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Old 17th August 2001, 06:24 PM   #1
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I was thinking about building an Aleph 3 and was wondering if any of you had built one, or had any opinions on it? Does anyone have an idea of how much it would cost to build, or how to keep the cost down? Should a first timer even try this project? When looking at the Aleph service manuals I noticed that most of the amps used 4 25,000 microfarad caps in the power supply, but the Aleph 3 uses 8 22,000 microfarad caps why is this?

Rob
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Old 17th August 2001, 08:58 PM   #2
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If you look at the Volkamp Aleph 30 service manual, (Goto 'What's New' on the Pass site at the bottom, you'll see a link for Volkamp. In downloads you'll see service manuals.) You'll see the Aelph 30 & 60 are balanced and updated versions of the Aleph 3. I'd go with the 30 or 60 instead, only because it's drawn out for you.

I can't answer the caps question. Maybe it's what the designer had on hand at the time.

Vince
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Old 18th August 2001, 06:41 PM   #3
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Hi DIY-student.
8x22.000uF gives approximately twice the capacitance as 4x25.000uF. That may be 1 reason. Another reason may be that the availability of the 22.000uF is better. The reasons can be many.
A designer faces many problems/challenges when designing a product, which You'll no doubt find out, if You start building an amp.


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Hoffmeyer ;0)
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Old 20th August 2001, 12:24 AM   #4
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Numerous factors come into play when selecting caps for a circuit:
1) Pricing. The important thing to note here is that the pricing for caps is *not* linear. For instance, when I was buying caps for a project a year or two ago, 30,000 uF caps were *more* expensive than 32,000 uF caps (same manufacturer, same series, same voltage, etc.). This is normal. Don't assume that larger value caps will be more expensive; usually, there is some optimum ratio between price and capacitance.
2) Form factor. If, for whatever reason, you're limited to a certain amount of space in your chassis, you may need to choose a smaller cap than you might otherwise want.
3) Sound quality. As a general rule, more is better, but costs more. At some point you draw the line and say that's as far as you'll go, for both price and space reasons. Note that, while there's not a 'maximum' amount of capacitance that you can add, there is a minimum. A certain amount of capacitance is necessary to yield reasonably steady DC for your rails.
4) Availability. (Same as Hoffmeyer said.)
5) Inrush current. The larger the cap bank, the more charge it takes to bring it up to operating voltage. Depending on the rest of the power supply, the inrush current can get so large that you trip breakers or pop the fuses in the amp. The answer is a slow-start circuit, but then you're increasing the cost and complexity of the circuit.
Put all of the above in a pot and stir. Season to taste. The resulting stew doesn't have to please anyone but you.

Grey
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Old 23rd August 2001, 10:13 AM   #5
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Join Date: Aug 2001
Location: Malaysia
Hi there,

Can someone give me comment on which mosfet can replace IRF244
beside IRFP240, IRFP140 or IRF240?

What about IRF640? Ihe parameter and specs are quite closed to IRF240?

Which manufactures (beside IR) offer the best mosfet and price? Among intensil, ST ...etc....


anyone??

Thank you.
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Old 24th August 2001, 10:25 AM   #6
Koy is offline Koy  Czech Republic
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How can I adjust the gain of the Aleph 3 - which resistors?
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Old 26th August 2001, 04:06 AM   #7
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The ratio of R102/R104 sets the gain.
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