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Aleph 2 build questions
Aleph 2 build questions
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Old 23rd June 2018, 11:53 AM   #1
Narside is offline Narside  Russian Federation
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Default Aleph 2 build questions

Hello everybody. I intend to build Aleph 2 amp. The amp has benn chosen due to tube-like sound (based on the feedback from this forum). So by now i've encountered couple of questions while designing the amp in CAD.
1. What is the matching criteria for MOSFETS and BJTs?
2. What is the proper area of radiator to be used?
3. If i replace original IRF244 by IRFP240 -the amount of output stages should be the same (X6)? The question is due to different capacities.
4. By replacing of original IRF244 by IRFP240 - what are the sonic diffences?

Last edited by Narside; 23rd June 2018 at 11:59 AM.
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Old 23rd June 2018, 12:13 PM   #2
Zen Mod is offline Zen Mod  Serbia
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Aleph 2 build questions
1.mosfets - matched input pair , matched upper group , matched lower group

bjt - no matching

2. what is dissipation per channel and what case/set of heatsinks you have on disposal/easy acquired list?

3.same number of mosfets ;

4. no difference in sonics , nor in any other area
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Old 23rd June 2018, 12:53 PM   #3
KatieandDad is offline KatieandDad  United Kingdom
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There are several threads on here regarding MOS-FET matching.

As Zen Mod said, you only need to match the 6 x devices in the upper half of the circuit to each other, and the 6 x devices in the lower half together (NOT all 12).

Devices from one batch will not necessarily match (and probably wont), you just need a bucket full of them and pick out sets of 6 that are a close match to each other.

You are matching for Vgs / Ids. ie at a set Vgs all 6 x devices should be within a few mA of each other for Ids.

How close you want to match them is up to you, 1mA max discrepancy will be fine.

The upper six and the lower six can be wildly different as can the other channel. It is only important to get each set of 6 closely matched.
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Old 23rd June 2018, 01:25 PM   #4
Narside is offline Narside  Russian Federation
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Thank you, Zen mod and Katieanddad
I'm going tu build chassis with heatsinks at both sides (classic design). Currently i have nob of them, so im asking which of them to consider in terms of area for proper dissipation.

Last edited by Narside; 23rd June 2018 at 01:40 PM.
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Old 23rd June 2018, 07:11 PM   #5
Gyuri is offline Gyuri  Hungary
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You can see here my early attempt, it is working even now, but it only get the opportunity to work at winter season:

My good old-new Aleph

this is I built sometime around the turn of the last millennium.
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Old 23rd June 2018, 07:30 PM   #6
Zen Mod is offline Zen Mod  Serbia
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Aleph 2 build questions
if you go at Forum's fave case manufacturer site , appropriate page is Frontale 10mm

look at 5U/500 case

that one will be approximately enough for one monoblock , dissipating 300W of heat
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Old 23rd June 2018, 08:09 PM   #7
KatieandDad is offline KatieandDad  United Kingdom
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Sadly Dad's Aleph 4 is dead at the moment and I don't have the 400 to replace the suspect caps.

These beasts generate some serious heat, 400-500W in the case of the Aleph 4. It shares the same 24 x MOS-FETs as the Aleph 2.

This one has cooked its PSU capacitors.
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Old 23rd June 2018, 08:16 PM   #8
Narside is offline Narside  Russian Federation
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Wow! This beast looks like nuclear box thank you guys for your assistance
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Old 23rd June 2018, 08:19 PM   #9
Narside is offline Narside  Russian Federation
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Looks like pc coolers are essential if i plan to install 2 boards in 1 case
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Old 23rd June 2018, 08:22 PM   #10
Narside is offline Narside  Russian Federation
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And one more question-is there a proper way to decrease the output power as long as thermal dissipation?
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