Amp is intermittent

[DD_Davo]

Hi, i posted about my amp about a month ago with problems regarding it generally not working and the problem seemed to be power, Well i know now it isn't just power. Its the Velleman K4003 i have built and its very intermittent. Once i power it up it tends to work fine for about a minute then the audio disapears and white noise replaces it (like an off-tuned radio station kind of noise) then it all dies.

However i have also found that sometimes before it fully dies the audio looses complete bass and goes very tinny and treble like. I am now very puzzled to what the fault is. Could it be the IC or can any of the capacitors including the electrolytic ones cuase this. The main problem is that it works for a short period of time then cuts out.

If you'd like to see the circuit http://www.velleman.be/Downloads/0/Manual_K4003.pdf there's the link with all the info. The IC is a phillips TDA1521

Thanks for any help you may offer
Dave

 

[Nuuk]

Very difficult to say! Check all your solder joints and then check the voltages around the circuit.

How hot does the chip get?

 

[Sherman]

I'm with Nuuk on this one. It sounds as if a bad solder joint is warming up and then breaking contact. I would start checking all solder joints. Start with the ones closest to the chip and work methodically away.

Also as Nuuk said check the voltages around the circuit both at immediate power up (when the amp is working as it should) and then again when it stops working. If you find a significant change (and I think you will) you may be able to locate the bad connection by following the traces.

 

[DD_Davo]

well the solder joints seem fine when checked with a multi meter. The IC running on two Duracell M3's (18V total) gets 'luke' warm. If i use two 1A 12V PSU's it soon gets warm but not overly hot with the heatsink on.

Its a basic circuit anyway. The 4 diodes work as a rectifier for AC current but i'm using DC and they are correctly positioned so power is getting through, then theres the large 4700UF capactiors which i think are to smooth out any AC current then theres the other capactiors and 2 resisitors. Then the IC.

So its not like theres a great deal to go wrong but obviously something isn't right. I;m not sure what effect any other component would have on the amp if damaged (other than the IC)

Thanks for the reply

 

[DD_Davo]

Ah thanks, i didn't see your reply. Well i'll go all over the connections again, when checking voltage it seemed to be pretty close to either the 24V or 18V mark on the input side. I'll re check soldier joints. I suppose it will be that or a faulty component. Thanks

 

[Nuuk]

Just to make quite sure - where are you feeding in the DC voltage from the batteries? Is it before or after the rectifier diodes?

 

[DD_Davo]

When i run it on batteries i run it before the rectifier, if you look in the link http://www.velleman.be/Downloads/0/Manual_K4003.pdf last page it shows the circuit diagram, and i feed DC current in before the rectifier. But shouldn't that still work, since the current is travelling through in the correct direction.

I also have rechecked solder joints, and they seem sound

Thanks

 

[Nuuk]

I wouldn't put DC into a rectifier bridge. I'm not sure what it would or would not do but I'm sure that it would be better to connect it after the bridge!

 

[DD_Davo]

i shall try that now thanks....

Well i get a lot of popping and crackling when i place the wires after the diodes. Everynow and then i get a 1/10th of a second audio clip but thats it. The crackling is loud though so the amp is amplifying but there is definately a source into the amp as if you bridge the input and output pins audio travels to the speakers without being touched by the amp.

 

[dsavitsk]

I wouldn't put DC into a rectifier bridge. I'm not sure what it would or would not do but I'm sure that it would be better to connect it after the bridge!

Both this Velleman PS (http://www.partsexpress.com/pe/showdetl.cfm?&DID=7&Partnumber=320-216) and Tangent's new TREAD PS (http://www.tangentsoft.net/elec/tread/) allow using either AC or DC at the same input before the rectifier.

I don't think DC through a rectifier makes any difference.

-d

 

[DD_Davo]

yep, it doesn't seem to make any difference anyway. So if its not the solder joints, and its not the DC current rectifier problem.... its got to be one of the parts. But which? Its odd how it works but then dies. Oddly, i can sometimes get a very short burst of audio maybe half a second, after disconnecting the batteries (this is when the amp doesn't work when the bastteries are connected.)

I don though when using the PSU's. ABout a week back i had it running on the PSU's for about 10 mins, but then it just randomly died again and ceased to work. The temp of the chip was quite hot but nothing incredibly high, the heatsink seemed to do its job and even when cooled down it refused to work again.

 

[Nuuk]

Both this Velleman PS (http://www.partsexpress.com/pe/show...tnumber=320-216) and Tangent's new TREAD PS (http://www.tangentsoft.net/elec/tread/) allow using either AC or DC at the same input before the rectifier.

OK if they so then it msut be OK. It just seems a little strange to me.

Other things to look at are the polarity of the caps , power supply connections and any possible shorts.

 

[DD_Davo]

well theres only two electrolyitics capacitors. They are correctly placed. But i admit i foolishly put them in reverse polarity and placed power through the amp several weeks back. I don't know if this could have an effect on them?

Power connections well they seem ok power is definately reaching the amp.

Shorts, i checked round the IC for that but nothing seems to be touching.

Thanks again

 

[Nuuk]

Replace those caps!

 

[DD_Davo]

Ok will do thanks. Do you know where i can get replacements from? These are 4700UF 25V electrolytic capacitors. But searching mapins, they don't sell 4700UF electrolytic ones.

Thanks

 

[Nuuk]

I use Farnell for most of my requirements.

Order code 303-6340 should be fine but check the size and pitch.

You can find Farnell here .

The only problem is that they have a minimum order value.

 

[DD_Davo]

Thanks I'll have a look, the only place i can find is rapid http://www.rapidelectronics.co.uk/r...CAT_CODE=31198&STK_PROD_CODE=M62556&XPAGENO=1 (if that doesn't work... code is 11-0755)

Do you know what the minimum order value is, i'll take a look round the site. Thanks

 

[Nuuk]

The Rapid ones will do. The Panasonic FC's are very good.

You need to spend at least 10UKP with Farnell in order to pay by credit card.

 

[DD_Davo]

I'm tempted by the panasonics then. Only thing is what else can i possibly buy to make up to the £10. They don't sell my IC (TDA1521) otherwise i'd have one of them incase too. hmmm

Thanks

 

[Nuuk]

Bits for another Gainclone?

Speaker plugs/sockets, phone plugs/sockets, solder, multimeter, other tools, wire, switches, fuse holders/fuses...........................