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Old 1st March 2006, 08:40 PM   #1
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Default Want to build amplifier

I decided to build amplifier with mosfet output devises. I have one with bipolars, so it will be interesting to build with mosfets. So I need AB class amplifier schematic capable to drive 4 ohms speakers, aprox 100 watts. I have a few schematic, but I know nothing about theirs sounding. I need god sounding amplifier, any suggestion are welcome.
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Old 4th March 2006, 11:12 PM   #2
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I wanted build Zenquito, but I cant' find output devises, there are any substitutes.
Second variant was crescendo, but it has problem with oscilations, so I change my mind.
And the last one this (shematic below), but with irfp240/9240 output devises. Did someone tryed to build this amplifier?
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Old 4th March 2006, 11:12 PM   #3
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Shematic
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Old 5th March 2006, 12:15 AM   #4
lineup is offline lineup  Sweden
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This is the 'HEXFET Elektor Amp'
with IRF540/9540
and Common Collector output with a bit of voltage gain.

It is a good amplifier, and not too complicated.
I think, you can replace with those other HEXFET IRFP240/9240
without only small changes.

But best is of course using original IRF540/9540.
Because this is what it is designed for.
There is nothing that makes amp better, using other transistors.

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Old 5th March 2006, 12:27 AM   #5
ilimzn is offline ilimzn  Croatia
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Quote:
Originally posted by lineup
...I think, you can replace with IRFP240/9240
...But best is of course using original IRF540/9540 because this is what it is designed for.
...There is nothing that makes amp better, using other transistors.
Well, that's what you think
P240/9240 are not true complements, and 540/9540 are even less so. IRFP140 and 9140 would be approximate equivalents for the 540/9540 with the notable exception of vastly improved power dissipation capability. Another combination would also give you pretty decent complementarity (which, BTW this topology could use to an advantage). So yes, it can be improved by changeing transistors - as long as you know what you are doing.

There was a whole thread here on that amp, with several suggested modifications, as well as a report of a board member that did carry them out.
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Old 5th March 2006, 12:36 AM   #6
lineup is offline lineup  Sweden
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Quote:
Originally posted by ilimzn


Well, that's what you think

There was a whole thread here on that amp, with several suggested modifications, as well as a report of a board member that did carry them out.
Still, the original amplifier worked very well with non-complementary pair.
There is no reason why IRF540/9540 cant and should not be used,
as the circuit take into count differences, capacitance, RDSon or whatever, that exists.
At least these differences are not allowed to mess up this designs performance.

And yes, IRF540 / IRF9540 is far from 'true complementary'.
This more a rule than an exception for MOSFET / HEXFET, and even often for bipolar transistors.
So much for building 'symmetrical amps'.

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Old 5th March 2006, 11:28 AM   #7
DIYdo is offline DIYdo  United Kingdom
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That is quite an interesting design. It doubt anyone without experience in fabricating PCBs would be able to get good results with that topology. That design IMO looks inherently unstable. It will work fine if constructed properly, certainly not one for the unexperienced in amplifier construction.
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Old 5th March 2006, 04:14 PM   #8
ilimzn is offline ilimzn  Croatia
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Agreed, and it has proven to be so in practise. One of the more bothersome things are the fuses in the source lines of the MOSFETs... as well as compensation.
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Old 5th March 2006, 09:45 PM   #9
suzyj is offline suzyj  Australia-Aboriginal
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Default Re: Want to build amplifier

Quote:
Originally posted by andriusha
So I need AB class amplifier schematic capable to drive 4 ohms speakers, aprox 100 watts. I have a few schematic, but I know nothing about theirs sounding. I need god sounding amplifier, any suggestion are welcome.
I'm currently building a pair of amplifiers based on David Tilbrook's AEM6000 design, originally published in an Australian electronics magazine in 1987. It may also be of interest to you.

They use Hitachi 2SK1058 and 2SJ162 lateral MOSFETs in the output, and the input uses a JFET diff-pair with bipolar cascodes. The design simulates well, with THD of 0.001% at 1KHz driving 200W into 4 Ohms (+/-60V supply). I've laid out a two layer PTH PCB for it as well, and am currently getting the bits together to build a couple. The MOSFETs aren't cheap!

See the following for more info:
It's probably a little on the complex side, but should (I hope) be a rewarding project. By all indications they should sould fantastic.

Cheers,

Suzy
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Old 5th March 2006, 10:13 PM   #10
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Hi looking at the 6000 schem. i see a lot of stages there it all
looks impressive the stages look well thought out but at the
same time i look at zen and wonder at the extent to which
amp design varies between america and england

the vast architecture of the 6000 and fully symmetry is a work
that demonstrates clearly that superiority is it

but the humble zen bets on the fact that the designer is a guru
like NP, wine, class-a,...etc

cheers
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