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The datasheet does mention using a FET for gain control: ?"Gain control can also be done by capacitively coupling a resistor (or FET) from pin 1 to ground." ? That's about the same as adding capacitance between pins 1 and 8 (like the 1uF we have on the Bitx40). ?Reducing the impedance between pin 1 and AC ground, assuming pin 2 is grounded as it is on the Bitx40). ?However you choose to implement this, the lower impedance will increase the LM386 voltage gain to something beyond the standard issue 20. ?You can add stuff in parallel with the 15k resistor between pins 5 and 1 to reduce gain, but only down to a voltage gain of 9, ?below which the LM386 ?becomes unstable. ??

You will have to go to that NJM386 datasheet to find mention of muting with pin 7, they likely filched that idea from the articles in Sprat.

Here's a cut-and-paste from the LM386 datasheet, page 8:
9.2.1.2 Detailed Design Procedure 9.2.1.2.1 Gain Control To make the LM386 a more versatile amplifier, two pins (1 and 8) are provided for gain control. With pins 1 and 8 open the 1.35-kΩ resistor sets the gain at 20 (26 dB). If a capacitor is put from pin 1 to 8, bypassing the 1.35-kΩ resistor, the gain will go up to 200 (46 dB). If a resistor is placed in series with the capacitor, the gain can be set to any value from 20 to 200. Gain control can also be done by capacitively coupling a resistor (or FET) from pin 1 to ground. Additional external components can be placed in parallel with the internal feedback resistors to tailor the gain and frequency response for individual applications. For example, we can compensate poor speaker bass response by frequency shaping the feedback path. This is done with a series RC from pin 1 to 5 (paralleling the internal 15-kΩ resistor). For 6 dB effective bass boost: R ~= 15 kΩ, the lowest value for good stable operation is R = 10 kΩ if pin 8 is open. If pins 1 and 8 are bypassed then R as low as 2 kΩ can be used. This restriction is because the amplifier is only compensated for closed-loop gains greater than 9.

Jerry, KE7ER