audio-talk

Usually flashing over indicates the first capacitor value is too big. I ruined two 6X5 like that. Look at the rectifier's datasheet to see what the max cap value is. And it will probably also say you have to add resistors in series with the anodes, which add to the transformer winding resistance. So the resistor values are, what it says (anode resistance I think) minus the winding resistance.

EDIT: quite possible tho that the winding resistance is the right value, or as good as.

My Audionote copy pre amp has been at Nicks for examination, and Nick has found the problem to be leaking Audionote coupling capacitors.

Well done Nick.

Anyway, after discussions with Nick I've decided to get them replaced with Mundorf MCap Supreme Silver Gold Oil Capacitors.

I'm not due back up north for several weeks but I'll report on how it sounds when it's back home.

Good result .. course I'm in the Mundorf Zn camp .. but it warns me off the Audio Note PIO's for good - cheers !"

It was made worst in this case by the cap going to a 1M grid resistor. I have seen more than one case of them getting leaky over the years. Its a nice pre, full of black gates.

Nick wrote: ↑Thu Mar 28, 2019 12:07 am It was made worst in this case by the cap going to a 1M grid resistor. I have seen more than one case of them getting leaky over the years. It's a nice pre, full of black gates.

I got it from Philip Ramsey (of Bluebell Audio) and he had made it from the very best components for his own use. I got it at a VERY good price for several reasons, one of which was an unknown issue that affected the performance at times. Now we know what it was.

It was not hard to find. You said it was ok then went wrong. Just set up pre on analyzer, set for 1v output, distortion 0.1%, went away for a bit, came back one channel 5% the other 2.5%. There was not much in the thing, so not many things to test, checking voltages before and after what looked like a coupling cap between stages. 100v on one side, 5v on the other (that was connected to ground by a 1M resistor). Replaced cap with 0.1uf fim I had in the box and the problem went away.

As I said, its not the first time I had found one of them leaking a little.

When I got the Audionote copy preamp back from Nick I put it in the system and played a few favourites.

To be honest it sounded OK, but not brilliant, but I left it playing to see if the new coupling caps needed burning in. After a week I went back to my Pre 3, and it made the Audionote copy seem bland.

Anyway, I still have an issue with Pre 3, sounds like a dry joint somewhere, but I can't find it.

So, back goes the Audionote copy, and this time it's really sounding great.

The cause was the rear switch that selects RCA or balanced output, it was in the wrong position causing the RCA outputs to be muted/muffled.

DOH !!

Excellent, congrats.