LM1875 power supply

[Chricket]

This is the schematic from SC.

This is the PCB layout

 

[!]

Popped cap was probably just defective (or old, dried out or needed foil oxide reformed) unless the polarity was reversed but AFAICT in the picture it looks like polarity was right.

Some say film caps sound better, but your ceramic 100nF should work too.

 

[AndrewT]

The component values and ratings in the schematic should not fail. All look OK.

The 220uF 35Vdc cap that failed was either defective, or inserted back to front, or a fake.
The 2u2F could be a non-polar electrolytic, but I would recommend a film type. Cheapest type that would obtain much of the potential performance would be MKT or MKS.

The 22uF non-polar electrolytic can be replaced with a 150uF or 220uF polar electrolytic. A low voltage rating is OK here. Try 16Vdc or even 10Vdc. It should be quite small and cheap. But add those protective diodes across the cap pins.

Now to transformer and PSU voltage.
A high regulation 20Vac transformer can easily give +-33Vdc at the amplifier. Any higher transformer voltage risks blowing up the 35Vdc rated capacitors.

 

[kroto]

Am I using the wrong type of 100nF caps? here's a picture of my circuit. The left 220uF cap smoked.

I tried using a 22uF 16v polarized cap like the one in this this post
http://www.diyaudio.com/forums/chip-amps/120616-lm1875-pcb-use-2.html#post1474466 and it's still intact.


The PBC layout was of Silicon Chip's. The 2.2uF NP cap is a bit big.

Before the cap smoked, I heard a loud hum on the speaker.

* what is the voltage rating of the smoked 220u?? the size in your pic' seems to small for a 220u/35V unit.
* where is the heatsink?
* do you direct solder the fuse? check it, it might be broken off.

 

[!]

^ agreed those caps do look pretty small, I think I'd swap in higher voltage caps, higher capacitance, or at least use a lower ESR cap model if not all of the above.

 

[Chricket]

The cap is 35v, and I didn't solder the fuse. I used a DIY fuse holder.The fuses are ok.

here's the pic

I think I can use two polarized caps in series ---|-)-(-|-- to make it non polar right? Just double the value, divide it by two, so it will result to the desired value. Am I correct?

 

[Chricket]

I removed the heatsink after the test by the way.

Now to transformer and PSU voltage.
A high regulation 20Vac transformer can easily give +-33Vdc at the amplifier. Any higher transformer voltage risks blowing up the 35Vdc rated capacitors.

I'm using 18-0-18 transformers that outputs 25v.

 

[AndrewT]

you don't need to use back to back series capacitors for the NFB DC blocker. A Polar electrolytic can and will do the job. Just make sure it is large enough to do the job adequately.

 

[Chricket]

you don't need to use back to back series capacitors for the NFB DC blocker. A Polar electrolytic can and will do the job. Just make sure it is large enough to do the job adequately.

I used 220uF cap as an alternative. I replaced the blown cap with 220uF 50v. However, it still hums. And it doesn't pick anything from the input. same config as before. I just changed the caps.

What could be wrong?

 

[AndrewT]

you need to start measuring voltages around the circuit (relative to Ground Zero Volts) and voltage drops across components.
Paste these results onto your schematic and let us have a look.

 

[vijay tambatkar]

why for LM1875 ic we use sometime dual power supply and sometime single one