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Sbitx v3 speaker amp trouble

 

I finally got around to hooking up an internal speaker. If I set the audio above 70 the speaker output drops to almost nothing and all I hear is random cracks or pops that increase when there should be a loud signal. 8ohm speaker. Tried a second speaker. When the audio goes to popping mode I can turn audio down to 50 and wait about 20 secs before slowly increasing again and it will recover until it spends a few secs above 70 again. 70 is not really loud enough for me. Earphone audio is perfect right up to 100 and web audio is OK also.

Any suggestions?

73
Glenn VE9GJ
 

Glenn,
the IC type of the audio output stage is LM380N (14 pin) which works with 8 Ohm speakers. Recommended supply voltage between 10-22V.
What is missing? The speaker is polarity sensitive, which means that if you connect it the other way around, the voice coil moves inward and can collide.
Simply swap the wires to allow the speaker diaphragm to move outwards. Does the speaker you installed work correctly in other environments?
--
Gyula HA3HZ
 

Thanks for the suggestion Gyula but reversing the polarity made no difference. The speaker amp seems to have deteriorated as now I get faint audio with loud pops when set above 95 and nothing at all when under 90. Tried a third speaker with no change. Earphone still works fine.

73
Glenn VE9GJ

On 2024-04-13 17:10, HA3HZ wrote:
Glenn,
the IC type of the audio output stage is LM380N (14 pin) which works with 8 Ohm speakers. Recommended supply voltage between 10-22V.
What is missing? The speaker is polarity sensitive, which means that if you connect it the other way around, the voice coil moves inward and can collide.
Simply swap the wires to allow the speaker diaphragm to move outwards. Does the speaker you installed work correctly in other environments?
--
Gyula HA3HZ
 

I had the SMD resistor, that goes to the Vcc supply pin, open up some on my dropping to supply voltage to the amp chip and the speaker would only work marginally but headphones worked perfectly. RD23 was at something like 77 ohms or some such and it was shutting down the chip. I just bent the legs on a thru-hole resistor and soldered it to the SMD pads and it has worked ever since.

David
WK4DS
 

Hi Glenn,

The earphone jack gets its audio from just before the LM380 audio output circuit, so this would indicate that the LM380 chip is bad or the snubber cap C32 470ufd. There has been a few LM380 failures that I know of one of which was my sBitx V2 card i received. If you have the ability to change it that would probably fix you problem.

Joel
N6ALT
 

Thanks David and Joel. I will check the dropping resistor and if OK I Will order a new LM380 and try that. Inside notice on the schematic that the earphone audio is before the amp.
73
Glenn VE9GJ


On April 13, 2024 5:47:31?p.m. ADT, Joel Caulkins/N6ALT <caulktel@...> wrote:
Hi Glenn,

The earphone jack gets its audio from just before the LM380 audio output circuit, so this would indicate that the LM380 chip is bad or the snubber cap C32 470ufd. There has been a few LM380 failures that I know of one of which was my sBitx V2 card i received. If you have the ability to change it that would probably fix you problem.

Joel
N6ALT

 

Glenn,

is your power supply ok?
If the supply voltage drops below 10V, the audio output stage will not work.
You will then only hear sound through the headphone output.
When I used the battery in the initial period, I once did so that the battery was very low and the sound was muted.
So this audio amplifier IC is the best low voltage monitor.
Then I was also thinking about replacing the IC!

--
Gyula HA3HZ
 

Hi Gyula
Power supply is solid. I am using my Astron 35amp shack supply for testing. I suspect I may find a bad resistor or cap or IC? as David and Joel suggested. Hopefully I can investigate later today.
73
Glenn VE9GJ


On April 14, 2024 6:19:12?a.m. ADT, HA3HZ <gyula@...> wrote:
Glenn,

is your power supply ok?
If the supply voltage drops below 10V, the audio output stage will not work.
You will then only hear sound through the headphone output.
When I used the battery in the initial period, I once did so that the battery was very low and the sound was muted.
So this audio amplifier IC is the best low voltage monitor.
Then I was also thinking about replacing the IC!

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