Talema toroidal transformer news

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

jhaible

Well-known member
Joined
Jun 24, 2004
Messages
530
Location
Germany
A little background (skip if this is boring): I wanted to make a power supply for a tube circuit, using two ordinary transformers back to back:
230V:25V (transformer #1) -> 25V:230V (transformer #2)
Works nicely, it's often done, my version is here:
http://www.oldcrows.net/~jhaible/opto_compressor/jh_schematics_4_psu.jpg

Nothing special - the downside is that I only get ca. 230V instead of the 250V that were called for in the circuit I wanted to clone. Also, 250V seem to be quite common in the tube world.

So my idea was to connect transformer #2 as an auto-transformer (not shown in the drawing, but you know what I mean), connecting primary and secondary of #2 in series, thus adding the 25V to the 230V.

The problem I saw is the isolation voltage. As in that specific application, I wanted to use the second secondary of transformer #1 for other parts of the circuit (low voltage, near GND level), so with #2 not isolating anymore (auto-transformer ...), I would need the whole isolation voltage between first secondary and second secondary of transformer #1. So I emailed Talema to get the data for that specific isolation voltage (I'll come back to that below), and of course the isolation is not good enough. It's just two wires wound in bifilar way - no real isolation. They test it with 500V, which is next to nothing compared to 4200V test voltage between primary and secondary. (Remember the test voltage must be many times higher than the voltage in your application !!)

So the auto-transformer idea does not work. (It will work if you don't use two separate secondaries on transformer #1. For instance, if you use a separate, 3rd transformer for tube heaters etc.)

There is another method that will work, however: Use two rectifiers, one for the intermediate 25V, and one for the second-secondary 230V, and then stack the two pulsing DC voltages (where the rectified 25V must be connected near GND, not the other way round, for obvious reasons).
Simulations have shown that you don't even need two capacitors for stacking the two rectified voltages: Just stack the raw rectifier outputs and run the combined voltage into your typical 450V-rated capacitor. I have *not* tested this yet, but simulation is promising, and isolation voltage apparently is good enough for this.

I don't think I'm th efirst to do this, but for me it was brand new, so I thought I'd share the idea.

Ok, back to talema - I'll make a follow-up posting for this.

JH.
 
So I had sent this mail to Talema, and was called back withing a few hours from a very friendly man from their German branch, and we had a very nice talk about toriodal transformers.

I was surprised that they are making custom toroidal transformers starting from 130,00 EUR (single quantity!) which isn't that much in the light of typical transformer prices for "tube" voltages.

There are specialities that apply to toroidal transformers at high secondary voltages: They need an extra insulation layer for each multiple of 125V. So a 250V secondary will be thicker than a low (standard) voltage, and you will need a 80VA size for a 50VA transformer, for instance. But I think it's still worth considering, as that would be a toroidal, after all, with all its advantages, instead of an ordinary version with higher stray field, or instead of a set of 2 or three standard toroidals.

He also said if you want to go for even higher volatges (like 500V ct instead of 250V, to avoid a bridge rectifier), you'd need such a lot of extra insulation layers that the transformer becomes _much_ bigger, so this unfortunately isn't very promising. 8-(

Anyway, for a little project that needs 250V and 6.3V and maybe a third low secondary, this custom service might be interesting for 130 EUR.

Just wanted to pass this on.

JH.
 
JH, www.multipcb.de is making customized teroides.
I have an example quote:

VA: 18,6
Dmax.=ca.60mm, Hmax.=ca.30mm
Inkl. Montagezubehör bestehend aus 1 Druckplatte mit Befestigungsloch und zwei Gummischeiben
1.Prim./Volt 115
2.Prim./Volt 115
*
mit Schirmwicklung !!!
*
1.Sek./Volt 8 A. 0,80 VA. 6,4
2.Sek./Volt 8 A. 0,80 VA. 6,4
3.Sek./Volt 20 A. 0,02 VA. 0,4
4.Sek./Volt 20 A. 0,02 VA. 0,4
5.Sek./Volt 250 A. 0,02 VA. 5,0

1 Stück a 26,00 ?
2 Stück a 21,00 ?
10 Stück a 16,20 ?
20 Stück a 14,30 ?
+VAT

I choosed this voltages to feed tubes and opamps in one box. 2x8V/0,8A is for the heating. 250V/20mA is for the tubes. 2x20V/20mA is for the opamps.

Looks like something for a group order.
 
[quote author="Michael Krusch"]JH, www.multipcb.de is making customized teroides.
I have an example quote:

VA: 18,6
Dmax.=ca.60mm, Hmax.=ca.30mm
Inkl. Montagezubehör bestehend aus 1 Druckplatte mit Befestigungsloch und zwei Gummischeiben
1.Prim./Volt 115
2.Prim./Volt 115
*
mit Schirmwicklung !!!
*
1.Sek./Volt 8 A. 0,80 VA. 6,4
2.Sek./Volt 8 A. 0,80 VA. 6,4
3.Sek./Volt 20 A. 0,02 VA. 0,4
4.Sek./Volt 20 A. 0,02 VA. 0,4
5.Sek./Volt 250 A. 0,02 VA. 5,0

1 Stück a 26,00 ?
2 Stück a 21,00 ?
10 Stück a 16,20 ?
20 Stück a 14,30 ?
+VAT

I choosed this voltages to feed tubes and opamps in one box. 2x8V/0,8A is for the heating. 250V/20mA is for the tubes. 2x20V/20mA is for the opamps.

Looks like something for a group order.[/quote]


Great! Now *this* is unexpensive! I'll check them out.

JH.
 
[quote author="kubi"]I you need 250V + 6.3V only you might want to take a look at these:
http://www.die-wuestens.de/trafo.htm
custom made torrodials, for much less than 130EUR.

kubi[/quote]


Very good to know - thanks for passing this on!

