I have two amplifiers using LM386. One of them I plan to use for normal amplifier and the second one I want it to be a low pass amplifier/bass amplifier and both of them will be connected to same speaker. My question is: is it possible to run two amplifiers in the same speaker with different frequency (there is no high tone in second amp) and how should I wired them, bridge or parallel?

  • \$\begingroup\$ Why do you want to do this? Normally you'd connect a bass amplifier to a different speaker. You can't sensibly wire them to the same speaker. \$\endgroup\$ – pjc50 Jul 28 '14 at 12:54
  • \$\begingroup\$ i want to build small speaker unit that run only by the external battery 5v (power bank for phone)which can be brought to anywhere so i can't make big third subwoofer speaker \$\endgroup\$ – aji Jul 28 '14 at 13:45

No. Connecting the output of two amplifiers to the same speaker in parallel is not a good idea.

Slight variances in amplified signal at specified periods of time produce a voltage (difference of potential). In this situation you'll have something similar to shortcircuit.

Of course, you could add some series resistors, but this would modify speaker impedance and reduce output power, which isn't too much when using LM386.

You could wire them as a bridge configuration. Something like this:

enter image description here
Source: seekic.com

As you can see, it has only one input. So, you should use a simple preamplifier to mix the different frequency input signals.

  • 1
    \$\begingroup\$ There's nothing wrong with feeding two different signals to the two amplifiers in a bridge configuration. If they're both noninverting (or both inverting) amplifiers, the speaker will get the difference signal. If only one is inverting, the speaker will get the sum. \$\endgroup\$ – Dave Tweed Jul 28 '14 at 13:11
  • \$\begingroup\$ but what if i want a "bass boost" switch that activate second amplifier that boost only the bass freq? \$\endgroup\$ – aji Jul 28 '14 at 13:42
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    \$\begingroup\$ Why can't you 'bass boost' by switching on (or off) some filter before your amplifier? AFAIK that is how the rest of the world implements this! \$\endgroup\$ – Wouter van Ooijen Jul 28 '14 at 13:49
  • \$\begingroup\$ because i have limited power supply, so i could simply switch the "bass boost" on when the power is sufficient enough, is that possible in that configuration? \$\endgroup\$ – aji Jul 28 '14 at 13:49
  • \$\begingroup\$ @aji you could use a low-pass filter before the bass amplifier input. See electronics-tutorials.ws/filter/filter_5.html \$\endgroup\$ – Cornelius Jul 28 '14 at 13:50

You are probably overthinking this. Use passive filters for your tone circuit. Should not affect your battery power. If you are only interested in bass boost...try connecting a 10k resistor in series with a 0.033uf capacitor between Pin 1 and Pin 5 (you should get up to 5 dB bass boost).


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