Wanting to add a simple passive tone section to this LM386 amp kit

Should I try to add a "dirt" channel as well?

  • Yes

    Votes: 1 100.0%
  • Yes

    Votes: 0 0.0%

  • Total voters
    1

Thread Starter

Cjax

Joined Oct 21, 2017
3
Hey again,

I bought a cheap little amp kit (http://www.icstation.com/icstation-lm386-mini-power-amplifier-audio-amplifier-board-module-kits-p-5025.html) and I wanted to turn it into a basic guitar amp. But I still want it to be somewhat usable. I've attached the diagram to the mini-amp, where would I put a tone knob if I were to add it to the signal path? I wanted to use G&L's passive 2 band tone design. Very straightforward little mod I like to do. The tone knobs on my bass are G&L style.

I'm not the best with circuit design, so any advice would be much appreciated.

Thanks!
 

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Audioguru

Joined Dec 20, 2007
11,249
A guitar speaker usually has poor high frequency response so the pickup is allowed to resonate at about 5kHz with the capacitance of the connecting cable. The resonance is a high impedance so a high input impedance Jfet preamp is used at the amplifier. The high impedance pickup produces a whopping high output level so not much gain is needed.

BUT your LM386 amplifier has a fairly low input impedance that is less than the 10 k ohms volume control and your tone controls circuit has a high impedance that is loaded down by the LM386 circuit. The guitar pickup can drive the tone controls circuit which can drive a Jfet preamp that can drive your LM386. The LM386 amplifier has a very sensitive input for a low level microphone so it will be over driven with the output of the Jfet preamp so keep its volume control turned down.
 

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ian field

Joined Oct 27, 2012
6,539
A guitar speaker usually has poor high frequency response so the pickup is allowed to resonate at about 5kHz with the capacitance of the connecting cable. The resonance is a high impedance so a high input impedance Jfet preamp is used at the amplifier. The high impedance pickup produces a whopping high output level so not much gain is needed.

BUT your LM386 amplifier has a fairly low input impedance that is less than the 10 k ohms volume control and your tone controls circuit has a high impedance that is loaded down by the LM386 circuit. The guitar pickup can drive the tone controls circuit which can drive a Jfet preamp that can drive your LM386. The LM386 amplifier has a very sensitive input for a low level microphone so it will be over driven with the output of the Jfet preamp so keep its volume control turned down.
A powered PC speaker makes a fair practice amp, but the volume pot is usually 5k, so a JFET stage of that type is necessary - I usually make a source follower stage with the volume pot as the source load.
 
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