Input Impedance in Buffer

[jojofogarty01]

I'm building this buffer pcb from generalguitargadgets.com to put in a junction box for my pedalboard. Mason from vertex effects swears by a 1m input impedance for buffers and a low output impedance. Judging by this schematic, I'm assuming this design has a 2.2m impedance (based on r4 and r6). Can I just drop that down to a 1m resistor to achieve that input impedance? Thanks.

 

[jojofogarty01]

anybody?

 

[Big Monk]

anybody?

There should functionally be no difference between the 2.

 

[benny_profane]

That bozo is still in business? Yeah, anything above 500k is more than adequate. There's nothing special about 1M. You'll see higher resistance there if an anti-pop resistor is needed to bleed off a leaky cap.

 

[giovanni]

You actually have 3 resistors in parallel here: R1, R2 and R4, which gives you about 730 Kohm. The reason for that is that the small signal equivalent circuit makes Vcc equals to ground so R1 is parallel. The cap behaves like a short circuit for signal.

 

[giovanni]

(Technically that’s also in parallel with the input impedance of the op amp but that’s usually really really high so it doesn’t contribute much to the parallel).