PC Supplies used as Audio Amp SMPss
MODERATORS: Please bump this to the Power Supplies Forum. THX!
Hi Carlos,
Yes, this is a great thread you started here!
There are several threads dealing with this subject:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=49374&highlight=
http://www.diyaudio.com/forums/showthread.php?s=&threadid=10753&highlight=
http://www.diyaudio.com/forums/showthread.php?s=&threadid=28028&highlight=
http://www.diyaudio.com/forums/showthread.php?s=&threadid=17274&highlight=
http://www.diyaudio.com/forums/showthread.php?s=&threadid=70764&highlight=
I like the last one here as it has some very good advice. it's not the longest one, but it hasa some really good advice.
I have a few comments I would like to share about using old AT & ATX power supplies for sudio applications:
1) Yes, they can be used for audio applications, BUT, some modifications will be necessary. The extent of modification will be determined by what type of amp you want to run. For example, if you want to run a gainclone, or any amp (discrete or chip-amp) that requires a bi-polar supply in excess of +/-12V, then you're in for at the very least, a trasnsformer rewind, major diode rectifier replacement and re-working of the output voltage sensing section.
2) In my experience, AT supplies lend themselves to modification a little better than ATX ones, unless you're going to use that +5Vsb housekeeping supply to run some things while the main converter is off. But please, Carlos, don't let this dissuade you from trying an ATX.
3) Jackinnj has posted several times on the DIY forum, the link to QEX magazine article that covers converting an old AT or ATX supply to put out +13.8V at something like 15-20A, specifically for use to power ham radio gear. Although it could just as easily power a BLT chip amp, like an NEC uPC1230H2. Perhaps he could be pursuaded to post that like here. Please Please Jack!
4) Carlos, referencing your post about the noise at 30-40kHz, this is the PWM chip's switching frequency (usually 36kHz). For most AT & ATX Power Supplies, this PWM chip is almost always a TL494. Sometimes, it is labelled "7500" or "KIA7500", but it is the same chip. Since the '494 is a dual output PWM chip, the chip's oscillator frequency is actually double the switching frequency, because it has to turn on each transistor alternately for one complete cycle. The chip's oscillator frequency can be easily be changed by substituting the timing resistor, R(t), for a different one. Be careful on changing the frequency more than +/- 15%, because the transformer windings, core material and alot of other things in the PSU are designed around this frequency. If you were going to kick it up to, say, 100kHz, or even 200kHz, you are in for a major re-design. A little trick to deal with the noise, is to replace the timing resistor with one, say, 10% lower and putting a panel-mounted potentiometer of 20% of the original timing resistor's value in series with this pot. This will give you a frequency adjustment of +/- 10%, allowing you to "slide" the noise off the band you are on, or ourt of thre audio range. If the noise re-appears, simply re-adjust the pot, now called a tuning pot, until the noise again disappears.
See this link about the '494 to get a good idea how it operates:
http://www.onsemi.com/pub/Collateral/TL494-D.PDF
Page 6 of the Datasheet gives some insight on how to set the oscillator frequency.
5) I have to agree with EVA on not using a ferrite toroid in place of the existing transforemr core. Adding the three layers of transformer tape would make it even more difficult to deal with winding. Since you already have a good core, use it.
I think I have emptied my head out of all I can think now, since I have been typin this for about an hour now, so I will stop here.
Just throwing my two cents' worth in the pile.
'73, de N8XO,
Steve
MODERATORS: Please bump this to the Power Supplies Forum. THX!
Hi Carlos,
Yes, this is a great thread you started here!
There are several threads dealing with this subject:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=49374&highlight=
http://www.diyaudio.com/forums/showthread.php?s=&threadid=10753&highlight=
http://www.diyaudio.com/forums/showthread.php?s=&threadid=28028&highlight=
http://www.diyaudio.com/forums/showthread.php?s=&threadid=17274&highlight=
http://www.diyaudio.com/forums/showthread.php?s=&threadid=70764&highlight=
I like the last one here as it has some very good advice. it's not the longest one, but it hasa some really good advice.
