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Sci.Electronics.Basics -> LM380 Amplifier Volume Not Working

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Author: Dave.H
Date: 10:27 06-06-08

I am having trouble with a small battery operated amp based on the
LM380 chip. The volume control isn't working, all it does it change
the amount of crackle in the speaker when iPod volume is up high, and
also isn't loud. I had the prototype amp working excellent (with same
pot) and even tried two different chips, same result. I really want to
get this amp working for a regen radio, so any help is appreciated. I
checked everything against the schematic (which can be found in the
link below) a few time, but my tired eyes could have missed
something. I'm running the whole thing of a single 9 volt battery.

http://www.dse.com.au/cgi-bin/dse.filereader?4849476303bce49a273fc0a87f9c06fd+EN/catalog
s/SUPZ6080

Thanks
Dave

Author: John Popelish
Date: 11:18 06-06-08

Dave.H wrote:
> I am having trouble with a small battery operated amp based on the
> LM380 chip. The volume control isn't working, all it does it change
> the amount of crackle in the speaker when iPod volume is up high, and
> also isn't loud. I had the prototype amp working excellent (with same
> pot) and even tried two different chips, same result. I really want to
> get this amp working for a regen radio, so any help is appreciated. I
> checked everything against the schematic (which can be found in the
> link below) a few time, but my tired eyes could have missed
> something. I'm running the whole thing of a single 9 volt battery.
>
>
http://www.dse.com.au/cgi-bin/dse.filereader?4849476303bce49a273fc0a87f9c06fd+EN/catalogs/
SUPZ6080

If the prototype works then I suspect you have made some
error in the final construction. I think the design would
be better if the two input 2u2 caps were in series directly
at the input, one turned each way, to handle a DC bias in
either direction (with the pot wiper connected directly to
pin 6), but that is not your problem.

If you want help with a visual inspection, You will have to
post a link to some close up photos of your assembly.

If that is difficult, you might post a list of pin voltages
with the negative probe on pin 7.

--
Regards,

John Popelish

Author: Dave.H
Date: 11:47 06-06-08

On Jun 7, 1:18 am, John Popelish <jpopel...@rica.net> wrote:
> Dave.H wrote:
> > I am having trouble with a small battery operated amp based on the
> > LM380 chip. The volume control isn't working, all it does it change
> > the amount of crackle in the speaker when iPod volume is up high, and
> > also isn't loud. I had the prototype amp working excellent (with same
> > pot) and even tried two different chips, same result. I really want to
> > get this amp working for a regen radio, so any help is appreciated. I
> > checked everything against the schematic (which can be found in the
> > link below) a few time, but my tired eyes could have missed
> > something. I'm running the whole thing of a single 9 volt battery.
>
> >http://www.dse.com.au/cgi-bin/dse.filereader?4849476303bce49a273fc0a8...
>
> If the prototype works then I suspect you have made some
> error in the final construction. I think the design would
> be better if the two input 2u2 caps were in series directly
> at the input, one turned each way, to handle a DC bias in
> either direction (with the pot wiper connected directly to
> pin 6), but that is not your problem.
>
> If you want help with a visual inspection, You will have to
> post a link to some close up photos of your assembly.
>
> If that is difficult, you might post a list of pin voltages
> with the negative probe on pin 7.
>
> --
> Regards,
>
> John Popelish

List of pin voltages
1: 4.13
2: 011.9 - 012.0
3: 0
4: 0
5: 0
6: 0
8: 4.09
10: 0
11: 0
12: 0
13: 7.82

I won't post pictures as the wiring isn't the neatest, and it's hard
to tell what's going on from a photo.
3:

Thanks,
Dave

Author: Dave.H
Date: 11:49 06-06-08

On Jun 7, 1:47 am, "Dave.H" <the19...@googlemail.com> wrote:
> On Jun 7, 1:18 am, John Popelish <jpopel...@rica.net> wrote:
>
>
>
> > Dave.H wrote:
> > > I am having trouble with a small battery operated amp based on the
> > > LM380 chip. The volume control isn't working, all it does it change
> > > the amount of crackle in the speaker when iPod volume is up high, and
> > > also isn't loud. I had the prototype amp working excellent (with same
> > > pot) and even tried two different chips, same result. I really want to
> > > get this amp working for a regen radio, so any help is appreciated. I
> > > checked everything against the schematic (which can be found in the
> > > link below) a few time, but my tired eyes could have missed
> > > something. I'm running the whole thing of a single 9 volt battery.
>
> > >http://www.dse.com.au/cgi-bin/dse.filereader?4849476303bce49a273fc0a8...
>
> > If the prototype works then I suspect you have made some
> > error in the final construction. I think the design would
> > be better if the two input 2u2 caps were in series directly
> > at the input, one turned each way, to handle a DC bias in
> > either direction (with the pot wiper connected directly to
> > pin 6), but that is not your problem.
>
> > If you want help with a visual inspection, You will have to
> > post a link to some close up photos of your assembly.
>
> > If that is difficult, you might post a list of pin voltages
> > with the negative probe on pin 7.
>
> > --
> > Regards,
>
> > John Popelish
>
> List of pin voltages
> 1: 4.13
> 2: 011.9 - 012.0
> 3: 0
> 4: 0
> 5: 0
> 6: 0
> 8: 4.09
> 10: 0
> 11: 0
> 12: 0
> 13: 7.82
>
> I won't post pictures as the wiring isn't the neatest, and it's hard
> to tell what's going on from a photo.
> 3:
>
> Thanks,
> Dave

13 on that list should be 14.

