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Old 15th September 2006, 04:50 AM   #1
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Default Passive pre order?

This isn't a tube question but doesn't really belong in a specific forum, so I post it here:

I'm finally getting around to building a passive pre with parts I've saved up, CMLI-15/15B tx's from the Cinemag group buy and a 4 deck switch from Triode El, set up as a stereo ladder.

So, what would be the best way to wire these up? Does it make a difference if the attenuator is before or after the tx (best CMR)? What is the best resistance of the ladder for generality (both SS and tube amps)?
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Old 15th September 2006, 06:40 AM   #2
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Default Re: Passive pre order?

Quote:
Originally posted by leadbelly
...So, what would be the best way to wire these up? Does it make a difference if the attenuator is before or after the tx (best CMR)? What is the best resistance of the ladder for generality (both SS and tube amps)?

The attenuator must have the same impedance as the transformer (before and after the transformer); pls. think about a constant impedance pad.

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Old 15th September 2006, 05:01 PM   #3
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Default Re: Re: Passive pre order?

Quote:
Originally posted by AndreasS
The attenuator must have the same impedance as the transformer (before and after the transformer); pls. think about a constant impedance pad.
Sorry, could you dumb it down a bit for me?
How do I match the impedance of a 1:1 transformer? Are you saying that the attenuator impedance must match the amp input impedance for best results?
I stated I was making a ladder attenuator, so isn't that constant impedance? What do you mean by "constant impedance pad"?
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Old 16th September 2006, 02:54 PM   #4
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Attenuator before the transformer: R = Z (6,28 x L x f)
R: "output" resistance of the attenuator pad (constant for all attenuations, may be a T type attenuator)
L: primary inductance of the transformer
f: lowest frequency

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