Guitar Effects PSU

I've been thinking about building one of these (link) and then some DIY guitar effects to go with it.

It looks pretty straight forward, but why the 25V transformer? Isn't that quite a lot of waste and therefor heat for the regulator? Wouldn't it be better to use a 12V transformer for something like this?

Matt

hi matt,
i've built one similar to that one from guitargadgets.com and did it with a spare 15V toroidal i had. works fine and i've got tons of current available (especially for effects). put it in a small enclosure but could only fit 9 outlet jacks because of board space and transformer. easy to perfboard (which i did), but guitargadgets.com has files for self-etch pcbs as well.
regards,
grant

Yes - a 25 volt AC transformer will produce 35 volts DC across the smoothing capacitor - and into the input of the regulator, which will have to drop 26 volts..... If it is feeding 1 amp to the load, that would be 26 watts of heat to get rid of and be of great help to 'Global warming'.......

Crazy!

The use of a 12 volt transformer, as you suggest, would be far better - making a huge saving in cost (and weight) for a giant heatsink!

If you are planning to feed many pedals, consider making a few regulator PCB's - each of which can feed just a few pedals, with improved performance and increased redundancy (a short circuit cable won't bring ALL your pedals down).

this is little offtopic;
but when putting big lytics (someting like 0.5F) for psu is it better to put capasitor(s) before or after regulators?

or find a 7809

12AC transformer should be enough.

if it is for effects(how many effects and how much current is needed total) you should not need large value caps(.5F) sometimes they can add problems

I'm making psu for dual micpre, and ive got some big capasitor from work (for free), thought I use them for that.

I wonder what application you have that might need such large capacitance? Normally a capacitor of this size would be placed VERY close to the load (such as a power amplifier) - to supply short term transient bursts of power.

So putting it before a regulator would be a waste and actually constitute bad design surely?

Similarly - putting it after a regulator might also cause problems with some regulator types that might think they are looking into a short circuit!

So really for a PSU to feed guitar pedals, 4700uF before the regulator and something quite small on the output - say 10uF will produce a very quiet supply.

Simple and cheap.

JG

ok. i save them for something else