Need a 15vdc- 400ma - 0 + adapter. any ideas?

[jimbob]

I cant find one anywhere! Its for a Tonebone Hot British distortion. bought  new without it..no one has one it seems..ideas?

[Jim Jones]

Ummm, build one?  

Jim

[Peter Snowberg]

15VAC transformer => bridge rectifier => big filter cap => LM317 regulator => stabilizing cap => effect.

Take care,
-Peter

[mr_winter_]

more simple and effective:

any transformer up 15 vac or 15vac + a 7815 voltage regulator + big filters to output....

READY!!!!!

[David]

15?  Wait a minute...

R.G. is always talking about how the rectifier and the voltage regulator each eat some voltage.  In order to get 9V, you have to start with something like 12 to 15.  To get regulated 15V, shouldn't you start with at least 18 or better yet 24?

[Peter Snowberg]

There is a small range of voltages where you can use an AC measurement like this. When you add the bridge rectifier, you end up multiplying the input voltage by approx. 1.4 so 15VAC in becomes approx. 21VDC. From there the regulator takes it back down to 15.

You need about three volts over the output voltage to get stable regulation so you can use a 9VAC transformer to make 9VDC with a 7809 regulator, but go lower than 9 volts and this trick no longer applies (9 * 1.4 = 12.6 - 3V regulator requirement). You can't use a 5VAC transformer to make 5VDC with a 7805 for instance. (at least until you switch to a low dropout regulator like the LT1129-5 which only needs 0.4V above the output voltage)

If the input voltage is too high you end up cooking the regulator. If you wanted 20VDC out from an LM317, the bridge recitifer would output approx. 28 volts from a perfect 20VAC transformer which is just under the 30V absolute maximum that the LM317 will accept.

Keep in mind that a 20VAC transformer will give you 20VAC at full load so with nothing being drawn it might be outputting 27VAC for instance. That will let the blue smoke out of the regulator.

Take care,
-Peter

[mr_winter_]

you are right!!!

this the way: 18vac >>> 15vcc w/reg.

sorry... sometimes I forget any things..

:?

[RedHouse]

Yep, just build a 15v 500mA unit, you'll be fine.

I had a Tone bone Hot British, sold it on e-bay a month ago, I liked it for practicing, but 2 things changed my mind. I recorded it, and it sounded really raspy (crappy to my ears) but the real surprise was when I opened it up and started tracing out the schem-o,  never finished because I quickly realized it was a Tube screamer with a 12AX7 cathode follower and some tone switching... not exactly my idea of tube distortion.