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Old 9th October 2006, 02:35 PM   #11
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Don't know if you've tried this, but I found that high quality tin snips are great for cutting metal. There's an article on a computer modding site that I found really helpful: http://forums.silentpcreview.com/viewtopic.php?t=2307
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Old 12th October 2006, 11:43 AM   #12
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Default Teflon Silver Wire

Hi 1 & all,
I got the silver teflon wire, however, it's not shielded? Do I need to buy some shielded cable? Or will it be sufficient?
Started mounting the power supplt components last night and have a good image in my head of the final amp!!!
Anyway, cheers and I'll keep you posted.
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Old 28th October 2006, 03:49 PM   #13
lgreen is offline lgreen  United States
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Default Wire

that teflon wire is good stuff you don't need to shield it. If you get a lot of hum over the speakers you may want to re-route the wire away from the transformer or put in some shielding. However for me shielded wire in a GC has been unnecessary.
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Old 29th October 2006, 09:41 AM   #14
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Hi guys,
Will do on the silver teflon and thanks.
Can you use a pre-amp with a lm4780 gainclone or is it better to build a seperate 'passive' out of a selector switch plus attenuator?
Cheers!!!
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Old 29th October 2006, 12:36 PM   #15
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Default Re: Lm4780

Quote:
Originally posted by wotsascott

Hi guys,
I'm new to this stuff <mostly>, but have contructed 2 amps. 1 a sterio lm3876 non inverting <esp> and 1 sterio LM3886 non inverting using Brians boards. Both sounded ok, but looked very bad. Since improving my DIY electronics skills, as well as wading through tonnes of gainclone sites I've decided to run with 2 LM4780 <each in paralell, giving me my 2 channels out of 4 LM3886's> using audiosectors gold boards.
Anyhow, I have a couple of questions before I begin construction, so if anyone out there can help it will be well recieved.
So:
1/ I have 2 150x50x50 finned heatsinks going begging and wondered if these would be adequate?
2/ Do said sinks have to be isolated from the chassis?
3/ I have 2 toroidal 25x25 300va transformers, which gives me roughly 36 volts, with 4 ohm speakers, would this give me a decent output?
Any help would be awesome!
Scott.
The heat sink you describe has a thermal impedance of about 3 C/W -- with +/- 36V -- the heat you have to dissipate is 65 watts -- this is the heat not going into the load -- if the device temperature is to rise only 75 degrees from ambient, you need a much, much larger heat sink. Sorry, that's how the math works.
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Old 30th October 2006, 11:13 AM   #16
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Much appreciated info on the sinks! I now have four of said sinks. Is there anyway I could link them together, making 4 into 2?
After talking about the silver teflon a friend of mine had 20ft of shielded lying in his shed!! This I pinched most quickly.
So, shielded or not shielded that is the question???
Anyone wishing to give me some feedback on the pre-amp thing??
Cheers and happy halloween for tomorow geezers!!
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Old 27th November 2006, 09:02 PM   #17
Hara is offline Hara  United States
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Hello,

Still working on my audio sector kit and have some questions:

You say 330VA 25-25 is good for parallel amps but what about both on stereo for 4 channels, and another possibiility of one on stereo and the other bridged?

I was debating of getting this
http://www.partsexpress.com/pe/showd...number=122-640
or the 500VA version, or 2 of the 330VA

What is the recommended method of isolating chip from the heatsink?
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Old 27th November 2006, 10:56 PM   #18
Hara is offline Hara  United States
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Scratch the isolation question, I think I'll have the chip attached directly to an isolated heatsink for better thermal coupling.

As for the transformer question I'm still curious because I recall some posters saying there are disadvantages to large transformers because of noise and surge protection. Also I do not know effect on the audibility when having seperate transformers for each chip.
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Old 28th November 2006, 08:23 AM   #19
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Hi,
I got away with 160va 25/0/25 for each psu on a 2 channel gainclone, sounds very good!
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Old 29th November 2006, 05:35 PM   #20
flraer is offline flraer  Sweden
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I also have one little question about the powersupply.

Can I use one withe these specs:

300VA, 2x24 Volt, 2x6.25A



/ Fredrik.
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