Resistors valus for shunt stepped attenuator? - Page 3 - diyAudio
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Old 31st October 2010, 12:43 PM   #21
AndrewT is offline AndrewT  Scotland
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post 13 shows values for 100M and 100k.
Borbely's 1M lies between these example values.
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Old 31st October 2010, 02:06 PM   #22
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So is between -20.00001dB & -20.08dB instead the -20dB calculate at the stepped attenuator, not bad at all!!!!!
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Old 31st October 2010, 03:08 PM   #23
AndrewT is offline AndrewT  Scotland
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and part of the reason for the very low error is that the ratio of Rin:Rs is >=1M:2k5

Instead of the more usual 10:1 or 20:1 ratio you have >=400:1

The error also becomes less as attenuation is increased (lower Rs) and conversely becomes higher as attenuation is reduced.

Watch that 1M. we have moved away from high input impedances as valve gear has become less common.
We usually find that lower input impedances result in less interference and less noise. Having a, permanently connected, very low Rs helps avoid much of any disadvantage of High Rin.
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Old 31st October 2010, 03:11 PM   #24
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how can be corrected?
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Old 31st October 2010, 03:42 PM   #25
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by AndrewT View Post
Having a, permanently connected, very low Rs helps avoid much of any disadvantage of High Rin.
Quote:
Originally Posted by merlin el mago View Post
how can be corrected?
why does it need to be corrected?
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Old 31st October 2010, 03:46 PM   #26
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Quote:
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why does it need to be corrected?
The input impedance of Borbely line amp it's very easy to tweak only changing 1 resistor per channel.

Last edited by merlin el mago; 31st October 2010 at 03:50 PM.
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Old 31st October 2010, 03:48 PM   #27
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Quote:
Originally Posted by AndrewT View Post
We usually find that lower input impedances result in less interference and less noise. Having a, permanently connected, very low Rs helps avoid much of any disadvantage of High Rin.
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Originally Posted by AndrewT View Post
why does it need to be corrected?
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