filter for amplifire ,for telephone systems , (300Hz-3.4KHz)

[hm_fa_da]

Hi all ,

i made an amplifire using LM324 and connected it's input to out put of tel-transformes ,in my circuit some other frequencies except 300-3400Hz ( voice ) are running like 16KHz and 12KHz , how can i make a filter which only passes the 0.3-3.4 KHz voice frequency ? a simple circuit is enough not an exact and complicated circuit ,
please give me the link or it's schematic ,

Thanks ,
and best Regards.

 

[IanP]

Re: filter for amplifire ,for telephone systems , (300Hz-3.4

You may try to use single stage low-pass filter, or two-stage band-pass filter ..
If your amplifier is based on LM324 opamp you can easily implement 2-stage band-pass filter/amplifier ..
Goto: **broken link removed**
for examples of opamp-based active filters ..
Regards,
IanP

 

[ptmsl]

Re: filter for amplifire ,for telephone systems , (300Hz-3.4

Depending on your application you must define the attenuation you want at the stopband. A good place to start is the FilterPro program (freeware) from ti that gives you a full schematic and calculates both frequency responce and component values (**broken link removed**) . Prefer the MFB topology. If you need a very high order filter go for a switching capacitor filter. Linear (LTC) has a very good program Filtercad, for designing switching capacitor filters and it is free. With switching capacitor filters you can also implement up to 8th order Elliptic (Cauer) transfer function with just one chip. If you use switching capacitor filters however remember to filter frequencies higher than the filter clock to avoid aliasing (you can do that with a simple RC).