Saturday, April 30, 2016

Phono Preamp

I know that all this electronic stuff and pictures of circuit boards is kind of boring for those of you who like cars and motorcycles.  But I like it.

The latest project is a phono preamp that uses vacuum tubes.  Why vacuum tubes you ask?  Isn't that old fashion?  Well, I'm new to it too, but the designer says that vacuum tubes have certain advantages like a wide dynamic range and, besides, he likes the way they look.  OK.  Good enough for me.

If you are curious why it's on a piece of plywood,  I hope to build a DIY turntable and stand in the future.  That may turn out to have a triangle shape.  Since the preamp should "fit" with the turntable and stand, I'm waiting until all that gets decided before designing the preamp enclosure.  What do you think, a big triangle with the points cut off?  Or maybe a trapezoid?

One of the unusual things about vacuum tubes is that they essentially need 3 power supplies and those are often in a separate enclosure to keep the tubes quiet.  In other words, there was lots to learn on this project and an extra dollop of complexity.

Tubes also take time to warm up and turn on.  Maybe 30 seconds before there is a little glow in the top of each tube.  No music comes out before that.  Kind of strange for our normal "instant on" solid state life.

Speaking of the separate power supply enclosure, I tried something a little unusual in the paint job.  I was going for "old leather", but I don't quite get there.  Oh well.  The power supply will sit in back on a bottom shelf, so no one will really see it.

The good thing is that it sounds great!  Background noise as good as a CD and a very dynamic presentation.  I guess I need to buy a few new records.