I'm starting probably the wrong side of things by asking this question before I even have a basic understanding of building an amp but I would like to know if I could make it extremely cheap by parting out old powersupplies. Is this possible? I work at computer renassaince so it's easy to grab parts from these. What do you think?
I'd suspect the power switching MOSFET would be perfect. Might be able to use the diodes for 12V supply for a similarly low-voltage supply with low switching noise (they have to switch very fast, so switching noise from the diodes turning on&off will be to a minimum at 60Hz).
They usually have a 78xx or 79xx type regulator inside, might use one of those for a low-level supply (for preamp/gain stages, etc...).
That's about all I can think of in my tired state. HTH!
Tim
They usually have a 78xx or 79xx type regulator inside, might use one of those for a low-level supply (for preamp/gain stages, etc...).
That's about all I can think of in my tired state. HTH!
Tim
actually the inductors in a PC power supply are pretty robust -- don't forget that these are designed for hundreds of watts. You also have EMI filters etc. I wouldn't bother with the diodes and transistors -- not worth the time unsoldering them.
I have used inductors from PC supplies to make switching supplies -- my LM3875 (was/is) in the old MB used the core from a PC power supply -- and the entire thing is encased in a PC Power Supply case -- you have to "characterize" the core first -- in order to know the turns etc. (Do you really want me to get into this, a geek at UCBerkeley told me how about 5 years ago).
I have used inductors from PC supplies to make switching supplies -- my LM3875 (was/is) in the old MB used the core from a PC power supply -- and the entire thing is encased in a PC Power Supply case -- you have to "characterize" the core first -- in order to know the turns etc. (Do you really want me to get into this, a geek at UCBerkeley told me how about 5 years ago).
I'd suspect the power switching MOSFET would be perfect
The old PSU's that I've taken apart have all used BJT's for the switching transisters rather than MOSFET's , but thats not to say that the more modern ones don't.
FWIW , the ones that I took out ( old AT PSU's ) were 2SC2625's and are nice TO247 high voltage breakdown devices ( 400-450v ) , but only handle about 80W .
I've used them in a car ignition controller, and they handle the coil voltages fine , although they do have a typically low hfe of about 10.
The high voltage caps are nice too , and the ferrites are also useful.
problem is that the best project for all these parts is SMPS....
😎
ray
The old PSU's that I've taken apart have all used BJT's for the switching transisters rather than MOSFET's , but thats not to say that the more modern ones don't.
FWIW , the ones that I took out ( old AT PSU's ) were 2SC2625's and are nice TO247 high voltage breakdown devices ( 400-450v ) , but only handle about 80W .
I've used them in a car ignition controller, and they handle the coil voltages fine , although they do have a typically low hfe of about 10.
The high voltage caps are nice too , and the ferrites are also useful.
problem is that the best project for all these parts is SMPS....
😎
ray
And a fan... lol.. 🙂 Power conmnectors, a switch (or 2) and the actual transformer would be good for a switchmode powersupply if it was rewound.... or, you could even just add windings to it to run an amplifier from teh switchmode powersupply.. 😀
JBL said:
Yes, but sadly a 7.2AH sealed lead-acid battery is about 2mm too wide to fit in one.. 🙁
I would use the complete powersupply, Just take some of them, put them in series for enough voltage, and use as amp powersupply. 2 (12V+12V)should be enough for a OPA548 /549/544 etc amp.
SkinnyBoy said:
Ahh, you mean the ones that come from old UPS units...
A used PC power supply has a lot parts good for making a SMPS. You can reuse the transformer if you soak it in acetone. All of the varnish will come off, and you can then pull the wires off, and start with a perfectly good 250W core. I have built several SMPS from old pc supplies.
-Dan
dkemppai said:
lol, no, like the one my dad bought that is now sitting there doing nothing... I wanted to make my own ups, using a DC-DC powersupply and battery all in the standard size computer powersupply, with an external powersupply to charge the battery, and run the computer.....
I was told to put the transformer in the oven to melt the glue that held the 2 halves together.... I ahev done this, but it only worked with some transformers.. lol
converting computer power supplies
this appeared on the ham radio homewbrew newsgroup -- a comprehensive article on surplus PC power supplies and their conversion:
http://www.qsl.net/vk4ba/projects/index.html
this appeared on the ham radio homewbrew newsgroup -- a comprehensive article on surplus PC power supplies and their conversion:
http://www.qsl.net/vk4ba/projects/index.html
Great and cheap start for a SMPS. Unfortunately only old (286,386) powersources have the ferites large enough to make a SMPS with them.However many good part for free in an disabled PC powersource.
