|28th October 2003, 11:54 AM||#1|
Join Date: Jun 2003
My little passive preamp
It's not Aleph ,but I hope Nelson and others won't mind putting it here.This is my small toy I built some time ago,after I found nice 22 positons,4 deck switch in local surplus store.The piece of wood was a part of old (over 50 years) shelf that I found in attic.You can see those little holes made through years by insects.
This is ladder type 4,7K attenuator.After some reaserch I found that even Elma and Gold Point ladder type attenuators are not really ladder becouse in some couple of close positions they work as shunt types.
This is becouse of lack of calculated values (one would have to custom order resistors values).I figured that both resistors (signal and ground) can be built of two in parallel.Then creating Exel sheet with regular values and the formula for paralleling resistors gives hundreds of values that one never finds in regular production values.
The bad side is that I needed twice as much resistors and the benefit: the input impedance is rock steady regardles of position (-/+ 2-3ohm).
It took me three days to solder them.Was it worth it? I'm not sure ,probably not,but I had fun.
Also I found local company that produces custom values high quality resistors (0,1% , 10ppm , non-inductive) so next time I might try them.
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