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Old 14th November 2008, 06:49 PM   #1
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Question Double-die mosfets in P101?

Hi all!

I'd like to know if it's possible to use double-die mosfets instead of the single-die ones presented in the original project, in order to raise the rail voltage and get a higher output power.
What other modifications should I do?
AFAIK, the effect of using these mosfets is the same of putting 2 pairs in parallel.

page of the project: http://www.sound.westhost.com/project101.htm
original transistor datasheet: http://www.jaycar.com.au/images_uploaded/2SK10568.PDF
double-died transistors: http://www.profusionplc.com/images/d...s/ecf20p25.pdf

Thanks for the attention!


Daniel
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Old 15th November 2008, 07:09 AM   #2
Mooly is online now Mooly  United Kingdom
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Hi Daniel,
A single pair is usually more than adequate for domestic use.
The main problem is keeping them cool, and a double die device makes things worse of course. If you really want to build a powerhouse of an amp use separate ( 2 pairs of outputs ) as these will dissipate the heat better.
The double die types really are just two separate devices in one package. Being laterals you can just parallel them up with no worries on current sharing etc.
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Old 15th November 2008, 05:32 PM   #3
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Hi Mooly!

If I double the number of mosfets in output stage (paralleling them) and use huge heatsinks and also forced ventilation, I don't think heat will be that much of a problem. I'd like to use this amp for professional use also.

The matter is how far I can go from the original 70/0/70v, so that I can achive more power. I also need these figures in order to order the toroid.

Thanks for the attention and best regards

Daniel
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Old 15th November 2008, 05:42 PM   #4
jaycee is offline jaycee  United Kingdom
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The P101 circuit is really not suitable for more than 70V rails. There is more to it than simply making the output stage more powerful.

You are probably best looking at one of Anthony Holton's designs as he deals with high power output. Even better, he uses vertical mosfets which are easier and cheaper to get.
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Old 15th November 2008, 07:09 PM   #5
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I had a look at his website and it seems that his products are far more expensive than the p101!

And what about the sonic differences between a lateral and vertical mosfet design?
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Old 16th November 2008, 01:53 AM   #6
jaycee is offline jaycee  United Kingdom
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There is a reason for the price increase - high power output is not a simple task!

The P101 is an amp designed for domestic use and for fairly low power - note that Rod says the absolute maximum is 70V.. that is his words for "if you realy want to push it, but i dont recommend it!"

Look for the Holton AV800 schematic. It should be floating around on here. You might have to do your own PCB though. If you really want a high power amp for pro use, you are going to need to invest cash in big heatsinks, a big transformer and smoothing capacitors... or at least have a broken PA amp you can reuse.

If you're trying to do this cheap - forget it. You could buy a PA amp for cheaper than you could build one.
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Old 16th November 2008, 06:45 AM   #7
Mooly is online now Mooly  United Kingdom
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Hi Daniel,
Lateral Mosfet's used sympathetically are unbeatable for a domestic amp IMO.
You ask about power output, laterals are not the preferred device for huge amps for various reason such as the relatively high resistance of the Drain-Source channel even when fully conducting. It costs big time effeciency wise, but for domestic use that's not a problem.
70 volt rails, let's say you lose 12 volts over the devices etc, that give a max output of just over 200 watts rms ( 8 ohm ) assuming the supply holds up.
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Old 16th November 2008, 10:07 AM   #8
djk is offline djk
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The Hafler DH500 and XL600 use the Exicon transistors you linked to.

The DH500 used ±90V and three pair to deliver 600W/3R.

The XL600 used ±90V (and a high voltage tier for the front end) and four pair to deliver (at clipping):
360W/8R
500W/4R
750W/2R
900W/1R
1KW/8R (mono)
1.5KW/4R (mono)

This was continuous duty cycle across the audio band. Depending on impedance, time may be thermally limited to several minutes.

The DH500s I built from a kit in 1981 are still running strong, and get regularly used for mids, highs, and floor monitors. I tried them on bass but they sound a bit muddy for my taste.
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