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Post by jphoward on Mar 19, 2009 11:56:48 GMT
Got my poly 4.7u input caps from Jaycar today, and in my excitement to listen to the result, I mixed up +ve and -ve when connecting up to the PSU... As a result, the opamp literally exploded, sending shrapnel right across the room! So 1st, a couple of suggestions: - Don't take your goggles off when you've finished soldering, but haven't yet tested turning the power on
- Plug the -ve of the PSU to the -ve of the amp, and visa versa ;D
And 2nd, a question: after replacing the opamp, all seems to be working fine. However I'm not sure it sounds quite right... This could just be because I'm a bit shaken up after the bits of LM4562 flying by my ears, or it could be because I've damaged some components in the amp. Am I likely to have damaged anything other than the opamp? If so, what parts should I consider replacing (I'd rather not replace the whole thing!) Are there some tests I can do to check for damage?
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robertkd
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Post by robertkd on Mar 19, 2009 12:22:11 GMT
Got my poly 4.7u input caps from Jaycar today, and in my excitement to listen to the result, I mixed up +ve and -ve when connecting up to the PSU... As a result, the opamp literally exploded, sending shrapnel right across the room! So 1st, a couple of suggestions: - Don't take your goggles off when you've finished soldering, but haven't yet tested turning the power on
- Plug the -ve of the PSU to the -ve of the amp, and visa versa ;D
And 2nd, a question: after replacing the opamp, all seems to be working fine. However I'm not sure it sounds quite right... This could just be because I'm a bit shaken up after the bits of LM4562 flying by my ears, or it could be because I've damaged some components in the amp. Am I likely to have damaged anything other than the opamp? If so, what parts should I consider replacing (I'd rather not replace the whole thing!) Are there some tests I can do to check for damage? Ouch that hurts, ok the possible items to check the main electrolytics would have coped the reverse supply connection would crtianly look for signs of swelling on these, probably just replace them. I take it the 4 LED's all lite-up and are about the same brightness ? likely they would survive. The output transistors may also have survived intact, a quick check would be to remove the op-amp unplug the headphones and power up. Then measure the DC volts on the left and right outputs to GND (0 volts), it should be within 0.5 volts of ground. A recommendation, grab a couple of 1N4007's and connect them across the plus and minus supplies on the fused side of the circuit. have a look at my diagram in the Silicon Chip Head Phone Tweaks, ask if you need more input. so is this your first magic smoke letting
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Post by PinkFloyd on Mar 19, 2009 12:38:48 GMT
I couldn't help laughing when I read that Fortunately it was only the chip that exploded and not a large capacitor..... even more fortunate you didn't have your face anywhere near it or it could have blinded you / singed your hair ;D Your caps probably escaped damage but, as Robert says, maybe best to replace them just incase.... everything else should be 100% fine
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Spirit
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Post by Spirit on Mar 19, 2009 12:52:05 GMT
I must admit I too had a laugh, but wasn't game to comment saying just that... Now that some good advice has been offered however
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Post by jphoward on Mar 19, 2009 13:54:31 GMT
I couldn't help laughing when I read that Well... everyone enjoys a bit of schadenfreude. Except perhaps the victim...
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robertkd
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Post by robertkd on Mar 19, 2009 14:27:52 GMT
I couldn't help laughing when I read that Well... everyone enjoys a bit of schadenfreude. Except perhaps the victim... Jeremy, whilst this is certainly a disaster which could have had dire and serious consequences and i know at the time it happened it was bad but looking back on the event you will gain some retrospective hummer over this. Mike and even myself draw on similar experiences we chalk it up to life the universe and dumb frell-ups . we learn we move on, welcome to the real world Robert
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insomniac
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Post by insomniac on Mar 19, 2009 18:33:16 GMT
Good to see nobody got hurt! Let me recommend a useful safety device for times like this... 15 Meters away is a pretty safe distance to be before flicking the on switch
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Will
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Post by Will on Mar 19, 2009 19:35:48 GMT
Thats what I do, insomniac, hide a bit away and do a remote switch on using an extension lead. Probably because I'm a big girly poof, and not as hard as the rest who switch on close up Welcome to the club, jphoward, glad you're OK! You are now officially a proper bloke who tats around with electronics. We've all let the magic smoke out, and had "brown" events, and at the time it's not funny, especially if you cop at 220V belter (or even worse a 415V ) but soon enough it becomes bragging rights with like minded people, and it my even get you a pint down the pub! Just think about your next 'first' power up
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Post by Deleted on Mar 19, 2009 19:56:57 GMT