Author: Dave.H
Date: 11:51 06-06-08

Author: John Popelish
Date: 12:44 06-06-08

Dave.H wrote:
> On Jun 7, 1:47 am, "Dave.H" <the19...@googlemail.com> wrote:
>> On Jun 7, 1:18 am, John Popelish <jpopel...@rica.net> wrote:
(snip)
>>> If that is difficult, you might post a list of pin voltages
>>> with the negative probe on pin 7.
>>> --
>>> Regards,
>>> John Popelish
>> List of pin voltages
>> 1: 4.13
>> 2: 011.9 - 012.0
>> 3: 0
>> 4: 0
>> 5: 0
>> 6: 0
>> 8: 4.09
>> 10: 0
>> 11: 0
>> 12: 0
>> 13: 7.82
>>
>> I won't post pictures as the wiring isn't the neatest, and it's hard
>> to tell what's going on from a photo.
>> 3:
(and from another post)
> 13 on that list should be 14.

> Also pin 6 is 11.3 mV.

Pin 14 is the supply voltage, so your 9 volt battery must be
a bit low, but the chip should function at reduced power
output with a 7.82 volt supply.

http://www.jaycar.com.au/images_uploaded/LM380.PDF

Pin 1 is a bias divider that is supposed to roughly halve
the supply voltage, so that is about right for this supply
voltage, and the output on pin 8 should track that voltage,
and this checks out.

The ground rail (negative side of the supply) should be hard
connected to pins 3,4,5,7,10,11 and 12, (most of them form a
heat sinking path). I see no measurement for pin 7.

The input pins, 6 and 2 should both be very near zero volts.
That is so, if the number for pin 2 is in millivolts (it
has to be or the output voltage would be way off).

So it looks like you may have everything wired up right as
far as supply for the chip is concerned. Make sure you
haven't swapped two of the capacitors around, input to
output, or lost a connection through the volume control at
the front end or a speaker ground at the output end.

--
Regards,

John Popelish

Author: Dave.H
Date: 13:01 06-06-08

On Jun 7, 2:44 am, John Popelish <jpopel...@rica.net> wrote:
> Dave.H wrote:
> > On Jun 7, 1:47 am, "Dave.H" <the19...@googlemail.com> wrote:
> >> On Jun 7, 1:18 am, John Popelish <jpopel...@rica.net> wrote:
> (snip)
> >>> If that is difficult, you might post a list of pin voltages
> >>> with the negative probe on pin 7.
> >>> --
> >>> Regards,
> >>> John Popelish
> >> List of pin voltages
> >> 1: 4.13
> >> 2: 011.9 - 012.0
> >> 3: 0
> >> 4: 0
> >> 5: 0
> >> 6: 0
> >> 8: 4.09
> >> 10: 0
> >> 11: 0
> >> 12: 0
> >> 13: 7.82
>
> >> I won't post pictures as the wiring isn't the neatest, and it's hard
> >> to tell what's going on from a photo.
> >> 3:
>
> (and from another post)
>
> > 13 on that list should be 14.
> > Also pin 6 is 11.3 mV.
>
> Pin 14 is the supply voltage, so your 9 volt battery must be
> a bit low, but the chip should function at reduced power
> output with a 7.82 volt supply.
>
> http://www.jaycar.com.au/images_uploaded/LM380.PDF
>
> Pin 1 is a bias divider that is supposed to roughly halve
> the supply voltage, so that is about right for this supply
> voltage, and the output on pin 8 should track that voltage,
> and this checks out.
>
> The ground rail (negative side of the supply) should be hard
> connected to pins 3,4,5,7,10,11 and 12, (most of them form a
> heat sinking path). I see no measurement for pin 7.
>
> The input pins, 6 and 2 should both be very near zero volts.
> That is so, if the number for pin 2 is in millivolts (it
> has to be or the output voltage would be way off).
>
> So it looks like you may have everything wired up right as
> far as supply for the chip is concerned. Make sure you
> haven't swapped two of the capacitors around, input to
> output, or lost a connection through the volume control at
> the front end or a speaker ground at the output end.
>
> --
> Regards,
>
> John Popelish

Checked everything and marked off every component on the schematic and
swapped the fixed resistor around, as I'd found I somehow put them in
the wrong place before, same result. I just realized that the
terminals I used for the ground connections aren't connected to each
other, I think this may be may problem. Will fix this straightaway.
Such an obvious problem, how the hell I missed it, I'll never know.

