Aleph 30

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mik

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Joined 2001
#1
Hi all !
I'm following this forum for a while,and like someone said before in this forum I decided to stop reading and start building something.My choice is Aleph 30 and before I start I have two questions.I'm buying parts mostly in Germany because where I live(Yugoslavia) it is imposible to find heatsinks that big but also searching shops where I usually buying(Conrad,Reichelt and other) the biggest I found was rated 0.4c/w so I'm wondering:

If putting together three peaces rated 0,7K/W( ) would be enough for one chanel and second question is about mosfets, how meny i should buy to get 12 matched.



Thans in advance!

P.S
Sorry for my bad english!
 
#3
If you take 3x0,4 c/w for one channel it will be working fine, if you take less it will get to hot.
You must not buy to many mosfets because you need 4 groups of 3 matched mosfet and that is much easier than matching 12 for the same value, so i guess 20 will be enough even in the worst case.
 
#6
I second the 100 W but still 3 times 0.4 is too much (unless that is what you want of course) and the 3 times 0.7 will do just great adding another 6 C to the 17.5 Harry had ( 33 % more dissipation is 33 % more temp rise..) giving a total of 23.5 C rise which is hot but not too hot (IMHO). My Zen R is running 1 sink at 0.3 per side ( Austerlitz KS300.6 @ 100 mm height) and gets rather hot but not too hot (with about the same dissipation at 43 V and 2.4 A roughly).

/UrSv
 
#7
100W it is....

I plan to start construction on a modified XA later this year and given that we commonly have 35 degrees C in summer here i find myself having to take even more extreme measures to ensure that my expensive hardware does not self destruct during operation. I'm also trying desperately to rationalise the purchase of a AUD$900 Dot Matrix Vacumn Fluorescent Display for the multichannel control unit I plan to build (it will control the dd/dts/ac3 etc decoder, all the dacs and the preamps).


Good luck with your project.

Regards,
Daniel.
 
#8
Bias currents

I took my numbers from the bias current on the schematic (0.5 amps per device in stead of about 1 amp as it should be). Looking at the bias circuit on the Aleph 3 and factoring the increase in number of output devices is probably more like 125 to 150 watts a channel. 50 watts times 0.7 is 35 degrees above ambient or about 60 degrees which is about 5 to ten degrees above the stated temperature for the Aleph 30 which is stiill aceptable in my eyes. I feel fine running my amps at these temperatures.
 
#9
I have heatsinks 4 X 0,4 c/w for both channels together and it gets to hot to touch, but the aleph 30 didn´t break for two years and i dont switch it off very often.
The sinks are from conrad and it could be that the 0,4 c/w are just wrong because i found the same heatsink(20x15x4) at schuro and they say 5,5 c/w .
 
#10
How did you get 125 or 150 watt?
Is it more than 2 ampere per rail? Than my calculation must be wrong. But i remember 2 ampere 100 watt from the manual. But Nelson Pass doesnt care for the dissipation values in the manuals too much, acording to the manuls the aleph 3 must have more output (4 ohm) with less bias than the aleph 30...
 
#12
Bias currents

I concede on 100 Watts and promise not to believe any bias currents shown on Passlabs schematics in the future. I based my numbers on .5 volts across 0.47 ohms from the Aleph 3 manual which uses the same bias scheme and source resistor values as the Aleph 30 but 4 instead of 6 output mosfets per channel. Any other differences in the A30 schematic we should know about?

H.H.
 
#14
Service manuals

It never stopped anyone else and I am damn happy to have them. Besides, what an amp or two of bias current in the grand scheme of things. I will read the DIY articals for more exact theory on bias current. Back to work on the Tex-X. Thanks for being a good sport Nelson.

H.H.
 
#16
so I'm convinced...

I think I'll build an Aleph 30.

Not that I have any really good reasons, but it seems fairly simple to build (not my first project) and it has attracted my attention a couple of times.

So, if the service manual is not a good start, where should I start? I would like to design the PCB myself, just for the fun of it. I like TO3's.

Or is the service manual the only way to do it?

(or should I go for another aleph instead?)

//magnus
 
#17
The service manual is fine. I was giving Mr. Pass a hard time over the bias voltages shown across the source resistors being incorrect on the schematic. Lot's of people have built home made Aleph 5s and you should get plenty of support with questions posted on the forum. I thinks the TO247 output devices will be MUCH easier to find.

H.H.
 
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