Got my poly 4.7u input caps from Jaycar today, and in my excitement to listen to the result, I mixed up +ve and -ve when connecting up to the PSU... As a result, the opamp literally exploded, sending shrapnel right across the room! So 1st, a couple of suggestions: - Don't take your goggles off when you've finished soldering, but haven't yet tested turning the power on
- Plug the -ve of the PSU to the -ve of the amp, and visa versa ;D
And 2nd, a question: after replacing the opamp, all seems to be working fine. However I'm not sure it sounds quite right... This could just be because I'm a bit shaken up after the bits of LM4562 flying by my ears, or it could be because I've damaged some components in the amp. Am I likely to have damaged anything other than the opamp? If so, what parts should I consider replacing (I'd rather not replace the whole thing!) Are there some tests I can do to check for damage? jphoward Do as Robert has suggested about the electros etc. After the electros have been replaced , let us know, and providing that it still appears to be working, we can then go through a few more measurements to check. At least yours didn't go up in flames, so not too bad after all. As the rest of the guys have said "Welcome to the club!" I just hope that you never have a close encounter or 2 with 230VAC like some of us have had. Trust me, you don't want to ! Alex P.S. It's always a good idea to test with a cheaper but compatible opamp plugged in after completing. (if you have a suitable opamp)
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leo
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Post by leo on Mar 19, 2009 20:14:47 GMT
Unfortunately reverse voltage is one of the main circuit killers, there could be a few components damaged from this I'm afraid. Replacing the electrolytics is a must IMO 230v AC is bad, 1200v DC from a big SET amp is also bad or the HT from a tv is damn nasty too You have to respect this stuff guys ;D
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Post by PinkFloyd on Mar 19, 2009 20:22:32 GMT
Poofter! I go straight in with the nose and fingers at switch on.... if anything explodes I take a direct hit in the face like a real man! The worst I ever had was an exploding capacitor that, believe it or not, burnt half my right eyebrow off.... I was about 12 inches from the amp and POW! got it right in the boat All good stuff and all part of the fun IMO
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leo
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Post by leo on Mar 19, 2009 20:34:06 GMT
I use a blast shield, basically a small piece of perspex over the thing, you can closely see what bits burn or explode then during switch on
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Will
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Post by Will on Mar 19, 2009 20:54:28 GMT
...and one time I shorted out a live thyristor in a three phase (415V) industrial oven using an allen key... as I said, bragging rights....
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jonclancy
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Post by jonclancy on Mar 19, 2009 21:31:27 GMT
I use a blast shield, basically a small piece of perspex over the thing, you can closely see what bits burn or explode then during switch on Now THAT is a bloody good idea!!
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Post by Deleted on Mar 19, 2009 21:47:24 GMT
Poofter! I go straight in with the nose and fingers at switch on.... if anything explodes I take a direct hit in the face like a real man! The worst I ever had was an exploding capacitor that, believe it or not, burnt half my right eyebrow off.... I was about 12 inches from the amp and POW! got it right in the boat All good stuff and all part of the fun IMO All of you, except for Mike, are wimps ! ;D
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Post by jphoward on Mar 19, 2009 22:50:57 GMT
Jeremy, whilst this is certainly a disaster which could have had dire and serious consequences and i know at the time it happened it was bad but looking back on the event you will gain some retrospective hummer over this. I was just teasing about the 'schadenfreude' remark. As I'm sure you noticed from the composition of my original post I can already see the humour in this. Frankly, I just like have any excuse to use that rather nifty German word - perhaps this is a good time to quote a great Simpsons moment: Homer is reveling in the apparent demise of the Leftorium, a store operated by his hated neighbor, Ned Flanders. Homer’s daughter Lisa isn’t happy with him.
Lisa: Dad, do you know what schadenfreude is?
Homer: No, I do not know what shaden-frawde is. Please tell me, because I’m dying to know.
Lisa: It’s a German term for “shameful joy,” taking pleasure in the suffering of others.
Homer: Oh, come on, Lisa. I’m just glad to see him fall flat on his butt. He’s usually all happy and comfortable, and surrounded by loved ones, and it makes me feel. … What’s the opposite of that shameful joy thing of yours?
Lisa: Sour grapes.
Homer: Boy, those Germans have a word for everything.
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Post by PinkFloyd on Mar 20, 2009 1:53:34 GMT
I use a blast shield, basically a small piece of perspex over the thing, you can closely see what bits burn or explode then during switch on LUXURY! you Southern folk don't know you're born.... the nearest I'll ever get to a perspex shield is a piece of used cling film (If I'm lucky enough to find a piece in a dustbin)..... " perspex"? you bastard southern bastards... you don't know you're born!