I have a few comments I would like to share about using old AT & ATX power supplies for sudio applications:
1) Yes, they can be used for audio applications, BUT, some modifications will be necessary. The extent of modification will be determined by what type of amp you want to run. For example, if you want to run a gainclone, or any amp (discrete or chip-amp) that requires a bi-polar supply in excess of +/-12V, then you're in for at the very least, a trasnsformer rewind, major diode rectifier replacement and re-working of the output voltage sensing section.
2) In my experience, AT supplies lend themselves to modification a little better than ATX ones, unless you're going to use that +5Vsb housekeeping supply to run some things while the main converter is off. But please, Carlos, don't let this dissuade you from trying an ATX.
3) Jackinnj has posted several times on the DIY forum, the link to QEX magazine article that covers converting an old AT or ATX supply to put out +13.8V at something like 15-20A, specifically for use to power ham radio gear. Although it could just as easily power a BLT chip amp, like an NEC uPC1230H2. Perhaps he could be pursuaded to post that like here. Please Please Jack!
4) Carlos, referencing your post about the noise at 30-40kHz, this is the PWM chip's switching frequency (usually 36kHz). For most AT & ATX Power Supplies, this PWM chip is almost always a TL494. Sometimes, it is labelled "7500" or "KIA7500", but it is the same chip. Since the '494 is a dual output PWM chip, the chip's oscillator frequency is actually double the switching frequency, because it has to turn on each transistor alternately for one complete cycle. The chip's oscillator frequency can be easily be changed by substituting the timing resistor, R(t), for a different one. Be careful on changing the frequency more than +/- 15%, because the transformer windings, core material and alot of other things in the PSU are designed around this frequency. If you were going to kick it up to, say, 100kHz, or even 200kHz, you are in for a major re-design. A little trick to deal with the noise, is to replace the timing resistor with one, say, 10% lower and putting a panel-mounted potentiometer of 20% of the original timing resistor's value in series with this pot. This will give you a frequency adjustment of +/- 10%, allowing you to "slide" the noise off the band you are on, or ourt of thre audio range. If the noise re-appears, simply re-adjust the pot, now called a tuning pot, until the noise again disappears.
See this link about the '494 to get a good idea how it operates:
http://www.onsemi.com/pub/Collateral/TL494-D.PDF
Page 6 of the Datasheet gives some insight on how to set the oscillator frequency.
5) I have to agree with EVA on not using a ferrite toroid in place of the existing transforemr core. Adding the three layers of transformer tape would make it even more difficult to deal with winding. Since you already have a good core, use it.
I think I have emptied my head out of all I can think now, since I have been typin this for about an hour now, so I will stop here.
Just throwing my two cents' worth in the pile.
'73, de N8XO,
Steve
Missing components
I forgot one other thing, Carlos. In your pics of the 200W AT board there, see the missing components L1, C2, C3 &C4?
These were left off to minimize the cost of making the unit. They form the AC line filter that keeps the switching noise generated by the TL494 PWM chip from getting out onto the AC line. Some manufacturers cut these necessary components out, just to shave some of the costs off, and boost their profit a bit. When you're making millions of units and you save, say, 50 cents, then the "savings" can add up quickly. however, this occurs at the expense of the supply not meeting EMC or noise requirements of the various regulatory agencies.
If you can calculate the values of these missing components, and replace the jumpers with the correct values, then you will attenuate the noise considerably.
Also, see the jumpers across where L5 &L6 are supposed to go? Same thing again, just trying to shave a few cents off the manufacturing cost. If you can replace the jumpers with a couple of inductors at the right value, you should improve the noise reduction a little bit more.
I forgot one other thing, Carlos. In your pics of the 200W AT board there, see the missing components L1, C2, C3 &C4?
These were left off to minimize the cost of making the unit. They form the AC line filter that keeps the switching noise generated by the TL494 PWM chip from getting out onto the AC line. Some manufacturers cut these necessary components out, just to shave some of the costs off, and boost their profit a bit. When you're making millions of units and you save, say, 50 cents, then the "savings" can add up quickly. however, this occurs at the expense of the supply not meeting EMC or noise requirements of the various regulatory agencies.
