I want to start small, have a question about a toroid

[beerman]

I decided I want to build a small chip amp for my PC using a single LM1876.

This unit from digikey is called a "mini". It is a 50va with 12v secondaries.

Will that suffice for a small 15w per channel stereo amplifier?

[bremen nacht]

Just about, a bit on the small side but probably a lot better than most of the PC systems advertised as 60W or more...

[Leolabs]

Yes,with something like the LM1875.

[beerman]

Originally posted by Leolabs
Yes,with something like the LM1875.

If I recall, the 1876 is two 1875s in a single chip?

[twitchie]

I think you'd be better off with a chia-yu xformer from apexjr for 12.50

http://www.apexjr.com/miscellaneous.html#Toroids

12V will be on the low side

[beerman]

Originally posted by twitchie
I think you'd be better off with a chia-yu xformer from apexjr for 12.50

http://www.apexjr.com/miscellaneous.html#Toroids

12V will be on the low side

I'll admit to being a newbie on this subject.

I'm trying to stay "safe". I will want to run 4ohm drivers with this amplifier at one point or another.

Correct me if I'm wrong: if the drivers are low impedance, shouldn't the PSU send lower voltage to the chip? (I don't remember the reason, I'm no engineer, but I do remember reading it somewhere.)

But that is a decent deal.

[bremen nacht]

Originally posted by beerman


I'll admit to being a newbie on this subject.

I'm trying to stay "safe". I will want to run 4ohm drivers with this amplifier at one point or another.

Correct me if I'm wrong: if the drivers are low impedance, shouldn't the PSU send lower voltage to the chip? (I don't remember the reason, I'm no engineer, but I do remember reading it somewhere.)

But that is a decent deal.

Yes, that's right.

The required voltage into a given impedance speaker for a given power is V = sqrt(PR) where sqrt is 'square root'. So you need less V into 4 compared to 8. You could keep the supply high, but you'd increase the power dissipated in the amp chip.

So for 15W in 4 ohm you need 7.5V RMS = 11V peak. Add a few (or look at the data sheet) volts for losses in the amp, so it looks like 15V rails will do the job. A 12V transformer will give about 15V after rectification, so there you go.