max values of Rin ?

[djull]

I have searched about the range of acceptable imput resistors (Rin and Rfbk) values in order to increase imput impedance without sacifying the gain but i did not find max acceptable values

Is there some disadvantage tu put Rin about 50k and Rfeedback about 80k ?

I know that with these values i should take in acount the value of the input cap which should maybe be changed.

[krilli]

Here's some good discussion of input impedance: Working with Cranky Op-Amps by Tangent (a true DIY guru and teacher).
http://tangentsoft.net/audio/hs-opamp.html

See especially the "New Problem 3: Resistor Noise", which gives equations on how to calculate the thermal noise you'll get from the raised impedance. Tangent also discusses DC offset changes related to the input / feedback resistor impedance - I don't know how Tripaths behave in that regard.

Hope this helps!

(My capsule answer is that if you raise them enough, say by a factor of 10, you'll get a more noisy amp. 50/80K should be fine!)


--- edit ---

... and p.s., I wouldn't worry too much about the input cap. If you raise the impedance, it's the same as "multiplying" your input cap, e.g. increasing its capacitance, compared with the original impedance. The input plop might get a little worse so if the plop is bothering you you'll want to tune the cap. Otherwise the cap is just getting further out of your way, sound quality wise.

[djull]

Thanks for the link, very interesting.

I think I will certainly raise the imput impedance a little, in order to have a correct combination with my 10k pot. (passive pre)

[Saturnus]

Yeah, otherwise the effective range of the pot is only a few dB, I'd look for a larger pot instead though, something like 100K is more suitable.

[djull]

Perhaps it is the case with an active pre but I understood that it is more suitable to use 10k in a passive preamp. Then I can easily respect a factor of 10 between impedances of source (<1k), pot (10k) and amp (I think that i can increase his impedance around 100k without too much noise)

Maybe i have not well everything understood I'm not yet skilled in impedance understanding