Several articles on external sites have suggested the idea of using an AC adapter to convert mains current to safe DC current for powering a low powered amplifier. I have not been able to find much information on this forum on the pros and cons of doing this.
See the switched mode power supplies on this site:
Some of these can handle upto 2 amps.
1. Does it mean that providing DC power by this means into the amplifier enclosure means the amplifier is 'totally safe'?
2. What about the hazard of an electrical shock?
3. Hazard of fire? Assume the enclosure is of plastic or wood.
See the switched mode power supplies on this site:
Some of these can handle upto 2 amps.
1. Does it mean that providing DC power by this means into the amplifier enclosure means the amplifier is 'totally safe'?
2. What about the hazard of an electrical shock?
3. Hazard of fire? Assume the enclosure is of plastic or wood.
In the UK we have strict manufacturing quality rules that must be applied to. Any switched mode or otherwise power supply with a genuine CE sticker or Conformity notice is safe to use as per the manufacturers installation instructions and by definition safe to use.
2 amps? I have a 12V 10A powering my ITX.
Cost is the main reason. Along with safety. Because safety adds costs - more things to consider when you have AC voltage running inside your chassis: Clearance/isolation, parts (connectors, buttons, insulation, and of course electronics) rated for AC application, and certification.
On the other hand if you buy a power adapter it is supposed to have all the above covered. And if people die from it you can push the blame to the PSU maker.
Of course, "totally safe" is subjective. I prefer to call it "technically safe". As in that $3 power supply from China brand weighing less than cardboard is "technically" able to supply 100W.
Cost is the main reason. Along with safety. Because safety adds costs - more things to consider when you have AC voltage running inside your chassis: Clearance/isolation, parts (connectors, buttons, insulation, and of course electronics) rated for AC application, and certification.
On the other hand if you buy a power adapter it is supposed to have all the above covered. And if people die from it you can push the blame to the PSU maker.
Of course, "totally safe" is subjective. I prefer to call it "technically safe". As in that $3 power supply from China brand weighing less than cardboard is "technically" able to supply 100W.
I use an ac adapter to power my T-amp: it increases the separation between the switching coils inside the PSU and the analog audio cables of the amplifier, and I can use the same power supply for several amplifiers. I use a 60W HP power supply originally bundled with a business laptop.
There are several grade of power supplies. The cheaper ones have limited insulation and regulation capabilities, and are NOT safe to use. Beware of unmarked adapters. I received one of these unmarked power supplies with a cheap tablet I ordered from China. No reference to the manufacturer and a simple "CE" and "double insulation" sticker badly applied to one side. I opened it before putting it in the trash and I was horrified: almost no insulation between high and low voltage sections, the transformer was half the size of similas specs power supplies, and the capacitors had a voltage marking lower than required, the plastic enclosoure was thin and prone to cracking. Totally unsafe.
There are several grade of power supplies. The cheaper ones have limited insulation and regulation capabilities, and are NOT safe to use. Beware of unmarked adapters. I received one of these unmarked power supplies with a cheap tablet I ordered from China. No reference to the manufacturer and a simple "CE" and "double insulation" sticker badly applied to one side. I opened it before putting it in the trash and I was horrified: almost no insulation between high and low voltage sections, the transformer was half the size of similas specs power supplies, and the capacitors had a voltage marking lower than required, the plastic enclosoure was thin and prone to cracking. Totally unsafe.
Thanks for all your replies! 🙂
I have some further questions: Jon, could you direct me to websites that sell the aprroved AC/DC adapters? For long term use I may just feel it worthwhile to get it shipped down here. We use the 220V system here as well.
I like your site "Surprising what 50years of experience can achieve."
Repair and re-use has gained a lot of attention lately with the shipping of toxic electronic waste overseas: did you know a CRT contains several pounds of lead? Over here we are very much into re-use, which is good.
I use adapters daily and was not really aware that there are safe/unsafe ones. I have a broken one which I will photograph and post here for comment.
"wwense" what is the adapter you are using? 12V 10A - is it available online - just for future reference. Why doesn't everyone use external power supplies like laptops?
"pcan" - how do you choose a correct laptop adapter? I have on or two lying around but I am not sure if I will burn them out by using. Do they have current protection internally- no need of a fuse?
Is there a move generally to move to domestic DC current? I was never really comfortable with 220v we use here, although we have circuit breakers.
This is interesting:
I have some further questions: Jon, could you direct me to websites that sell the aprroved AC/DC adapters? For long term use I may just feel it worthwhile to get it shipped down here. We use the 220V system here as well.
I like your site "Surprising what 50years of experience can achieve."
Repair and re-use has gained a lot of attention lately with the shipping of toxic electronic waste overseas: did you know a CRT contains several pounds of lead? Over here we are very much into re-use, which is good.
