LM380 Amplifier Volume Not Working

[Dave.H]

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

Thanks
Dave

 

[Dave.H]

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.

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

 

[Dave.H]

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.

 

[Dave.H]

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

Also pin 6 is 11.3 mV.

 

[Dave.H]

(and from another post)


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.

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.

 

[Eeyore]

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

 

[Dave.H]

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

 

[Dave.H]

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

 

[Dave.H]

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

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.