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Old 30th May 2008, 02:40 PM   #1
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Default Another first chipamp

This is my first ever project: the "heat sink chipamp"

http://www.flickr.com/photos/1157168...7603119448350/
(check the fire extinguisher on the last photograph... boys, do not try that at home... )

This a carlosfm lm3886 design with his snubberised psu using a 2x22 300va toroid. I decided to go for p2p and I think the job was Ok for a newbie.

I have not decided which enclosure I will use so the whole amp was made "portable" but solid despite being p2p. Amp and terminals are mounted on the heat sink in order to provide strength to the connections and give mechanical stability while making it easy to move to different enclosures without putting any stress on the joints.

DC offset using a 10 ohms resistor without a source connected was 64mv.

I powered it up and got a nice and clean sound on first attempt even with very poor sources (an fm radio). Then I connected a good preamp an cheap Sony cd player and a decent speaker (B&W 601) and was very pleased with the result. I have not tried them with my full range Jordans JX92s MLTL, for which the amp/psu were designed.

I had it running for few hours at medium volumes and the heat sinks became just slightly warm but not hot at all.

The grounding and design was done using by MikeF ideas in dogbreath.de (thanks Mike for having your projects so well documented and with excellent photographs). I also used lots of ideas from http://www.vikash.info/audio/p2plm3886/ (thanks vikash)

There were only two issues:

1- The highs were clear but maybe I expected them to be a tinny little bit crispier. Maybe the problem are my ears or the speakers or the fact that the preamp is running with a very noisy USA- UK mains transformer. Actually, I do not know if some burning-in will help the highs. Will it?

Also I suppose that eventually hearing the two channels will also make the difference.

2- Within a period of about 3 hours I heard a couple of small clicks coming from the speaker. I do not know if this is what is called clipping and I hope it is easy to solve. Any ideas?


I take the opportunity to give very special thanks to Dennis Hui, Nuuk. Andrew T, Danielwritesback and all the others who have helped me to clarify my doubts.


Regards

Antonio
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Old 30th May 2008, 05:13 PM   #2
Bluto is offline Bluto  United States
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Pretty impressive as a new builder to this Guy - especially with a 1/3 of a bottle of Smirnoff gone.

Bluto
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Old 30th May 2008, 05:21 PM   #3
Nordic is offline Nordic  South Africa
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DC offset is measured with the input shorted.
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Old 30th May 2008, 05:27 PM   #4
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Quote:
Originally posted by Bluto
Pretty impressive as a new builder to this Guy - especially with a 1/3 of a bottle of Smirnoff gone.

Bluto
As I mentioned, that was the fire extinguisher...

Antonio
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Old 30th May 2008, 05:29 PM   #5
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Quote:
Originally posted by Nordic
DC offset is measured with the input shorted.
Thanks Nordic

Should I short it just with a cable? or I connect a live source?

Antonio
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Old 1st June 2008, 04:28 AM   #6
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Default Re: Another first chipamp

Quote:
Originally posted by A Sanchez
T
There were only two issues:

......
2- Within a period of about 3 hours I heard a couple of small clicks coming from the speaker. I do not know if this is what is called clipping and I hope it is easy to solve. Any ideas?

Any input on this issue would be very appreciated.

I do not know if the reason for the clicks I heard could be because the gain was set to the lowest level ie. 20db as recommended in the original design on the assumption that the preamp was was going to provide the additional gain. However, maybe my preamp (A Conrad Johnso Sonographe SC1) does not provide much gain so maybe I should increase the gain of the amp a little bit.

Many thanks in advance.

Regards

Antonio
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Old 1st June 2008, 06:19 AM   #7
amc184 is offline amc184  New Zealand
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Sometimes intermittent single clicks are something like a fridge cutting in and out, maybe this is your problem?
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Old 1st June 2008, 08:45 AM   #8
Nuuk is offline Nuuk  United Kingdom
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I agree, I don't think what you heard was clipping but more likely interference from a switch somewhere in your home.
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Old 1st June 2008, 10:19 AM   #9
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Thanks! That makes sense. I was trying the amp in my kitchen (fridge and boiler) when this happened. What a relief !!!

Also, as a matter of fact the system is delivering plenty of power. I think I would not be able to reach half the way with the preamp volume without blowing up the house windows..and the speakers.

Now I can start building the other channel

Regards

Antonio
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Old 1st June 2008, 11:25 AM   #10
AndrewT is online now AndrewT  Scotland
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Hi,
buy some switch snubbers and fit them to the troublesome appliances to suppress the interference at source.
They are available as combined R+C in a plastic package and rated for mains use.

Add an RF filter to the front end of your power amp.
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