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Old 12th August 2005, 10:04 PM   #1
Pelle is offline Pelle  Sweden
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Default Feedback - Choke loaded Zen w. input buffer

Hi!

I'm currently building a modified Zen that is intended to drive my midrange and tweeters using some parts found in old battery chargers. I need some feedback before I proceed with a PCB for the amplifier (no, I don't like P2P ).

I have chosen to connect the speaker directly across the inductor because of its low resistance, which also saves me some money on a big capacitor. I would also like to have the input DC-coupled but I am afraid that will mess up the bias to much if the source has some DC-offset.

Currently I am planning on using IRFP260 (!!!) as gain devices because I have loads of them and I hope this will not cause to much of a problem when using the input buffer.

This is the current schematic and I would like to know what you think about it (the powersupply is not shown, it consist of 1000VA 1x28VAC transformer + rectifier + 33000uF + 6mH + 22000uF),

Click the image to open in full size.

and this is how one channel will look (the heatsink will be cooled by a fan),

Click the image to open in full size.

Regards
Pelle
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Old 14th August 2005, 12:59 PM   #2
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Hur går det med bygget?
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Old 14th August 2005, 01:19 PM   #3
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How much current flows in each of the output MOSFETs?
Choke loading can give *very* good results. I have a 50+50W that uses a source-follower and a chokes of 80mH 50mR and the speaker is connected directly across it. There is 325mV drop across the choke and therefore the speaker, but this is no problem at all.

Keep at it.
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Old 14th August 2005, 11:36 PM   #4
Pelle is offline Pelle  Sweden
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Circlomanen:
I will bring the amplifiers to my small apartment in Luleå tomorrow and there I can make the PCBs. So hopefully in a week or so I will be able to test them.

Circlotron:
I've simulated with about 1.4 amps per mosfet giving about 50 watt each. They will be cooled by a fan so I hope this will work.

-Pelle
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Old 15th August 2005, 12:42 AM   #5
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Pelle,

I can't see any bias source for your input MOSFET. Missing resistor?

Morgan
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Old 15th August 2005, 09:13 AM   #6
Pelle is offline Pelle  Sweden
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Morgan L:

Since the input mosfet is a P-channel and its gate sits at ground potental the 3.3k + 68 ohm resistors will try to pull the source of the mosfet to the rail voltage making it turn on.

-Pelle
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Old 16th August 2005, 08:17 PM   #7
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Very nice looking. I'm impressed.
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Old 17th August 2005, 05:28 AM   #8
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I must have been very tired and cross-eyed to miss the fact that it's a P-channel... sorry about that.
It IS a very appealing schematic (and that's coming from a valve guy who happened to stray to the "wrong" forum...).

Morgan L
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Old 18th August 2005, 12:21 AM   #9
Pelle is offline Pelle  Sweden
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Thank you for your kind words! I have done the PCB-layout today and will etch them as soon as I can.
I will get back to you when I have done some preliminary testings.

-Pelle

This is how the PCBs will look (50x37 mm and 25x37mm),
Click the image to open in full size.

edit:
Morgan: Nice to see some people not far from home that has the right interests! I'm from Vännäsby originally and I suspect you know where that is.
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Old 21st August 2005, 08:53 AM   #10
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Pelle:
'Morgan: Nice to see some people not far from home that has the right interests! I'm from Vännäsby originally and I suspect you know where that is. '

Indeed I do. And I forgot to say that I like you innovative breadboard design, esp. the transformer covers! I'm also fond of using oak board pieces for prototypes, etc., in "open" designs. Much less messy than cutting metal in the "reseach kitchen"!

Morgan
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