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Old 7th April 2010, 09:34 AM   #1
Pigy is offline Pigy  Serbia
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Question Can this scheme works like this?

The first scheme is original with NE5534 and BD243/244
The second scheme was modified so that instead of bipolar transistors are placed MOSFET
The latter scheme was modified by my friend who is already 20 years old designer audio amplifier, but again I do not know whether this scheme can work like this?
The second question, the description states that the original scheme-first has the power of 6W into 8 ohms, is it not so much with too little voltage, is not it should have greater power amplifier?
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Old 7th April 2010, 11:57 AM   #2
wahab is offline wahab  Algeria
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These kind of schematic are just plain catastrophic ,
as the op amp supply rail are modulated with the signal.
Furthemore, a NE5532/5534 need a decoupling cap across
the supply lines to tame down eventual oscillations, so this
amp will surely oscillate..

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Old 7th April 2010, 12:24 PM   #3
sregor is offline sregor  United States
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Interesting circuits. Unless I'm mistaken - these circuits are current sources (Output current is a function of input voltage. There has been some discussions somewhere about lower distortion with certain drivers at certain ranges, but most speakers are designed to run with a voltage source, and anything with a resonance will have a huge peak. Might be good for driving ribbon type drivers.
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Old 7th April 2010, 12:30 PM   #4
ilimzn is offline ilimzn  Croatia
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Not a good idea for several reasons.
It's a current output amp, which is not a great idea except for driving certain very specific kinds of speakers. Wahab has a point too and the whole thing is not too good to begin with.
I don't know what your friend has been doing for the last 20 years but he certainly has not learned a lot about lateral MOSFETs, with all due respect. They require quite a lot of Vgs for higher currents because they have low transconductance, so the rail loss will be high, and further aggravated by the source resistors which are completely unnecessary for a single pair of laterals (and mostly for multiple pairs if some selection is done). The current sensing resistor makes it all even worse.
It is, however, possible to construct a simple amp with the components given.
The simplest wat is to drive the MOSFETs directly, although rail loss wil be increased. NE5532/5534 is actually capable of driving these fairly well. The relatively low supply voltage will make things more difficult as you end up in the non-linear input capacitance region of the MOSFETs for fairly low output power already.
A better solution would be a common base - folded cascode driver. Another solution is an 'inverted' configuration where the output power supply is floating, see 'transnova' topology.

Last edited by ilimzn; 7th April 2010 at 12:33 PM.
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Old 7th April 2010, 01:07 PM   #5
ontoaba is offline ontoaba  Indonesia
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Using lateral mosfet like that is waste, high voltage capabilty, high power dissipation, thermal stability and its linearity will no use but waste.
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Old 7th April 2010, 08:32 PM   #6
Pigy is offline Pigy  Serbia
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I'm asking friends to help me to use MOSFET transistors as the output instead of bipolar transistors.
He's drawn-restated it and said that this scheme should work.
Did you find friends like this can not work?
What happened to the original scheme, how power can be ... 6W?
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