I'd like to use a pair of R-core transformers for a Class A power amplifier PSU.
Around 130w per channel dissipation, dual mono, 28V secondaries with additional 18V taps. I'd oversize the transformers, around 500VA per channel.
I understand the primary goes on one bobbin with the secondaries on the second bobbin on the opposite side of the core.
I'm in the UK - 230-250V AC - so in principle I'd prefer UK or EU suppliers. Those I've found include:
James Transformer, China: http://jamestransformer.com/en/transformer/R_core_transformer.html
Yuan-Jing, China: https://www.yuan-jing.com/r-core
Shilchar Technologies, India: https://shilchar.com/ent/product/linear-transformers
Kitamura Kiden, Japan: https://kitamura-kiden.co.jp/r-core/
Has anyone had experience of these or other suppliers?
Any advice or thoughts on specifications or options to request?
Thanks!
John
Around 130w per channel dissipation, dual mono, 28V secondaries with additional 18V taps. I'd oversize the transformers, around 500VA per channel.
I understand the primary goes on one bobbin with the secondaries on the second bobbin on the opposite side of the core.
I'm in the UK - 230-250V AC - so in principle I'd prefer UK or EU suppliers. Those I've found include:
James Transformer, China: http://jamestransformer.com/en/transformer/R_core_transformer.html
Yuan-Jing, China: https://www.yuan-jing.com/r-core
Shilchar Technologies, India: https://shilchar.com/ent/product/linear-transformers
Kitamura Kiden, Japan: https://kitamura-kiden.co.jp/r-core/
Has anyone had experience of these or other suppliers?
Any advice or thoughts on specifications or options to request?
Thanks!
John
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Hey John I only have experience with James Transformers and I have to say apart from one mistake on an O-Core which they rectified quickly with a new one, they make a good product. James himself will respond quickly, you can ask directly by mail or use their online order from, you can even specify custom lead lengths and colours. His prices are very decent.
He will help you if you are new to ordering transformers, tell him about the type of rectifier / power requirements and desired output / load regulation etc
This is a pic of a 260VA R-Core I ordered ages ago for a STAX headphone amp:
For UK specify 235V AC primary input, that puts you nicely in the middle of our range.
28V AC secondaries will give you approx. 40V DC after rectification. So for dual mono you can ask for centre tapped or dual secondaries depending on your power supply design. Example: CT: 28-0-28V AC / 28-0-28V AC or DUAL: 2 x 0-28V AC / 2 x 0-28V AC
For 500W you might want at least 600VA which will be a beast, these things have much bigger footprint than toroids.
You can ask for a certain VA grade, or if you know the current requirements of the amp boards then specify the current load, for example: 5.2Aamp / 5.2Amp per secondary if you get me. They will work out the size for you, obviously add some headroom for peak load. I think I asked for 8% regulation.
This is an example of what an order would look like: (you put in what you need for secondaries, the RMS numbers are a guess)
R-CORE
Power rating: 600VA
Primary: 0-235V @ 50Hz
Secondaries: 2 x 0-28V / 2 x 0-28V (dual mono) @ 5.57A rms + 15-0-15V (CT) @ 1A rms
Regulation: approx 8% (28V sec’s) & 4% (18-0-18V sec)
Lead-outs: approx 300mm long flexible (stranded)
Audio grade construction - electrostatic shield
Also consider O-cores, they are very good. Ask for electrostatic shield if you do.
This is my new 150VA O-core from James in a AEM6000 50W amp I'll hopefully finish this weekend:
Sorry I just realised you want two transformers, then just spec normal secondaries 2 x 0-28V or CT.
Remember to have 'real' dual mono you need separate power cables to each transformer. One power cable just means 'dual supply' with shared ground.
He will help you if you are new to ordering transformers, tell him about the type of rectifier / power requirements and desired output / load regulation etc
This is a pic of a 260VA R-Core I ordered ages ago for a STAX headphone amp:
For UK specify 235V AC primary input, that puts you nicely in the middle of our range.
28V AC secondaries will give you approx. 40V DC after rectification. So for dual mono you can ask for centre tapped or dual secondaries depending on your power supply design. Example: CT: 28-0-28V AC / 28-0-28V AC or DUAL: 2 x 0-28V AC / 2 x 0-28V AC
For 500W you might want at least 600VA which will be a beast, these things have much bigger footprint than toroids.
You can ask for a certain VA grade, or if you know the current requirements of the amp boards then specify the current load, for example: 5.2Aamp / 5.2Amp per secondary if you get me. They will work out the size for you, obviously add some headroom for peak load. I think I asked for 8% regulation.
This is an example of what an order would look like: (you put in what you need for secondaries, the RMS numbers are a guess)
R-CORE
Power rating: 600VA
Primary: 0-235V @ 50Hz
Secondaries: 2 x 0-28V / 2 x 0-28V (dual mono) @ 5.57A rms + 15-0-15V (CT) @ 1A rms
Regulation: approx 8% (28V sec’s) & 4% (18-0-18V sec)
Lead-outs: approx 300mm long flexible (stranded)
Audio grade construction - electrostatic shield
Also consider O-cores, they are very good. Ask for electrostatic shield if you do.
