Aleph X with BJT, anyone? - diyAudio
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Old 15th April 2011, 04:16 PM   #1
3nity is offline 3nity  Austria
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Default Aleph X with BJT, anyone?

Hello Folks!

I was toying around some Pspice simulation around the following version of a BJT Aleph X.
Didn't put the mcmillan res.

Don't know if it works properly.
Anyway I'm showing the results. Glad to know what you think.
Thank you.
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Old 1st November 2011, 01:21 PM   #2
Jay is offline Jay  Indonesia
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One critical question is: how much is the efficiency of this amp!
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Old 3rd November 2011, 06:57 AM   #3
h_a is offline h_a  Europe
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Efficiency does not change only by using BJTs; it's still single ended ClassA, so the usual 25% or so. If you want efficiency, have a look at push-pull designs (about 50%) or ClassAB.

Hannes
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Old 3rd November 2011, 09:01 PM   #4
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130+ watts per output device?
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Old 4th November 2011, 06:31 AM   #5
h_a is offline h_a  Europe
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It's not uncommon to simulate only with a single output pair, but use multiple in the real design. Sure it is not entirely exact concerning stability, but in the end the spice models usually aren't either Hannes

EDIT: just saw

Quote:
Don't know if it works properly.
Well, so beware then.
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Old 4th November 2011, 07:33 AM   #6
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Very Cool !!!
I have been working sort of a hybrid type using a Power NPN for the CSS and a mosfet on the bottom.

jer
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Old 4th November 2011, 11:17 AM   #7
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take a look at Q14 dissipation. Perhaps use a darlington connected output to reduce the drive current the input stage must provide. Then you could use devices better suited to differential pair duty.
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Old 4th November 2011, 12:16 PM   #8
ARCANE is offline ARCANE  United States
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Honestly, I don't see the point of replacing MOSFETs with BJTs. BJTs are older technology, less stable and prone to thermal avalanche. On the other hand, MOSFETs are more modern, very stable and will progressively shutdown when too hot, giving you more safety for your amps and speakers.

But I respect the intellectual exercise....

Yves
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Old 6th November 2011, 10:40 AM   #9
h_a is offline h_a  Europe
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Quote:
I don't see the point of replacing MOSFETs with BJTs
Well, if you want a cool amp they're the better choice if you want lower distortion. Hannes
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Old 9th November 2011, 05:12 AM   #10
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In my application I am designing a small amp to use on 12v from a spare 145watt computer switching supply.

All I have are a bunch of IRF510's to work with for the moment and can still be found at the local radio shack store should any one want to give it a try ,once I get a working version done.

In my simulations I have found that I can get a lot closer to the 12v rail voltage using a 2N3055 BJT in the CCS (constant current source)in the top half than I can using the FET's.

This also reduces my parts count as well as the PD of the 2N3055 is 115 watts compared to 20 watts of the IRF510.

I know that this is irrelevant using normal practices with a higher power supply voltage and proper higher power FET's.

But I thought that it would be fun to build a smaller version using some junk box parts.

And it would be a low cost way to venture in to the realm of Class A to see what it is all about.

For normal listening with my little Sony bookshelf speakers 18" away on a desktop 20 watts is more than enough and quite loud at those levels, In fact I have never needed them any louder than that.

I have a much larger system when I need to rock out.

jer
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