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Old 19th January 2013, 12:53 AM   #1
vadi is offline vadi  Austria
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Default simple three steps attenuator

Hi, I need line level attenuation in about 3 steps maybe. The "fine" steps are going to be done at the source digitally (a PC), and the main purpose is to lower the noise induced into the signal from the PC, when listening at low levels. Something like a -20dB switch with a value in between. I'd have to control four inputs.
I think this would be some kind of resistive network, but I wouldn't want any pops when switching and I am not sure what to look for.

Thanks.
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Old 19th January 2013, 10:31 AM   #2
AndrewT is offline AndrewT  Scotland
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Use two 10k resistors in series.
The top and bottom is fed by your source.
The middle and bottom feeds the amplifier.
This gives you an input impedance of 20k and -6dB. The output impedance is 5k. The 5k will roll off the treble, so you MUST ensure the minimum of capacitance loading on the attenuator.

Switch in 2k7 in parallel with the lower resistor. This changes the attenuator to 10k + 2k1 for an attenuation of ~-15dB. The new Zin=12k & Zout=1k8

Switch in 680r in parallel with the lower resistor. This changes the attenuator to 10k + 0k64 for an attenuation of ~-24dB. The new Zin=10k6 & Zout=600r

You can change the extra paralleling resistors to other values to adjust the coarse setting attenuations.

Yet another unhelpful post?
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Old 19th January 2013, 01:56 PM   #3
vadi is offline vadi  Austria
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Thanks for your post and I will try to understand it well.
I wanted to ask: what did you mean by
Quote:
Originally Posted by AndrewT View Post
Yet another unhelpful post?
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Old 19th January 2013, 03:30 PM   #4
forr is offline forr  France
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Hi,

Here is a six steps attenuator I use and which may inspire you.
It is both simple and very effective. There no click at all and the output impedance is quite constant about 300 or 75 Ohm.

The "cursor" progressively bypasses SW1, SW2, SW3...


Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

Here is an economic six ways - six positions switch could be used to build a similar one to mine :

Click the image to open in full size.

Of course, you can get a more simple switch with less ways and less positions to suit your needs.
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Old 20th January 2013, 12:48 PM   #5
vadi is offline vadi  Austria
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Thanks a lot!
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