This is my new 150VA O-core from James in a AEM6000 50W amp I'll hopefully finish this weekend:
Sorry I just realised you want two transformers, then just spec normal secondaries 2 x 0-28V or CT.
Remember to have 'real' dual mono you need separate power cables to each transformer. One power cable just means 'dual supply' with shared ground.
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@passive420 Thanks for the detailed reply, and vote of confidence in James Transformers.
Mine won't be 'real' dual mono as the 230V AC input will be shared between two transformers - shouldn't make too much difference as it's high voltage/low current and I don't think splitting it at the transformers will be much different to splitting it earlier.
Have you been able to compare the O-core to the R-core? I think I saw a suggestion somewhere that the cylindrical shape of the R-core core, which keeps the windings parallel, helps reduce noise and emissions.
Mine won't be 'real' dual mono as the 230V AC input will be shared between two transformers - shouldn't make too much difference as it's high voltage/low current and I don't think splitting it at the transformers will be much different to splitting it earlier.
Have you been able to compare the O-core to the R-core? I think I saw a suggestion somewhere that the cylindrical shape of the R-core core, which keeps the windings parallel, helps reduce noise and emissions.
Having used hundreds of R-core transformers, I have neither seen nor measured any evidence that the primary windings and secondary windings are completely on separate legs of the core.
https://www.diyaudio.com/community/...on-an-r-core-transformer.394068/#post-7249237
That said, there may be a manufacturer who is able to wind the primary windings on one leg of the core and the secondary windings on the other leg without causing hum and vibration, or failing that, has access to segmented / flanged bobbins that can be used to minimize primary-to-secondary capacitive coupling, even if the primary and secondary windings use both legs of the core.
Please let us know if you are ever able to find a cooperative transformer manufacturer.
hth
All good pal My replies to questions always waffle on a bit it seems.
No direct comparison within the same project as such, R-cores for DACs and head phone amps, toroidal types for more power seems better to me but this comes down to size and cost limitations. Noise might be the same for O-cores and Rs.
If you have the funds and space no reason not to get the R-cores. I have never seen a large power amp with R-cores, I feel there may be a good reason for this but essentially the Rs for the same power rating will be expensive and larger. Get quotes for both types to see.
Again I missed some info in your question - you are building a 1000W amp! Sh*t the bed mate Ok so you may want over 600VA per channel just for 8ohm load, 4 ohms needs more. Once this is built you'll need to install a high beam lifting crane!
Don't be too swayed by the idea that an R-core is better for your application, they are perfect for when critical sensitive circuits are nearby such as DACs (and medical equipment) , your behemoth amplifier will not be affected, and I will dare to suggest you absolutely will not hear the difference between a standard toroid and R-core. I doubt you will hear the difference between two transformers and a single well made one with dual mono windings into two PSU boards. It is your dollar and peace of mind however. An excellent PSU circuit will mitigate any differences between these.
Don't forget you can ask for the toroidal types, including O-cores, to be encased in sexy metal cans that shield everything, this may be better for you. James's website shows the options for this.
You'll need plenty of capacitance on the rails, the inrush will be no joke so a tasty soft start and limiting circuit is needed. Definitely speaker protection.
Go on my son. God help the neighbours and wife....
My replies to questions always waffle on a bit it seems.No direct comparison within the same project as such, R-cores for DACs and head phone amps, toroidal types for more power seems better to me but this comes down to size and cost limitations. Noise might be the same for O-cores and Rs.
If you have the funds and space no reason not to get the R-cores. I have never seen a large power amp with R-cores, I feel there may be a good reason for this but essentially the Rs for the same power rating will be expensive and larger. Get quotes for both types to see.
Again I missed some info in your question - you are building a 1000W amp! Sh*t the bed mate
Ok so you may want over 600VA per channel just for 8ohm load, 4 ohms needs more. Once this is built you'll need to install a high beam lifting crane!Don't be too swayed by the idea that an R-core is better for your application, they are perfect for when critical sensitive circuits are nearby such as DACs (and medical equipment) , your behemoth amplifier will not be affected, and I will dare to suggest you absolutely will not hear the difference between a standard toroid and R-core. I doubt you will hear the difference between two transformers and a single well made one with dual mono windings into two PSU boards. It is your dollar and peace of mind however. An excellent PSU circuit will mitigate any differences between these.
Don't forget you can ask for the toroidal types, including O-cores, to be encased in sexy metal cans that shield everything, this may be better for you. James's website shows the options for this.
You'll need plenty of capacitance on the rails, the inrush will be no joke so a tasty soft start and limiting circuit is needed. Definitely speaker protection.
Go on my son. God help the neighbours and wife....
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@passive420 1000W no! 😂
Class A 140-150W per channel dissipation. Rule of thumb is to scale transformer VA by 3x which is almost 500VA per channel.
So 2x 500VA or 600VA transformers. With a soft start 😄
@jcarr I thought the R-core secondaries could be wound over the primaries, or separately, but maybe my misunderstanding.
One secondary overwound on a primary would be one bobbin. There always seems to be two bobbins so how does that work?