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robertkd
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Post by robertkd on Mar 20, 2009 6:02:09 GMT
well chips exploding is one thing, what about when the fish explodes
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Post by rbrook on Mar 20, 2009 6:21:13 GMT
well chips exploding is one thing, what about when the fish explodes Is that before or after you put the lemon juice on it
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robertkd
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Post by robertkd on Mar 21, 2009 12:39:18 GMT
no I think in this case it was lashings of mayo ;D
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Post by jphoward on Mar 22, 2009 2:30:34 GMT
The output transistors may also have survived intact, a quick check would be to remove the op-amp unplug the headphones and power up. Then measure the DC volts on the left and right outputs to GND (0 volts), it should be within 0.5 volts of ground. You mean just after the 47ohm resistors, right? On both of my boards (the one that blew up, and the one that didn't), the side closer to the power block has 0.25V to ground, but the other side has 0.7V (on the blown up board), and 1.2V (on the other board). I'm using the poly input caps, and all AK's tweaks (except for the Toshiba trannies). Am I doing something wrong?...
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Post by Deleted on Mar 22, 2009 3:45:45 GMT
jphoward As you are a beginner, I would suggest that you replace all the transistors on the faulty board , as well as all the electrolytic capacitors. In the absence of further construction faults, this should get it working again, and cost around $11 in parts from Jaycar. This will also save a lot of time and frustration. SandyK
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Post by jphoward on Mar 22, 2009 5:46:20 GMT
As you are a beginner, I would suggest that you replace all the transistors on the faulty board , as well as all the electrolytic capacitors. In the absence of further construction faults, this should get it working again, and cost around $11 in parts from Jaycar. I've bought new capacitors today which I'll put in tonight. I've also got the Toshiba trannies on their way from WES, so they were due for replacement anyway. However, I'm concerned that even my board which didn't blow up has a higher voltage than Robert expected. It seems like either I'm measuring it wrongly, or both my boards have been put together incorrectly, or for some reason the tweaks result in different voltages. Any suggestions?
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Post by Deleted on Mar 22, 2009 5:59:56 GMT
The output transistors may also have survived intact, a quick check would be to remove the op-amp unplug the headphones and power up. Then measure the DC volts on the left and right outputs to GND (0 volts), it should be within 0.5 volts of ground. You mean just after the 47ohm resistors, right? On both of my boards (the one that blew up, and the one that didn't), the side closer to the power block has 0.25V to ground, but the other side has 0.7V (on the blown up board), and 1.2V (on the other board). I'm using the poly input caps, and all AK's tweaks (except for the Toshiba trannies). Am I doing something wrong?... Jeremy Why don't you post a decent resolution photo of the board that works ? I presume that you are talking about the 4.7 ohm emitter resistors. In the working amplifier, you should have somewhere around .13 and .14V across these resistors , and < 5millivolts from the 68 ohm resistors either side to the centre screw of the 3 terminal power supply block on the main PCB . The tweaks will make very little difference to voltage readings. On the faulty board, I would still replace the BC547 and BC557 transistors as a precaution,BEFORE installing the 2SA1930/2SC5171 the other way around to previously with the BD139 and BD140. Alex
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robertkd
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Post by robertkd on Mar 22, 2009 9:10:58 GMT
The output transistors may also have survived intact, a quick check would be to remove the op-amp unplug the headphones and power up. Then measure the DC volts on the left and right outputs to GND (0 volts), it should be within 0.5 volts of ground. You mean just after the 47ohm resistors, right? On both of my boards (the one that blew up, and the one that didn't), the side closer to the power block has 0.25V to ground, but the other side has 0.7V (on the blown up board), and 1.2V (on the other board). I'm using the poly input caps, and all AK's tweaks (except for the Toshiba trannies). Am I doing something wrong?... I have just rechecked on my "stock" build and that variation is acceptable, you may also notice that the voltage would tend to drift with time, what I really wanted to verify was that the output voltage wasn't at or near either of supply rail voltages. as this would indicate either a faulty output transistor(s) or problem in the bias circuits. Would suggest if you have fitted the new capacitors powering off the unit let the capacitors fully discharge wait until the LED's go out and then maybe half a minute more, fit the next sacrificial op amp observing correct orientation, switch on leap back and observe for gently rising smoke. ;D Then check that between ground (either on the head phone socket of center terminal of the power terminal block) and the left and then the right output that the voltage is in the order of only several mV +/-0.00X expected. If that is achieved your likely ready for some listening tests Robert
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