Hi audioguru,I have made many audio amplifiers using ICs and never used a voltage regulator. None of them produced hum in the speaker.
Why are people talking about 50V supplies and 20W or 22W into an 8 ohm speaker?
Rwind said he has a 12.6V transformer. Its peak is 17.8V and the full wave bridge rectifier drops it down to 15.8V which is too low for the LM1875. With a 16V supply a graph shows that its power into an 8 ohm speaker is only 2.5W when it is already clipping a little.
rwind has 2 transformers of 12V and he was advised to put them in series. I also advised him against regulators.
He is lucky to have you taking over the case. I'm sure you'll give the best help.