Is this power supply knackered?

Psean

I have been using a power supply from Mantech like this:

I soldered the correct jack on and changed the polarity and it's been working perfectly for a good few months now. I recently went to get another one like it for my girlfriend to use with her bass stuff and found out that it's been discontinued and replaced with what seems to be a near identical model. I bought it and attempted to do the same socket and polarity swap I'd done on mine. I've now resoldered the jack three times (and used two new jacks) but it keeps making a squealing/hissing noise when I plug it in - it reads the correct voltage and polarity on the multimeter and the pedals all power up but it makes quite a noise. A small loose piece of the coax did momentarily short the positive to ground when I forgot to unplug it after checking the polarity - could this have messed it up and be causing the noise? It still puts out 9v so I'm hoping there's a fix and I haven't buggered it up.

Thanks
Sean

psyx

I know what sound you're talking about. Ive seen it happen to a laptop charger. It worked fine except that it got very very hot and made that hissing sound. Eventually it just stopped working. So I think you will have to replace it sooner or later. Not sure what exactly is wrong with it though...

Psean

Damn >☹ I was hoping it wasn't something like that.

ezietsman

Psean wrote Damn >☹ I was hoping it wasn't something like that.

Is the supply itself making that noise, or do you hear it through the amp? Those switch-mode supplies don't provide clean dc, it has a significant ripple at something like 100kHz, but one of the subharmonics may manifest itself in the audible range as a hum/squeal/hiss/noise (I got explained this by my engineer friend). I have one just like it and it is noisy as all hell with my 18 watt (Which I run cranked, naturally). Better to get a regulated supply in the end.

Psean

The noise comes through the amp. I have an almost identical unit and it's dead quiet even when my amp's cranked so I was surprised when this one made so much noise.

exsanguinator

might be the noise suppressor is gone..
its a rectangular resin filled box with 2 wires on the ac side

Psean

Thanks, I'll have a look on the weekend and see if I can open it up. Any shock risks - caps storing charge and all that? Or does that happen on the 9v side?

Psean

So this is what's inside:

Which one would be the noise suppressor and how would I know if it's gone?

Psean

Bump

Anyone got any info? Thanks ?

Psean

I'm on a budget, so would something like this help for the time being?
http://www.beavisaudio.com/projects/Huminator/index.htm

AlanRatcliffe

I'd be extremely wary of using a faulty supply at all - It's not worth the risk. Too much chance of something going horribly wrong and taking pedals out.

Hopefully the bump will now be seen by someone with more electronic knowledge.

Psean

Thanks Alan. I think I'll wait. Hopefully someone will have an idea of what is actually wrong with it.

mtmattan

Hey dude,

As Alan says, rather suck it up and buy a new PSU.

Sounds like the electro caps may have blown.
They are responsible for the power supply filtering.
Doesn't look like its a SMPS (switched mode power supply) as u can see the transformer right there.

The other option would be to use the PSU for effects such as modulation effects which are less sensitive to the PSU compared to say drive pedals.

TomCat

That supply is a very basic switch-mode supply with no suppression......I'd avoid it and get a good old linear supply.

Psean

Thanks guys. Look like I'll have to replace it with something else then.

It is a budget PSU and I wasn't expecting wonders from it but the thing that's puzzling me is that I'm using a unit that seems to be pretty much identical and it works perfectly for the few pedals I have - this one is so noisy it's unusable :-\

peterleroux

Psean wrote Thanks guys. Look like I'll have to replace it with something else then.

It is a budget PSU and I wasn't expecting wonders from it but the thing that's puzzling me is that I'm using a unit that seems to be pretty much identical and it works perfectly for the few pedals I have - this one is so noisy it's unusable :-\

The hassle with these is that they're not built for low noise applications,so some of them might be quiet, but I'd be surprised if checking noise is part of the QC before they leave the factory. So you might get one that is dead quiet, through pure luck, and another that is really noisy, but they both function within the spec for a cheap power supply. Within reason, most digital equipment doesn't care how noisy it's power supply is, it's only once you start doing signal processing like analog audio and video that you notice these things.

Consider that the tolerance on some capacitors is twenty percent up or down from the alive written on the side and the variation between them becomes understandable

Psean

peterleroux wrote
Psean wrote Thanks guys. Look like I'll have to replace it with something else then.

It is a budget PSU and I wasn't expecting wonders from it but the thing that's puzzling me is that I'm using a unit that seems to be pretty much identical and it works perfectly for the few pedals I have - this one is so noisy it's unusable :-\
The hassle with these is that they're not built for low noise applications,so some of them might be quiet, but I'd be surprised if checking noise is part of the QC before they leave the factory. So you might get one that is dead quiet, through pure luck, and another that is really noisy, but they both function within the spec for a cheap power supply. Within reason, most digital equipment doesn't care how noisy it's power supply is, it's only once you start doing signal processing like analog audio and video that you notice these things.

Consider that the tolerance on some capacitors is twenty percent up or down from the alive written on the side and the variation between them becomes understandable

Yeah, I guess QC won't be great on these.
Guess I'll be getting something else some time then.

Thanks