If you can calculate the values of these missing components, and replace the jumpers with the correct values, then you will attenuate the noise considerably.
Also, see the jumpers across where L5 &L6 are supposed to go? Same thing again, just trying to shave a few cents off the manufacturing cost. If you can replace the jumpers with a couple of inductors at the right value, you should improve the noise reduction a little bit more.
Some useful schematics for better understanding of simple off-line half-bridge self-starting SMPS:
Typical ATX power supply:
Typical AT power supply:
A custom made 13.8V 40A PSU using the same topology and working principles as above:
Anyone interested in PC PSU modification should study and understand these schematics first (I take that kind of things to the sofa or the bed for detailed analysis).
N-Channel:
Believe it or not, these slow-switching old designs based on bipolar transistors and positive-feedback-turn-on are really EMI-quiet in comparison with the MOSFET things full of RF ringing that are more in fashion nowadays, they may even pass conducted EMI tests without any filter.
Typical ATX power supply:
An externally hosted image should be here but it was not working when we last tested it.
Typical AT power supply:
An externally hosted image should be here but it was not working when we last tested it.
A custom made 13.8V 40A PSU using the same topology and working principles as above:
An externally hosted image should be here but it was not working when we last tested it.
Anyone interested in PC PSU modification should study and understand these schematics first (I take that kind of things to the sofa or the bed for detailed analysis).
N-Channel:
Believe it or not, these slow-switching old designs based on bipolar transistors and positive-feedback-turn-on are really EMI-quiet in comparison with the MOSFET things full of RF ringing that are more in fashion nowadays, they may even pass conducted EMI tests without any filter.
I knew you'd chime in right away, EVA!
The 40A Supply comes from the DEC 1998 issue of QST. It was a good article, and it is good for 40A continuous because the author stacks something like 4 or 5 cores together to enable the supple to handle that power level.
The real key here is the saturation value of the driver transformer. This needs to be kept much smaller than the that of the main power transformer to enable the self-starting, since the PWM chip is on the secondary side of the supply.
The 40A Supply comes from the DEC 1998 issue of QST. It was a good article, and it is good for 40A continuous because the author stacks something like 4 or 5 cores together to enable the supple to handle that power level.
The real key here is the saturation value of the driver transformer. This needs to be kept much smaller than the that of the main power transformer to enable the self-starting, since the PWM chip is on the secondary side of the supply.
The transformer of the 13.8V 40A power supply is strongly oversized, maybe because the author didn't calculate it properly, because he didn't got the self-starting thing right, or because he wanted to operate the cores at very small flux densities. With a proper design, the same power may be just obtained from a single E42/21/20 transformer. As you know, in my 32Khz power supply with a similar topology (full bridge really) I'm getting 1.8KW from just two E42/21/20 transformers (15V 125A output fully regulated). And my transformers are usually operated around 100mT (if I remember properly), quite far from saturation, while having a lot of free winding space.
Don't you remember? That thread covers it:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=60969
It's a full bridge made with just four transformer driven TO-220 bipolar devices, and tricky base drive. Also, I have a few IR2110 in my parts box that I have not tried yet, I think that each one costed me as much as the four MJE13009 bipolars
http://www.diyaudio.com/forums/showthread.php?s=&threadid=60969
It's a full bridge made with just four transformer driven TO-220 bipolar devices, and tricky base drive. Also, I have a few IR2110 in my parts box that I have not tried yet, I think that each one costed me as much as the four MJE13009 bipolars
Yes, Eva, now I remember it. Ouch! That's expensive! 
I have some '13009s laying around, but I was gonna use them to upgrade some '13007s in another AT supply I am thinking of modding.
Hey Carlos, sorry if we've strayed off subject here. Hope all this back-and-forth is helpful for you in your decision on how to best proceed........
I have some '13009s laying around, but I was gonna use them to upgrade some '13007s in another AT supply I am thinking of modding.Hey Carlos, sorry if we've strayed off subject here. Hope all this back-and-forth is helpful for you in your decision on how to best proceed........
