Heat dissipation in high temp enviroments

[navin]

Hi all,

I live in India. Here ambient tempretures easily reach 40deg C+ often a bit higher. This is coupled with high humidity for about 6 months of the year (May-Oct).

I have been thinking of building a Aleph design but worry that with all the ambient heat they will not perform as they should and add even more heat to the listening room.

I like the concept of SE class A. The 2 SE amps (albeit low watt tube) amps I have listened to bith produced a very nice sound.

I wonder if Mr. Pass or anyone else out here has any design that is suitbale for enviroments where heat dissipation is a problem. Sort of like a Cool Class A SE (is this an oxymoron)? My need is for a 100W and a 50W amp. I intend to biamp my speaker with 100W for the bass and 50W for the mids and HF.

[Circlotron]

My favourite approach to this problem - and fast becoming my trademark so it seems - is to use a source follower output stage with a 100mH or so choke in the source leg. Speaker is wired across the choke, maybe with a blocking cap depending on the choke dc voltage drop. This approach only needs half the supply rail voltage of an Aleph style class A cct and therefore has only half the dissipation and half sized power supply. My particular version has 27 and a bit volts supply rail and 3.5 amps quiescent per channel and makes almost 50w aside into 8 ohms. Sound is unexpectedly good. You may already have seen it but the thread is here. My first ever Class A amp.

[SY]

As soon as you go Class A (real Class A, not sliding bias) and single ended, you have to kiss efficiency goodbye. That means most of your power is going into heating the room. It's a sad thing, but it's basic physics.

[russbryant]

Is it 40 C in the house? We have the same temps here in Tucson, just not in my listening room


Russ

[vpharris]

Navin:

Your case (high ambient air temps) might be one of the ones that really would benefit from the idea of water cooling. It would be a fun little engineering project, and I think not too difficult. Still, in the end, the heat must be transferred to the air since you would want to recycle the water in a closed-loop system. But with something like a small automotive radiator or oil cooler and a fan that runs off the mains, it would work well I think. A potential problem is where to put the thing. I would like to do this someday, and plan to put it in the crawlspace beneath my house.
Alternately, just outside a window, in a little micro-shed. Live in a flat? Hmmmm. Maybe in the kitchen under a counter?

[Sch3mat1c]

Maybe you could hook it up to the house's hot/cold water supply somehow, so it heats the water tank? (You got modern plumbing, right? )

If you can even just put the output devices out a window, then you won't have to deal with the heat indoors. And face it, SS can take 100°C. Don't worry about a 40°C temp rise...
An added plus to having the heatsink outdoors is it'll stay real cool during monsoon season.

I agree with Circ's output choke idea, much more efficiency...(such that it still is ).

Tim

[navin]

i'd love to use the great outdoors to cool the amps.

Q1: the transistors are normally attached to teh heatsinks. by water cooling these heatsinks (either using recirculation or rain) what happens if these transistors get wet. Also what do I do with the heat from the trnasformer or is this not significant. We also have 90%+ humidity for 6 months. This humidity can settle on the transistors. It settles on furniture.

Q2: I live in an apt. In bombay everyone but real big and old money does. A lower watt version of the Aleph would sufffice. Is there one?

Q3: My stereo as to double as AV/HT too. Given that I will be locating the power amps somewhere else can i build 10 channels in one box, fed from a single large transformer but having seperate rectifiers and caps? I hope my front 3 channels will be a biamped 3 way and the 4 rears will be a 2 way. 50W per amp is adequate.

I am looking a a big 3KVA transformer which will feed 10 seperate bridge rectifiers and 6x10,000uf of caps per channel.

[Sch3mat1c]

If your transistors are above the dewpoint, obviously condensation won't be a problem. Even at 100% humidity - by definition - dewpoint can't go above ambient (if it did, the air would turn to fog).
Water could be a problem, but that's why you do a quality job. Could have the amp stuck in a window, with the heatsink pointing out the back. A sloped top would keep rain outside and direct it onto the heatsink. Use plenty of silicone to seal the joints to keep the water out.

Even so, if it does get in, it shouldn't do much. Rain water has little conductivity, so it won't short out any but the highest impedance circuits. (I don't know anything about the Aleph but I can't imagine it using anything greater than 10kohms, in which case rain won't load it too much. If the amp is built to run a little hot, it will also dry out quickly. )

Hmm.. probably wouldn't be a bad idea to put some vents on the indoors side, so the moisture can get out, if some does get in.

Good luck!

Tim

[Circlotron]

How about if you had the entire amp enclosed in a case, heatsinks and all, and had a single air exhaust hole with a length of 100mm diameter circular flexible ducting leading away to outside, with a fan sucking the air out at the far end so you can't hear it where the action is. Sort of like a large diameter vacuum cleaner.

[feralear]

Hi Navin
I'm in Karachi and the weather is not too dissimilar to Bombay's. I'm using an Aleph 3 clone with a slightly higher than normal bias with forced air cooling without any problems. Four computer fans run at six volts blowing air through four heatsinks. The fans are quite silent and only audible up close.
Regards, Hussain