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Old 12th June 2010, 05:26 AM   #1
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Default What can I do with these MOSFETs?

Hey guys,

I have this big 'ole array of MOSFETs (MTM55N10s) that I'd like to use in a power amp. Any clue was to what I could build? I haven't a clue what these came out of, but if they are audio quality, I'd love a medium-to-high power amp!

Click the image to open in full size.

Thanks!

Kyle
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Old 12th June 2010, 06:09 AM   #2
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100V 55A Max. Looks like Motorola version of IR devices.

You may use them for a stereo class A amp, one as a source follower, another one as a current source. Output power and load resistance would depend on heatsink's capability to dissipate heat.
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Old 12th June 2010, 12:21 PM   #3
adason is offline adason  United States
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maybe this...
Mini-MosFet Audio Amplifier - RED - Page123
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Old 12th June 2010, 01:16 PM   #4
Jay is offline Jay  Indonesia
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That's N-channel mosfet for switching. How many transistors do you have? With only 4 transistors you cannot parallel them to get high power amp, unless you purchase another 4 P-channel mosfets.

Those mosfets have 5000pF of input capacitance. That's not a good thing, especially if you have to build class-B amp (to get high power). Search for Pass' modified Citation 12. It uses 2 N-channel mosfets per channel. I think it is 50W I'm not sure. If you have 12 mosfets you can build Quasi Amp (search in this forum). It depends on one's standard but to me such mosfet can never sound good enough in class-B.

Class-A is low in power but the sound quality is a good compensation. You can get relatively higher power using Aleph current source such as in Aleph J amplifier. But your heatsink may be too small for the heat.
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Old 12th June 2010, 08:28 PM   #5
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Yeah, I only have those four. But I like that Mini-MOSFET amp. I might try putting that circuit together once I get a big 'ole 40V power supply. Any suggestions for that?

Thanks for the great suggestions! I've got a lot of projects right now (and a new one today; more on that later), but I have quite a bit of time ahead of me to work on some more amps.

Kyle
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Old 12th June 2010, 09:02 PM   #6
shaan is offline shaan  India
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You may also consider this simple but elegant amplifier. With Vgsmax of 4v at 100deg C these FETs seem to be okay for this amp.

>>> MOSFET Power Follower <<<

Use the schematic shown in Figure 4.

When driven by a great preamp like Death of Zen, I think you will like it.

Sound is audiophile 17 watts.
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Old 13th June 2010, 01:19 AM   #7
djk is offline djk
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"Any suggestions for that?"

What are you going to use for the P-channel FETs?

Build the Pass Citation 12 for a good medium power amplifier.

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

.
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Old 13th June 2010, 05:37 AM   #8
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Oh shoot...you're right! I guess I can't build the Mini then!

The MOSFET Citation 12 looks very nice. Do you suppose these MOSFETs will work just fine in that circuit? And how do I know exactly what to bias that amp to?

Thanks!

Kyle
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Old 13th June 2010, 07:13 AM   #9
infinia is offline infinia  United States
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Be aware that one of the major drawbacks of the MOSFET Citation 12 as presented, is under use of the PS (much lower power than the original). This is because the gate drive needs to be at least 8 to 10V higher than the main supply rails.
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Old 13th June 2010, 08:42 AM   #10
djk is offline djk
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" is under use of the PS (much lower power than the original). This is because the gate drive needs to be at least 8 to 10V higher than the main supply rails"

Is 10W 'much lower'? It's less than 0.8dB lower than the rated 60W of the original Citation.

In fact, since he doesn't have the Citation 42V supply, he can build something more robust. Pass himself suggested using a high voltage tier for the front-end. The MTM55N10 is a 250W device (the IRF part was only 150W), so a 100W/8R stereo amplifier could be built with the four MTM55N10 and the heatsink he has.
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