We are not so off-topic: My PSU started as a modified AT PSU capable of 15V 20A output (I removed redundant stuff, added a voltage adjustment pot, replaced rectifiers and increased a bit the current limit). Then I bumped it to 36A with additional (breadboarded ) synchoronous rectification and by rewinding the transformer to a convenient 7:1 turns ratio. Then I abandoned the AT case, PCB and transfomers and jumped to a full-bridge with a E42/21/20 12:1 transformer and a masive output inductor to get 72A...
) synchoronous rectification and by rewinding the transformer to a convenient 7:1 turns ratio. Then I abandoned the AT case, PCB and transfomers and jumped to a full-bridge with a E42/21/20 12:1 transformer and a masive output inductor to get 72A...
One consideration to add,that I havn't seen posted yet (But I only skimmed the thread ) is that PC supplies are usually grounded to earth/saftey ground,that is,the 0V rail is bonded to earth/safety ground.
In the first diagram in the thread,with the 2 seperate supplies for (+) and (-) voltages,this grounding setup would become an issue!
The power supply on the right would be shorted out!
You would need to 'lift'/isolate the 0V rail of atleast one supply (the right-most one in the diagram) if not both.
One more modification to make and/or trace to cut.
) is that PC supplies are usually grounded to earth/saftey ground,that is,the 0V rail is bonded to earth/safety ground.In the first diagram in the thread,with the 2 seperate supplies for (+) and (-) voltages,this grounding setup would become an issue!
The power supply on the right would be shorted out!
You would need to 'lift'/isolate the 0V rail of atleast one supply (the right-most one in the diagram) if not both.
One more modification to make and/or trace to cut.
I love that freedom, not only to me but also to forum friends.
Some deviations from the main subject are natural, as they result from the dinamics of conversations.
One matter goes pushing another thing....but already related supplies and pulse width, or switching supplies.
thank you all, very kind from you to have this conversation here, a lot of informations are beeing good to me.
Line up
Your amplifiers will work fine, as you will have enormous power reserve....the supply can feed amplifiers producing more than 40 watts of power.
N Channel
Good to know that there are several threads to read about that subject...this will be great to me...now i have a lot of things to read and to learn....related to move..... related me, it is all rigth, if moderators decided this way, it is ok to me.
Eva
Mosfet things Ahahahahha!, me gusta mucho la verdad, i like those trues that we use in our words...our opinnion...in this case they may be problems...ahahahaha...very nice.
I have four 13009 in my junkbox...waiting the change to work.
Thank you by the schematics, now i will understand how those supplies works
Digital Junkie
Very good to have you here too.
regards,
Carlos
Some deviations from the main subject are natural, as they result from the dinamics of conversations.
One matter goes pushing another thing....but already related supplies and pulse width, or switching supplies.
thank you all, very kind from you to have this conversation here, a lot of informations are beeing good to me.
Line up
Your amplifiers will work fine, as you will have enormous power reserve....the supply can feed amplifiers producing more than 40 watts of power.
N Channel
Good to know that there are several threads to read about that subject...this will be great to me...now i have a lot of things to read and to learn....related to move..... related me, it is all rigth, if moderators decided this way, it is ok to me.
Eva
Mosfet things Ahahahahha!, me gusta mucho la verdad, i like those trues that we use in our words...our opinnion...in this case they may be problems...ahahahaha...very nice.
I have four 13009 in my junkbox...waiting the change to work.
Thank you by the schematics, now i will understand how those supplies works
Digital Junkie
Very good to have you here too.
regards,
Carlos
A transceiver transformer has to be stable at about 100mA AND 20 amps (rx and tx) -- so both the transformer and output inductor have to be designed for two scenarios.Eva said:
For our linear audio amplifiers the situation isn't that bad.
N-Channel -- somewhere Texas Instruments has a white-paper on a frequency hopping SMPS chip which greatly reduces the noise which is of paramount consideration in communications products (which is why people are finding the Drake R4C to be such a good receiver.)
That's good Eva, i also will need time to understand and to colect the data inside my
AT supply.
This is good, that slowly you will giving us some explanations....giving time to reflections and to studies that i will have to make of your informations during the comparison of data with the AT supply sample i have.
ahora jo tiengo que descobrir este transformador referido, que tiene dupla salida simetrica que se une con diodos para la utilizaccion de las duas phases, con consequente acrescimo en la corriente de salida.
