Couple of questions regarding Aleph 5

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rwagter

rwagter

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Joined 2002
#1
Dear experts,

3 crazy persons from the Netherlands who have never met eachother have some strange plan to all build an Aleph5, there has been an ongoing discussion on the dutch hifi forum

http://forum.hifi.nl/index.php?act=ST&f=27&t=1417&st=0

with regard to a number of wellknown issues:

1.- cap banks + filtering
2.- heatsinking
3.- pcb

These are of course well discussed point but nevertheless want your advise on:

1.- On the Aleph-X thread there was a breef note of usi NTC (CL-60) between caps for HF filtering. When using 100000 uf per channel divided over 10x10000uf where and how much of these do I use? Is it the same when using 5x22000uF


2.-
An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

We'll use 1 per channel be enough with a height of 150mm, it's 300 mm long, anodized black.

3.- Can I use the PCB of Kristijan (http://web.vip.hr/pcb-design.vip ) of the Aleph 2. I would prefer to p2p the mosfets and don't want to mount the PCB to the heatsink. I think the design of the Aleph 2 (frontend) PCB is more flexible.

There are only some other values for:
r16 = 75ohm (aleph 5) versus 150 ohm (aleph 2)
r19 = 221k (aleph 5) / 56,2k (aleph2)
r21 = 453 (aleph 5) / 681 (aleph2)
c7 = 27nF (aleph 5)/ 1 nf (aleph2)

Which values to use (You understand by now my lack of EE background) ??????

All answers will be greeted with appreciation

Ralph Wagter
 
#2
The k/w diagram of your heatsink is a little confusing.
Thermal resitance seems to drop near zero at 200 mm length.
Perhaps you might use this instead:
 

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#3
This was the alternative but with a much worse c/w, notice that the fins are ribbed of the sk271.

I read that the c/w curves are shown to be to optimistic (60 degrees above ambient)
But with a height of 150mm I should be able to get 0,20 C/W (hopefully
 
#4
HBarske said:
The k/w diagram of your heatsink is a little confusing.
Thermal resitance seems to drop near zero at 200 mm length.
Perhaps you might use this instead:
Click to expand...

I'm one of those fools 🙂

The cost of the Seifert KL-271 and de Fischer SK157 is the same, so (given the thicker base and the ribbed fins) the Seifert should be the better deal (I guess).
 
#5
Did I mention a fool ?, perhaps slightly deranged participation this hobby of ours.

But back to the topic.

Nobody ideas about the sinks ??? and the NTC's.

Ralph

p.s. Thank you Kristijan for the mail clearing this up regarding the PCB (we'll probably use the one for the aleph 4 which has the sam layout as the Aleph5)
 
#6
Hello Ralph,

nice to hear about these Seifert heatsinks after I´ve ordered 4xSK157......
Can you tell me what they cost?

One should be enough for one channel of Aleph5 (about 70x2=140watts) even if you crank up the bias.

Now to the other question:

r16´s value depends on the amount of fets and the max current. I don´t think this is critical because it just put´s a brake on the amount of current through the output fets. Use A5 value with3 or A2 value with 6 fets.

r19 sets the dc value and has to be set experimentally. Use a trimmer for the right dc bias and then substitute it with a resistor.

r21 sets the ac-current gain wich should be set as you like it (described many times in this forum)

c7 is connected differently in A5 and A2 but has the same fuction. you can choose whatever you like (also a theme worth a search)

hope this´ll help

william
 
#7
William,

you reaaaaally do not want to know what the seiferts cost. Ok €49,80 ex vat (19%) per piece so the grand total is €117 incl tax.

The PCB's will be the Aleph4 boards cause they are routed the same way as the aleph 5 board.

I saw you have a CLC caps bank did you also use NTC's (besides for current inrush ?)

Ralph
 
#8
Ralph,

that is really cheap!!!!! I wil pay 96euro per SK157 (although these are 200mm high) and I thought that was a good price.

Where did you order those Seifert parts?

No I don´t use NTC´s not for inrush (soft start) and not between the caps. Eventually I will use two as a connection between chassis earth and amp earth for each channel.

william
 
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