Clarifications on Ruby amp build

[J M Fahey]

Please remember that transformers are rated in AC volts (because that's what they deliver), but then you rectify them with diodes, store them in filter capacitors, they become DC voltage (what your amp will actually use) ,  around 40% higher.
So a 12VAC transformer will supply raw 16V DC.

In your particular case, fine, TDA2003 will be *happy* with a 16V supply and present you with extra watts, how's that?

But in most other cases , 40% extra is too much, so do the proper Math before ordering.

[Jtommi]

Anyway I wanted to add a voltage regulator after the rectifier to eliminate ripples and they require a bit more V than the desired output. I also thought about splitting it in 12V and 9V (for preamp, distortion etc) and according to this Youtube video there also can be a voltage drop (although he's not sure about the specs of his transformer).

On that note, would it make sense to add a resistor (1/2W or 1W) before the 7809 in order to reduce the 16V and relieve the 7809 (i.e. providing 11V to the 7809 instead of the full 16V).

[stormbringer]

I would not pre-regulate with a resistor, it will get really hot. Use the regulator instead, a preamp shouldnt need much power, so the 9V regulator with a small heatsink (not even sure you need one, but there are so many cheap ones) would be fine. I have read about pre-regulation quite a bit, but the only really good way in my opinion would be some sort of switching circuit, and with the small amount of power needed for a preamp it would be overkill. Also, leaving about 3V or more headroom for he regulator is a good thing for stability.

You could also regulate the 9V from the 12-rail, if you think the total power will exceed the maximum the 7812 can handle, google 7812 Pass transistor. That way you can put a bigger transistor, that can handle the additional power in the circuit, you will need to heatsink it anyway though.

[J M Fahey]

You can feed straight 16V to TDA2003 because it's within ratings and provides a couple extra watts

You can feed the 9V preamp with a small, TO92 sized 78L09, fed raw 16V .

Power is very low, in this case no need to preregulate, nor heatsink.