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TroelsM 1st March 2006 02:32 PM

N-Channel with bipolars?

I've got 24 MJ15003 and was wondering if its possible to make a class AB with only those N-channels in the output-stage.

I seem to remember an old Elector Electronics schematic with approx 40W/8 Ohms that used 2n3055 in the output-stage. The Output was made up with two "super-transistors" each build with a 2N3055, a few other transistors and a handfull of resitors.

I actually build one of those and it worked very fine.

I'm noy looking for super-hifi, but a decent qual.


Eva 1st March 2006 02:37 PM

Yes, it is possible to produce output stages with NPN power devices and it was extensively done before 1980s, until suitable PNP power transistors become affordable.

You should ask for "quasi-complimentary" output stages instead, as N-channel refers almost exclusively to MOSFETs.

DIYdo 1st March 2006 02:54 PM

Use an EF configuration to the V+ rail and a CF on the V- Rail. Use the Baxandal diode linear configuration on the CF transistors. You can modify most amps that where either CF or EF OPS to run QCS with this approach.

latala 1st March 2006 07:06 PM

lindseyhood got a credible 0.01% with his 75 watt design and npn output devices this is still a credible circuit allthough not to complex i would start there theres also the quad 303
and even a 405 all npn devices
or go the whole hog and build a npn armstong 521 all the devices would be npn now there is a challenge rather a lot of capacitors though !
regards trev

massimo 1st March 2006 08:11 PM

One of the best "british made" small integrated amp was using a Quasi Complementary topology.
The name? Cyrus One ;)

DIYdo 1st March 2006 08:40 PM

Take this as an example


Connect the collector of Q5 and Q7 (your NPN device) directly to the V+ rail, Connect the emmiter of Q5- base of Q7 with R11 going from output to emmiter of Q5 (base of Q7) and the emmiter of Q7 to output. Leave Q6 and Q8 in the same configuration, however instead of the E of Q6 going directly to C of Q8, put a 1N4004 diode in series with the E of Q6 (paralell the diode with a 220 ohm resistor).

After that modification you will want to track the temperature of the OPTs instead of the drivers, so mount Q9 directly to the heatsink. This I'm sure will give you more than satisfactory results.

quasi 1st March 2006 09:46 PM


At the request of another member (Zeonrider) I posted a schematic of my N-channel mosfet amp modified for bi-polar outputs. If you are patient I will build the prototype over the next 2 months or so. The schematic is shown here.

As a guide the design is intended for +/- 75 volt rails and 8 output transistors per board. This will deliver around 220 watts into 8 ohms and around 380 wats into 4 ohms.


stoN_Cold 5th March 2006 07:30 PM

For Quasi & only for Quasi !
Hi Quasi , at last post you sad 2 months, but now is 05 03 2006, N chan. Mos fet work perfect. CHEERS 1

quasi 5th March 2006 09:33 PM

Good to hear the mosfet amp works well. The bi-polar amp will still be a coupple of months away....sorry too many other projects, I still haven't finished the other mosfet amp...I need the world to stop for 2 weeks.

DIYdo 5th March 2006 11:01 PM

This is something I designed to run a subwoofer. It sounded very nice on full range speakers also. It was intended for a sealed enclosure so hence the lack of VI limiting. If you want something simple, this should be more than adequate. Note that Q3 could be replaced with a BC546 if you wish.

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