Wall warts!....the fewer the better it seems

[Barry]

The most common arrangement in the non switch-mode variety is a thermal fuse embedded in the transformer winding. It is indeed rare to find any sort of user replaceable fuse but then again it's also pretty unlikely that the thermal fuse will go unless there is a genuine problem. They are at least cheap if they do have to be replaced.....

Thanks for that Jez.

I was puzzled as they all sport the "C E" mark (not that that means much)! The charger for my camera battery is so small (about 1.5 x the size of the battery itself), there doesn't seem room for a transformer?

On a completely different tack - what do you know about the safety of those air freshners that plug into the mains? It seems odd that the heater element is only protected by the 30A fuse or circuit breaker of the ring main.

[Arkless Electronics]

Your camera charger will be a smpsu.

I can't comment on the air fresheners as I have never seen one apart from the adverts for them!

Thanks for that Jez.

I was puzzled as they as sport the "C E" mark (not that that means much)! The charger for my camera battery is so small (about 1.5 x the size of the battery itself), there doesn't seem room for a transformer?

On a completely different tack - what do you know about the safety of those air freshners that plug into the mains? It seems odd that the heater element is only protected by the 30A fuse or circuit breaker of the ring main.

[bobbasrah]

Heater element cannot draw any high current and will blow itself like a fuse, much the same as a very low power light bulb blows a filament rather than the fuse. The bulb cannot blow the fuse, only a wiring short does that....

[Barry]

Heater element cannot draw any high current and will blow itself like a fuse, much the same as a very low power light bulb blows a filament rather than the fuse. The bulb cannot blow the fuse, only a wiring short does that....

I can assure you when an incandescent light bulb blows, it can often cause the circuit breaker to trip.

[Mark Grant]

There is nothing specifically wrong with wall warts as such. They are just a transformer, rectifier and smoothing cap in a plug top encapsulation. Often these days of course they are also just as likely to be a fairly crude switch mode PSU (smpsu), which has its own problems due to switching noise (at supersonic frequency usually).

I cant think of any new device that has a transformer in the wall wart, as far as I am aware everything is switch mode now, even 'high end' hi-fi brands include a switch mode wall wart.

Most likely to comply with the less than 1 watt standby requirements. ( as well as being lower cost and light weight to ship in quantity)

http://en.wikipedia.org/wiki/One_Watt_Initiative

[Arkless Electronics]

I cant think of any new device that has a transformer in the wall wart, as far as I am aware everything is switch mode now, even 'high end' hi-fi brands include a switch mode wall wart.

Most likely to comply with the less than 1 watt standby requirements. ( as well as being lower cost and light weight to ship in quantity)

http://en.wikipedia.org/wiki/One_Watt_Initiative

There's plenty Switch modes are becoming more and more widely used though of course... A few weeks back I was trying to source an unusually high output wall wart which was definitely fairly easy to obtain five years ago and in this particular output it was now only available in switch mode.

[StanleyB]

Switch mode power supplies can be made to produce an acceptable level of audio quality performance without costing a lot. I had designed for me a relatively low noise 12V SMPS for use with my DACs. I use it in two DACs that don't have any muting relays to hide the noise that an SMPS can inject into the power rails. But you can't hear any SMPS noise coming from the RAC/PHONO sockets.

[Arkless Electronics]

Switch mode power supplies can be made to produce an acceptable level of audio quality performance without costing a lot. I had designed for me a relatively low noise 12V SMPS for use with my DACs. I use it in two DACs that don't have any muting relays to hide the noise that an SMPS can inject into the power rails. But you can't hear any SMPS noise coming from the RAC/PHONO sockets.

Indeed yes this is sometimes the case. The noise from smpsu's is generally at supersonic frequencies and so well beyond human hearing anyway.... The thing is that this can cause issues at lower frequencies for a whole range of reasons. In some cases it won't of course. It all depends on the design of the equipment being powered and the exact nature and level of the HF noise being generated by the SMPSU. Another problem that can occur is "mode switching" and instability in the control loop of SMPSU's which can in fact cause them to generate very audible noise! This is less of an issue these days though than it once was due to improved design and parts used in SMPSU's. It can limit the universality of the SMPSU though as it will often be triggered by things such as insufficient load on the SMPSU.... That issue aside though, as I mentioned earlier the noise can be filtered out and a linear regulator used after the filter = jobs a good 'un. This will increasingly have to be the way things are done in the future as conventional transformers become more expensive and hard to get.

As an aside, it is becoming more and more of a problem these days to obtain certain parts required in quality hifi which were common 10 years ago... the valves which were once predicted to become unobtainable are now readily available but some semiconductors which were designed for precision and low noise applications (in industry as well as hifi) are now very hard to find as they were never used in mass market gear anyway and most of the applications outside hifi have been replaced with digital or integrated options....