Schematics for a fixed attenuator on DCX outputs - diyAudio
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Old 15th January 2006, 09:51 PM   #1
akunec is offline akunec  Canada
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Default Schematics for a fixed attenuator on DCX outputs

Does anyone have the schematic for a fixed attenuator with a 12 db attenuation? I need it as simple as possible.
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Old 15th January 2006, 10:41 PM   #2
moamps is offline moamps  Croatia
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Balanced or not?
Which load impedance?
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Old 15th January 2006, 11:56 PM   #3
akunec is offline akunec  Canada
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not balanced. I believe the load impedance is 20k.
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Old 16th January 2006, 12:05 AM   #4
moamps is offline moamps  Croatia
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L-pad, R1=15k, R2=6k8

or go to

http://www.lalena.com/audio/calculator/lpad/

and use for driver impedance 20000
and for attenuation 12dB

Regards,
Milan
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Old 16th January 2006, 04:56 AM   #5
akunec is offline akunec  Canada
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Thanks
That worked perfect for my single ended amps.

Now for a more difficult question..... I have a bridged amp where the inverted amp has an output impedance of 4.7k and the noninverted amp has an output impedance of 48k. Would the L Pad work for this? or would it cause one portion of the amp to have a higher gain then the other?
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Old 16th January 2006, 07:17 PM   #6
moamps is offline moamps  Croatia
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Quote:
Originally posted by akunec
I have a bridged amp where the inverted amp has an output impedance of 4.7k and the noninverted amp has an output impedance of 48k. Would the L Pad work for this? or would it cause one portion of the amp to have a higher gain then the other? [/B]
Hi:

You must be referring to the amplifiers' input impedances. The input impedance of your bridged amp is parallel connection of two input impedances - 4k7 and 48k - which is almost 4k7, so you can use the same spreadsheet to get R1 and R2 values. Btw, this spreadsheet calculates R1 and R2 so that the input impedance with and without L-pad is the same value, which is in this case 4k7. This is sometimes too small and it's better to the way described below.

You'll need my Excel spreadsheet att1.xls in the aX downloads part (http://www.audioxpress.com/magsdirx/...enda/index.htm) for calculating resistors in a series attenuator. Fill the desired input impedance in Ratt cell (for example 10k) , amplifier input impedance in Rina cell (4k7) and write 12(dB) in the second attenuation step cell in Sattn row. All other steps should be 100. You will get 6k2 and 3k8 for R1 and R2.

Using the L-pad will not change the gain of your amps (normally it doesn't).

Regards,
Milan
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