Author: Eeyore
Date: 13:12 06-06-08

"Dave.H" wrote:

> I just realized that the
> terminals I used for the ground connections aren't connected to each
> other, I think this may be may problem. Will fix this straightaway.
> Such an obvious problem, how the hell I missed it, I'll never know.

It's often the way.

Graham

Author: Dave.H
Date: 13:19 06-06-08

On Jun 7, 3:12 am, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
wrote:
> "Dave.H" wrote:
> > I just realized that the
> > terminals I used for the ground connections aren't connected to each
> > other, I think this may be may problem. Will fix this straightaway.
> > Such an obvious problem, how the hell I missed it, I'll never know.
>
> It's often the way.
>
> Graham

Problem solved now listening with the iPod connected. I feel so stupid
for having missed the ground connections, still at least it let me
notice the resistor where in the wrong places. Thanks for everyones
help, greatly appreciated, I shall enjoy this amp for years to come,
now I just got to build that regen radio to go with it, (gonna be a
Hiker's One, heard good things about them)

Thanks
Dave

Author: Dave.H
Date: 13:36 06-06-08

On Jun 7, 3:19 am, "Dave.H" <the19...@googlemail.com> wrote:
> On Jun 7, 3:12 am, Eeyore <rabbitsfriendsandrelati...@hotmail.com>
> wrote:
>
> > "Dave.H" wrote:
> > > I just realized that the
> > > terminals I used for the ground connections aren't connected to each
> > > other, I think this may be may problem. Will fix this straightaway.
> > > Such an obvious problem, how the hell I missed it, I'll never know.
>
> > It's often the way.
>
> > Graham
>
> Problem solved now listening with the iPod connected. I feel so stupid
> for having missed the ground connections, still at least it let me
> notice the resistor where in the wrong places. Thanks for everyones
> help, greatly appreciated, I shall enjoy this amp for years to come,
> now I just got to build that regen radio to go with it, (gonna be a
> Hiker's One, heard good things about them)
>
> Thanks
> Dave

I read that the LM380 is supposed to be soldered directly to a PCB
with the 3 centre pins on each side tied to a copper ground. Is this
necessary? I have the LM380 in a socket (don't like soldering directly
to IC's) and the ground pins all connected to separate wires. This
was how it was done on the prototype model, the IC showed no signs of
heat after a few hours. Should I leave it the way it is or what?

Thanks
Dave

Author: John Popelish
Date: 13:58 06-06-08

Dave.H wrote:

> I read that the LM380 is supposed to be soldered directly to a PCB
> with the 3 centre pins on each side tied to a copper ground. Is this
> necessary? I have the LM380 in a socket (don't like soldering directly
> to IC's) and the ground pins all connected to separate wires. This
> was how it was done on the prototype model, the IC showed no signs of
> heat after a few hours. Should I leave it the way it is or what?

If it is running cool, you don't need the heat sinking
possible through the copper area solder connection.

--
Regards,

John Popelish

Author: Dave.H
Date: 14:03 06-06-08

On Jun 7, 3:58 am, John Popelish <jpopel...@rica.net> wrote:
> Dave.H wrote:
> > I read that the LM380 is supposed to be soldered directly to a PCB
> > with the 3 centre pins on each side tied to a copper ground. Is this
> > necessary? I have the LM380 in a socket (don't like soldering directly
> > to IC's) and the ground pins all connected to separate wires. This
> > was how it was done on the prototype model, the IC showed no signs of
> > heat after a few hours. Should I leave it the way it is or what?
>
> If it is running cool, you don't need the heat sinking
> possible through the copper area solder connection.
>
> --
> Regards,
>
> John Popelish

I didn't think so, just thought I'd better ask.

Thanks for your help, It's still playing beside me, I can't wait to
build the Hiker's one for it now.

Author: Tim Wescott
Date: 18:43 06-06-08

John Popelish wrote:
> Dave.H wrote:
>> I am having trouble with a small battery operated amp based on the
>> LM380 chip. The volume control isn't working, all it does it change
>> the amount of crackle in the speaker when iPod volume is up high, and
>> also isn't loud. I had the prototype amp working excellent (with same
>> pot) and even tried two different chips, same result. I really want to
>> get this amp working for a regen radio, so any help is appreciated. I
>> checked everything against the schematic (which can be found in the
>> link below) a few time, but my tired eyes could have missed
>> something. I'm running the whole thing of a single 9 volt battery.
>>
>>
http://www.dse.com.au/cgi-bin/dse.filereader?4849476303bce49a273fc0a87f9c06fd+EN/catalogs/
SUPZ6080
>>
>
> If the prototype works then I suspect you have made some error in the
> final construction. I think the design would be better if the two input
> 2u2 caps were in series directly at the input, one turned each way, to
> handle a DC bias in either direction (with the pot wiper connected
> directly to pin 6), but that is not your problem.
>
> If you want help with a visual inspection, You will have to post a link
> to some close up photos of your assembly.
>
> If that is difficult, you might post a list of pin voltages with the
> negative probe on pin 7.
>
If you haven't torn down the prototype, compare the voltages and
behavior of the two circuits, pin-for-pin, and see where there are
differences.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

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