Re: Rod Piazza mod

[Markburness@xxxxxxx]

Hi Dave,

Whilst I agree that most guitar amp inputs are of a sufficent impedence to 
"work" for a crystal mic (other factors such as circuit and output/speaker 
configuration will have more of an effect on final tone) there doesnt seem to 
be much of an advantage in using a 10Meg volume pot over a 5Meg pot... if 
you're still going into a 1Meg input, the mic is still going to see just less 
than 1 Meg.

The DC resistance of Astatic elements is hundreds of megaohms, I have found 
that a 20Meg load is too much for good fidelity with a crystal  with no pot). 
It's not so much a case of "matching" impedence but more reducing losses at 
each stage prior to the signal reaching the preamp tube's grid. An Astatic 
with a 5Meg pot into an amp's input will sound thinner than the same mic with 
no pot, hence my suggestion of increasing the load to a value that will keep 
the input circuit's impedence closer to the value of the pot. Luca's 
suggestion of switching out the grid resistor and just using the pot as a 
load is a good one (Don D has also suggested this in the past). You will also 
have the same problems when introducing in-line effects.

Regards, Mark.