Tube DIY Asylum: PSUD tuning by John Swenson

I've done a lot of experimentation and correlation between experiments and PSUD analysis. I now spend a lot of time designing my power supply on PSUD before building them.

For me in everything I've built the power supply tuning has made a significant difference in the sonics. I found a strong correlation between what I saw in PSUD and what it sounds like. And its not just power amps. It even works for the PS for my USB DAC!

What I do is use the step current tap to provide about a 10% variation in output current and look at the results. I've found the best sonics occur when you get a slight overshoot on the step, ie a slightly under damped circuit. Overdamped ones sound dead and lifeless and under damped (ie ones that ring) sound harsh.

The fun part is getting a design to that point taking into account everything else you need to accomplish. Even for a simple circuit its not that easy. With multiple stages it gets down right difficult sometimes.

Make sure you take the DCR of the transformer as well as the chokes into account, the transformer DCR can make a HUGE difference in tuning.

Then after you find something you like, PSUD is great for letting you know if you can implement it, are the voltage ratings on the caps, recifiers etc good enough.

An important issue is cap type and tuning. In some cases you find you need a fairly large amount of capacitance to get proper tuning, but that usually means electrolytic caps, which usually don't sound as good as film caps, even in PS use. So do you go with several huge film caps in parallel, go with the electrolytic and live with the sound, or redisign the PS so you don't need as big a cap? Then you find the ripple is now too high. So you have to go with another stage to get the ripple under control and still let you use smaller film caps. But then you have to choose the right chokes to make all that work. It usually can all be worked out, but its not a slam dunk, it takes some time trying a bunch of different configurations and and a lot of different values in PSUD.

My experience has been that if you spend the time in PSUD to get a good design you will get very good results right out of the box.

One design a while back took me two months playing with the power supply design. thats when I started modeling everything in PSUD and doing the correlation studies, I would rather spend a few days with PSUD than 2 months buying different caps and chokes until I get it right.

I know I'm a little fanatical about this right now, I even built an optimized choke filtered supply for my audio computer! (and yes it DOES sound better!)

John S.