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Old 26th August 2012, 06:54 AM   #1
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Default 200W mosfet Amplifier

HI hear is amplifier when i browsing i found this amplifier i want good discation on it
i want to build it please help me on it
link http://www.siliconchip.com.au/cms/A_...ntArticle.html
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Old 26th August 2012, 07:40 AM   #2
AndrewT is offline AndrewT  Scotland
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The Signal Ground (sig IN -) is connected to the power ground trace between the Medium Frequency local decoupling. This will ruin the amplifier.
This PCB has not been thought through.

I don't like the idea of running the LTP at <500uA, the Vas @ 8mA and direct driving the outputs from the low current Vas stage.

And the LTP is running right up at the Vce max rating of the devices (is it beyond the max rating?).
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Old 26th August 2012, 08:16 AM   #3
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With 200W / 8 Ohm (given the supply rails) there's too few output pairs, you want at least 3 pairs. The VAS current is indeed rather low, but it's doable. With those current settings you shouldn't expect a very high bandwidth though, which sorta shows by the applied Cdom of 10pF in conjunction with a relatively high ohmic feedback of 33K.

Edit Vce of the input transistors is reduced some by the series restances in the circuit. When operating normally Vce is honoured, however during startup Vce is dishonored briefly for most of the transistors.
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Last edited by MagicBox; 26th August 2012 at 08:18 AM.
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Old 26th August 2012, 08:19 AM   #4
Bone is online now Bone  United Kingdom
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This looks like a Silicon Chip design but I dont know which Issue its in. If SC have published it then they usually get it right.
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Old 26th August 2012, 07:33 PM   #5
amptech is offline amptech  Scotland
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BONE, your right it was published by sc and more so it was de-rated to this 200w watt @ 4 ohms and 140 ish @ 8 ohms (it's a pro sound amp design)

Having build this amplifier and using double die fet's plus adding a transistor within the bias circuit to track the o/p stage.. it gave a good performance..
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Old 27th August 2012, 03:59 AM   #6
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Hi all is it good for home use as a HI FI stereo system
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Old 27th August 2012, 10:52 AM   #7
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In a word - No. It is intended to be cheap and robust for pro sound or PA use. I know of 2 examples at work in my area and that is their purpose and end use. Only one has needed service over 10 years, due to being dropped in transport between gigs.

There is more than a little resemblance to the UK Maplin module kits of many years ago and since this published design is inspired by the kit retailer, Altronics, you might see why it could be considered marginal to the conservatives here but rest assured, it works fine in PA.
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Last edited by Ian Finch; 27th August 2012 at 11:11 AM.
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Old 27th August 2012, 01:24 PM   #8
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Quote:
Originally Posted by Ian Finch View Post
In a word - No. It is intended to be cheap and robust for pro sound or PA use.
Hi Ian,

would you concur that would also apply to the Goldmunds and many other cheap amps using the same topology.

I guess all amp circuits are really cheap. What makes an amp audiophile is the expense added by the metal work.
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Last edited by Nico Ras; 27th August 2012 at 01:29 PM.
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Old 27th August 2012, 06:00 PM   #9
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And not cutting on a transistor here and there to get implemented new concepts in topology
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Old 27th August 2012, 06:11 PM   #10
wahab is offline wahab  Algeria
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BC546/556 have 65V Vce and should be replaced with 2SC1845/2SA992.

For good performances 2SA1360/2SC3423 are to be used instead of MJE340/350.
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