P
Phil Allison
- Jan 1, 1970
- 0
Hi to all,
Natsemi do not supply a noise spec for their LM386 audio amp.
This has become a sore point with a poster called " Tom " .
Having a spare LM386N ( 8 pin DIL) in my bits box meant is was easy for me
to test one.
I used the most basic circuit with a gain of 20 dB and fitted a 47uF bypass
cap on pin7.
Input pins 2 & 3 were grounded to pin 4, DC supply came from a 9 volt radio
battery.
The output signal on pin 5 was fed first to a 60dB gain mic pre-amp and then
a 22Hz to 20 kHz audio band filter with 12 dB/ oct roll-off slopes.
The noise signal was observed on a scope and found to be hum free, then
measured with a True RMS voltmeter with over 100kHz bandwidth. The reading
was 144mV rms.
So, the LM386's output noise level was 144 uV rms.
Hence the EIN = 14.4 uV rms.
Input noise density = 100 nV/ rt Hz ( !!! )
Little wonder it is NOT speced.
Relative to a 3 volt rms output level, the s/n ratio is around 87dB.
Fine for the intended applications.
........ Phil
Natsemi do not supply a noise spec for their LM386 audio amp.
This has become a sore point with a poster called " Tom " .
Having a spare LM386N ( 8 pin DIL) in my bits box meant is was easy for me
to test one.
I used the most basic circuit with a gain of 20 dB and fitted a 47uF bypass
cap on pin7.
Input pins 2 & 3 were grounded to pin 4, DC supply came from a 9 volt radio
battery.
The output signal on pin 5 was fed first to a 60dB gain mic pre-amp and then
a 22Hz to 20 kHz audio band filter with 12 dB/ oct roll-off slopes.
The noise signal was observed on a scope and found to be hum free, then
measured with a True RMS voltmeter with over 100kHz bandwidth. The reading
was 144mV rms.
So, the LM386's output noise level was 144 uV rms.
Hence the EIN = 14.4 uV rms.
Input noise density = 100 nV/ rt Hz ( !!! )
Little wonder it is NOT speced.
Relative to a 3 volt rms output level, the s/n ratio is around 87dB.
Fine for the intended applications.
........ Phil