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f.pelosa 18th January 2013 01:51 PM

toroid and r-core
what about R-core transformers?
Googling around, not so many people uses them for PSUs although they seem to me what you'd go for in a high-end system.

Or am I totally wrong?

KatieandDad 18th January 2013 02:30 PM

In reality it doesn't make that much difference if your power supply is well designed.

However, Toroids are good at passing HF noise from Primary to Secondary, an effect which is lessened in EI transformers.

Why R core - I don't know. I always use Toroids with a well designed PSU.

cotdt 18th January 2013 03:01 PM

The way to find out would be to measure the frequency response and see which is better at cutting out high frequency noise.

f.pelosa 18th January 2013 03:07 PM

KatieandDad can you point me to a 'good design' by the way?
thanks a lot

KatieandDad 18th January 2013 03:10 PM

It all depends on what you are driving.

Each design needs to be trimmed for each application.

f.pelosa 18th January 2013 03:22 PM

I'm going to the P3A, a 60W on 8ohm amp from ESP, starting with a 500VA transformer (of some kind: toroid or r-core I still have to decide) 25-0-25. Have you got any suggestion for a PSU for such an amp?

jacco vermeulen 18th January 2013 03:25 PM


Originally Posted by f.pelosa (
Or am I totally wrong?

R-cores are superior to toroidals in power supplies for low signal components, for power amps they're also limited by the available size.

Example of a preamp from 1998 with R-cores in the PS : SPHINX laboratories test project eight
(one transformer for each channel, a third for the peripherics)

Telstar 18th January 2013 05:40 PM

This is an interesting discussion :)


Originally Posted by jacco vermeulen (
R-cores are superior to toroidals in power supplies for low signal components

Superior in what?

cotdt 18th January 2013 06:03 PM

I expect R-cores to filter out high frequency noise better than toroidals, but have never measured it myself.

f.pelosa 18th January 2013 06:08 PM

They seem to be better in stopping noise in the mains, as well as the classic 50 (or 60)Hz noise.
The one info I found on diyaudio is this one:
[...] R-core transformers usually have split-bobbin primary and secondary windings, which cuts down on interwinding capacitance and makes it considerably more difficult for non-50/60Hz noise components to pass in and out of the power supply. Additionally, R-cores have low levels of radiated magnetic flux and mechanical vibration, which allows them to be positioned closer to sensitive aplification circuitry without causing problems. [...]
from user "jcarr" on this thread:

I found other sources speaking positively about r-core transformers, but go find them again!

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