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If I put my notes here, I might be able to find them again later!
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Modification of the S.M.S.L. sAp VI headphone amplifier

Posted 14th January 2013 at 11:29 AM by rjm (RJM Audio Blog)
Updated 28th January 2013 at 12:33 AM by rjm

I couldn't even build it myself for the price they are selling it at, $50 on ebay. It caught my eye for the linear, split power supply. I love the chrome 3-pin power connector, too.

As is usual when you buy cheap ultra-Chinese audio gear via eBay some adjustments are needed, however.

The basic problem seems to be a little mix up with the input coupling capacitors. It came with polar electrolytic capacitors, following the markings on the circuit board. If you lstudy the schematic I sketched up below you will notice the input signal and DC offset can swing in both positive and negative directions relative to the op amp inputs - polar capacitors in this position are a bad idea.

I recommend anyone buying this to replace the input caps with Nichicon Muse ES or similar 4.7 uF or 10 uF bipolar electrolytic caps. (I have some extra I can mail out. pm me if interested.)

Other than that it's a pretty solid circuit as far as I can see....
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