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Old 20th January 2014, 07:09 PM   #21
Zen Mod is offline Zen Mod  Serbia
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R12 - yes

but value of R12 is transposing further exactly voltage resulted across R23-R26

so - do not alter their value unless you know what you're doing

tip - even if you can't grasp what's going on - just print all original Aleph schematics and study them

one of them will suit your needs , then follow it blindly

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Old 20th January 2014, 07:12 PM   #22
6L6 is offline 6L6  United States
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Quote:
Originally Posted by cowneko View Post
For the heatsinks, here the big babies
You are building a 6- device Aleph with 32V rails.

Your heatsinks are not all that big...

But they will work.

Quote:
Originally Posted by Zen Mod View Post
one of them will suit your needs , then follow it blindly
Probably Aleph 5 or 2.

Last edited by 6L6; 20th January 2014 at 07:32 PM.
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Old 20th January 2014, 07:16 PM   #23
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The sense resistor value fits into the equation, but we usually play with the smaller cheaper ones. The gain is set by the ratios of R20 to R12 and R23-26 net to R35, 37, 39 net parallel. With the sense resistors equal to half the parallel source resistors and R20= R12 we get ~50% AC gain, IIRC.

Yeah, those heat sinks are sissy sinks for the build you planned. They probably will be awful hot at 180W. Cut back to 4 pairs. Looks like store cases packaging. The 3 pair 30V rail amp needs the 5U case.

Last edited by BobEllis; 20th January 2014 at 07:19 PM.
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Old 20th January 2014, 07:27 PM   #24
cowneko is offline cowneko  France
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Maybe the pictures doesn't do those heatsinks justice, but they are 5U heatsinks (300mmx210mmx40mm) given for 0.2C°/W

I just find them huge cause I never came across heatsinks those big
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Old 20th January 2014, 07:29 PM   #25
Zen Mod is offline Zen Mod  Serbia
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4U is good up to 100W diss per side , confirmed in real life ( though , not in Bombay )

5U is for not much more ..... say 125W max
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Old 20th January 2014, 07:30 PM   #26
6L6 is offline 6L6  United States
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You might need a fan.

No worries, moving a little air makes a big difference.
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Old 20th January 2014, 08:35 PM   #27
cowneko is offline cowneko  France
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Well, I have to think of something for the cooling then..... maybe a 120mm bequiet computer fan (15db at 12V)
be quiet! Silent PSU & Cooling for your PC
Witch will be placed on the top plate of the amp in blowing mode (outside air pumped inside the chassis

with a little 30VA 2x15v (for the Speaker protections) and 1x9v (for the fan)
Transformateurs torique - Transformateur torique 30VA 2x15V + 1x09v

plus a little regulator psu to feed the fan with DC voltage
Alimentation linéaires - AMC - kit Alimentation régulée 1.5/30VDC 3A LM1085

I will make a BOM for the amp, I hope you'll be able to tell me if there's something odd with it
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Old 20th January 2014, 08:57 PM   #28
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Save yourself a transformer and the fan controller - use the same transformer for protection circuit and fan. Set it up ct, use a bridge for +/- and a single 1n4007 followed by a small cap for the fan supply. You can make very simple fan speed control with a pot and a mosfet. You can add an extra cap across the resistor to help starting if slow speed operation becomes a problem. All fits on a small piece of perfboard. Layout not critical.

Papa posted a circuit for this many years ago, I will try to redraw it when I get home, but will try to describe it;

1N4007 and 100 uf (value not critical) cap create a ~9V supply from a 15VAC winding and ground.

10K pot connects across the 9V and ground. Can be single turn, 10 turn or 25 turn if you really like turning things.

To +9V connect the fan +

To fan - connect the drain of an n channel mosfet. General purpose anything like IRF610, IRF510, etc. (to name what's in my parts bin)

Source of mosfet to ground.

Wiper of pot to gate of mosfet.

1-10 uf from mosfet gate to V+ if needed to help startup.

The voltage at the mosfet gate controls current, which is controlled by the voltage divider created by the pot. The cap from V+ to gate creates a spike on turn on that will give the fan plenty of juice to start and then drop down to a lower running speed.
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Old 20th January 2014, 09:22 PM   #29
cowneko is offline cowneko  France
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Thanks a lot BobEllis, I think I will learn a lot with this project and everybody advises (even if some of them are still little obscure form me right now)

I'm eagerly waiting for your drawing, but I will try to understand the concept from your description.
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Old 20th January 2014, 09:29 PM   #30
Zen Mod is offline Zen Mod  Serbia
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oomph
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