LM380 Amplifier Volume Not Working

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.

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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.

Also pin 6 is 11.3 mV.

(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.

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.

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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.

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

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

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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.

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.

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

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