caveats? resistor in series /w speaker to raise impedance

[aletheian]

I made am oopsie, and bought a reansformer for a gainclone project that I am working on that is rated for 115v when I THOUGHT it was rated for 120V... as a result, my power supply is ALLL thrown off.

I am not using this for hi-fi... just a little subwoofer , so would there be an issue with running a high wattage resistor in series with the speaker to raise the impedance and trick the chip into NOT overdissapating?

I COULD just re do the whole power supply and regulate it down... but that is a lot of current to regulate... and a lot more effotr.

Thanx

[I_Forgot]

It can't be "thrown off" by more than a couple volts. What chip are you using and what is the power supply voltage you are getting, and what was the voltage you thought you were going to get?

Let's say you looking at +/- 30V for the power supply. That's 60V rail to rail. If you use a 120V input transformer and the line voltage goes up 2V, your rail to rail voltage will go up by 1V (120/2=60 122/2=61).

A resistor in series with the output isn't usually a good idea.

I_F

[Nigel Goodwin]

Yes, the voltage difference in the transformer is only very small, nothing to worry about. Adding a resistor in series with the speaker isn't a good idea (for any reason, and certainly NOT for this one), as it ruins the damping factor.

[neutron7]

what was the desired voltage and what did you end up with?

[aletheian]

Actually, looking at my diagram now, I was looking at the wrong diagram last night the tranny is completely wrong... I was misteken in my original post.

The one that I drew up for this project was a snubbered but unregulated supply for a 18v+18v tranny with a 115v input to run a paralleled lm3886 amp into a 4 ohm load, so I was planning on having around 28v pos/neg (the voltage from my wall runs pretty high here). That would give me 75-80 watts into the 4 ohm speaker.

But with the 16+16 at 115v, I don't think I'll squeeze more than 23-24v pos/neg out of it, leaving me with under 50w.

I could switch to bridge mode, but the 4 ohm speaker will present a 2 ohm load to each chip, and my voltage will be too high. Just running the math in my head real uick, I think I would have to drop the rails from 23v to 18 or 19 volts to keep the chip from frying in 2 ohm bridged... which is not a good idea anyeay.

Suggestions?