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Old 13th June 2009, 05:22 PM   #3991
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by bobodioulasso
I usually double this rating for a 2x100w class AB amp
Quote:
Originally posted by AndrewT
1kVA for 100W+100W ClassAB is unusually high. I don't think there are many here who would recommend that VA to W ratio and few builders who would follow that advice.
Quote:
Originally posted by bobodioulasso


I do not give any advice, just telling what i do.

For a 2x 100w/8 ohms capable of 2x400w/2 ohms
so which is it that you use?
a 100W+100W amplifier powered by a 1kVA transformer
or
a 200W+200W amplifier powered by a 1kVA transformer
or
a 400W+400W amplifier powered by a 1kVA transformer.

I will answer "advice" by private Email, it's too far off topic to expand here.
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Old 13th June 2009, 06:01 PM   #3992
tinitus is offline tinitus  Europe
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Multiply by factor 10, and you are in the clear

But that gets exceedingly difficult with high power amps

Maybe one reason to choose smaller amps
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Old 13th June 2009, 06:44 PM   #3993
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Quote:
Just so there is no confusion bias current through each output mosfet is the same as original version.
I was understanding 1,3/3 amps each, sorry...
So your proposal is power hungry.
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Old 13th June 2009, 07:43 PM   #3994
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Andrew,
Large transformers having a better regulation, the rails are stiffer, giving a tighter response which is a plus , something like an iron fist, never mind calculations.
Just make it big and enjoy!
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Old 13th June 2009, 09:05 PM   #3995
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Yes it is power hungry, but it is not extreme.
It certainly is still doable. You would need 500VA transformer per channel.
The the heatsinks would need to be something like this:
MF35-151.5 http://www.conradheatsinks.com/produ..._350.html#MF35
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Old 13th June 2009, 10:40 PM   #3996
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Quote:
The the heatsinks would need to be something like this: MF35-151.5 http://www.conradheatsinks.com/prod...0_350.html#MF35
These are just enough for a normal F5. So you'll need three pairs of them here for stereo.
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Old 13th June 2009, 10:57 PM   #3997
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There is 30 Watts (heat dissipation) per device, multiply by 6, and you get 180Watts total per channel.
Hence the heat sinks suggested earlier should be adequate.

I know this can be done because I have a JLH class A which dissipates 160W (heat) per channel, and the heat sinks I have are smaller. and I can touch the heatsinks no problem (temp is below 60 degrees Celsius)

Well to be on the safe and conservative side you could buy 4 and make a cube just like the Aleph 3 http://calab.kaist.ac.kr/~cgkim/audi...ages/a3_lg.jpg
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Old 14th June 2009, 10:04 AM   #3998
AndrewT is offline AndrewT  Scotland
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Quote:
Originally posted by bobodioulasso
Large transformers having a better regulation, the rails are stiffer,
Just make it big
enough.
Yes, I agree.

But you have chosen to not answer the question I asked.
What size of two channel amplifier is your 1kVA transformer driving?
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Old 14th June 2009, 01:17 PM   #3999
56oval is offline 56oval  Australia
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Hi All

A mate of mine gave me a pair of F5 boards (peter danials design)
I check out diy-tech site and they don't have matched pairs of the jfets ,how important is it to have these matched .

Cheers

Mal
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Old 14th June 2009, 01:27 PM   #4000
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According to N.P. recommendations, it is not necessary to match them, just use the same group. ( GR, BL...).
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