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Old 27th August 2004, 04:42 PM   #1
Nexus is offline Nexus  Netherlands
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Default N-Channel mosfet amplifier schematic needed

Hello dear DIY'ers,

I am looking for a working N-Channel mosfet amplifier schematic.

I looked into several threads, but didnot manage to find a complete schematic which is operative.

All schematics (with one or more mosfet pairs in the output stage are OK).

You can use my mail adress.

Thank you in advance:
Nexus
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Old 27th August 2004, 05:09 PM   #2
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What quality level are you looking for?

Hifi or PA?

How much power is needed?

I intend to publish a new N-channel design shortly.

Best regards

Lars Clausen
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Old 27th August 2004, 05:21 PM   #3
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In the JLH 10w Class A thread is a N-channel version which can be run in class B without modification.. it is a working design and it is build by me and another forum member... but also N Pass citation 12 mosfet version ... and some more which have not been build yet but have been simulated only so far...

goodluck


PS
Looking forward to your design Lars

edit

And offcrouse how could I forget.. X-pro's design... that's a real nice one.. look for x-pro posts...
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Old 27th August 2004, 05:25 PM   #4
Nexus is offline Nexus  Netherlands
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Hello Lars,

I am looking for a hifi design.

And I am looking forward for your design!


Best Regards:
Nexus
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Old 27th August 2004, 05:28 PM   #5
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Thank you for the input Tschrama.

I am looking for a design of about 40W.

Best Regards.
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Old 27th August 2004, 06:17 PM   #6
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Nexus: OK my current design is somewhat bigger than that, but
i will cook something up for you, and also test if it actually works in the real life :-) I will send you some schematics within a few days.

BTW do you go for simplicity or high performance? My ref design is ultra wide bandwidth, from 5 to 250.000 Hz (+0-1dB) and stable in any load of course.
However if 5-50.000 Hz is adequate it could be reduced in parts count.

Lars

40 Watts On the brink to War of Clones?
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Old 27th August 2004, 07:22 PM   #7
Nexus is offline Nexus  Netherlands
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Hello Lars,

I like the wide bandwidth, some more power is also OK (max. 50W).

I have developped a few amplifiers myself, but I have virtually no experience with mosfets.
(And currently no time to experiment ).

Best Regards:
Nexus
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Old 27th August 2004, 09:30 PM   #8
jleaman is offline jleaman  Belgium
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um the nchannel puts out a hell of alot more than 50watts why not choose something other than the n-channel ? what is wrong with getting the schematic off of www.aussieamplifiers.com
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Old 27th August 2004, 10:03 PM   #9
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Nexus: Now after a glass of wine, and a couple of hours, it's up and running in a 50W version. Quite easy to get it working actually, very stable, and sound is pretty good, i would say. But then it's also a nice red wine

It's based on 2 x IRF640N (the smallest MOSFET in the drawer). IRF530N or IRF540N would do just as well for 50W. (N versions have somewhat lower capacitances than the old ones).

I think most of us don't have much time to experiment, although this is really the fun part of DIY audio IMO. It helps tremendously to have a cradle setup, a unit with a safe power supply, heatsink with holes, in/out plugs, everything you need at hand, just ready to connect and play. Just mount in the parts, and turn on the power.
I think it took me just under two hours to build this 50 W amplifier from scratch.

The parts cost of the amp is LOW maybe 2-5 $ total, depending on where you buy.
Will send you the schematic when i get it drawn up. (Pretty soon).

Alll the best

Lars
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Old 27th August 2004, 10:51 PM   #10
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ok, maybe 2$ is a bit optimistic .. L
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Old 28th August 2004, 02:41 AM   #11
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http://www.passdiy.com/pdf/citation.pdf

My cost on the 214 watt IRFP250N is $0.77 each

Good inexpensive amp.
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Old 28th August 2004, 09:16 AM   #12
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djk: Pretty good price for IRFP250N.

One pair of IRFP250N will produce up to 360 Watts audio power. (At 100 degrees C)
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Old 28th August 2004, 11:59 AM   #13
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OK!!

Thank You Lars,

I will look forward to the schematic.

Best Regards:
Nexus
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Old 28th August 2004, 12:34 PM   #14
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Nexus: Since i'm going to make a nice small experimental PCB for this amp anyway, i can instead of the schematic, send you a couple of working amplifier modules, for your project. (Free of course).

Please send me your postal address by e-mail.

It may take a month or so before the PCB's are through, so please have a little patience.

All the best

Lars
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Old 28th August 2004, 10:39 PM   #15
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Hello Lars,

I send you the adress, can you us supply a glimpse of the schematic?

