Possible to use this transformer for LM3875 PS?

[Skitch72]

Found this at parts express, seems like maybe it would be usable?

Would it be possible to put them in "series" and use 2 of them as the two halves of a center tapped transformer?

Any thoughts?

http://www.partsexpress.com/pe/showd...number=129-035

[AndrewT]

Hi,
the two transformers in series will work.
It might be better to keep them separate and use a bridge rectifier on each to generate your dual polarity supply.
Some chipamp PCBs are designed for exactly this arrangement.

But there is a big down side.
100VA toroid could have regulation around 10 to 15%.
a 50VA EI could have double this regulation i.e. 20 to 30%.
using two does not improve the regulation of either transformer nor of the combination.

The disadvantage of high transformer regulation is higher quiescent power of the chipamp requiring an even bigger heatsink.
The supply sags badly on low frequency transients and gives the impression of poor low bass response.

[Skitch72]

Fair enough, thanks for the quick reply. Being mostly a DIY tube guy this is my first jaunt into the solid state realm. I am mainly looking into a simple "get my feet wet" project. I hadn't thought about the advantages of the toriod but that makes sense to me. Would heavy supply filtering help offset that issue? I have seen some of these chip amp supplies with quite a bit of capacitor filtering...


Thanks again
Tim

[AndrewT]

Hi,
a high regulation transformer or one that is a little too small can get some/most of the lost performance back by increasing the smoothing capacitance.
There are many who say high capacitance ruins the sound quality.
I promote adequate smoothing by suggesting +-20mF/channel for good bass response into an 8ohm speaker. Some builders advocate as little as one tenth this amount.
Get your feet wet.