Simple transformer questions

[frejohg]

Hi!

Im trying to design a power suppy for a lm4780 chipamp for my cerwin vega vs10 6ohms 125watts rating.

I have two toroid transformers, they are labeled 25V. Is it 25V RMS or peak?

They are not center tapped, can i still make a +/- voltage supply?

What voltage will i get after the rectifier?

I have a lot of free capactiors, is more capacitors always better?

[nigelwright7557]

25 volts RMS. About 36 volts after rectification.

You can make a dual supply from one transformer winding using 2 diodes.
But it will only be half wave rectified.

[mastodon]

What voltage will i get after the rectifier?

+ and - 18V if you do as Nigel suggests. See here ('half wave rectifier'): Basic Rectifier Circuits

I have a lot of free capactiors, is more capacitors always better?

There's a law of diminishing returns. Based on the maximum load, run a simulation using a computer tool (e.g. Duncan Amp's PSU designer or LTSPice). Chipamps usually have a good power supply ripple rejection (PSRR), so you don't need as much filtering as you may think.

[frejohg]

OKay then.

Half wave rectifier will give me about +/1 11 V. That is way low.

If i could use both transformers, what is the best setup?

As i said i want to get as much power as possible for my Cerwin Vegas.

[Andy5112405]

Are the two transformers identical ?

If they are then it is a simple job to make a +/- supply.

Connect each transformer to its own Bridge Rectifier. You will then have two completely separate 35V DC supplies.

Then connect the +ve of one Bridge Rectifer to the -ve of the other Bridge Rectifier. This common point will be your 0V or Ground.

The unconnected -ve of the first BR will be -ve 35V.
The unconnected +ve of the second BR will be +ve 35V.

[Andy5112405]

It's as simple as that.

In your application you will probably need two regulators to bring the voltage down to a useable voltage as +/- 35V is probably too high.

Andy

[AndrewT]

Originally Posted by frejohg

I have a lot of free capacitors, is more capacitors always better?

adequate capacitance is always better.
More capacitance = bigger volume = bigger weight = bigger maintenance/replacement cost = bigger transformer and rectifier pulse current = bigger mains fuse = more risk of failure.
For 6ohms and reasonable bass performance I'd suggest +-10mF as the main smoothing capacitance. F-3dB of input filter ~5Hz giving ~10Hz for F-1dB LF bandwidth.
For excellent performance for all bass frequencies, I'd fit +-30mF for each channel for 6ohm speaker. F-3dB of input filter ~1.5Hz giving ~3Hz for F-1dB LF bandwidth.

BTW,
I can never recommend the dual version of the chipamp. It's manufactured to allow lower assembly costs for automated mass production.