Now i will have to discover that transformer you made reference, the one that uses double output (( think), the simetrical output that is joined together using those diodes to have both phases joined increasing output current capabilities.
regards and thanks,
Carlos
AT supply.
This is good, that slowly you will giving us some explanations....giving time to reflections and to studies that i will have to make of your informations during the comparison of data with the AT supply sample i have.
ahora jo tiengo que descobrir este transformador referido, que tiene dupla salida simetrica que se une con diodos para la utilizaccion de las duas phases, con consequente acrescimo en la corriente de salida.
Now i will have to discover that transformer you made reference, the one that uses double output (( think), the simetrical output that is joined together using those diodes to have both phases joined increasing output current capabilities.
regards and thanks,
Carlos
Carlos,
I don't know much about computer PSUs but isn't the higher voltage
windings at low power.
Anyway, I would just try to ad as much cap as needed and listen to it !
If it stays quit its probably fine......
If the supply has any tendency to foldback it might not start with too
much cap on the output.
(I´m gonna be hanged by the experts for this approach, I know)
If you have a scope you may take a peak somewhre related to the
feedback-no oscillations-fine.
/ Mattias /
(Brave wired-half burned)
I don't know much about computer PSUs but isn't the higher voltage
windings at low power.
Anyway, I would just try to ad as much cap as needed and listen to it !
If it stays quit its probably fine......
If the supply has any tendency to foldback it might not start with too
much cap on the output.
(I´m gonna be hanged by the experts for this approach, I know)
If you have a scope you may take a peak somewhre related to the
feedback-no oscillations-fine.
/ Mattias /
(Brave wired-half burned)
....By the way,
Speaking of big supplies, many amps.
The biggest supply I have contributed to was 54Vdc, 250A, 0.7mVrms noise wideband.
3phase wide input, 93.4% eff, 680W/litre power density, 65C ambient.
Input THD=1.6% at 50-100% load.
Need I say there where afew other guys involved.
/ Mattias
Speaking of big supplies, many amps.
The biggest supply I have contributed to was 54Vdc, 250A, 0.7mVrms noise wideband.
3phase wide input, 93.4% eff, 680W/litre power density, 65C ambient.
Input THD=1.6% at 50-100% load.
Need I say there where afew other guys involved.
/ Mattias
Do not know Ekaerin,maybe the product of voltage and current stays the same, not sure
about that....maybe different related my imagination.
But i will not try anymore, i made studies and changes in the oscilating frequency and also in the transformer ratio.....i could double the voltage, but the oscilating transistors were too much hot.....also i forget to increase the output condensers, some of them explode.
They were substituted with a bigger voltage units...but to check if they were working cold, i touch something near the oscilator and i received a very violent electrical shock that left me without talk and breath for many seconds.
Well...i will continue with my old transformers.....at least, those ones i understand and i know how to avoid problems.... also i know how to construct and modify them.
Eva..... the electrical shock was enougth to me.... i will return to my old heavy transformers.
Thank you all guys...if you want to continue to study this subject, the thread is yours, go ahead and keep it nice the way it is .
hehe...i will prepare some transformers and forget those electrocution boxes for a while.
regards,
Carlos
about that....maybe different related my imagination.
But i will not try anymore, i made studies and changes in the oscilating frequency and also in the transformer ratio.....i could double the voltage, but the oscilating transistors were too much hot.....also i forget to increase the output condensers, some of them explode.
They were substituted with a bigger voltage units...but to check if they were working cold, i touch something near the oscilator and i received a very violent electrical shock that left me without talk and breath for many seconds.
Well...i will continue with my old transformers.....at least, those ones i understand and i know how to avoid problems.... also i know how to construct and modify them.
Eva..... the electrical shock was enougth to me.... i will return to my old heavy transformers.
Thank you all guys...if you want to continue to study this subject, the thread is yours, go ahead and keep it nice the way it is .
hehe...i will prepare some transformers and forget those electrocution boxes for a while.
regards,
Carlos
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