Class A 140-150W per channel dissipation. Rule of thumb is to scale transformer VA by 3x which is almost 500VA per channel.
So 2x 500VA or 600VA transformers. With a soft start 😄
@jcarr I thought the R-core secondaries could be wound over the primaries, or separately, but maybe my misunderstanding.
One secondary overwound on a primary would be one bobbin. There always seems to be two bobbins so how does that work?
Do you have an idea what kind of weight a 150W class A amp with a passive heat radiator and a 600VA transformer will be? Only one?
Also 600VA seem quite overdimensioned. Even 400VA will be more than enough in any case. Even if you use it as a subwoofer amp at full output, the voltage will not drop by a single volt...
There is a point where more capacitors and more power from the transformer simply don't give any improvement.
Also, even the toughest power supply will not make an old, once state of the art amplifier cirquit a high end product with todays competition. Sometimes the expectations for class A are set too high. Something like a "done right" chip amp with 6x LM3886 leaves most older A amp concepts in the dust. Just as a hint for something you can DIYS and use as a final amp.
My once fantastic, 20 year old "A" amps, have a hard time to keep up with even some modern "D" amps.
PS consider a separate transformer for the driver voltages. You don't have any influence from the main voltages at all that way and can use stock transformers.
Also 600VA seem quite overdimensioned. Even 400VA will be more than enough in any case. Even if you use it as a subwoofer amp at full output, the voltage will not drop by a single volt...
There is a point where more capacitors and more power from the transformer simply don't give any improvement.
Also, even the toughest power supply will not make an old, once state of the art amplifier cirquit a high end product with todays competition. Sometimes the expectations for class A are set too high. Something like a "done right" chip amp with 6x LM3886 leaves most older A amp concepts in the dust. Just as a hint for something you can DIYS and use as a final amp.
My once fantastic, 20 year old "A" amps, have a hard time to keep up with even some modern "D" amps.
PS consider a separate transformer for the driver voltages. You don't have any influence from the main voltages at all that way and can use stock transformers.
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The primaries and secondaries are almost always equally spread between both legs: half a primary on one, and half a secondary +the same on the other leg.
The half-windings can be series-connected or paralleled, but they should not be used separately.
Having the primary and secondary on different legs would create a large leakage inductance, and a horrific leakage flux under load
In general, the various windings of each bobbin are already prewired internally.
If it is the case, you don't have to worry. However, if you clearly see that the windings of each bobbin are completely independent, you should avoid using one leg per polarity.
The series or parallel connection is unimportant, and is determined only by the winding voltage: for example, for a 115V mains, you would chose a primary parallel connection, and a series connection for 230V
If it is the case, you don't have to worry. However, if you clearly see that the windings of each bobbin are completely independent, you should avoid using one leg per polarity.
The series or parallel connection is unimportant, and is determined only by the winding voltage: for example, for a 115V mains, you would chose a primary parallel connection, and a series connection for 230V
I emailed James Transformer (info@jamestransformer.com), and chased them, and Kitamura Kiden and have had no replies.
@passive420 I think you recently bought a transformer from James? Any problems getting a reply? Is there a better email?
@passive420 I think you recently bought a transformer from James? Any problems getting a reply? Is there a better email?
@Giallograle sorry to hear that mate, just checked my emails and the one you have is correct, he usually is very quick with reply, they might be very busy or he is on a break. Give another week or so maybe. I have another order with him at the moment for small 15VA R-cores for my DACs. The turn around is anything from a few days to a couple of weeks.
Try their online order from instead.
You have limited yourself with wanting R-cores, if you can see yourself having good old Toroids made to perfection then try Toroidy of Poland.
Tiger Toroid's here in the UK are also very good audio grade option.
Try their online order from instead.
You have limited yourself with wanting R-cores, if you can see yourself having good old Toroids made to perfection then try Toroidy of Poland.
Tiger Toroid's here in the UK are also very good audio grade option.
Turnaround sounds fine, just wondered whether I was going to hear back at all.
I'd prefer R-cores if I can get them.
Toroidy are less flexible with customising, afaik, but Tiger look more accommodating.
I'm looking for some chokes for the PSU, Hammond's the obvious choice but maybe Tiger can do air-cored. And they're quite close to me
Have you used them?
I'd prefer R-cores if I can get them.
Toroidy are less flexible with customising, afaik, but Tiger look more accommodating.
I'm looking for some chokes for the PSU, Hammond's the obvious choice but maybe Tiger can do air-cored. And they're quite close to me
Have you used them?
I bought transformers from Trafomatic Serbia. They now have their audio equipment brands but still running and selling transformers .
@kodza Thanks for the suggestion, I'll contact them, although their website omits any mention of transformers. https://www.trafomaticaudio.com/
And I've had a reply from Kitamura Kiden - although their production is in China I think they may be expensive.
Tiger Toroids are very helpful with choice of inductors for my CLC PSU.
And I've had a reply from Kitamura Kiden - although their production is in China I think they may be expensive.
Tiger Toroids are very helpful with choice of inductors for my CLC PSU.
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I've had a reply from James - looks promising - and emailed Trafomatic at the address on https://www.trafomatic.com/eng_home.htm