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LM386 Pin 7 Question

Geoff Vane
Prodigy 20 points

Other Parts Discussed in Thread: LM386

Hello good people,

The LM386 has pin 7. Normally it seems one just should put it to ground with a fat cap for stability reasons.

I want to create a small guitar amp with the LM 386. Although clean sound must be possible, hifi response is not wanted at all.

An example is the Ruby amp, with Volume and Gain control. Volume is made with a pot at the input.

Gain is created with a cap and pot between pin 1 & 8.

A bass boost is created with a filter between pin 1 and 5.

Can I have a gain and a bass boost at the same time?

Now some say pin 7 can either be used as a distortion option, by feeding back the output into pin 7 with an extra capacitor.

Others say it can serve as a crude compressor by connecting pin 7 to ground with two diodes.

Can someone elaborate on how to actually make use of pin 7?

Can I use a potmeter to get a stable amp with either a crude compression option or variable "grit" function?

  • 0
    TI__Prodigy 385 points

    Hello,

    Pin 7 is the half supply point of the LM386.  By design, a capacitor should be connected to Pin 7 to keep power supply noise from reaching the output.  The easiest way to control gain is with a pot on the input.  Set up the 386 for the max gain you want and use the pot to reduce it.  Additional gain can be created by using pin 1 and 8.  Bass boost can also be created by adding a cap and resistor across pins 1&8. 

  • 0 in reply to Jeffrey Bridges
    Prodigy 20 points
    LM386 questions Thanks for your reaction but this is not the exact information I was looking for.  A. What happens here at pin 7 with the Noisy Cricket? How does is work and is the amp still stable this way? http://www.beavisaudio.com/projects/NoisyCricket/Noisy_Cricket_Schematic.gif B. How can the out decoupling cap value alter the tone of the Smokey amp? http://www.beavisaudio.com/projects/NoisyCricket/oldpics/SmokeyTone.gif C. What happens here at pin 7 with Bill's crude compressor design? How does is work and is the amp still stable this way? Can I go into compression with a pot and if so, how? http://www.wentztech.com/radio/resources/Technical-Info/_LM386/Boosing-the-lm-386.pdf D. Can the below application note bass boost be combined with variable gain and will the amp stay stable?  Page 6: amp with bass boost, combined with amp with gain schematic.  http://www.ti.com/lit/ds/snas545a/snas545a.pdf  I want to use two volume pots anyway; one for volume and one for gain, to drive the guitar amp into distortion.