I use adapters daily and was not really aware that there are safe/unsafe ones. I have a broken one which I will photograph and post here for comment.
"wwense" what is the adapter you are using? 12V 10A - is it available online - just for future reference. Why doesn't everyone use external power supplies like laptops?
"pcan" - how do you choose a correct laptop adapter? I have on or two lying around but I am not sure if I will burn them out by using. Do they have current protection internally- no need of a fuse?
Is there a move generally to move to domestic DC current? I was never really comfortable with 220v we use here, although we have circuit breakers.
This is interesting:
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Most modern adapters (the "light" type) are current limited because they have a high frequency transformer with electronic drive (they are called SMPS - Switched Mode Power Supplies); older adapters (the "heavy" type) have a simple 50/60 Hz transformer followed by a rectifier and a capacitor, they just become hotter and hotter if overloaded. Some have a thermal fuse that will trip before reaching dangerous temperatures. This kind of obsolete power supply is banned in EU for new sales, you may only find it on vintage devices. Laptop adapters usually don't have backflow protection. If you put a big reservoir capacitor directly on the power connections of the chip amp board (as recomended by some sources), be sure to add a backflow protection diode between the power supply and the chip amp. A 10A skottky diode or a P-Mos connected as diode is enough.
Backflow protection - well thanks that's one to keep in mind.
I think this discussion needs to be moved to 'power supplies' since the subject matter applies to all power supplies.
Using a internal but enclosed power supply something I have already done - on a computer. It is like replacing a power supply on a computer, which I have done. So the risk factor is really not that great, after all. The PS will be attached to the metal enclosure, or possible a non-metal enclosure, in which case the chance of shock is greatly reduced.
Using an external AC/DC adapter is not strictly necessary to lower the risk of shock, it seems, in any case one could use a separate power supply enclosure.
Parts Express these for sale.
Locally available as well.
I think this discussion needs to be moved to 'power supplies' since the subject matter applies to all power supplies.
Using a internal but enclosed power supply something I have already done - on a computer. It is like replacing a power supply on a computer, which I have done. So the risk factor is really not that great, after all. The PS will be attached to the metal enclosure, or possible a non-metal enclosure, in which case the chance of shock is greatly reduced.
Using an external AC/DC adapter is not strictly necessary to lower the risk of shock, it seems, in any case one could use a separate power supply enclosure.
Parts Express these for sale.
Locally available as well.
It will depend on your amps Voltage and amperage requirements. Do not over volt! as for amperage, more than it needs is ok, It's only going to draw the amperage it requires. As to voltage, if it is under powered it will not perform as intended or worse, if it is over powered voltage wise it will go POOF! and you will have more work to do. I would purchase the required PSU from a supplier. Call them tell them what you want to power and I'm sure they will recommend something for you with the proper plug/adapter included.
You could pay $$$ for a new adapter, plus customs fees and possible theft at the port. If you import it yourself from the far east you are likely to get the most counterfeit of trash, whoever pays google the most.
By contrast printer, race car, appliance charger and computer accessory systems go to the trash all the time here and the supply becomes redundant. I buy the wall transformer supplies at charity resale shops for $1-# all the time. The 3 amp 32 v ones from copier/printer/fax machines are getting up in to the 100 W category, and vendors HP, Xerox Lexmark don't buy much trash even if it came from the same country.
The hard part is designing a system that works without a center tap. See the LM3886 datasheet about makeing a fake ground for the signal etc. The same technique should work on a LM1875 or equivalent.
If you're going to buy new and risk getting through customs, I'd get a transformer with a center tap or a two winding toroid. Some of them have the extra +- 15 winding for op amps etc. And there used to be a guy in HK under vendor forums that had an attractive SMPS at 50 to 500 W with the extra op amp vollage for not much. Some people really had nice things to say about him. Name began with a C - I don't see his forum under vendor forums anymore.
By contrast printer, race car, appliance charger and computer accessory systems go to the trash all the time here and the supply becomes redundant. I buy the wall transformer supplies at charity resale shops for $1-# all the time. The 3 amp 32 v ones from copier/printer/fax machines are getting up in to the 100 W category, and vendors HP, Xerox Lexmark don't buy much trash even if it came from the same country.
The hard part is designing a system that works without a center tap. See the LM3886 datasheet about makeing a fake ground for the signal etc. The same technique should work on a LM1875 or equivalent.
If you're going to buy new and risk getting through customs, I'd get a transformer with a center tap or a two winding toroid. Some of them have the extra +- 15 winding for op amps etc. And there used to be a guy in HK under vendor forums that had an attractive SMPS at 50 to 500 W with the extra op amp vollage for not much. Some people really had nice things to say about him. Name began with a C - I don't see his forum under vendor forums anymore.
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