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Dominic Rivron

I've just built an audio amplifier using an LM386, and found that though
it amplifies, there is an annoying level of backgound hiss, irrespective
of the volume setting or input. Also, it tends to oscillate at full
volume. Can anyone offer any suggestions?

regards
Dominic Rivron
-- 

Pulse 8

#27

If I'm not mistaken, there's a +15V gain on the LM386.... I think I read
this from National Semiconducter's PDF file on constructing sine wave
shapers...look on google, in the PDF file there's a couple of good
alternatives that don't suffer from the noise pickup.

Joshua

----
"I'm not a slave to a world that doesn't give a shit."
Pulse 8 - aim:jkerseyVCSO

Show quoted text

----- Original Message -----
From: "Dominic Rivron" <karen.rivron@...>
To: <Electronics_101@...>
Sent: Monday, April 16, 2001 4:55 PM
Subject: [Electronics_101] LM386 amp

I've just built an audio amplifier using an LM386, and found that though
it amplifies, there is an annoying level of backgound hiss, irrespective
of the volume setting or input. Also, it tends to oscillate at full
volume. Can anyone offer any suggestions?

regards
Dominic Rivron
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Darren Reid

#29

Hmm. Did you build it straight from the app notes, or some other schematic?
Can you point us to the schematic you used, somewhere on the web? The hiss
might be from lack of a true ground...

I'm new to the world of electronics myself. I have successfully built an
LM386 amp, though....I think I used a mish mash of app notes and general
opamp theory to come up with my schematic, and I didn't get any hum or
oscillation. I *did* get nasty clipping artifacts when I turned up the
volume on my guitar :)

I built it in an empty 10-pack diskette box, BTW. They make rather
convenient small project boxes.

-Darren

Show quoted text

----- Original Message -----
From: "Dominic Rivron" <karen.rivron@...>
To: <Electronics_101@...>
Sent: Monday, April 16, 2001 6:55 PM
Subject: [Electronics_101] LM386 amp

I've just built an audio amplifier using an LM386, and found that though
it amplifies, there is an annoying level of backgound hiss, irrespective
of the volume setting or input. Also, it tends to oscillate at full
volume. Can anyone offer any suggestions?

regards
Dominic Rivron
--

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Dominic Rivron

#30

Darren Reid wrote:

Hmm. Did you build it straight from the app notes, or some other schematic?
Can you point us to the schematic you used, somewhere on the web? The hiss
might be from lack of a true ground...Thanks for this (and thanks to Joshua too. The amp in question is part
of:


Dominic
-- 

Darren Reid

#31

"Dominic Rivron" <karen.rivron@...> sez:

Thanks for this (and thanks to Joshua too. The amp in question is part
of:
Wow. Truly bizarre. I am too new to all this to comment usefully on such an
arcane construction...what the hell is that transistor on the inputs for? It
would seem to account for your prediliction to oscillation, if I can follow
what's going on. Anyway, you'd have a constant hum alright; there'd always
be something flowing across one of the inputs, right?

If you want a simple LM386 amp, check out National's app notes for the chip.
Use it like you'd use a standard op-amp, and you would be worlds ahead of
that strange device :)

-Darren

Dominic Rivron

#32

Funnily enough, your comment re the true earth provided the answer,
thank you. I rearranged it, and it works like a dream. Arcane it may be,
but it works very well:-) I thought the design looked strange -the
battery symbol's back to front for a start I think- so I've built it a
bit at a time (so as not to waste time). So far (I've done the rf and af
amps) it's worked very well. There are photos of a constructed Desert
Ratt at the end of

(I think that's the right link).

Dominic
Darren Reid wrote:

Show quoted text

Wow. Truly bizarre. I am too new to all this to comment usefully on such an
arcane construction...what the hell is that transistor on the inputs for? It
would seem to account for your prediliction to oscillation, if I can follow
what's going on. Anyway, you'd have a constant hum alright; there'd always
be something flowing across one of the inputs, right?

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--

Darren Reid

#33

Funnily enough, your comment re the true earth provided the answer,
thank you. I rearranged it, and it works like a dream. Arcane it may be,
but it works very well:-) I thought the design looked strange -the
battery symbol's back to front for a start I think- so I've built it a
bit at a time (so as not to waste time). So far (I've done the rf and af
amps) it's worked very well.Cool. Glad to have been of help, even if I barely had a clue :)

Anyone know how to quieten a switching power supply for use in audio
circuitry? I have a cheapy power supply laying around, and am curious...

-Darren

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LM386 amp