Building an Aelph 1.2

Hello all Aelph fans, I am in the planning and aquisition stages of an Aelph 1.2 project. I have an Aelph 5 well underway, but for this forum I would like to concentrate on the Aelph 1.2.

I will be using Plitron 750 VA 2x45 VAC toroidals, I have one and I am waiting for the second one. I have yet to purchase the boards, probably from PCB design. I have some of the mechanicals and a few parts.

I am undecided on incorporated power supplies or a stand alone power supply module common to both channels in a seperate enclosure.

What I really want to start the thread with is a question on Heatsinks. What would be considered an adequate Heat sink solution? Here is the Heat sinks I plan on using in a dual Mono construction layout.

[IMGDEAD]http://ebay3.ipixmedia.com/abc/M28/_EBAY_951f16045eb92ffd441c20f7a25feb91/i-1.JPG[/IMGDEAD]

[IMGDEAD]http://ebay3.ipixmedia.com/abc/M28/_EBAY_951f16045eb92ffd441c20f7a25feb91/i-2.JPG[/IMGDEAD]

They have 560 Sq." of surface area each. they measure 9.875 wide x 4.875 long x 2.375 high with a .22 base. I am not sure of the Q coeffecient. I was originally thinking that 6 per mono block, with 3 on either side.

This would mean 12 output FETS on 3 of these panels. The panels would all be mounted to a .125 aluminum panel which would be incorporated into one side of the chassis, two panels (2 sides) per chassis.

For some reason I am now thinking that I may need 4 Heatsinks per panel. 3 heatsinks is about 14.5" in chassis depth, where 4 is just over 19" in chassis depth.

This thread is now open for feed back.

Thanks

Anthony
 
Somehow I'm under impression that you are building Aleph 2.

Hello Peter, I am building an Aelph 5, of which you have seen the photo's of the chassis I believe.

The Aelph 1. 2 is in fact 200 Watts class A, where the Aelph 2 is 100 Watts class A as you are well aware I am sure. I think your question is right on, is the A1.2 twice the dissapation of an A2?

I am hoping there is some agreement that a thermal coefficient factor of less than 100% increase exists between the two amps.

Anthony
 

UrSv

Member
2002-01-31 5:48 pm
Sweden
AFAIK it is quite simple. The Aleph 1.2 is a 200 W amp idling at 500 W per channel. The Aleph 2 is 100 W amp idling at 300 W per channel. Dissipation figures are from the manuals. You want to stay as far below 60 degrees centigrade on the sinks that you can afford (and these seems to be the USD 10 sinks with a volume discount so that sghould not be a big problem). 60 degrees is 30 degrees above ambient if you are in a reasonably hot place and listen to music in the summer. So for the Aleph 2 you need 30 (sink temp rise)/ 300 (dissipation) = 0.1 degrees/w and 30 / 500 = 0.06 for an Alep 1.2. Get the specs for you sink and start dividing this number until you hit something lower than either 0.1 or 0.06 depending on what you actually build (See Peter's comment). So if they are 0.45-0.50 or similar (which seems about right - but don't take this for a fact please) you need 4 or 5 of them for Aleph 2 and at least 6 for Aleph 1.2 PER CHANNEL.

/UrSv
 
Regarding your 750VA transformers, I think they are OK for Aleph 2, but for Aleph1.2 you need at least 1000VA and even more would be recommended.

Regarding the heatsinks, I think 4 are OK for Aleph2 and 6 maybe just the minimum for Aleph1.2. Also I wouldn't use 1.25 panel to attach the heatsinks and then mosfets to the sheet meatal panel (if that was your intention), but rather use some sort of bars or angles to keep sinks together and attach FETs directly to the sinks. Heat transfer would be better, and with 1.2 beast you might need all efficiency you can get.;)
 
but for Aleph1.2 you need at least 1000VA and even more would be recommended.

oohh... that's big, so you mean 2 x 1KVA or 1 2KVA. I was planning on 1 x 750VA per channel, well that changes things a little.



use some sort of bars or angles to keep sinks together and attach FETs directly to the sinks

Actually this is one of the topics I was hoping to get feedback on as well. I am / was thinking of Bars or straps to bind the heat sinks together as opposed to a 9 x 14 panel. The trade off in my mind is increasing the thermal coefficient of the 3 heat sinks by mechanically making them one, as opposed to the individual coefficients. Of course your point is valid as to the thermal conductance value in respect to a direct mount to the heat sink or through a plate.

Decisions, Decisions.

Thanks Peter

Anthony
 
Here is a Zip PDF drawing of my intended Chassis layout.

Here is my Chassis layout for my Aelph 1.2, please note there are actually 8 heat sinks. They are arranged 4 on top of 4, the drawing is a top down view so it appears only as four heat sinks. The total height would be 9.75 from base plate to top plate. They are arranged this way so the heat sinks are in chimney fashion as opposed to length way which would impede heat dissipation with out a fan. As they are external a fan is out of the question, I will probably include a chassis fan though.

Anthony
 

Attachments

  • aelph1.2 chassis.zip
    8 KB · Views: 332
You like tall amps, aren't you?

Well yes I do, but I was hoping for something more mainstream for this project. A 10" base would be a little unstable I believe. These Amps are going to be stacked on the floor, much the way your A75's do peter.

[IMGDEAD]http://www.passdiy.com/images/gallery/a75-p7-f5.jpg[/IMGDEAD]

Admittedly mine will be a little deeper but the idea is the same.

Anthony
 
My concern with using 6 in place of 8 now that I look at my drawing is the orientation of the heat sinks will change.

6 per channel or 3 per Chassis side, would result in the flue (space between the fins) being in the wrong orientation, Horizontal as opposed to Vertical.

This is the part of design where aestetics and good engineering can conflict. So as a follow up question: Can you have too much heat diissapation on an Aelph Amp?

Anthony
 
vertically or horizontally

Your original post says the heatsink has this dimension 9.875 wide x 4.875 long x 2.375 high and you said that with 3 heatsink per side, you get a depth of about 14.5" and that tells me that you have the heatsinks fins going horizontally on the sides. Your pdf file shows a "front" which means the "front" is not the "top" which tells me that you're stacking the heatsink as I described above but your sketch shows fins going vertically which does not match the depth.

My question is did you get the dimension orientation all mix up or did I misunderstood your post? I personally would always want the fins to point vertically up, not sideways.