Amplifier Heat Generation

Michael G. -- Thu, 03/10/2011 - 13:09

I intend to purchase a TAD CR-1 speaker, which has a low efficiency of 86 db and a 4 ohm impedance. Recommended amplifer power is 200 watts into 8 ohms and 400 watts into 4 ohms.  I have heard these with Pass lab amplifers and liked the sound, although I am certainly open to recommendations from this forum.
My question is on the generation of amplifer heat. Somewhere on this forum, a poster said that he did not listen to his 200 watt Pass lab amps in the summer because they generated too much heat. Do others have this experience, not necessarily with Pass Lab amps but with any amps of similar power rating?
Michael G.

Ded Frag -- Sat, 03/12/2011 - 19:05

 Most of Nelson Pass's designs run in either pure Class A or Class A for a high % of their power output. All Class A amps generate huge amounts of heat, some more than your average valve amp. There are dozens of amps with similar power ratings to the Pass amp but first off you'd best tell us how much you want to spend on one. We may need to eliminate any 'silly money' designs from the equation.

Michael G. -- Sun, 03/13/2011 - 11:36

The Pass Labs XA100.5 sells for $16,500. I would be OK with that but that would be near my upper cutoff limit.

Cam -- Thu, 05/19/2011 - 11:15

I just got a Simaudio W-8 amp that puts out 250 watts per channel into 8 ohms and 500 watts per channel into 4 ohms (and doubles down again into 2 ohms).  It is only class A for the first 5 watts and then switches to class A/B.  It runs quite hot compared to the Simaudio i-7 integrated I used to use....but I don't intend to put the W-8 away for the summer just because it runs hot...but I've got central air conditioning :)

Mullard EL34 -- Tue, 05/24/2011 - 05:39

To answer the question of the impact on the room temperature, the simplest approach would be to perform a low-cost, low-tech simulation.  Determine the standing BTU output of the power-amplifiers of interest, then just get some work-light fixtures at the local hardware store (designed to provide temporary lighting for work-sites) and install a sufficient quantity of incandescent light-bulbs that total up to the specified heat-load.  Power-up the work-lights in your music room and observe the impact on the room temperature.  For example, the Pass Labs XA100.5 has rated idle power-consumption of 300 watts ( , so you'd want to deploy 600 watts of light-bulbs in the work-light fixtures to simulate the heat-load of an idling pair of XA100.5 power-amplifiers.  Be cautious not to exceed the ratings of the work-light fixtures.  Yes, it's going to be wicked bright in your music room during the heat-load simulations... ;-)

Michael G. -- Tue, 05/24/2011 - 09:42

Mullard EL34- That is an excellent suggestion, which should be a valid simulation.of the heat generated by the amplifier. The Pass Labs brochure, from the link you cited, quotes a temperature for the XA100.5 power amplifier of 53C=127F. The details of that temperature are not given, whether taken at idle or peak conditions, but that will certainly heat up a room over an extended listening session.

Mullard EL34 -- Tue, 05/24/2011 - 10:15

Nelson Pass has specified on numerous posts on DIYaudio that he targets an idling heatsink temperature of about 50 degrees Celsius, even for his Class-A/B designs. With the massive heatsinks that Nelson deploys on his Class-A power-amplifiers, the temperature cited is the result of the optimal standing bias current for his output stages (essentially, you can touch the heatsinks once the power-amplifier has warmed-up, but self-preservation would lead you to not want to continue to grasp the heatsinks over an extended period of time). However, that temperature specification won't help with the simulation under consideration, unless you're going to build a replica of the XA100.5's output stage and bias the output semiconductors at the same voltage/current levels; that would be a lot of work for a room-temperature simulation. The incandescent work-light simulation will absolutely get you within 10% or so of the nominal heat-load on the music listening room at a pretty low cost.

SundayNiagara -- Sun, 06/17/2012 - 07:47


Steven Stone -- Mon, 06/18/2012 - 15:44

Got 'em.

It's electronic wack-a-mole, let me tell you...

Steven Stone
Contributor to The Absolute Sound,, Vintage Guitar Magazine, and other fine publications

Keladrin -- Wed, 11/21/2012 - 09:19

The issue is not how much heat an amp generates per unit time but how fast this heat is dissispated. If you place an amp that produces virtually no heat in a stack such that heat is not allowed to escape then it will eventually overheat. The questions are therfore
 'how hot will it get in normal use in the way I propose to use it'
'will this temperature adversly affect the performance of the amp (or anything else)'
I suppose an inefficient amp will also wast energy but since you are proposing to spend around $16K  on an amp this may not be a major consideration

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