input impedance LM3875

Diy martin · 29th June 2007, 07:36 PM

Hello diy members,

How can I increase the imput impedance of my Audiosector LM3875 amp , now it is 22Kohm. Can I get problems with dc offset

All info is welkome

jaudio · 29th June 2007, 08:10 PM

Quote:

Originally posted by Diy martin
Hello diy members,

How can I increase the imput impedance of my Audiosector LM3875 amp , now it is 22Kohm.

Just change the 22kohm resistor at the input(input to ground)

Quote:

Originally posted by Diy martin
Can I get problems with dc offset

When you rise the input impedance,offset will go up a few mv.

justblair · 29th June 2007, 08:26 PM

How much do you need to increase it by?

Diy martin · 1st July 2007, 08:57 PM

To match my passiv crossover I will need about 100k imput impedance.

BWRX · 1st July 2007, 09:04 PM

An op amp buffer would work well for what you want to do.

justblair · 1st July 2007, 09:33 PM

Or visit Decibel dungeon and have a look at some of the discrete buffers in buffered gainclones
Buffereed gainclones

NUUK has gathered a few there, designs that you will find on other sites plus Nicks listening experiances of them.

You should find something that you like.

AndrewT · 1st July 2007, 11:11 PM

Quote:

Originally posted by Diy martin
To match my passiv crossover I will need about 100k imput impedance.

passive crossover comes between the power amp and the drivers.
The input impedance is irrelevant to this.

What impedance can your source feed?

Davey · 1st July 2007, 11:28 PM

Quote:

Originally posted by AndrewT
passive crossover comes between the power amp and the drivers.

Well, not necessarily. There are a number of passive line-level crossover options that might work well. Maybe that's what he has in mind.

Raising the input impedance of a power amplifier would tend to minimize circuit interaction with the crossover network.

Cheers,

Davey.

29th June 2007, 07:36 PM	#1
Diy martin diyAudio Member Join Date: Apr 2003 Location: papendrecht	input impedance LM3875 Hello diy members, How can I increase the imput impedance of my Audiosector LM3875 amp , now it is 22Kohm. Can I get problems with dc offset All info is welkome

1st July 2007, 09:04 PM	#5
BWRX diyAudio Moderator Emeritus Join Date: Jan 2005 Location: Pennsylvania	An op amp buffer would work well for what you want to do. __________________ Brian

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29th June 2007, 08:26 PM	#3
justblair diyAudio Member Join Date: Jan 2007 Location: Glasgow, Scotland	How much do you need to increase it by?

1st July 2007, 08:57 PM	#4
Diy martin diyAudio Member Join Date: Apr 2003 Location: papendrecht	To match my passiv crossover I will need about 100k imput impedance.

1st July 2007, 09:33 PM	#6
justblair diyAudio Member Join Date: Jan 2007 Location: Glasgow, Scotland	Or visit Decibel dungeon and have a look at some of the discrete buffers in buffered gainclones Buffereed gainclones NUUK has gathered a few there, designs that you will find on other sites plus Nicks listening experiances of them. You should find something that you like.

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