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The LM386 has a single ended output.
It MUST be coupled to the load through a capacitor (value depends
on load impedance, 100-250uf is fine). One end of speaker or
headphone to ground is OK if capacitor is present at '386 output.
On 8/12/21 9:24 AM, Larry Acklin wrote:
I second that LM386 thought.
cribbed from Stackexchange.com-
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.
= 15,000 x 2 / (Ra + Rb)
Initially Ra + Rb = 0.150 k + 1.350 k = 1.5k
So gain = 2 x 15,000 / 1.500 = 20.
Shorting the 1.35K FOR AC increases gain to 2 x 15k/.15k =
reducing gain by pulling out the cap if it is there.
an lm386 is overdriven, it will oscillate too. And be
careful- I seem to remember that you can't ground either
of the outputs- like a headphone jack would ground one
I would take a look at the preamp circuit first and
then the gain on the LM386
This is just a guess since I don't have your schematic
in front of me.
On Wed, 11 Aug 2021 21:25:37 -0400, Richie Chambless
I've recently built a receiver using the Hycas amplifier
and I am have some oscillation issues. First, here is the
basic layout of my test receiver:
Antenna > 40 Meter BPF > SBL-1 > TIA Amp (copied
from uBitx) > 12 Mhz SSB filter > Hycas amp (L match
retuned for 12 Mhz) > SBL-1 > LM386 AF Amp with
When I power up the Hycas amp and AF section (with no TIA,
LO, or BFO running), I get a loud motorboating sound. When
I jumper across the AGC off pins, the motorboating stops.
When I turn the rest of the receiver on, I get a high
pitched oscillation with a frequency that varies with
turning C2. I can null out the squeal and here some
stations, but the noise floor (hiss) is very high. But,
when I jumper the Mute pins, the gain is reduced and I am
able to hear stations at a comfortable level. Now, I know
this module wasn't designed to be used on mute, so I know
I have something wrong. Any suggestions on where to start?
Is there any particular thing I need to do, such as
decoupling caps or shielding? I appreciate any help you