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Old 19th May 2012, 05:56 AM   #1
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Default oneplustwo Aleph X build thread

I'm not going to bother asking this time... you're getting another Aleph-X build thread like it or not. The F5 is barely broken in and already working on what this might look like.

Current plan is to build monoblocks 100W/ch version. Thinking each of the enclosures would be about twice the heat sink of my F5 with four sets of mosfets each on a 11"x5"x2" sink. That seems about right given how much dissipation I expect out of the Aleph X vs. the F5 and the fact that my F5 heat sinks are relatively cool (can hold hands on them indefinitely.)

Not sure if I'm going to make a separate PSU enclosure or not. Either way, it will be dual mono CRC. Thinking two Antek 800VA 20V transformers. Trying to decide on caps. I was thinking six 47000uF 35V caps for each but after reading a bit, I think I might be able to get away with less capacitance and perhaps 25V caps. That could cut my cap cost by half or so. Any commentary on this?

Thinking these vs. these.

Also, does Q6 also need to be matched to Q5 and Q7? I didn't think so, but wanted to make sure. I was thinking about building my own matching rig, but I don't do this often so I'll probably just buy a couple pairs from ebay.
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Old 19th May 2012, 06:33 AM   #2
Luke is offline Luke  New Zealand
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20V transformer will give ~28V rails. you need the 35V caps. You could getaway with 4 X 47K uF per channel, but 6 is better.
On one of the aleph-X threads, there is a spreadsheet for working out the power supply requirements, power dissipated for different voltages and bias settings. I suggest you find it, it should help you work out what you need for sinking.
BTW there is a thread for the aleph-X, if you post your questions there, you will more likely get assistance from the people who are subscribed to that thread already
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Old 19th May 2012, 06:39 AM   #3
mace_be is offline mace_be  Belgium
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Hello,

I am also planning on building an aleph jX.
You can use less capacitance, but make shure that the ripple does get to big.
Also dont forget about the ripplecurrent. The first C from your CRC filter has to handle big ripple currents.

I would go for the 35V version.
Has also 7.7A ripple current instead of the 5.5A of the 25V one.

You could use PSU designerII from duncanamps.com to check the ripple current.
When i did my simulation of an CRCRC filter for my AJX 100w. my ripple current was something like 30 or 40A. So i am going to probably use multiple C's in the first C of my CRCRC to cope with the ripple current and also lowers ESR. I am using 1kva 20V sec toroid, i am going for 35V caps.
Check out digikey. they are maybe cheaper.
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Old 19th May 2012, 05:03 PM   #4
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Thanks for the input.

I'll go with the 47000uF 35V ones. I was leaning that way anyway and you guys validated that.

Any preference on the "R" for the CRC? I know there's pros and cons to smaller and larger sizes. I was thinking .33R or .47R.

To clarify, my setup is CCRC.
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Old 19th May 2012, 05:17 PM   #5
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Originally Posted by oneplustwo View Post
Thanks for the input.

I'll go with the 47000uF 35V ones. I was leaning that way anyway and you guys validated that.

Any preference on the "R" for the CRC? I know there's pros and cons to smaller and larger sizes. I was thinking .33R or .47R.
it does not matter if they are 0.33R or 100R. its the total R that matters.
and 0.1-0.2R is a nice value. i will say 25W is a minimum.

i am more worried about your heatsinking. this is a very big demand on this amp.
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Old 19th May 2012, 05:25 PM   #6
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My PCB will parallel 5 resistors so I was planning 5W each. I thought larger value means better filtering but higher losses? Is that what you mean by total R?

I am also worried about heat sinking. I may use the same profile but taller. Continuing to research...
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Old 19th May 2012, 05:36 PM   #7
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Originally Posted by oneplustwo View Post
My PCB will parallel 5 resistors so I was planning 5W each. I thought larger value means better filtering but higher losses? Is that what you mean by total R?

I am also worried about heat sinking. I may use the same profile but taller. Continuing to research...
by total R i meen for all the resistors. so 5 pc 5W resistors is good.
then you can use 1ohm resistors. that gives you 0.2R total and 25W.
the higher R you use the more dynamic you loose. and that you don't want

regards to heatsinks. bulding high is not the best way to go.
if you dobble your hight you only gain 40% on C/W rating.
if you place them side by side you gain 100% on C/W rating.
you need C/W rating of 0.2C/W pr side or lower.

f.ex. if you have 2pc of 0.4C/W sinks on top of each other. you get around 0.32C/W. if they are placed sid by side, you get 0.2C/W.
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Old 19th May 2012, 05:43 PM   #8
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Yes, higher is less incremental. But 2 of my F5 heat sinks side by side is already 20" long. Not sure I want to go 30" long. Plus, having 6 sinks for four quads just doesn't feel right. So going taller... might be the best compromise.
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Old 19th May 2012, 05:50 PM   #9
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okei. 20" lons is a little max
witch heatsinks is it? par metal?
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Old 19th May 2012, 05:55 PM   #10
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Yes, the par-metal ones here: HS-11

I used the 5" ones in my F5. They can cut longer so I was thinking about 8". The C/W numbers on their specs don't make sense to me. But if I look at the (3) 6"x10" sinks that Eric used, I figure (2) 8"x10" would be about the same.
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