A saw an indea in a gainclone post somewhere - to use readily available halogen lighting transformers. As far as I get it they're 12v rated switching power supplies. The good thing about them is that they can come on a very good price and their size/shape makes them very convenient for use in a minimalistic amplifier. They also come with extra protection circuitry, for shorts and the like, so there's the extra safety factor added there. The power range of those can be anything between 60 and 200VA.
Now - the issue there is that we'd like to have 20-24v instead of 12. Since their output is +12, -12V - is there a way to chain two of those modules to acheive +24, 0, -24 output that can be passed on to the the rest of the power supply circuitry? I get how that can be done with traditional transformers, but to be honest, i'm quite clueless on how halogen lighting SMPS work.
Of course, I realize that SMPS have their disadvantages and many people woudn't consider them in a sound amp, but if all that is feasible, it'd be worth the try, perhaps with a tweak or two to clean up the output of any power jitter.
Now - the issue there is that we'd like to have 20-24v instead of 12. Since their output is +12, -12V - is there a way to chain two of those modules to acheive +24, 0, -24 output that can be passed on to the the rest of the power supply circuitry? I get how that can be done with traditional transformers, but to be honest, i'm quite clueless on how halogen lighting SMPS work.
Of course, I realize that SMPS have their disadvantages and many people woudn't consider them in a sound amp, but if all that is feasible, it'd be worth the try, perhaps with a tweak or two to clean up the output of any power jitter.
I thought I had seen this done before on this forum and I finally found the post.....
http://www.diyaudio.com/forums/showthread.php?postid=989044#post989044
http://www.diyaudio.com/forums/showthread.php?postid=989044#post989044
Hm, I'm not really motivated to actually open up the halogen transformer and fiddle with the secondary winding myself. The point was, if possible to use something easily available in terms of power supply, given that it's cheap and then after building up the amp see if it'll be worth improving.
By the way the original suggestion came from http://orlygoingthirty.blogspot.com/2007/09/building-gainclone-chip-amplifier.html . But he doesn't mention in what way you actually wire them in series, which is the part I don't get.
Also, if i'm wring up two supplies rated at +- 12 volt, where am I loosing the 5 volt for the drop to 17?
By the way the original suggestion came from http://orlygoingthirty.blogspot.com/2007/09/building-gainclone-chip-amplifier.html . But he doesn't mention in what way you actually wire them in series, which is the part I don't get.
Also, if i'm wring up two supplies rated at +- 12 volt, where am I loosing the 5 volt for the drop to 17?
Atilla.
The confusion is that you seem to think these "electronic transformers" are SMPS that deliver rectified and stabilised DC at the output. AndrewT knows that it is not.
The common thing is that mains voltage is rectified and the resulting DC is hacked into AC by some fast-switching transistors. That AC is transformed to 12V and at that point the "electronic transformer" is complete, while the SMPS has a second rectifier stage and usually a voltage regulator. In short that means your transformer delivers AC at the output.
If the AC was a sine wave, like what you get when you use a transformer with mains voltage, you would "win" 5V with the smoothing or power supply by-pass capacitors that you have to add. 12V times sqrt(2) ~17V, you may recognize the equation. You will win less, because these transformers are not transforming sine waves but square waves that are probably not very "clean".
Your reluctance to fiddle around with the secondaries is very healthy. Don't start fiddling.
The orlygoingthirtythread uses conventional transformers as opposed to the "electronic transformers" in the thread theAnonymous1 specified. Easy to copy. Lay the two transformers side by side. Connect the two secondary terminals that are now in the middle together and use them as your center tap. The other two terminals are your two 12V outputs. But...
you will be better off with a good audio transformer.
The confusion is that you seem to think these "electronic transformers" are SMPS that deliver rectified and stabilised DC at the output. AndrewT knows that it is not.
