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Chip Amps Amplifiers based on integrated circuits

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Old 23rd August 2013, 06:23 AM   #11
AndrewT is offline AndrewT  Scotland
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Shorting a V+ to ground should have blown the mains fuse.
That would shut down the PSU leaving the chip undamaged.
What size of fuse did you use?
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Old 23rd August 2013, 11:31 AM   #12
Mihkus is offline Mihkus  Estonia
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Is components smoke, they get cancer and cant be saved anymore.
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Old 23rd August 2013, 11:36 AM   #13
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AndrewT - I agree but it looks like he used a similar approach when mounting the amp boards. Who knows what has been shorted out.

I would start with repairing the PSU and then hope that the amp boards are OK.
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Old 23rd August 2013, 03:34 PM   #14
davym is offline davym  Scotland
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This is madness! If I can help someone else avoid this happening to them it would be something though I suppose.

The fuse was a 3A slow blow, it blew but obviously too slowly!

I just spent over an hour ordering parts from farnell! I hate their website so i have not bought from them in years. I finally ordered more than I need because they have a minimum £20 order below which they charge £5 handling. After finally finding everything and filling out the order for 10 x MUR860 2 x LM3886TF 10 x 3A slow blow and 10 x 3A standard fuses (min order of 10) I find that their website does not accept my maestro card or paypal!!!

After a half hour phone call they accepted my order, processed the maestro payment, then told me they had a £6 handling fee for phone orders under £30!

I was finally stung for £36.76 and was so hacked off I just meekly said ok, whatever, just let me off this dam phone!

I probably don't need all of that but it will probably all be used at some point, twenty 3A fuses could be handy eh, right!
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Old 23rd August 2013, 06:10 PM   #15
Mihkus is offline Mihkus  Estonia
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For amplifiers even ultrafast can be too slow.
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Old 23rd August 2013, 06:50 PM   #16
AndrewT is offline AndrewT  Scotland
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3A & 240Vac is a lot of power handling.

What VA is your transformer?

BTW,
fuses do not save semiconductors.
Correctly sized fuses prevent setting your house on fire.

But diodes can fail to short circuit.
If you overload a diode in a rectifier and that diode fails short circuit, that could send AC to the next stage.
AC will probably destroy the chipamp.

To help prevent this calamity, fuse the Mains input so that an overload shuts the whole thing down and hopefully this happens fast enough that as the diode fails the fuse blows and the chipamp never sees that AC.

A 600VA to 700VA needs a T3A fuse.
A 200VA to 250VA needs a T1A fuse.
A 160VA needs a T800mA
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Last edited by AndrewT; 23rd August 2013 at 06:58 PM.
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Old 23rd August 2013, 06:59 PM   #17
davym is offline davym  Scotland
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It's a 300VA so by your guide I used too high a rated fuse! I definitely read a post somewhere by a bloke saying that because of the current in-rush he needed a 2.5 to 3A fuse for that size transformer. He said a smaller fuse would not last very long without soft start.

I found the light bulb tester I made weeks ago in the boiler cupboard today while looking for something else. Doh!

I could not face ordering new diodes only to fit them and then find I needed to order new chips too so they are all now ordered and should be here next Tuesday (hopefully)

Last edited by davym; 23rd August 2013 at 07:10 PM.
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Old 23rd August 2013, 07:33 PM   #18
davym is offline davym  Scotland
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Just ordered some T2A fuses from an ebay seller.
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Old 24th August 2013, 05:28 AM   #19
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Quote:
Originally Posted by davym View Post
This is madness! If I can help someone else avoid this happening to them it would be something though I suppose.

The fuse was a 3A slow blow, it blew but obviously too slowly!

I just spent over an hour ordering parts from farnell! I hate their website so i have not bought from them in years. I finally ordered more than I need because they have a minimum £20 order below which they charge £5 handling. After finally finding everything and filling out the order for 10 x MUR860 2 x LM3886TF 10 x 3A slow blow and 10 x 3A standard fuses (min order of 10) I find that their website does not accept my maestro card or paypal!!!

After a half hour phone call they accepted my order, processed the maestro payment, then told me they had a £6 handling fee for phone orders under £30!

I was finally stung for £36.76 and was so hacked off I just meekly said ok, whatever, just let me off this dam phone!

I probably don't need all of that but it will probably all be used at some point, twenty 3A fuses could be handy eh, right!
I'd have ordered just the diodes from RS. OK there would be a handling charge but they wouldn't have cost £36.

Or for fault finding just fit some 1N4001's. Once it's working you can go on to glorious components.
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Old 24th August 2013, 07:01 AM   #20
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A 300 VA more or less needs a soft start. You could use my SST03. If you have a softstarter the fuse will protect better since the fuse value can be set for the actual maximum load, not to manage a start up.
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