QRP receivers: LM386 as audio filter + amplifier ?
 

I would like to build a minimalistic
AF chain for small HF receivers,
that would limit the audio passband
to either 300-2800 Hz or 700-900 Hz.

The LM386 audio amplifier has a tempting inverting input.
Did anyone try to design it into a 1-device
audio filter + power amplifier?

I looked around, pored over the applications sheet,
but found no examples.

I did this playing with TAA611's many years ago. Then I did find
rather clear indications on how to lower the high frequency cutoff -
but nothing similar with the LM386.

Any hints?

Or,
why isn't this done
as a matter of course,
as I
perhaps mistakenly
think it should?


73 de n1jpr/i2

http://filippo.ru.ru
http://webfools.net/filippo/desert-ratt.html

If you are going QRP there are now much lower ambient current devices than
the LM386 -- secondly, if you go to Texas Instruments website you can
download their FilterPro software -- you can program gain and Q into the
devices. Analog Devices also has some good interactive filter design
software.

Jack

"SpamHog" wrote in message
om...
I would like to build a minimalistic
AF chain for small HF receivers,
that would limit the audio passband
to either 300-2800 Hz or 700-900 Hz.

The LM386 audio amplifier has a tempting inverting input.
Did anyone try to design it into a 1-device
audio filter + power amplifier?

I looked around, pored over the applications sheet,
but found no examples.

I did this playing with TAA611's many years ago. Then I did find
rather clear indications on how to lower the high frequency cutoff -
but nothing similar with the LM386.

Any hints?

Or,
why isn't this done
as a matter of course,
as I
perhaps mistakenly
think it should?


73 de n1jpr/i2

http://filippo.ru.ru
http://webfools.net/filippo/desert-ratt.html

I've got just the LM-386 circuit for you, with graphs. Email me direct
and I'll send you a scan.

cheers
skipp025 at yahoo.com

: SpamHog wrote:
: I would like to build a minimalistic
: AF chain for small HF receivers,
: that would limit the audio passband
: to either 300-2800 Hz or 700-900 Hz.

: The LM386 audio amplifier has a tempting inverting input.
: Did anyone try to design it into a 1-device
: audio filter + power amplifier?

: I looked around, pored over the applications sheet,
: but found no examples.

: I did this playing with TAA611's many years ago. Then I did find
: rather clear indications on how to lower the high frequency cutoff -
: but nothing similar with the LM386.

: Any hints?

: Or,
: why isn't this done
: as a matter of course,
: as I
: perhaps mistakenly
: think it should?


: 73 de n1jpr/i2

: http://filippo.ru.ru
: http://webfools.net/filippo/desert-ratt.html

Thank you Jack!

If you are going QRP there are now much lower
ambient current devices than the LM386

Any specific device you would suggest?

Texas Instruments / Analog Devices

I'm heading there!


BR + 73

Filippo