The common thing is that mains voltage is rectified and the resulting DC is hacked into AC by some fast-switching transistors. That AC is transformed to 12V and at that point the "electronic transformer" is complete, while the SMPS has a second rectifier stage and usually a voltage regulator. In short that means your transformer delivers AC at the output.
If the AC was a sine wave, like what you get when you use a transformer with mains voltage, you would "win" 5V with the smoothing or power supply by-pass capacitors that you have to add. 12V times sqrt(2) ~17V, you may recognize the equation. You will win less, because these transformers are not transforming sine waves but square waves that are probably not very "clean".
Your reluctance to fiddle around with the secondaries is very healthy. Don't start fiddling.
The orlygoingthirtythread uses conventional transformers as opposed to the "electronic transformers" in the thread theAnonymous1 specified. Easy to copy. Lay the two transformers side by side. Connect the two secondary terminals that are now in the middle together and use them as your center tap. The other two terminals are your two 12V outputs. But...
you will be better off with a good audio transformer.
take care with phasing...
if you are linking the two outputs in series as suggested, you need ot make sure the outputs are connected in phase. Good cheap high output solution though - works well for me in both tube and GC applications, and the traffos are cheap as chips - last I bought were $5.00 each s/hand. Not bad for 60VA @ 12V outputs!
if you are linking the two outputs in series as suggested, you need ot make sure the outputs are connected in phase. Good cheap high output solution though - works well for me in both tube and GC applications, and the traffos are cheap as chips - last I bought were $5.00 each s/hand. Not bad for 60VA @ 12V outputs!
Thanks a lot for the clarifications.
Yes, I guess I got confused initially with a different type of power source, that does have DC output.
I'll see if I'm going to continue looking at the halogen transformers, the experiment will depend on whether I can find at least tow of them, with reasonable power rating for a cheap cheap, price.
Otherwise I've already got the part numbers and prices for two really good 2x24 12VA toroidal transformers. They will cost more than everything else I'll ever get for that amp, but at least a good power supply is always nice to have
Yes, I guess I got confused initially with a different type of power source, that does have DC output.
I'll see if I'm going to continue looking at the halogen transformers, the experiment will depend on whether I can find at least tow of them, with reasonable power rating for a cheap cheap, price.
Otherwise I've already got the part numbers and prices for two really good 2x24 12VA toroidal transformers. They will cost more than everything else I'll ever get for that amp, but at least a good power supply is always nice to have
when i was a kid
that is some long time ago i did some expiraments with that and ralized that a nomal circuit with 4diodes and one capacitor cannot convert the voltage to dc since this is not sine wave ....
square or what ever this pulse is will require other types of probably faster diodes to become dc ......
by the same logic if triacs are to be used to reduce mains then rectify this pulse that comes out of the triac at the time wasnt possible i never managed to do it ....
also as far as i know only the bob legend carver managed to work with this theory but after the triac existing transformer something like magnetic field ....so the result was actually a constant variable psu depending on the needs of the amp with the triac
but the idea also is not so good since this smps "trafos" fail very easily aspecially since they are not designed to drive reactive loads and also they have no feedback circuits but work with shelf ocilation provided from a secondary winding .....
not very stable i thing...... company i used to work for modified a circuit like that ( its very available if you want ) that was actually coming from this kind of lighting equipment to produce 40+40 volts dc ....to feed one amplifier 100w
it worked but eventually it all failed
then of course the secret is with the trafo .....
that is some long time ago i did some expiraments with that and ralized that a nomal circuit with 4diodes and one capacitor cannot convert the voltage to dc since this is not sine wave ....
square or what ever this pulse is will require other types of probably faster diodes to become dc ......
by the same logic if triacs are to be used to reduce mains then rectify this pulse that comes out of the triac at the time wasnt possible i never managed to do it ....
