Power transformer choice

[Pegasus123]

I am looking into a good EI, UI, or R-Core transformer for a DIY preamp and DAC. I will need a 2×15v for USA voltage however I am not looking for just okay performance. The best components I have heard with the right speakers are able to play at whisper volumes with no loss of details with everything etched in space.

- How good of an indicator of quality is the voltage regulation spec? From the same manufacturer I have found an EI transformer with 15% regulation, and others with 30% regulation
- I hear good things of UI core transformers. Their voltage regulation tends to be around 20-30+% however. Is this an issue?
- Being in the USA is there any way to order a japanese Kitamura Kiden R-Core (or Indian Shilchar)? Thoughts on shielded Zero-zone chinese r-core transformers on eBay?
- Thoughts on quality of a custom built EI core with proper shielding vs other options listed?

Thanks!

 

[AndrewT]

VA & Vac are probably the most important specifications.
Regulation comes way down the list.
Addition of interwinding screen and/or a guass band helps with some performance parameters, but again these can be way down the list.

 

[Pegasus123]

Thanks. Another question though. R-Cores tend to be pretty good but how sensitive are they to DC? There is very little information online although from what I have read EI and C-Core still have the advantage right?

 

[wg_ski]

For a high quality preamp, you want quiet above all else. That means EMI/RFI shielded, and operating way backed off from saturation. You may even consider using one rated for 2X your intended operating voltage, and running a 240V primary off 120V. That will be mechanically quieter, less susceptible to interference, and pretty much immune to DC on the mains. Any construction technique which minimizes RFI between primary and secondary, unfortunately, tends to hurt regulation. But in practice you can live with it. Regulation isn't all that important, because you'll be regulating the DC anyway. Oversize by a factor of 5 (pretty easy for a preamp, a little expensive for a power amp) and 30% regulation becomes 6%.