Wind a step down transformer, or find a variac, reduce the AC volts into the unit.
Zimble, as the Malabar people say.
Zimble, as the Malabar people say.
Yes, if there is space for a small transformer, this is a good solution, few hassles, easy. Buck–boost transformer - Wikipedia
Variac if handy can be used to set the input lower limit, some supplies create problems at less than minimum. Bucking transformer might buck too much, protection circuit may kick in, Another problem.
Just spent a lot of time attending a panic call, from my CPA, computers down.
Drained cells in wireless keyboard on one, and a doubtful RAM on the other, just switched keyboard and mouse, his main computer started working...When leaving he calls me back...some how put off Num Lock, would not take numbers.
The Logitech wireless keyboard has Caps Lock LED, not for Num Lock....
Spent two hours on a call, we don't charge each other, he does my taxes, I fix his computers...
Caused by some person putting cheap AAA cells, instead of alkaline, though why Asus cannot male AA cell keyboards is another issue.
Things like this make me recommend not playing with wound transformers, use a simple approach to fix the problem. Less issues to sort out.
Just spent a lot of time attending a panic call, from my CPA, computers down.
Drained cells in wireless keyboard on one, and a doubtful RAM on the other, just switched keyboard and mouse, his main computer started working...When leaving he calls me back...some how put off Num Lock, would not take numbers.
The Logitech wireless keyboard has Caps Lock LED, not for Num Lock....
Spent two hours on a call, we don't charge each other, he does my taxes, I fix his computers...
Caused by some person putting cheap AAA cells, instead of alkaline, though why Asus cannot male AA cell keyboards is another issue.
Things like this make me recommend not playing with wound transformers, use a simple approach to fix the problem. Less issues to sort out.
Last edited:
1. The one with the Blown Transformer Heat fuse, is just work which is the problem that I have to remove quite a few components so that Transformer can be removed.. at least 2 hours all in all.
It's not a problem replacing the fuse with a new one.. and there is nothing to fear about the heat.. Mains also have outside of the case a short protector so
if anything goes wrong it will blow Room MAIN FUSE.
More Case is all Aluminum 5mm thick and except for the fan inlets it's all sealed and I'm quite confident that installed Protection works.
The Amp which I do not have Fans anymore is the new Class A Amp I build..
as this one is drawing only full current on full load, and otherwise is in the range below 1AMP, the heat is not a question.. Heat sinks are very large..
Also with heat Protection Sensors - Switch on the Heat sink as well on the transformers..
I will make a small Docu when changing that fuse on the transformer the fuse is similar with those ones which are used in Electric Stoves.. Onetime blow only..NO reset. I change to RESET Automatically but one has to switch of the power and then back on that the reset of the works.
Regards
Chris
Thank you to everyone for their inputs and advice.
However, my plans to get the toroidal transformers is not looking good due to high costs of courier, and then customs clearance and broker fees etc. It is possible that the landed cost will become close to 3X of the actual cost of the transformers. 🙁
I may have to opt for getting the transformers made locally, and in that case will have to settle for EI core transformers. The upside is that I can get them made exactly according to the voltage spec that I require. For most DIY solid state builds DIYers nowadays choose toroidal transformers, but I still see EI cores being used in commercial amplifiers.
Would love to hear the thoughts of the knowledgeable members of the forum regarding opting for EI core and any guidance I should give to the transformer winding company.
However, my plans to get the toroidal transformers is not looking good due to high costs of courier, and then customs clearance and broker fees etc. It is possible that the landed cost will become close to 3X of the actual cost of the transformers. 🙁
I may have to opt for getting the transformers made locally, and in that case will have to settle for EI core transformers. The upside is that I can get them made exactly according to the voltage spec that I require. For most DIY solid state builds DIYers nowadays choose toroidal transformers, but I still see EI cores being used in commercial amplifiers.
Would love to hear the thoughts of the knowledgeable members of the forum regarding opting for EI core and any guidance I should give to the transformer winding company.
Last edited:
What happened to the option of just add some windings? Almost zero cost and an hour work?
Did I miss something?
Jan
Did I miss something?
