Ruby amp debug, accidently put 15V in

[Kain]

Hi, I accidently put 15V in to my previously working Ruby amp (used DC 15V input cord to my power brick instead of DC 9V output cord from power brick). LM386 melted a bit, so I switched it, still no sound. Replaced MPF102 also, no sound. Any clues?

It does hum if there is no cord plugged and its on, but if I put cord in it won't say anything.

Voltages

LM386
1 1,35 V
2-4 0 V
5 4,37 V
6 8,90 V
7 4,41 V
8 1,34 V

MPF102
G 0 V
S 1,89 V
D 8,90 V

[Gurner]

You say your LM386 melted a bit - that'll be too much current!

Was this melting instant or was sit a while before you noticed.

When it melted, was that with a signal into it? if so are you sure your speaker wasn't damaged.

[GibsonGM]

Also, try to determine the voltage rating for each cap in the circuit.  I'd imagine it would be the 220u and the 100u PS cap.  Make sure they are rated high enough.  If rated 16V, one or both could be bad.

2nd though: Was the polarity of the 15V supply the same as the normal supply?  Cuz if not, you have bigger troubles than you might think!  The "melting" 386 sounds suspicious - it should not have 'melted' at 15v.  What is the unloaded DC output of that cord? Could be more like 22V or so with no load....

[Kain]

Also, try to determine the voltage rating for each cap in the circuit.  I'd imagine it would be the 220u and the 100u PS cap.  Make sure they are rated high enough.  If rated 16V, one or both could be bad.

2nd though: Was the polarity of the 15V supply the same as the normal supply?  Cuz if not, you have bigger troubles than you might think!  The "melting" 386 sounds suspicious - it should not have 'melted' at 15v.  What is the unloaded DC output of that cord? Could be more like 22V or so with no load....

I put the cord in and took it out in about five seconds. I heard some clicks from the Ruby during that time.

"Melting" was a little brown mark on one of the legs + an extra dot on top of the IC. Electrolytics are 16V.

Checked the polarity and it was different, DC output 15V on DMM. So caps/speaker are most possibly bad because of the different polarity? Gotta try to replace the caps first.

[petemoore]

  The speaker's probably ok, and can take 15vdc for a short while, 1.4vdc -9v is a good power supply for speaker coil test, if it doesn't click when power is touched across the coil, then it is blown or a wire's loose, don't hold DC on the coil except for a quick touch.
  Audio probe, the Jfet looks like it may be working, it'll put up with that better than the 386. Caps, if reverse polarized, should be replaced.

[Kain]

Replaced the caps, now its much better = sound again. Thank you all.

[Top Top]

Depending on the version of 386, several of them can take 15V, though obviously something went wrong if it melted. I've made numerous ruby amps that run on 15v that have worked over a period of several months consistent use. The transistor should be rated above that. I'd look at any electrolytic caps to see their rating.

Edit: whoops just noticed your last post!

[Kain]

Depending on the version of 386, several of them can take 15V, though obviously something went wrong if it melted. I've made numerous ruby amps that run on 15v that have worked over a period of several months consistent use. The transistor should be rated above that. I'd look at any electrolytic caps to see their rating.

Yea, this was LM386N-1 max voltage 12 V. N-4 can take 18 V. Wrong polarity was definetely the other cause for catastrophe. BTW, is there any easy way to check caps without removing them from the board?

[Brymus]

Yeah for a really loud 386 build try two of the 18V 386 IC's bridged and run at 18V.(will need heat sinks for long term usage)
I did > it was loud enough my wife couldnt hear the TV on the other end of the house with my door shut,boy was she PO'd that time...