15V to 13V regulator

Hello, I just bought a 230VAC/15VAC transformator and just cant figure out how get the 15V down to 13V...
Its going through a rectifier and some 20000uF to feed a small Class D amp...
So, I can only test it without load... :) I dont want to hook up the amp before I know what will feed in to the amp...
Any suggestions?
Last edited:


2013-01-11 2:58 pm
Thanks for your reply! But I must say that I used a switching regulator and had bad interfearances in my analog radio through the amp...
Tried also a 12V lead gel battery and all was good... :)
Dont know what to do...
Is there a old school methode without useing a switching regulator?

Do you have more details on the specs of this class-D amp?
min/max power voltage (no seperated plus and minus supply needed?)
max current


2013-01-11 2:58 pm
Its a SMSL SA-S3... with the TA2021b chip...
T-Amp IC Tripath TA2021B
Output Power 2 x 25W @ 4ohm, 2 x 13.5W @ 8ohm
Dynamic Range 100dB
Power Efficiency 81% @ 25W, 4ohm, 88% @ 13.5W, 8ohm
Audio input: RCA x 1
Power socket (5.5mm/2.5mm) x 1
Circuit board : 1.6mm thick, full-fiber, deep golden

would do something like thisbut with only one 3055:
(and smaller caps, 4700uF should do it)

Making the mat, the chip says 25W @ 4Ω, does not say if is only one or both channels simultaneously. Lets suppose that is single channel only (Worst case). Then, I = √(25W/4Ω) * 2ch * √2 = 4√3 = 6.9Amper peak. So U will need a power supply capable of deliver about 10Amper. A couple of TIP36 plus a LM317 may do the job.