Jan
Jan,
I do not have the transformers yet, I was planning to buy a pair of 300VA toroidal transformers. If you look at the commercial off-the-shelf (COTS) offerings, most brands have 30V secondaries or 35V secondaries. Only Antek has readymade units that comes in 2V increments. I wanted to get transformers with 35V secondaries and hence my earlier question on lowering the voltage by 2-3 volts. Duty to significant postage and clearing costs I am being forced to think about not buying from an international source. However, I have not given up on the idea totally.
It also looks like many of the COTS toroidal transformers do not have interwinding shielding or a GOSS band. With custom toroid winders you can specify those features and they will incorporate them. How important is it to have them?
I do not have the transformers yet, I was planning to buy a pair of 300VA toroidal transformers. If you look at the commercial off-the-shelf (COTS) offerings, most brands have 30V secondaries or 35V secondaries. Only Antek has readymade units that comes in 2V increments. I wanted to get transformers with 35V secondaries and hence my earlier question on lowering the voltage by 2-3 volts. Duty to significant postage and clearing costs I am being forced to think about not buying from an international source. However, I have not given up on the idea totally.
It also looks like many of the COTS toroidal transformers do not have interwinding shielding or a GOSS band. With custom toroid winders you can specify those features and they will incorporate them. How important is it to have them?
Custom wound toroids are expensive and bad quality in India.
Use EI cores, tell him thinnest steel of standard transformer quality. And thicker than expected winding wires.
Or get from Delhi / Kolkata if Customs not high, because imports from here may have less duty.
Use EI cores, tell him thinnest steel of standard transformer quality. And thicker than expected winding wires.
Or get from Delhi / Kolkata if Customs not high, because imports from here may have less duty.
I think the snake is eating its tail.
the equation is simple.
either you modify the primaries of your transformers.
either you go up a voltage grade on you capacitors (50to63v).
in fact I do not understand.
it's a fairly simple problem to solve, isn't it?
your diagram imposes an imperative of tension on you?
@zman
Some more things to think about -
1. Mains voltage variations can be up to 10% from nominal. Not sure what your country specs. are, but the UK's nominal 230V can be 253V. It was max. 6% up from 240V, which it actually still is. The variation will potentially offset your 2-3V difference.
2. Not having an interwinding screen does not seem to be a problem for many people.
Generally I would say that it is really only needed if the output supply had to float, for any reason. The effect is to prevent coupling some of the mains voltage electrostatically, which may be problematic in some kit but not usually audio.
3. However, an electrostatic screen would protect against some mains interference as well, but that is often unnecessary if a standard mains input filter is used (common mode choke etc).
My first amps were built with EI transformers without an interwinding shield. The coupling capacitance can be quite high and electrostatic voltages of 100V (but almost no current) were possible.
That has largely changed with the split bobbin where the windings are side-by-side. The interwinding capacitance is in the order of a tenth of what it used to be.
My first 100W amp used a home-made EI core with a split bobbin. Nothing wrong with EI cores, but I did run the core at a reduced mag field (around1T). It has to be lower than a toroidal because the field crosses the grain in a couple of places, and lowering further allows plenty for (unusual but possible) peak mains. It runs very cool, compared to some COTS devices. Toroidals do have lower reduced magnetic fields, but I have not had a problem with the EI core causing hum on the output of the amp. A lot of that is to do with careful layout/screening and amplifier PSRR as ripple on the supply lines can be a bigger issue.
If you go for toroids, just use higher voltage caps. It'll give better margins against peak mains.
If you go for EI, specify split bobbin (which tends to be normal these days) but low mag field. Also go for higher voltage caps!
As I mentioned, I have ordered a toroidal transformer in the past but specified low mag field even in that. (Around 1.2T instead of peak which could be 1.7T in GOSS 0.35mm laminations). That also runs cool.
Having said that, the only kit I have seen with a magnetic screen around transformers are valve kit (where valves are much more sensitive to electrostatically induced voltages due to the higher impedances) such as old tape recorders, valve preamp/mixers) but also record decks where a magnetic cartridge would be used and sensitive transistorised test gear, where low level induced currents would be critical. Oh, and the old oscilloscope tubes which had their own screens.
Some more things to think about -
1. Mains voltage variations can be up to 10% from nominal. Not sure what your country specs. are, but the UK's nominal 230V can be 253V. It was max. 6% up from 240V, which it actually still is. The variation will potentially offset your 2-3V difference.
