Where to find some good R-core transformers

[Dyonight]

Hi!

Anybody knows where to find proven good quality R-Core transformers?

I'd like three 18v-0v-18v at roughly 1A.

I found a bunch on ebay from China but I have no idea how to know if they're good or noisy half assed crap.

I want to power 3 bank of 8 API preamps clones and the toroidal I have right now inject a noticeable hum in the audio when mounted in the case.  I hope R-Cores can rectify this.... or maybe I'm asking too much?

Anyway, thanks for any help!

 

[abbey road d enfer]

I want to power 3 bank of 8 API preamps clones and the toroidal I have right now inject a noticeable hum in the audio when mounted in the case.  I hope R-Cores can rectify this.... or maybe I'm asking too much?

Typically, R-core xfmrs radiate more than toroids. However, the flux direction is very different.
Typically, a toroid mounted flat would radiate vertically, when a R-core would radiate horizontally.
Have you tried re-orienting your toroids or simply moving the PSU away?

 

[Dyonight]

Thanks for your answer!

Yes I tried changing the toroidal's position and ended up putting it in a external enclosure cause it irradiated too much no matter how I placed it.

I have to point that this is a quite large 160VA transformer so it may be no surprise for some that it introduced some noise...

I'm powering 21 preamps with this and achieve stellar results but it is all in a huge 4U enclosure and I want to split all of them in 3 separate rack, so I'd like to get 3 separate power transformers and hope I'll be able to fit all this in each case without noise.

I heard that R_Core tend to be quieter so that's why I'd like to try those and be sure I can find good quality ones.

That said, if experienced builders think I won't get any benefits from using a R-Core tx, what would you recommend?

Thanks!

 

[abbey road d enfer]

I'm powering 21 preamps with this and achieve stellar results but it is all in a huge 4U enclosure and I want to split all of them in 3 separate rack, so I'd like to get 3 separate power transformers and hope I'll be able to fit all this in each case without noise.

Putting a transformer close to sensitive equipment is always a challenge. Very often it requires additional magnetic shielding, which prompts the use of an enclosure for the xfmr, made out of thick steel and/or mu-metal.

I heard that R_Core tend to be quieter so that's why I'd like to try those and be sure I can find good quality ones.

R-core xfmrs, offer the possibility to have separate bobbins for the primary and secondary, which reduces capacitive coupling of interference present on the mains line. Toroidals, by construction, do not offer this possibility, but they can include an electrostatic shield; however, most off-the-shelf toroidal xfmrs do not include that.
OTOH, R-core types radiate more magnetic stray flux, which seems to be your Nr. 1 issue.

That said, if experienced builders think I won't get any benefits from using a R-Core tx, what would you recommend?

Have you considered using SMPS such as
https://www.digikey.com/product-detail/en/xp-power/DNR10US24/1470-1087-ND/4487468
or
https://www.digikey.com/product-detail/en/xp-power/ECL05US48-T/ECL05US48-T-ND/4476522
I've done just that for a 6-pack. Just to make sure, I added some filtering to the rails (See attachment). I used a DC/DC converter to derive 48V because the 48V SMPS was not available at the time.
https://www.digikey.com/products/en?keywords=XP%20POWER%20-%20JCD0624D24%20
In fact, even though they're actually available, I would still use a DC/DC converter, because SMPS do not work well under minimum load.
They have a version that delivers +/-15V at 1A, but does not exist in +/-24.
https://www.digikey.com/product-detail/en/xp-power/ECL30UD02-T/1470-1206-ND/4487587

 

[supersonic]

Are you sure about this? Thats interesting. So worst would be to mount a toroid on the backpanel of a case.

Typically, a toroid mounted flat would radiate vertically...

 

[abbey road d enfer]

Are you sure about this? Thats interesting.

"a toroid mounted flat would radiate vertically" is a shortcut for a more complex reality. Flux lines concentrate along the axis of the toroid, but eventually curve so they close around.  Then you could find flux lines that would be horizontal, but the induction would be very low. Dominant radiation is along the axis.

  So worst would be to mount a toroid on the backpanel of a case.

In most cases yes, but you have to consider interference with other equipment. Mounting a toroidal horizontally would minimize interference with the apparatus it powers, but would maximize interference with equipment mounted right above or below.