bandpass filters?

Discussion in 'The Projects Forum' started by Neil Groves, Jan 6, 2012.

  1. Neil Groves

    Thread Starter Member

    Sep 14, 2011
    i Just built this circuit:

    well i have built it as far as the bass channel goes and thought i'd test it before i go any further, what i was expecting feeding the circuit with a sinewave was the bass channel L.E.D to start to glow at around 50Hz be fully bright at about 100Hz and then fade as i increased the frequency towards 200Hz, what i am getting in fact is the L.E.D starts to glow at 20Hz, is fully bright by 150Hz but then stays fully bright never dimming again as i increase the frequency well up to 6Khz and beyond, either i have an error in the way i have connected it on the breadboard, or there is an error in the schematic?

    what am i supposed to see on Pin 7 of IC1b? i was expecting a dc level but i don't get that till after the diode, then it gets to 0.7v and stays there which i understand means the transistor has fully saturated?

    can anyone give an insight to this circuit please?

  2. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    Double check all of your capacito/resistor placement values and all of your solder connections.

    Pay special attention to any solder bridges that may have been made, especially with SMD parts.
  3. crutschow


    Mar 14, 2008
    I simulated the circuit with LTspice. IC1B is connected as a bandpass notch filter with a 48dB peak in gain at 226Hz. The voltage at pin 7 is AC. The gain drops below 0dB at 15Hz and 3.4kHz. (See attachment).

    Do you have the virtual grounds on the op amp input connected to the virtual ground op amp output as shown on the schematic? Also be sure all other grounds go to power ground, not virtual ground. The schematic uses the same symbol for both grounds which is bad form and confusing.

    Bass Filter.gif
  4. Neil Groves

    Thread Starter Member

    Sep 14, 2011
    I'm going to go over my connections one more time, it's on a breadboard at the moment and i have in the past experienced circuit failure due to bad contacts on the board, maybe i'll just go ahead and use stripboard just to be sure.

    Thanks guys.