also as far as i know only the bob legend carver managed to work with this theory but after the triac existing transformer something like magnetic field ....so the result was actually a constant variable psu depending on the needs of the amp with the triac
but the idea also is not so good since this smps "trafos" fail very easily aspecially since they are not designed to drive reactive loads and also they have no feedback circuits but work with shelf ocilation provided from a secondary winding .....
not very stable i thing...... company i used to work for modified a circuit like that ( its very available if you want ) that was actually coming from this kind of lighting equipment to produce 40+40 volts dc ....to feed one amplifier 100w
it worked but eventually it all failed
then of course the secret is with the trafo .....
hehehe
sorry andrew - I was being ironic. I fully understand the phasing requirement - hence my earlier post. Our Indian "electronic engineer" is perhaps a little more challenged. But you may be correct - I have always suspected hte "gifted" label to be hyperbole. ANd the young isn't entirely accurate either...
sorry andrew - I was being ironic. I fully understand the phasing requirement - hence my earlier post. Our Indian "electronic engineer" is perhaps a little more challenged. But you may be correct - I have always suspected hte "gifted" label to be hyperbole. ANd the young isn't entirely accurate either...
lets be clear...
two transformers, attached to the same supply, will output voltages either in phase or 180 degrees out of phase as andrew notes. If the outputs are in phase, the secondary windings can be connected in series to provide (V1 + V2) output voltage. THe centre tap (where the two windings are connected) yields the midpoint of the two windings (assuming they are indentical windings...). THis can be used as a virtual 0v - a setup exploited in the first posts example. Of course, if connected out of phase, all you get is smoke. Can't be done with switched mode power supplies - or not easily anyway.
two transformers, attached to the same supply, will output voltages either in phase or 180 degrees out of phase as andrew notes. If the outputs are in phase, the secondary windings can be connected in series to provide (V1 + V2) output voltage. THe centre tap (where the two windings are connected) yields the midpoint of the two windings (assuming they are indentical windings...). THis can be used as a virtual 0v - a setup exploited in the first posts example. Of course, if connected out of phase, all you get is smoke. Can't be done with switched mode power supplies - or not easily anyway.
Example of two "electronic/transformerless" halogen power supplies:
- good "Power-Factor" specs, but, beware of high "Harmonic-Distortion..."
Electronic Transformer LVT 24V/150W
Power factor min. 0.985
Max. harmonic distortion 9%
http://electronictransformer.com/lvt151ac24v2.html
Electronic Transformer LET 24V/300W
Power factor 0.985
Max. harmonic distortion 2.3%
http://electronictransformer.com/let303ac24v2.html
- good "Power-Factor" specs, but, beware of high "Harmonic-Distortion..."
Electronic Transformer LVT 24V/150W
Power factor min. 0.985
Max. harmonic distortion 9%
http://electronictransformer.com/lvt151ac24v2.html
Electronic Transformer LET 24V/300W
Power factor 0.985
Max. harmonic distortion 2.3%
http://electronictransformer.com/let303ac24v2.html
bichi wrote
These and many others, so called electronic power supplies are NOT transformerless.
So do not connect their outputs in series.
Edit:The solution
Rectify the output ac of each power supply by using 2 times the output voltage rated diodes(or a bridge rectifier) rated for more current than the rating of the supply. Connect filter capacitors that can handle high frequency. Value need not be too big.This will give u the DC voltage. Now connect +(plus) output of one supply to the -(minus) output of the other psu. This will be your ground. Now u will have a dual supply for your gainclone.
Gajanan Phadte
These and many others, so called electronic power supplies are NOT transformerless.
So do not connect their outputs in series.
Edit:The solution
Rectify the output ac of each power supply by using 2 times the output voltage rated diodes(or a bridge rectifier) rated for more current than the rating of the supply. Connect filter capacitors that can handle high frequency. Value need not be too big.This will give u the DC voltage. Now connect +(plus) output of one supply to the -(minus) output of the other psu. This will be your ground. Now u will have a dual supply for your gainclone.
Gajanan Phadte
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