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traw 3rd August 2006 08:08 PM

aleph 30 project
 
2 Attachment(s)
so starting to put together an aleph 30 using briangt boards.

some questions...

planning to put one output board per heatsink, 4 of them, 2 to side as in picture. just barely fits width wise. are the sinks big enough? they are about 4.25 inch x 4.25 x 2 inch thick.

going to be a tight fit, 12 inch wide by 9.5 deep 'working' area. might need to get another .125 sheet and go 14 inch wide, overall chassis would be about 18.5 then though.

transformer is a 36-18-0-18-36 500VA. planning to use the 18-0-18... when they make transfo's like this and one uses the inner steps, still get full juice out of it? don't need to run any secondaries in parallel like that do i? how much juice does an aleph30 pull ? (on the secondary dc voltage side, not from the wall)

one last side question... often see 28-0-28 recommend for aleph 5 pulling down to 34v dc rails. I have 800va dual 31, can a simple zener emitter follower regulator be used to shave off some volts? so, also curious how much juice an aleph 5 would draw such that if shaving say 4 volts at X current, how much transistors burn off (thus want minimal extra heat sinking for the regulator). this is for a second project where i know i will need bigger heatsinks. doing the aleph 30 first to try.

mpmarino 3rd August 2006 10:09 PM

All IMHO:

Your sinks look a little light to me, especially if you want to ramp the bias up.



Quote:

still get full juice out of it?
Doubt it, actually no. You'd get 1/2 juice. I'd bet a dollar that if you cut that connector off of the toroid you would find 4 18v secondaries. I'd bet they are just in series right now to give that 36-18-0-18-36 spec. 4 18v secondaries is way more useful for the project and you'd get full 'juice'. I'd check if I were you.

The only practical way to drop a few volts in an amp like this would be a CRC or CLC in my opinion. Fortunately you'll lower your ripple too.:)

Good luck, it's a great project!

jleaman 4th August 2006 01:35 AM

Id say you need about 8 more of those heat sinks those things are going to melt.. Im running a heat sinks 5.5" x 1.5" fin's x 12" long on aleph mini's with a 1A Bias and they get warm.

traw 6th September 2006 11:44 AM

what are the symptoms of overheating? or, how do i know it's too hot?

built it... sounds nice. gets hot, but probably too hot. should i measure temp some how?

hifimaker 6th September 2006 03:08 PM

Your heatsinks are too small for 30watts output per channel. Also you would need about 20vac from the trafo before rectification.

An Aleph30 needs less than .3 c/w (corrected for ambient room temperature) per channel to disipate 100watts of power for 30 watts output.

I'm using one 13.8x6x1.9" per channel and they are about right. The sink temp after 2 hours is 150 degrees F.

I'd double up on the heatsinks or reduce the power output.

My Aleph30 uses http://www.conradheatsinks.com/produ...at100_350.html rated at .21 c/w at 80 degrees C. Applying a correction factor of 1.4 I get a .294 c/w rating for a typical room temp.

Here's a link to my Aleph30:
http://www.diyaudio.com/forums/showt...622&highlight=

Best of luck, The Aleph30 is fun to build.

-David

hifimaker 6th September 2006 03:12 PM

Quote:

Originally posted by traw
what are the symptoms of overheating? or, how do i know it's too hot?

built it... sounds nice. gets hot, but probably too hot. should i measure temp some how?


Nelson's rule of thumb for DIYer's has been, "if you can leave your hand on the heatsink for about 5 seconds, the temp is around 150 degrees F."

Any hotter than this and you risk greatly reduced lifespans for the output FETs. Also leave a decent amount of ventilation in the case for the other parts to remain cool. The other parts like capacitors have shortened lifespans as well in high heat environments.

-David

Algar_emi 6th September 2006 03:37 PM

2 Attachment(s)
You will also probably need a CRC filter so you don't get any excessive noise on the supply. So include an other set of capacitor and some provision for a voltage drop into the CRC resistor.

You can also use a CLC filter but choke are more expensive than power resistors. See my own CRC filter, one per channel to go a simili dual mono supply. The power resistors are mounted on the frame.

An again for the Aleph 5, you can use the CRC filter to remove some voltage from the supply...

Bye...

traw 15th September 2006 03:46 AM

2 Attachment(s)
will this chassis do better? current one works, but too hot after at about an hour. fans work but bah....

also switching to a 20x2 vac toroid as my current one sags down to 21 volts.

jleaman 15th September 2006 05:03 AM

Quote:

Originally posted by traw
will this chassis do better? current one works, but too hot after at about an hour. fans work but bah....

also switching to a 20x2 vac toroid as my current one sags down to 21 volts.


Very nice. When you build the chassis leave some room maybe 1.5" ish to allow air to rise through the fin's.

Jase

mtj 15th September 2006 04:44 PM

I like those heatsinks. Who manufactures them? They almost look like they are homebrew?

Just curious.

MJ


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