Pedro & Jim, Sounds good and works for me. If the 12KHz band actually has the lowest amplitude of any of the bands, I would invert the signal with an op amp configured as an inverting amplifier and then apply it to the LM567s. This would then give the 12KHz band the highest amplitude, otherwise, I would proceed with Jim's recommendations. Sincerely, Ned Seith Nedtronics 59 3rd Street Gilroy, CA 95020 (408) 842-0858 At 08:00 PM 8/2/01 -0500, you wrote: >Seeing no other replies - I'll jump in here with >my limited experience with the LM567 some >18 to 20 years ago ... > >My expereince, in the use of LM567's to do TouchTone >decoding, was that the more you can do to get the tone >(or tone range) of interest as the stonger signal - the >better, the cleaner, the fewer false outputs the 567 >will show. > >Seeings how you're working to detect a 12 KHz tone (or >signal) - why not high-pass (starting at, say, 10 KHz) or >bandpass in the 12 KHz area? > >My solution to TT decoding was to precede each bank >of 567's (two tone ranges) with an appropriate low or >high pass op-amp filter. The 567's would then actually >'work' whereas before operation could not in any way >be guaranteed ... > >Jim > >----- Original Message ----- >From: "Pedro Drummond" >To: >Sent: Thursday, August 02, 2001 6:06 PM >Subject: [EE]: Amplify then filter ? > > >Sorry for the missing tag lead. Here it goes again: > >----------- > >Hello, Gods' oracle. > >One question: > >I will be using the 567 filter IC to separate 12kHz signals from regular >audio. The problem is that the 12kHz has a much lower amplitude. Should I >amplify and then insert the full audio mixture to the 567, or will it be >able to detect a much lower signal, at the right frequency ? > >Thanks in advance. > > >Pedro. > >-- >http://www.piclist.com hint: The PICList is archived three different >ways. See http://www.piclist.com/#archives for details. > >-- >http://www.piclist.com hint: The PICList is archived three different >ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.