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Old 23rd October 2006, 11:18 AM   #11
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Quote:
Originally posted by Leolabs


For me,at least 250VA is required.
You can't generalise - it depends on the voltage of the transformer, and hence the output power you want to achieve.

I would agree with your suggestion if you were trying to extract the full 60 watts per channel from the IC. But for that project, I only wanted 25 watts per channel - any more would have required a bigger case with much more heatsinking. The 120VA device I used is generous in this application.

While over-engineering the power supply by using an over-large transformer might seem attractive, especially from a cost-per-VA viewpoint, be aware that it might bring other problems. For example, 250VA is getting close to needing an anti-surge circuit. It might have higher leakage current than the smaller unit, leading to hum problems. It might make more mechanical noise. The lower source impedance leads to higher peak charging currents. Etc...

Anyhow, just my opinion. Thanks for the compliments, and good luck JojoD with your P2P efforts. It's not that difficult, but you'll need good lighting, lots of time, and perhaps an eye-magnifier... There's some advice on my "construction" page about how I went about doing P2P - you may not choose to follow it all, but if you do, the finished result should last a lifetime. In a nutshell, get mechanical strength before adding solder!

Best regards,

Mark
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Old 23rd October 2006, 01:42 PM   #12
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Hi there Mark,

Thanks for the encouragement and the tips. I actually have built some tube projects in the past so p2p is, in a lack of the proper words, a fun challenge for me. I also made several p2p 3875 gc many years ago.

I actually have 2 4780 chips, so I wanted to run them (each chip) in parallel but still would only like to extract about 40W from each chip, just enough to cleanly handle those loud passages from classical recordings.

Regards,
JojoD
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Old 23rd October 2006, 03:31 PM   #13
Nordic is offline Nordic  South Africa
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I have just finished scaleing the PCB from the datasheet... and the holes realy don't seem that close as they do when holding the chip in your hand....

Is the datasheet version an OK implementation?
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Old 23rd October 2006, 04:13 PM   #14
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Quote:
Originally posted by JojoD818
Hi there Mark,

Thanks for the encouragement and the tips. I actually have built some tube projects in the past so p2p is, in a lack of the proper words, a fun challenge for me. I also made several p2p 3875 gc many years ago.

I actually have 2 4780 chips, so I wanted to run them (each chip) in parallel but still would only like to extract about 40W from each chip, just enough to cleanly handle those loud passages from classical recordings.
No problem

40-50W is easily attained from a transformer with two 24V windings. It's good that you're using them in parallel mode because that'll help with heat sinking (LM4780s have higher thermal resistance than a pair of LM3866's). As an aside, have you considered bi-amping?

Now we know the power you're after, we can say that the 250VA transformer mentioned earlier is about right. Although, you might consider using dual transformers? Say, 120-160VA each... Makes certain things easier provided you have enough space. Worked well with my (old) LM3875 prototypes (which are still on a lump of wood!).

Looking forward to seeing the pictures. Send me a link, and I'll add it to my site. That goes for anyone else who's done a P2P LM4780

Cheers,

Mark
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Old 23rd October 2006, 04:52 PM   #15
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The board shown in the datasheet is the one use to generate the graphs in the datasheet. National typically does this. But probably done with regulated bench supplies and not a unregulated supply running from a transformer like we and just about every manf. does.

-SL
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Old 28th December 2006, 04:38 AM   #16
m8o is offline m8o  United States
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In response to the OP, how 'bout using a ZIF socket at least? (the 28-pin is the one) I finally found these.

http://www.arieselec.com/products/zif.htm

http://solutions.3m.com/wps/portal/3...tBurnInSockets

http://www.elexp.com/ics_fs16.htm
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Old 28th December 2006, 02:23 PM   #17
m8o is offline m8o  United States
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where'd "edit" go? Would have done that. so, new post.

Please take the above with a grain of salt. I now notice the LM4780 pins are on 0.0394 centers. Additionally, if one doesn't want to bend leads to line the pairs up, you'd need a 54 or 52 pin socket and use 1/2 or them (52 can be used as pin-1 can float as it's a "NC" connection).

...but, I haven't found sockets to accomitate either however; either bending the leads to make pairs on a 28-pin socket with 0.394 centers or a 54 / 52 pin socket on those centers... so, ignore...
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