Banana jacks and impedance

[Magnus Danielson]

From: Paul Perry <pfperry at melbpc.org.au>
Subject: Re: Banana jacks and impedance
Date: Wed, 29 Dec 1999 09:47:39 +1100

> At 06:27 AM 28/12/99 -0800, Jim Johnson  wrote:
> 
> >The real question I have is, what sort of input impedances must my gear
> >have in order to work well with banana jacks? 
> 
> I think the question is more, "how low should the output impedances
> of my gear be?".
> 
> And, all I can say is "as low as possible", and I think that (to a first
> aproximation) pickup of radiated noise would be directly proportional to the 
> impedance.

Would that include negative impedance? ;)

> The output impedances must, in general, be heaps lower than the imput 
> impedances, or your signal will be cut down anyway.

Notice that you need to consider the active output impedance of a curcuit.

For instance, there are wounderfull op-amps that just happends to have a
128 ohm resistor in series with the output!

Now, if you do have such an op-amp, the real output impedance has to do with
how your feedback works for you.

Similarly you can do tricks to increase the impedance of both an output and
an input. The later is done regularly in op-amps so we don't have to bother
about it.

Anyway, for banana jacks you would like low output impedance (say a few ohms)
and high input impedance (say 50-100k Ohm). Neither would require any esoteric
solution.

Cheers,
Magnus