I am very curious.

Best Regards:
Nexus
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Old 28th August 2004, 11:08 PM   #16
jleaman is offline jleaman  Belgium
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Quote:
Originally posted by Lars Clausen
Nexus: Since i'm going to make a nice small experimental PCB for this amp anyway, i can instead of the schematic, send you a couple of working amplifier modules, for your project. (Free of course).

Please send me your postal address by e-mail.

It may take a month or so before the PCB's are through, so please have a little patience.

All the best

Lars

can i get a set of amp board moduels too or even just eh raw pcb's ill pay shipping for boards adn stuff. as im curiouse too..

J'
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Old 29th August 2004, 07:30 PM   #17
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I'm not going to post any schematics here, because of diyaudio's copyright rules. (I might get into trouble just from using my own design).

However a few pictures are no problems, first the birdsnest of the small 50W N-channel amplifier. It uses two IRF640N devices, but even smaller ones will do fine. You can almost see how i have made the output circuit in this picture, if you look closely. The green PCB in the back is a small folded cascode voltage amplifier, and power plug, to unplug everything in case of problems, when experimenting. :-) The voltage amplifier also features soft clipping and a total rail loss with N-ch devices of around 4 V (similar to a bipolar output device with 0.22 Ohms emitter resistors).

Just by replacing the IRF640N's to something bigger you can increase outut power to much higher levels. The rest of the circuit is calculated for +/-100 Volts supply, and 5nF capacitive load, so around 500 Watts in 8 Ohms should be no problem.
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Old 29th August 2004, 07:41 PM   #18
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Below you can see the output waveform. Note the frequency, 100 kHz is the highest this sinewave generator will go. But the amplitude is not even 1dB down compared to 1 kHz.

If you notice a small ripple on the top of the sine wave, it is due to the feedback being shifted to before the output circuit over 50 kHz. This is to maintain stability in high capacitive loads, without sacrificing bandwidth. See the ULCA thread for further details on that one.

Output power here is just 16W (the transformer is a 30VA, and it's sweating!)
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Old 29th August 2004, 07:45 PM   #19
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... and here is the picture ... :-)

Last let me emphasize that this is not a product of me, or my company. It is just a fun experiment, to find a good usable topology for building N-channel amplifiers with good sound quality.
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Old 30th August 2004, 01:38 PM   #20
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You can have a look here:

http://altor.sytes.net/ni/creek4330.jpg

Cheers

x-pro
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Old 30th August 2004, 03:27 PM   #21
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Thanks X-pro! Very interesting... allthough I don't understand the topology completely... If you happen to have some spare time, could you explain the topology a bit ? I do not seem to understand the 2 trasistor in the middel of the topology...Q6 and Q7?

Regards,
Thijs
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Old 30th August 2004, 04:05 PM   #22
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x-pro: Very interesting :-) Nice and simple design. And the rail loss is somewhat lower than the Citation 12 clone. In this design i would say something like 3.2 Volts on the first saturating rail, (the positive rail in this design). Pretty good!

Thijs: It seems that Q6 and Q7 are the pull-down current generator for the voltage amplifier stage (Q5).
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Old 30th August 2004, 04:53 PM   #23
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THx..... got it....

,
Thijs
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Old 30th August 2004, 05:08 PM   #24
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I hope am not irritating anybody, but I still don't get it... is r6 a way to provide some local feedback? What does r6 do?


regards,
Thijs
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Old 30th August 2004, 05:33 PM   #25
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2 tschrama

yes, R6 provides some local feedback and makes VA more linear.

2 Lars Clausen

This configuration of the output stage is a pretty good follower - THD into 8 Ohm would be around 0.2% without the overall feedback with 70-100 mA idle current. R21 allows for a correct temperature compensation of the output devices. As you may see, there is no source resistors on the output devices.

If somebody would try to repeat this circuit - few comments:

1) It is useful to add a small coil in parallel with 1 Ohm resistor in series with the output after Zobel R23 C7 - say 10 turns of enamelled wire 1mm diameter on a 2 Watt resistor. In production this inductance was provided by wiring to the output sockets.

2) Q8 should be touching the heatsink close to Q11 and Q12, and these should be mounted using mika washers and good thermal compound. If you use silicon rubber washers than the output would blow sooner or later.

3) It would be advisable to increase the value of R22 to 0.47 Ohm 6W W/W and add another same value resistor as shown in the attached picture - this makes the output stage much more tolerant of short circuit condition.

Cheers

x-pro
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