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I am attempting to design my own audio amplifier i have started the process with a block diagram. So far the "blocks" i have are:

Input audio signal → Band-pass filter → Preamplifier → Power amplifier → Load

The only restriction that has been imposed is:

  • No digital electronics

Is a buffer amplifier needed between the input and band-pass filter?

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    \$\begingroup\$ Only if the audio signal source can't drive the filter directly. But in that case, why wouldn't you just swap the order of "Bandpass filter" and "Preamplifier" in your diagram? \$\endgroup\$
    – Dave Tweed
    Mar 20, 2017 at 12:40
  • \$\begingroup\$ That seems like the best way to proceed, i did not think the order mattered as long as it was filtered and amplified before it reached the power amplifier. \$\endgroup\$
    – NewEng
    Mar 21, 2017 at 4:31

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The preamp would normally be the first stage, which is why it's called a preamplifier. It takes whatever the audio signal levels are (various line levels, mic level, etc) and normalises them. You put the equalisation and after that, and before the power amplifier (which has a high fixed current gain). Any level controls would normally be part of the preamp.

Basically, the preamp is the buffer.

Do you really need a band pass filter? What's it for?

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  • \$\begingroup\$ The band pass filter is required because I am supposed to block any frequencies above 12kHz or below 3kHz. I apologize for not including that in the original question i did not think it was relevant. \$\endgroup\$
    – NewEng
    Mar 21, 2017 at 4:26
  • \$\begingroup\$ That's a strange specification. What are you actually amplifying? \$\endgroup\$
    – Ian Bland
    Mar 21, 2017 at 21:13
  • \$\begingroup\$ I am amplifying an audio signal, the frequencies were chosen based on criteria set by my professor. \$\endgroup\$
    – NewEng
    Mar 22, 2017 at 11:25
  • \$\begingroup\$ It's a weird bandwidth. I'm just wondering what the intended application is. \$\endgroup\$
    – Ian Bland
    Mar 22, 2017 at 21:03
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Yes, the input resistor affects the band pass filter (or any other passive filter). So, you have three options:

  1. You can use an active filter (where you should use an op amp or something like that). This active filter provide a very high impedance so you don't have to use a buffer between the input stage and the filter stage. Active filters also provide convenience gain control.

  2. If you like to use a passive filter, you can use an opamp as a buffer between the input stage and the filter stage.

  3. If you don't want to use an op amp or any active components, you should measure the resistance of the device that generates the audio signals (input resistance) and adjust the resistances of the filter to match your required cut of frequencies.

If you need a simple but powerful solution for audio amplification, I suggest using LM386 it is a power amplifier (not only a voltage amplifier) and it can provide gain up to 200. It is designed for audio applications. It is a very powerful IC, and easy to use and requires few components. It's just great.

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    \$\begingroup\$ LM386 dates from 1983, more modern options are available. Even if you rule out the use of class D/T systems. \$\endgroup\$
    – pjc50
    Mar 20, 2017 at 14:01
  • \$\begingroup\$ @pjc50 Thank you for the information. I use it because it is the most famous in my country :) Would you tell us about better IC part numbers? or What are the better solutions? \$\endgroup\$ Mar 20, 2017 at 14:11
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    \$\begingroup\$ OPA series, possibly: ti.com/lit/ds/symlink/opa4134.pdf Some TDA suggestions: electronics.stackexchange.com/questions/117261/… \$\endgroup\$
    – pjc50
    Mar 20, 2017 at 14:26
  • \$\begingroup\$ Those OPA devices drive 600 ohms. \$\endgroup\$ Mar 20, 2017 at 16:00

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