Increasing ESP P3A input impedance

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christian.lenci

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Joined 2008
Hi all,
having a tube preamp with an output impedance of 5k or so, I just wanted to ask what do you think about increasing the P3A input impedance (~24K) to ~49K by increasing R2 to 47K. Obviously R5 would become 47K too, and R4 would be raised to 2k2 to mantain the same gain. C2 would be changed accordingly.

Would this be too detrimental for the amp's noise perfomance?

Thank you all,
Christian
 
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martinbls

Member
Joined 2009
christian.lenci said:
Hi all,
having a tube preamp with an output impedance of 5k or so, I just wanted to ask what do you think about increasing the P3A input impedance (~24K) to ~49K by increasing R2 to 47K. Obviously R5 would become 47K too, and R4 would be raised to 2k2 to mantain the same gain. C2 would be changed accordingly.

Would this be too detrimental for the amp's noise perfomance?

Thank you all,
Christian
Click to expand...

Hi!

I would like to do same thing on my P3A, but something isn't clear to me...

To achieve an input impedance of ~49k I would have to:
- increase R2 to 47k
- increase R5 to 47k
- increase R4 to 2,2k

Nothing more than that?

What does "C2 would be changed accordingly" mean?

What is the general disadvantage of a higher input impedance, e.g. why is the input impedance of most power amps around 20k and not around 50k, which would obviously be much better suited for source equipment with BOTH low and high output impedances, and of course it would make the use of passive pre's much easier.

Thanks a lot!!

Martin
 
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