Adjusting input impedance on ncx500 unbuffered

[grobalt]

Hi all,

i am using the purifi eval schematic to build my input buffer for these boards - and stumbled over input impedance of just 10.2k Ω

As i am building multichannel amps i was looking for their impedance -> all 47k Ω

Am i right that i can adjust by increasing these values to 47k Ω half -> 23k5 Ω ?

 

[fpitas]

May I ask, what can't drive a 10K load? I'd check the input bias current of those op amps before I increased the resistors a lot.

 

[grobalt]

As i am not deep into electronics .. i am just adjusting existing stuff and checked what other commercially available amps do ...

 

[fpitas]

As i am not deep into electronics .. i am just adjusting existing stuff and checked what other commercially available amps do ...

Most preamps etc will easily drive 10k, even 2k.

 

[grobalt]

For the Multichannel stuff i will use Trinnov Altitudes.
As i customize anyway .. it does not matter which resistor values i put in, is there a pro / con for 10k vs 47k ?

 

[fpitas]

For the Multichannel stuff i will use Trinnov Altitudes.
As i customize anyway .. it does not matter which resistor values i put in, is there a pro / con for 10k vs 47k ?

Yes, as I said the input bias of the op amp affects that. You'll get more input offset voltage.

 

[grobalt]

Yes, as I said the input bias of the op amp affects that. You'll get more input offset voltage.

many thanks for your quick answers - to be honest - i dont understand your last reply may i ask for a bit more explanation, example OPA1612 and SS3602 ?

 

[fpitas]

https://www.analog.com/media/en/training-seminars/tutorials/MT-038.pdf