Improving Wall Warts - power supplies for audio

[Oldpinkman]

I have a "live" need to improve a power supply, and an interest in the subject. This stands a chance of being nearly at my level for electronics. Alan's Firebottle MC amp arrived with a noise issue. That has now been dealt with by changing the gain stage and moving my Pip transformer away from intereference - but only on battery. The modified wall wart Alan supplied, and the unit I have been using with my headphone amp, both leave very audible (if now much lower level) noise. I am sure Alan can fix it, but I am keen to learn, and it would be nice to send it up to Ali with a working power pack solution. Where do we start? Can I build a separate filter stage rather than take a hacksaw to the existing case?:scratch:

The boy Jones and his missus are coming for the weekend, but I'll get the evil eye from Sue if I spend too much time on "boys" talk, and my priority is a cremated Pip 2.:(

[YNWaN]

The noise issues you mention are probably due to the fact that most 'wall-wart' power supplies are not earthed -or, if they are, they do not offer a mains earth to the equipment they power.

[Firebottle]

..... rather than take a hacksaw to the existing case?:scratch:
(

Best not to take a hacksaw to the case, they can be split open with a little skill. I did use quite a lot of superglue so I wouldn't advise that either because there is no room left inside as I have already added an extra filter stage.
Switch modes are notoriously noisy, apart from the noise at the switching frequency you do get some 100Hz modulation on the output as well.

The supply in question is more than adequate when used in MM mode, but due to the higher gain in MC mode the noise on the input power lead is induced into the front end.
I have wondered if fitting a screened power input lead will have much effect, I'm yet to try it.

The simplest way forward is to use a low noise linear supply.

:cool: Alan

[Arkless Electronics]

It is unfortunately becoming more difficult to get linear wall warts of late :steam:

It's easy to filter out the remaining hum from a linear one.... If you can obtain a suitable linear one then that is the way to go. 12V is still one of the easiest voltages to get hold of but I'm guessing you will need a couple of amps or so output.

A quick Google search has revealed that these are now very difficult to get hold of! It would have been easy only 5 years ago...

About the best/cheapest/most suitable option I can find is Maplins XM20W at £30.

[Oldpinkman]

Great. Thanks Jez. The current SMPS is rated at 2 amps so safest to have that. There seems to be a lot of "casual" product labelling out there with devices priced and appearing like SMPS being described as "linear". And much as a linear PSU sounds a fun project, I MUST focus on the dayjob. :rolleyes:

[Arkless Electronics]

Great. Thanks Jez. The current SMPS is rated at 2 amps so safest to have that. There seems to be a lot of "casual" product labelling out there with devices priced and appearing like SMPS being described as "linear". And much as a linear PSU sounds a fun project, I MUST focus on the dayjob. :rolleyes:

Indeed.....

The Maplins PSU is 3 A so more than enough there and will be regulated. Ideal for the job! Just a pity that linear wall warts are getting so difficult to find.... just a few years back a suitable one could have been bought for about £8.... rather than £30 for the admittedly much better unit from maplins...

[DSJR]

Richard, your recent 'new best friend by the same first name' also makes a MC phono preamp. maybe you should be trying that one instead?

[Oldpinkman]

Richard, your recent 'new best friend by the same first name' also makes a MC phono preamp. maybe you should be trying that one instead?

Nope. You've lost me. Can't work out who you are referring to. However, I am trying Alans amp for him because he asked me to, not because I am looking for a new preamp. I am more of a "Gordon" really - happy to have stuff I enjoy and not on a quest for the absolute best. And I have an astonishingly good preamp at the moment, which I can't imagine I will better without a serious wallet emptying. But I'd like to make sure Alan's amp leaves my hands in as good a state as possible, having had a chance to compare it against sensible alternatives.

As for best friends and MC phono amps - I'm happy with the old one, and looking forward to seeing him on Saturday for a few bevvies and night out listening to a live band :cool:

[Gordon Steadman]

. I am more of a "Gordon" really - happy to have stuff I enjoy and not on a quest for the absolute best.

And what makes you think that I don't think I already have that??

As always, there are two ways of looking at this. I have heard wallet crunching systems that I hated and cheapies that made music. After over 50 years of listening to reproduced music, I reckon my system is the best - for me:ner:

Ah, that's only one way of looking at it. That's OK, I have the franchise on always being right.:cool: (talking of which, I have just remembered a nice can of Draft is in the fridge - or is it draught?)

[Oldpinkman]

I don't you numpty. That's why I said "I am a Gordon". Happy with what I've got - because it is the best (for me)

Boy you're hard work. You have obviously lost your influence with your mate Alan. The Kent branch of Firebottle labs will be at it again shortly...:ner:

[Gordon Steadman]

I don't you numpty. That's why I said "I am a Gordon". Happy with what I've got - because it is the best (for me)

Boy you're hard work. You have obviously lost your influence with your mate Alan. The Kent branch of Firebottle labs will be at it again shortly...:ner:


Yeah but then, Alan is a nice bloke.

I practice being hard work, its good for the soul apparently.