whats makes sense to have class A amp?

[Mooly]

That would be simple enough to do with an LM35 temp sensor and comparator, but it the sensor would have to be outside the amplifier box. The original article (part 2) did not mention weather sensing, but it did say this:

"

I had a much bolder scheme in mind actually , an aux input to the bias generator (opto coupled naturally, to avoid any unwanted effects) that is fed from the central heating 'stat. The amplifier could then augment the room heating as and when needed.

Think thats probably enough on that one, mind you, didn't you once mention a heatsinking arrangement that could be used to heat water to make the tea !!

Who said engineers are a bit mad

 

[jacco vermeulen]

an amplifier that changed mode to suit the operating conditions.

Lord Self's post made me think of a constant temperature power amp, through real-time adjustment of the quiescent current level to keep the temperature of the heatsinks at a fixed value, seems easy enough to do with sensors such as the LM3*.
A sliding bias routine, but not quite the same as the ones that adjust the quiescent current level by tracking the input signal amplitude.
More like a high bias Class AB power amp with an added feature.

(though quite a few may not be in the market for blameless designs, i doubt many do not hail Mr Self as the majesty of audio amplifier design book writing)

 

[destroyer X]

hehehe... hot subject...i am already feeling the heat irradiated by those amplifiers

Hot!... too much hot!... incredible hot!... no chance for my environment, unless you have an amplifier with double function, one to produce sound and other alike oven or coffee machine.

I love when i find one to dismount.... good heatsinks, enormous transformers, nice electrolitic condensers.... so i love them deeply.... because they are good to provide me nice parts..good to dismount.

I have listened the JLH...many models from him... i found great!... very nice...but not enougth to accept all that heat.

Yes... sound can be "hot".... but temperature is hotter than the sonics.

Waste of energy.... in our new world, we have the need to avoid waste energy... this polutes!

Yep... i disagree they are burning Amazon...of course i disagree... wasting natural resources, and poluting... a crime against humanity...also North American Industries, and automobiles too... awfull thing.

regards,

Carlos

 

[destroyer X]

Please... keep your world clean, non poluted

for us....heheheheh!

Carlos

 

[CBS240]

I'm burning on idle ca25-30watt per channel in my amp, using hexfets.. Can't find any reason to go much lower or higher than that with hexfets.. with some other components maybe..

Sounds about right. My experience with hexfets is they like heavier bias. This is representative of the problematic transconductance drop as the device approaches cut-off. The temperature coefficient is positive, but less than that of a typical BJT. I find a BJT Vbe multiplier will over-compensate hexfet OPT. IMHO, I prefer to bias with a slight negative overall coefficient and use a higher initial bias. As the heat sink is heated, the bias will reduce wrt to heat. The bias is set to cover a range dependent on temp, maybe like 30% drop from 'cold' bias setting. For example, with a single pair of TO-220 size devices, I start at ~300mA and the bias drops to ~200mA when the heat sink is piping hot to the touch. The lowest bias setting is plenty for these transistors to work in class AB and still has the advantage at small signal levels of class A operation. Seems to work for me, so what if a little heat is wasted. It's worth the thermal stability.

... Noise was mentioned as well. I used too look at signal to noise ratios as an important parameter, but have long since come to the conclusion it's relatively unimportant. Not hum and PSU problems of course, I mean good old hiss. Does the ear use hiss as a form of "dither" to extract more detail and to stop it subconsciously "searching" for low level detail that is not there ?

I have different feelings about hisssss and other white and pink noise when it comes to home stereo Hi-Fi. Most of my home listening is at low levels so noise is a big factor for me. All of those subtle details that are lost below the noise floor at low levels are a travesty. IMO, the amp should reveal just how terrible your recordings really are. Detectable hisssssss noise as well as poor PSRR is unacceptable to me.