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Old 19th April 2003, 12:09 PM   #1
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Default 50w @ 8r / 100w @ 4r / 200w @ 2r

i desperately need a schematic of an AB/B class amplifier that could give 50w at 8, doubling this figure until at least 2 ... yes, a beast in a compact case ... being able to drive the most current thirsty speakers on the world ... shall be a truly symmetrical, stable design... preferably on mosfets....
any help shall be appreciated
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i am currently using 60,000 uF of capacitance in my preamplifier..
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Old 19th April 2003, 03:57 PM   #2
paulb is offline paulb  Canada
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How about www.aussieamplifiers.com ?
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Old 19th April 2003, 05:19 PM   #3
moamps is offline moamps  Croatia
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Default Re: 50w @ 8r / 100w @ 4r / 200w @ 2r

Quote:
Originally posted by costiss
i desperately need a schematic of an AB/B class amplifier that could give 50w at 8, doubling this figure until at least 2 ... yes, a beast in a compact case ... being able to drive the most current thirsty speakers on the world ... shall be a truly symmetrical, stable design... preferably on mosfets....
any help shall be appreciated
Hi,

in Elektor 10/90 was published "MEDIUM POWER AMP"
with some caracteristic:
60W/8E
110W/4E
170W/2E with 0.1%THD
PS is +/-24V
IM (1W) 0.01%
SR 30V/s
DF 100 on 20kHz, 200 on 100Hz
output devices BJT pairs (3x) BD911/912

Regards
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Old 19th April 2003, 05:27 PM   #4
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Default Ya Don't Get Ought For Nought.

To double power into lowering load impedences, a 'perfect' power supply is required.
This requires over rated transformers and smoothing caps, but pays nice dividends at all power and load impedence levels.
The downside is that this adds much cost.
IOW the supply voltages should not sag with lowering load impedence and power delivery.

Eric.
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Old 20th April 2003, 10:45 AM   #5
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i do know this mr feedback... its 12A peak @ 24v on a 2R load, plus a 50% margin 18A @ 28VDC 18A @ 21VAC -> 378VA per polarity... the point is, it is not going to run into a 2R load all the time.. most likely into the 8r the b&w 603 present.. the overspecification is to ensure that the amp will be stable with any (rational or irrational) fluctuation of the speakers impedance...caps? 4 x 47000uf @ 35V is enough (2ch) i think.....
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Old 20th April 2003, 05:59 PM   #6
Werner is offline Werner  Europe
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Being able to double output power into halving impedances and
stability are two entirely different things.
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Old 21st April 2003, 02:34 AM   #7
djk is offline djk
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"i desperately need a schematic of an AB/B class amplifier that could give 50w at 8, doubling this figure until at least 2 ... yes, a beast in a compact case ... being able to drive the most current thirsty speakers on the world ... shall be a truly symmetrical, stable design... preferably on mosfets....
any help shall be appreciated"

Are you hung up on mosfets?

The GAS Son of Ampzilla, Krell KSA50, and the Leach all come to mind.

All are full complementary from input to output using regular bi-polar transistors.

The GAS:

http://home.kimo.com.tw/skychutw/amp...pzilla_sch.jpg

A Mark Levinson design, the same basic topology with J-fet inputs:

http://home.kimo.com.tw/skychutw/Cir...schematics.jpg

If you insist on mosfets for outputs, the Hafler XL280 is the same topology as the Mark Levinson, just with fet outputs:

http://www.hafler.com/techsupport/pd...80_amp_man.pdf

An all hex-fet variation:

http://www.passdiy.com/pdf/A75p1.pdf

http://www.passdiy.com/pdf/a75p2.pdf

What I use:

http://users.ece.gatech.edu/~mleach/...aphics/ckt.pdf

http://users.ece.gatech.edu/~mleach/lowtim/

I get 450W/2R from three pair of outputs. I would strongly suggest using a regulted high voltage tier for the front end (like the GAS, XL280, and A75).

A 30-0-30V 400VA transformer per channel with 15,000~30,000F is all you need for 200W/2R. Two pair of outputs.
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Old 21st April 2003, 09:41 AM   #8
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Default Leach amp + 4 X 47,000uF = Fine.

Quote:
Originally posted by costiss
i do know this mr feedback... its 12A peak @ 24v on a 2R load, plus a 50% margin 18A @ 28VDC 18A @ 21VAC -> 378VA per polarity... the point is, it is not going to run into a 2R load all the time.. most likely into the 8r the b&w 603 present.. the overspecification is to ensure that the amp will be stable with any (rational or irrational) fluctuation of the speakers impedance...caps? 4 x 47000uf @ 35V is enough (2ch) i think.....
Yes 4 X 47,000uF should be all the snot that you need - many high power pro-amps run much less than this - like 30,000uF total for 2 X 1000W into 4 ohms.
With intelligent power supply and earthing arrangements, this should give pretty much limitless performance.

The Leach amp that Djk uses, although not mosfet ought to be good - I have not heard one but I do bellieve that they are pretty good.
Use 2SA1943 and 2SC5200 output transistors and it will never let you down.

Eric.

Eric.
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Old 21st April 2003, 09:51 AM   #9
PMA is offline PMA  Europe
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Default Re: Ya Don't Get Ought For Nought.

Quote:
Originally posted by mrfeedback
To double power into lowering load impedences, a 'perfect' power supply is required.
This requires over rated transformers and smoothing caps, but pays nice dividends at all power and load impedence levels.
The downside is that this adds much cost.
IOW the supply voltages should not sag with lowering load impedence and power delivery.

Eric.
Eric,

that's right. And have a look at the SOAR of output transistors, take to the account reactive compound of load impedance.

Pavel
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Old 21st April 2003, 11:41 AM   #10
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Default easy Soloution

Just run enough output transistors, and impedence compensate the drivers - and no problems.

Eric.
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