2. Not having an interwinding screen does not seem to be a problem for many people.
Generally I would say that it is really only needed if the output supply had to float, for any reason. The effect is to prevent coupling some of the mains voltage electrostatically, which may be problematic in some kit but not usually audio.
3. However, an electrostatic screen would protect against some mains interference as well, but that is often unnecessary if a standard mains input filter is used (common mode choke etc).
My first amps were built with EI transformers without an interwinding shield. The coupling capacitance can be quite high and electrostatic voltages of 100V (but almost no current) were possible.
That has largely changed with the split bobbin where the windings are side-by-side. The interwinding capacitance is in the order of a tenth of what it used to be.
My first 100W amp used a home-made EI core with a split bobbin. Nothing wrong with EI cores, but I did run the core at a reduced mag field (around1T). It has to be lower than a toroidal because the field crosses the grain in a couple of places, and lowering further allows plenty for (unusual but possible) peak mains. It runs very cool, compared to some COTS devices. Toroidals do have lower reduced magnetic fields, but I have not had a problem with the EI core causing hum on the output of the amp. A lot of that is to do with careful layout/screening and amplifier PSRR as ripple on the supply lines can be a bigger issue.
If you go for toroids, just use higher voltage caps. It'll give better margins against peak mains.
If you go for EI, specify split bobbin (which tends to be normal these days) but low mag field. Also go for higher voltage caps!
As I mentioned, I have ordered a toroidal transformer in the past but specified low mag field even in that. (Around 1.2T instead of peak which could be 1.7T in GOSS 0.35mm laminations). That also runs cool.
Having said that, the only kit I have seen with a magnetic screen around transformers are valve kit (where valves are much more sensitive to electrostatically induced voltages due to the higher impedances) such as old tape recorders, valve preamp/mixers) but also record decks where a magnetic cartridge would be used and sensitive transistorised test gear, where low level induced currents would be critical. Oh, and the old oscilloscope tubes which had their own screens.
Last edited:
john_ellis,
Thank you for sharing your findings / experiences.
Our mains voltage is also 230V, and nowadays I am getting around 240-245V most of the times. A few years back, it was lower, mostly hovering around 225V.
From your comments on EI core transformers, what I understand is that a split bobbin is preferable. With a split bobbin, the primaries would be wound on one part and the secondaries on the other part, and have lower capacitive coupling.
Thank you for sharing your findings / experiences.
Our mains voltage is also 230V, and nowadays I am getting around 240-245V most of the times. A few years back, it was lower, mostly hovering around 225V.
From your comments on EI core transformers, what I understand is that a split bobbin is preferable. With a split bobbin, the primaries would be wound on one part and the secondaries on the other part, and have lower capacitive coupling.
Last edited:
"primaries would be wound on one part and the secondaries on the other part, and have lower capacitive coupling"
Yes, that is right.
I should have said that toroidals have lower external magnetic field.
Yes, that is right.
I should have said that toroidals have lower external magnetic field.
I tend to avoid split bobbin EIs for high power application whenever possible. Yeah, there is less capacitive coupling, but poor magnetic coupling as well. Regulation is terrible. Useless as tube output transformers (no highs - so NO ONE does it). I had a big 2.5 kVA split bobbin which was 75-0-75 unloaded that turned out to be useless to make a big power amp out of. The +/-105 volt rails fell to +/-70 at full clip at 4 ohms. For a 2.5 kVA. I expected much better. That’s pretty much acting like a choke input filter. A 60-0-60 1kVA concentrically wound EI made it put out just as much power. Smaller ones suffer the same fate. I have some “36 volt” split bobbin EIs that put out 45 volts with no load. 6.3’s that put out almost 9. To hell with using them for tube heaters for development projects where it’s not at full load and load may vary. Back to the Antek toroid. Audio amps *can* live with that kind of regulation figure, but the unloaded supply required to get X watts starts to get ridiculous. +/-65 volt supplies to get 90 watts is not unheard of in HT receivers which use those split bobbin trafos. And you wonder why the damn power transistors keep burning out.
I've never used a split bobbin for audio transformers. For just the reasons you say. But we were discussing mains power transformers. Never have I suggested that a split bobbin with separate primary:secondary sections should be used for audio. I have only ever seen one example where a manufacturer did a split bobbin for audio once - I don't think they knew what they were doing.
For higher powers than I used (500-600W) then I also agree that you may well need a tightly coupled primary:secondary to improve regulation. I've not done anything above 600W.
