[sdiy] Debugging Hammond filter circuit

[Paul Perry]

This is in fact typical for most patents.
The patentee is forced to reveal the method, in order to secure protection 
against copying, for the length of the patent.
But, naturally, there is no desire on the part of the inventor to actually 
HELP any unknown prospective competitors.
Plus, being a legal document, patents have become encrusted with obscure 
styles and forms.
This is actually a pretty good description compared to some chemical 
synthesis patents, for example.
It's like those "Encyclopedia of Circuits" doorstoppers - a starting point, 
no more!

Also, some patents are taken out simply as a pre-emptive strike, to prevent 
any competign company using it.

paul perry Melbourne Australia

----- Original Message ----- 
From: "Donald Tillman" > Wow, this is a truly awful patent.   There are 
mistakes in the schematic, the resistor reference designators start from 
R142 for no reason, the plot has no tick marks or units, there are no 
voltages or levels specified...
>
> And it's not a very good circuit topology.  It's depending on the high 
> pass filter feedback at high frequencies where random phase shifts can 
> cause instability.  And the positive feedback thing looks like complete 
> trouble.