all old Class A amps they run extremely hot and are expensive to maintain due to worn out parts (mostly the caps) and your electricity bill could be skyrocketing
I measured my KSA-50Mk2 and it used around 300W (@230V) by sitting idle.
I've been told that the big ones like the KSA-200 use up to 1.2kW idle, thats the reason Krell switched to sustained plateau bias in the next series.

[gasfan]

Keep in mind that just because it's class A doesn't mean it's a good amp. The fact the question even exists is verification of the competitive quality of even class B. Naim are class B amps and superb. Crossover distortion is all but non-existent in the vast majority, good or bad, of class A/B, B amps. There are parameters far more importantly revealing when it comes to ranking amplifier performance since probably 1978. It's easy to find a class A/B amp which will compete handily with the best class A amps around, especially vintage wise. Linearity, transient response, IMD, TIM, DF, rise time, slew rate, and FR are the major factors to consider imo.

[Ducatista47]

When I next power my biamped 4345s it will be with a Denon PMA2000R and a First Watt F5. The Denon is rated at sixty watts but is a very high current JFET/MOSFET design, basically a poor man's PassLabs. The F5 is a twenty-five watt capacitor-less class A amp with .007% distortion at one watt and a bandwidth of DC to one Mhz (not a typo), also JFET/MOSFET. They make some nice stuff these days.

I have heard the J2 and it is spectacular, highly recommended. Would lesser endowed amps do a nice job too? Of course!

[fpitas]

I have heard the J2 and it is spectacular, highly recommended. Would lesser endowed amps do a nice job too? Of course!

The J2 is a great amp, and one of its many virtues as a horn amp is no turn-on or turn-off thump. Not sure the 25W would be enough for driving direct radiators, unless one listens at very modest levels. It's nice that Mr. Pass makes an amp that is appropriate for such a unique application.