Power supply for AMP1?

[simingx]

Hi all,
I need the +/- 30V supply an AMP1 that i'm planning to build, but I can only get 0-18 0-18 and 0-25 0-25V transformers here.
The 18V units would give me +/- 25V (a tad low) and the 25V units +/- 35V (which is marginally high).

Which one should I go for? I will be rectifying and filtering the two outputs from the transfomers seperately, so theoratically I will drop approx. 1.4 volts from each output, which would give me 23.6V and 33.6 volts... but I'd prefer not to rely on that.

Any suggestions?

[magpietim]

I had that problem but in the end i went for 25v rectified and i haven't found any problem with low power. Although i used a centre tapped transformer...18-0-18....
I think 25vdc is perfectly ok.
Maybe Jan has other ideas though.
Tim.

[Jan]

Hi,

The amp would work well with +/- 25V and even much lower. But not with the same maximum output power as with higher voltages. The under voltage protection will mute the amp at about 22V, unless you change the value of the sense resistors.

If you want the high power you can use the +/-35V and if the overvoltage protection kicks in (set att about +/-36V) you could add one or two 10A diodes in series with the rectifier, to decrease the voltage. Note a transformer will have a slightly higher voltage than specified, at idle. The specified output voltage is usually the full power voltage. A 300 VA transformer will output about 6-10% more at idle.

With +/-35V you could also build a stabilized power supp for something like +/-32V. For example the 5A LMS1585 fast response low dropout regulatore could be used. For high power you can use two of these in parallell. They are in TO220 packages and not expensive, typically about $2.50 each. They are rated 13V but that is the maximum in-out voltage difference and in your case this would be about 35V-32V=3V or perhaps a bit more at idle. But you would nbeed a careful analysis of what happens at startup and shutdown as you would be close to the voltage limits.

[Mike Andrew]

Does anyone know whether there's a negative voltage version of the LMS1585 5A LDO?

Thanks,

Mike Andrew

[locky]

You can use a positive regulator in each rail if you adapt the circuitry a bit. See the following link http://www.tcaas.btinternet.co.uk/jlhnewps.htm

[Mike Andrew]

Locky,

That's perfect!

Thanks,

Mike Andrew