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Posts posted by trigger

  1. audioguru,

    Noope I am not going to build this circuit. Just quote a pass experience in handling condensed microphone circuit in manufacturing products (say for example, an microphone preamp stage inside an analog cmos camera connected to your VCR/TV).
    The suggestion is to minimize the noise/ripples come from the path of the supply, which is generated by other parts of the circuit.
    You may noticed "humming" sound at the later amplify stage if that modification hasn't included.

    Remember, you got to eliminate the possible noise before tha amplify stage else no matter what opamp you are using, you are going to amplify both the required signal and noise..... and gradually make the circuit fails.

  2. this is the preamplifier I used-----R1 R3 R4=10K----R2+1K--R5=100K to 1M-----C1=0.1uf ---C24.7uf

    For me, I will divide R1 into two 5K ohm resistor in series and with a 22uF capacitor connected between these two resistors joint to gorund.

    That will reduce much noise from the power source to the microphone.
  3. batteries always start at 1.5V (some I have measured up to 1.7V)and then gradually down to 1.2V... and then dead.. so if you really want to power the circuit with exact 9V... AA or AAA are not fitted your application.

    try to use the 9V cells.... or more AA/AAA cells...

    For 100mA current.... it really depends on the power rating (check the datasheet or the graph on it) on the batteries.... say for example, alkaline AA cell is approx. 1000mAH (i.e. provide 1000mA an hour), divide this parameter with the current drawn and you will get your system will survive for 10hours..
    This calculation isn't the exact figure as the cells are usually not the same figure and this calculation assumed the circuit is constantly drawing 100mA... but it just give the goood estimation.

  4. The higher the power dissipated by the regulator, more the ripples at the output.

    It is what I learn from real product design.

    So my experience is the input voltage usually 20% more than the specification required in order to give that 20% safety margin. It will not cause much heat generated.

  5. I think I am wrong......
    because those ICs I mentioned isn't operate in 1.5V......

    And I think it is quite difficult to source for radio IC which operates in 1.5V for howbrew......

    I am playing now with Toshiba TA2104 but its minimum voltage is 1.8V........ :-[

    And MC3361 and MC3362 are not amp, they are IF front end where they are widely use for wireless intercom circuit for many years...

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