Ford_V6 said:
Dunno about that.. 🙄 But Most of the PSs I have looked have big enough core... Some are round, some are square, the round ones are taller and much easier to re-wind.. 🙂
how come a 400 watt ps can't handle 400 watts?
perhaps you'll have to change the switching frequency. as you change the frequency the primary inductance can be lowered. the peak current will change somewhat if you go from 100kHz to 500kHz.<p> see my post on SMPS transformer equations. I guess I should add other configurations.
perhaps you'll have to change the switching frequency. as you change the frequency the primary inductance can be lowered. the peak current will change somewhat if you go from 100kHz to 500kHz.<p> see my post on SMPS transformer equations. I guess I should add other configurations.
There are several components you can use from a typical AT or ATX power supply: If the power output is over 200W, then it is usually a half-bridge, immediately giving you 2 matched N-channel MOSFETS or 2 matched NPN bipolars. Beware of low Hfe on the BJT's though! 😱
The high-voltage electrolytics are usually pretty good, too. And don't forget the high-current output rectifiers and the cross-coupled inductor (usually a toroid). Then there are the smaller inductors that smooth out the several outputs.
Also, the PWM IC itself is usually good, too. It is almost a TL494, but sometimes is labeled KIA-7500, but is usually the same.
There are some low-current ultra-fast diodes for the -5V and -12V sections that might be useful.
The main power transformer is the heart of the supply that needs a closer look. It is usually made up of a high-permeability ferrite (like Amidon #77 material). There are several excellent power supply books out there that give plug-n-chug equations on how to choose a transformer for your application. But a 200W supply will supply 200W, regardless if the input is 115/230VAC or 12VDC. It's just a matter of how the transformer is wound.
OK, I'm babbling, now,😱 but just go to Google.com, or good ol' Yahoo! and type in switching power supplu book, and seewhat you get.
The high-voltage electrolytics are usually pretty good, too. And don't forget the high-current output rectifiers and the cross-coupled inductor (usually a toroid). Then there are the smaller inductors that smooth out the several outputs.
Also, the PWM IC itself is usually good, too. It is almost a TL494, but sometimes is labeled KIA-7500, but is usually the same.
There are some low-current ultra-fast diodes for the -5V and -12V sections that might be useful.
The main power transformer is the heart of the supply that needs a closer look. It is usually made up of a high-permeability ferrite (like Amidon #77 material). There are several excellent power supply books out there that give plug-n-chug equations on how to choose a transformer for your application. But a 200W supply will supply 200W, regardless if the input is 115/230VAC or 12VDC. It's just a matter of how the transformer is wound.
OK, I'm babbling, now,😱 but just go to Google.com, or good ol' Yahoo! and type in switching power supplu book, and seewhat you get.
till said:
would this work? i can get hol of PC PSs for free, so it would save money on the PS for my GainClone.
I would be careful connecting DC outputs from multiple supplies in series, as each one's DC ground is also tied to earth ground, and things could get bad very quickly when you throw the switch! 
I would just follow dkempaii's advice and rewind the transformer to put put the voltage(s) you need. Acetone is a great way to get the enamel off it, or a heatshrink gun if you're short on acetone.
Don't forget, if you increasde the output voltage, remember to change the output caps to a higher voltage, the rectifier(s) to higher piv ratings, and lastly, the output sensing network to compensate for this. Then things will be better.
If you're working with a 12V input, then you will probably have to "roll your own" pc board, but you still can use the transformer's bobbin and core. Best of luck.
BTW, the best book for designing a switched-mode power transformer is "High-Frequency Switching Power Supplies" (c) 1989, by George Chryssis.
I would just follow dkempaii's advice and rewind the transformer to put put the voltage(s) you need. Acetone is a great way to get the enamel off it, or a heatshrink gun if you're short on acetone.
Don't forget, if you increasde the output voltage, remember to change the output caps to a higher voltage, the rectifier(s) to higher piv ratings, and lastly, the output sensing network to compensate for this. Then things will be better.
If you're working with a 12V input, then you will probably have to "roll your own" pc board, but you still can use the transformer's bobbin and core. Best of luck.
BTW, the best book for designing a switched-mode power transformer is "High-Frequency Switching Power Supplies" (c) 1989, by George Chryssis.
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