In fact one manufacturer does use a split bobbin, I believe, for audio transformers but does not restrict the secondary and primary to the separate halves, but uses both bobbin halves for layers of both primary and secondary so as not to lose coupling. Lots of loose ends to tie together though I imagine.
As for transformers with poor regulation, some of that I have found to be due to pushing the wire current density too high (resistance in other words). At one time the standard was 3A/sq mm for low power transformers but many commercial designs use 4 or 4.5 A/sqmm. High power (kW+) transformers need to be run at 2A or even lower. One old table suggests 1.5A/sqmm (expressed as 1000A/sq inch). That is mainly down to the allowable power dissipation in the winding.
For higher powers than I used (500-600W) then I also agree that you may well need a tightly coupled primary:secondary to improve regulation. I've not done anything above 600W.
In fact one manufacturer does use a split bobbin, I believe, for audio transformers but does not restrict the secondary and primary to the separate halves, but uses both bobbin halves for layers of both primary and secondary so as not to lose coupling. Lots of loose ends to tie together though I imagine.
As for transformers with poor regulation, some of that I have found to be due to pushing the wire current density too high (resistance in other words). At one time the standard was 3A/sq mm for low power transformers but many commercial designs use 4 or 4.5 A/sqmm. High power (kW+) transformers need to be run at 2A or even lower. One old table suggests 1.5A/sqmm (expressed as 1000A/sq inch). That is mainly down to the allowable power dissipation in the winding.
Last edited:
I wasn’t suggesting using them for audio - just that the coupling is so bad that you CAN’T. Even the 2.5kVA split bobbin was as bad a regulation as a 100 VA toroid, with about the same % drop at full respective load. I’m sure a lot of those HT receiver trafos push it way beyond 3A/mm2. But when I rewind a salvaged split bobbin as a concentric I get less drop at the same VA, even using the same size wire on the primary and turns per volt. And consistently see unloaded voltages ridiculously high on off the shelf units from even respected names like Triad, Signal and Stancor. They don’t skimp on wire. And the old paper former concentric ones from yesteryear had much better regulation on the same size core.
I don't dispute your findings. I agree magnetic coupling is better if windings are concentric, but audio transformers are generally split into several layers sandwiching the primary/secondary/primary/secondary etc. Even then I haven't seen a real issue with electrostatic feed through of the signals. Haven't seen that reported as an issue either, but maybe someone has looked into that.
Some of the best audio transformers were reported to have thicker insulation layers between the wire layers to reduce interwinding capacitance.
If zman prefers, an EI core is fine if wound concentrically and if custom made could have an interwinding screen. I'd add one if I were doing a concentric, all I was pointing out was that my EI split bobbin works well for a 100W stereo setup, and my preference is for lower capacitance.
Some of the best audio transformers were reported to have thicker insulation layers between the wire layers to reduce interwinding capacitance.
If zman prefers, an EI core is fine if wound concentrically and if custom made could have an interwinding screen. I'd add one if I were doing a concentric, all I was pointing out was that my EI split bobbin works well for a 100W stereo setup, and my preference is for lower capacitance.
You are talking to a guy in Bangladesh.
He will be lucky if he gets electrical steel, mostly it will be ordinary cold rolled sheets with burrs causing air gaps in the cores, and good quality brass, rather than pure copper wire.
So he must specify a higher rating than you.
As for toroids, getting the cores in Bangladesh is kind of difficult, and in India also, custom made toroids are not well made.
Sad but true.
He will be lucky if he gets electrical steel, mostly it will be ordinary cold rolled sheets with burrs causing air gaps in the cores, and good quality brass, rather than pure copper wire.
So he must specify a higher rating than you.
As for toroids, getting the cores in Bangladesh is kind of difficult, and in India also, custom made toroids are not well made.
Sad but true.
It may be a situation of “take what you can get”, unless there is unlimited amount of money to throw at the problem. You can ALWAYS buy (or have made) the transformer that you *want*. Might cost a thousand dollars, but it can be done. May be more in taxes shipping and duties than actual goods. If you have less to spend than that the quality might not be there. Back in my penny pinching days I used to salvage and rewind for almost everything, because maybe $25 was my limit. Today it’s 50/50, with most of my custom winds for tube amps with no off the shelf solution, and custom still being a couple hundred that I won’t spend.