[sdiy] crystal bandpass filter / amplifier with CD4049UBC

Wed May 14 01:05:31 CEST 2003

Hi Bert.

If you are using buffers in the same 4049 package, you might as well
consider them well coupled...

They share the power supply and same die, capacitive, resistive and
inductive coupling up the wazoo !!!

I'd try (first) using separate packages. If that works you might try
the 4007 dual complimentaty pair plus inverter... which would allow
separate power supply decoupling, as well as some control over quiescent current, which the 4049 will not allow...

The 4049 does not have symmetrical source / sink current either. I've been very unhappy using that as a linear part, if that is what you are doing...

H^) harry

--------Original Message--------  

From: bert.schiettecatte at esat.kuleuven.ac.be
To: <synth-diy at dropmix.xs4all.nl>
Sent: May 13 2003 23:14
Subject: [sdiy] crystal bandpass filter  / amplifier with CD4049UBC

>hi all,
>i've been trying to build a very narrow and steep bandpass 
>filter / amplifier using a couple of hex inverting buffers, 
>some 1M resistors and 10Mhz crystals. 
>I need to amplify a very small 10Mhz sine signal, but it is 
>burried in noise. I've put a 1M resister in parallel with 
>each buffer and a crystal between buffer inputs / outputs. 
>I've made 6 stages of filtering / amplifying using a single
>4049. The circuit idea comes from one of the elektor circuit 
>books (306 circuits or something). 
>the problem is that the circuit is oscillating :( i can't 
>stop it.. anyone have an idea why?
>thanks
>bert