JH.
 
JH: they only sell to companies, so you have to be smart with your order. :green:

Kubi: Not yet, but I will. First I have finished some of the other projects laying around. I think this transformer is very useful for a tube Pultec or a G9 or a G7 or a PRR-compressor. Even buying only one is as cheap as buying two standard teroides.
 
[quote author="Michael Krusch"]JH: they only sell to companies, so have to be smart with your order. :green:

I'll be warned. (;->)

JH.
 
Whoha! 130euro is a lot money for a 50/80VA toroid :shock:

Talemas are nice but that's like 4-5 times too much. I pay that for custom EIs :wink:
 
Maybe you could ask them if they're interested in making audio transformers, since their power trannies seem to work?

See this also:

www.triodeguy.com/6as7_pp.htm
 
[quote author="sismofyt"]Whoha! 130euro is a lot money for a 50/80VA toroid :shock:

Talemas are nice but that's like 4-5 times too much. I pay that for custom EIs :wink:[/quote]


Well, they told me that power rating would be much less expensive if it wasn't for that minimum order figure. You will get a much bigger one for that price, but I haven't asked further.

JH.
 
from JH:
Works nicely, it's often done, my version is here:
http://www.oldcrows.net/~jhaible/opto_compressor/jh_schematics_4_psu.jpg

About the 26.5V section of your schematic, I've been looking at the arrangement with the BF245 & BC161. The complete section carries (N+1)*Idss if I'm correct but what then ? I mean, what's actually the idea here ? Perhaps common, but I haven't seen it being used like this. Just curious.

Thanks,

Peter
 
[quote author="clintrubber"]from JH:
Works nicely, it's often done, my version is here:
http://www.oldcrows.net/~jhaible/opto_compressor/jh_schematics_4_psu.jpg

About the 26.5V section of your schematic, I've been looking at the arrangement with the BF245 & BC161. The complete section carries (N+1)*Idss if I'm correct but what then ? I mean, what's actually the idea here ? Perhaps common, but I haven't seen it being used like this. Just curious.

Thanks,

Peter[/quote]


The idea was to build a PSU that is simple, has very low 100Hz noise, while load regulation isn't that important. (Keep in mind that originally I wanted to feed sensitive audio transistor circuits with this - I only changed to a tube audio path later.)

Basically, the zener diodes and emitter follower stabilize the output voltage. For improoved 100Hz ripple reduction, run the zener with a constant current. BC161 with two diodes and emitter resistor forms this current source. But these diodes _also_ like to see a constant current rather than just being fed by a resistor, so here's another current source, simply made by the FET.
I'm sure there are more elegant circuits, but this was a straight-forward minimum parts count unexpensive solution, and it has very good ripple suppression. (Load regulation was not a design goal.)

The whole thing has no overall servo loop - it's the old "no NFB" approach taken from audio and implemented for PSU.

JH.
 
from JH:
But these diodes _also_ like to see a constant current rather than just being fed by a resistor, so here's another current source, simply made by the FET.

Thanks for the explanation. Wasn't aware of this preference of zeners. Nice implementation of floating current sources & adjoined current mirrors.

OK, so it's now all reduced to load variations (if any) (and divided by beta-of-BD241) which now face those zeners. Sounds like an improvement for sure.


The whole thing has no overall servo loop - it's the old "no NFB" approach taken from audio and implemented for PSU.

No feedback equals street-credibility, right ? :wink:
(Sorry, I've just finished my work before holidays and am in a joyful mood :grin: )

Back to serious, must admit I don't know from experience to which extend higher quality & highest quality PSU-regulation really do matter w.r.t. ironing out all deficiencies w.r.t. PSU-related issues. Better safe than sorry though (lame formulation), and your approach looks beyond solid - as far as I'm allowed to speak in this respect.

Bye,

Peter
 
[quote author="clintrubber"]
No feedback equals street-credibility, right ? :wink:
[...] Back to serious, must admit I don't know from experience to which extend higher quality & highest quality PSU-regulation really do matter w.r.t. ironing out all deficiencies w.r.t. PSU-related issues. [/quote]

No servo loop means less problems with stability.

If you need precise output voltage, you need a servo loop. (If you want to use supply voltage as a reference voltage somewhere, which mostly is a bad idea btw.) If you don't need a precise voltage, you can concntrate on other goals, like low noise. In my circuit, low noise means low hum. If I's also need low wideband noise, an extra RC filter between the zener and the power transistor's base would be a good idea.
Generally, you can (and should) also filter the PSU locally with an RC filter in critical circuit parts. The time constant for these filters (i.e. the cap size for a certain resistor or voltage drop) can be much smaller if your PSU already deals with the 100Hz components.

All that isn't so important if you have opamps in your audio path (which normally have excellent PSRR at low frequencies), but it makes a difference with discrete circuits where a common emitter amp uses the vcc as a GND reference at its output.

You certainly can use integrated power regulators such as the LM317 or 78xx plus RC filters for the noise these produce. (They also work nicely to suppress 100Hz stuff.) But input voltage range is often a problem with these if you want rather high voltages.

JH.
 
Hello,

Thanks for the added info & explanation !
And thanks for the reminder about different PSU-requirements for opamps & various discrete circuits - easily forgotten.

Best regards & have a good weekend,

Peter
 
Just thought I would mention that my local Gyraf transformer supplier "Ulveco" has very reasonable prices, and they are very experienced in making low-disturbance toroids:

http://www.ulveco.dk/default.asp?lang_id=2057

I pay around 35?/pcs for a 250+48+15+2x15V/50VA transformers, shielded and with litze wires. They do one-off transformers for ca +15?

I haven't come across better toroids - and I've tried a lot..

Jakob E.
 
Back
Top