Univibe power supply Qs

[warioblast]

It took me a few months of trial and errors to make it sound right. So I finally boxed everything earlier this week. But a few days later I started noticing some background noise.
I built a vintage forum vibe, powering the LFO directly from a 24VDC regulated power supply and using a LM7815 for the audio.

I took my DMM and measured 24.2V from the PS and from 15.4V to 15.7V after the the 7815; I don't remember if it oscillated before this noise thing. I went in trial mode with a voodoo lab pedal power 2 +, making my own Y cable. Using lower powers like 18v and 21v attenuated the noise. After hours of trials, the noise went LOUDER. From a big shushing a slow speed to a bird chirping sound at higher speed. I decided to call it quits.
The next day I measured the output of the 7815 and I measured over 23v. So I guess I killed the regulator for good but I'm still trying to figure out what went wrong in the first place. I had the vibe unboxed for months and everything was fine regarding power supply.

I decided to try toying with the original power supply.

With the parts I had around this is what I came to

For R50 I tried 470R, 1k, 1k2 up to 1k5 to get 15.4V to the audio path. The pedal is noise free, the typical univibe throb is slightly quieter than  my Mojo Vibe.
My question is, can I use any kind of resistor for R50 without risking to fry anything ?

[R.G.]

A better question is why it made noise in the first place, and why the regulator died.

There are thousands of univibe clones out in the world with a 7815 for regulating the audio power, and they do not have what I think you're describing. Nor kill the regulator. I don't know about the "forum vibe", haven't looked into it. But the first neovibes were built back in 1999-2000 and are still at it.

It could well be that in putting it in the box, you accidentally shorted something, and in hooking up the other power supply, you un-shorted it. Don't know. If it were mine, I would not think it was fixed until I knew what caused it to break. In automotive terms, no amount of polishing your hubcaps or alloy wheels will fix an intermittent transmission problem.

And yes, you can use any kind of resistor for R50 as long as it doesn't get too hot.

[warioblast]

Is it normal for the ouput of the regulator to sligthly oscillate ? Or was it a sign that it already took a shot ?

The only change I made when boxing the board was using bared tinned wire for the ground connections. Everything looked pretty tight... but I guess that increases the chances of shorts.

I was looking at pictures of boutique vibes to see what capacitors were used in their RC filters and I noticed the 78L9 Reg writing at the bottom of the Sweet Sound Ultra Vibe. Without being too techy, can you tell me what's going on here ?

[rullywowr]

I was looking at pictures of boutique vibes to see what capacitors were used in their RC filters and I noticed the 78L9 Reg writing at the bottom of the Sweet Sound Ultra Vibe. Without being too techy, can you tell me what's going on here ?

The 78L9 is knocking down the voltage to a steady 9V.  The internal transformer is supplying this unregulated voltage. 

[antonis]

The internal transformer is supplying this unregulated voltage.

and unrectified..

[warioblast]

I know it's a 9v regulator. Why would you want 9V in a univibe ?