9volt Pedal Power Supply with 7.5v Midi Keyboard?

#1

I am currently running my shruthi on the same guitar pedal power as the rest of my live synths, but have a 7.5vdc powered midi keyboard I want to through in the mix. Is there any device or circuit I can use to bump the 9vdc down to 7vdc?

#2

My bet is that this thing works at 3.3V internally, has a 3.3V Vreg, but that they did not bother with heatsinking. I suspect it would just work with 9V except that something inside would get hot. But unless you open it to check it is done, don’t try this :slight_smile:

Try this with an adjustable Vreg:

I would increase C2 to at least 10uF and put a smaller 100nF cap in parallel.

It will work if:

  • Your input is a bit above 9V (most 9V wallwarts I’ve seen are delivering higher voltages anyway…)
  • Your keyboard doesn’t draw too much current (say in the 50mA).

Otherwise, 1.5V is too small of a dropout for a vanilla regulator, you’ll have to look into LDOs, for example a LM1117-ADJ…

#3

Thanks for chiming in,

I went ahead and took some pics of the internals:

http://toilville.com/pics/IMG_20120424_084540.jpg
And a close up of the power section:
http://toilville.com/pics/IMG_20120424_084437.jpg

I’m guessing that l101 is the power regulator for this? Anyway to measure it from in the circuit?

#4

No it’s an inductor for cleaning up the power input… I don’t see anything that looks like a Vreg on those pics.

#5

thanks!