input impedance

[pvsage]

If this has previously been dealt with in this forum, please direct me to the appropriate thread. I've already tried every search I could think of and came up with bupkis.

Just a few questions:

How important is it to have a low impedance option on an instrument amplifier? What ill effects, if any, would be encountered if a device designed for a low impedance input was connected to a high impedance input?

I've managed to puzzle out how to implement the standard Lo/Hi jack switching with a DPDT switch. (Not that hard, really - the poles are wired so that when one is closed, the other is open, and placed in the circuit where the jack switches would be.) Is there an advantage (besides tradition) to using input jack switching?

I understand the advantage of having a grid stopper wired directly to the tube socket. Is there *any* advantage to having the resistor(s) near the jack, as is suggested by the Fender schematics?

Are there any other considerations I should take into account?

[Steve Conner]

I've never liked the two-jack thing much. It uses up panel room. I just make all my homebuilds with the 68k series resistor and a 1M grid leak to ground.

Having said that I have one amp with two input jacks, one of them loads the signal with the 68k+68k divider, but the other one I modified so it doesn't. The low impedance one loads down and attenuates the guitar signal, giving a cleaner tone. The hi-Z one drives the amp harder.

On a bass amp, you often need some kind of input attenuator because the output levels of basses vary so widely, and bassists have different preferences in tone, too. One guy might want a fat, dirty P-funk bark from his low output bass, and another guy might have a high output active bass and yet want his tone crystal clean.

If you're using a resistor as a grid stopper it should be near the grid. I don't know of any other issues than that.