Feedback - Choke loaded Zen w. input buffer

Pelle · 12th August 2005, 11:04 PM

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),

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

Regards
Pelle

Circlomanen · 14th August 2005, 01:59 PM

Hur går det med bygget?

Circlotron · 14th August 2005, 02:19 PM

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.

Pelle · 15th August 2005, 12:36 AM

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

Morgan L · 15th August 2005, 01:42 AM

Pelle,

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

Morgan

Pelle · 15th August 2005, 10:13 AM

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

Nelson Pass · 16th August 2005, 09:17 PM

Very nice looking. I'm impressed.

Morgan L · 17th August 2005, 06:28 AM

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

Pelle · 18th August 2005, 01:21 AM

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),

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.

Morgan L · 21st August 2005, 09:53 AM

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

12th August 2005, 11:04 PM	#1
Pelle diyAudio Member Join Date: May 2003 Location: Luleå	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), and this is how one channel will look (the heatsink will be cooled by a fan), Regards Pelle

14th August 2005, 01:59 PM	#2
Circlomanen diyAudio Member Join Date: Sep 2004 Location: Göteborg	Hur går det med bygget? __________________ We live in a horizontal world, why use vertical topologies???

14th August 2005, 02:19 PM	#3
Circlotron diyAudio Member Join Date: Jun 2002 Location: Melbourne, Australia	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. __________________ Best-ever T/S parameter spreadsheet. http://www.diyaudio.com/forums/multi...tml#post353269

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15th August 2005, 12:36 AM	#4
Pelle diyAudio Member Join Date: May 2003 Location: Luleå	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

15th August 2005, 01:42 AM	#5
Morgan L diyAudio Member Join Date: Jan 2004 Location: Umea, Sweden	Pelle, I can't see any bias source for your input MOSFET. Missing resistor? Morgan

15th August 2005, 10:13 AM	#6
Pelle diyAudio Member Join Date: May 2003 Location: Luleå	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

16th August 2005, 09:17 PM	#7
Nelson Pass The one and only Join Date: Mar 2001	Very nice looking. I'm impressed.

17th August 2005, 06:28 AM	#8
Morgan L diyAudio Member Join Date: Jan 2004 Location: Umea, Sweden	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

18th August 2005, 01:21 AM	#9
Pelle diyAudio Member Join Date: May 2003 Location: Luleå	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), 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.

21st August 2005, 09:53 AM	#10
Morgan L diyAudio Member Join Date: Jan 2004 Location: Umea, Sweden	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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