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Old 19th December 2004, 05:53 PM   #1
SM7UYJ is offline SM7UYJ  Sweden
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Default LM3875 using single supply voltage?

Have been reading alot about GCs using LM3875 and have just got my two monoblocks with this chip in working order(+/-36V, 300VA transformer on each amp).
In the data sheets from NS on the LM3875 chip there is a circuit for single supply voltage. Anyone who have tried this? Have a couple of regulated power supplys laying around and some people in this forum claime that the chip sounds better with regulated DC (but with +/- DC) !?
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Old 19th December 2004, 08:51 PM   #2
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yes, everyone i have observed on this forum uses +- PS's, and a regulated or a snubbed PS sounds better than a psu without.

I have not tried the single suply on any of the LM chips, but i have heard it and a +- suply on a lm2040 based active speaker, and the +- beat the single suply when it comes to quality and sheer volume.

we used a 8200uf cap as dc blocker, so no linearity problems due to the cap being to small.

It really was like comparing a Lada against an Audi S4.. they both get you from A to B, but the way they both do so..

(I'l just add that the Rolls Roys was lying in the background laughing at the audi and the lada... the rolls being my snubbed lm3886 off cource )
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Old 19th December 2004, 11:42 PM   #3
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as I recall there are some 22uF electrolytic caps used in the single-supply version -- for best high end performance these should be bypassed with a higher quality 1uF polyester film or polypropylene cap.
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Old 21st December 2004, 07:55 PM   #4
SM7UYJ is offline SM7UYJ  Sweden
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Tnx for your replys,
I can imagine that the call for this aproach normaly is'nt of interest for the DIYer. I just had a bunch of PSUs on hand. I ended up conecting two 28V/7A supplys (uA723-3x2N3055+13 000UF) for +/- 28V.
Will listen to this solution for a couple of days and compare with the unrelulated 'original' PSU.
Gain clone nr.2 came to life in the early hours of this day !
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