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Learning Experience with Capacitance...

Posted by Lee of Omaha (D) on August 1, 2017 at 11:12:18

We had a customer's Jolida power amp in for light repair and the customer was interested in upgrade. We replaced the Audyn coupling capacitors with Russian K40Y paper in oil caps.

There are three coupling caps per channel, two .22uF and one .47uF. We missed the fact that one of them was .47uF at first and replaced it with a K40Y .22uF. We did one channel at a time so the customer and we could hear the difference between the stock Audyns and the K40ys.

We played the same cut in mono on the same speaker with both sides of the amp in turn.

With the inadvertently too-small coupling cap the sound was worse than original, with constricted dynamics and lack of detail. This is the opposite of what I've come to expect with K40Ys. That's when we went looking and found the undersized capacitor.

We then added a second .22uF in parallel for .47uF (close enough to the original .47uF). The sound then opened up with more detail and impact than the other channel, exactly what we expected initially.

It seems odd that a too-small coupling capacitor would affect dynamics and detail rather than bass, but that's exactly what happened. And using the right values of the K40Ys did what I've come to expect of them-detail, impact, macro and micro dynamics.

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