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Class A?  Really?
Class A?  Really?
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Old 31st August 2021, 08:55 AM   #11
acampm is offline acampm  United Kingdom
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I don't see any problem with building an A30 or any other related design offered for DIY with whatever suitable materials are available to you. If that means a kit of parts from China or anywhere else, then its a choice you make of low cost and simplicity V merchandising standards and integrity. It's often obvious from purchaser feedback whether a specific kit or its components is going to work properly when complete, so is there any good reason to buy the parts individually at much greater cost and still have to make the PCBs?

Generally, class A amplification is only necessary to drive the tweeters and 10-20W power is considered plenty for use there in domestic 3-way systems that could require 100W Bass/mid power. I know of a few impressive systems locally that use such active systems but the actual tweeter power levels have been estimated as surprisingly small, going by 'scope measurements, even at deafening, near destructive total 3-way SPLs.
Absolutely agreed. And I might even go this route. On the other hand life is simpler if you use six identical modules.

We'll see. This comes later. For now I'll be borrowing three Linn LK85s off other systems in the house. But at some point I'll want to give them back.
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Old 31st August 2021, 03:14 PM   #12
Mark Tillotson is offline Mark Tillotson
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Originally Posted by acampm View Post
The A30 power amplifier circuit is very stable. It can use a relatively small heat sink and the current is very large. When the heat sink temperature is 80 °C, the circuit can work very stably.
Just noticed this.


Ambient + 40C is the regulartry limit for side- and top-panel temperatures for metallic enclosures for commercial electronics I believe. 80C (176F) is well above that and considered a burn hazard. And of course the electronics inside will have a much shorter life with that sort of running temperature.
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Old 31st August 2021, 03:22 PM   #13
jaycee is offline jaycee  United Kingdom
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Class A is good for headphone amps, but for speakers? just a giant waste of energy unless you live somewhere cold
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Old 31st August 2021, 04:06 PM   #14
grunf is offline grunf  Croatia
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Ever since I made the first amplifier in the A class (Pass Zen some 20 years ago) I am still faithful only to the A class, I have made a pair of amplifiers with laterals in the output, but none of them have sound quality close to the A class.
I am currently listening to a 20W Hiraga A class.
The next target is a class A with triode-driven laterals.
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Old 31st August 2021, 04:09 PM   #15
wiseoldtech is offline wiseoldtech  United States
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Originally Posted by Mark Tillotson View Post
Just noticed this.


Ambient + 40C is the regulartry limit for side- and top-panel temperatures for metallic enclosures for commercial electronics I believe. 80C (176F) is well above that and considered a burn hazard. And of course the electronics inside will have a much shorter life with that sort of running temperature.

I agree.
+40C/+105F is reasonable enough as a limit.
Because at +50C/+123F my hot water from the sink faucet becomes uncomfortable to wash my hands in.
Why should anything get that hot and exposed to being touched?
I certainly wouldn't want my equipment to get that heated. (except for tube surfaces of course)
Nor does any of it, because if it did, I'd become concerned.
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Last edited by wiseoldtech; 31st August 2021 at 04:11 PM.
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Old 31st August 2021, 04:30 PM   #16
wg_ski is offline wg_ski  United States
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Heat transfer from water is *very* rapid, that’s why 50C hot water hurts more than touching a 50C heat sink. If you can *keep* a class A amp at 50C I’d say you’re doing quite well.
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Old 31st August 2021, 05:41 PM   #17
Bonsai is online now Bonsai  Europe
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Class A?  Really?
My kx2 runs at 55C and my earlier sx ran at nearly 60C. I used the sx for about 6 yrs before retiring it to use the case for the kx(2) amps. Modern semis are quite ok with these temps - most of this progress has come through improved bonding and encapsulation plastics that can handle thousands of temp cycles without failure driven by the demands of the auto industry. ABS mosfets for example are designed to routinely reach 150C during a braking event.
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Old 31st August 2021, 06:28 PM   #18
dreamth is offline dreamth  Romania
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Originally Posted by jaycee View Post
Class A is good for headphone amps, but for speakers? just a giant waste of energy unless you live somewhere cold
How's your last winter , by the way?
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Old 31st August 2021, 06:46 PM   #19
wg_ski is offline wg_ski  United States
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Too !@#$&*% cold. I hate having to fix busted plumbing.
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Old 31st August 2021, 07:27 PM   #20
ferret is offline ferret  South Africa
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Personally I will swear by Class-A, but then I have ESLs and they are an extremely difficult load to drive. I do not know of many A/B amps that can drive them. Impedance varies from 16 all the way down to 2 Ohms.
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