Electrically Quiet SMPSU Wall Warts

[dirkenstein]

Hi, I've been trying to find some aftermarket 9V DC and 15V DC SMPSU class II wall warts that have the following characteristics:

 

a) Are smaller and lighter than traditional magnetic linear regulated power supplies, can output 1-2A and support multi-voltage use.

 

b) Are electrically quiet enough to be used for guitar pedals and other high-gain audio applications. The Stontronics and other arbitrarily branded far eastern ones ones I've managed to buy from various online suppliers have all introduced a nasty 100Hz buzz. Linear PSUs used on the same pedals have been entirely silent.

 

c) Have good enough load regulation not to be suffer from voltage sag when subjected to the kind of current transients generated by mini amplifiers.

 

d) Are of reasonable build quality and standards compliant. Some very cheap and nasty eBay ones I bough a while back were actively dangerous in that the back cover could easily break off while unplugging them.

 

Do such devices even exist?

 

Any idea of alternative quality brands and sources? I'm willing to pay a reasonable amount extra for something that's both small and light and won't introduce buzz at high gains. If necessary, they can be class I devices with suitable filtering if that is the only way to achieve the buzz reduction.

[bigclive]

The biggest issue with the switchmode power supplies is that they usually don't use the earth connection, and apart from capacitive coupling across the windings, there's also a capacitor physically between the low and high voltage side for RF suppression reasons. On most of these unearthed supplies you can get a tingle from the output to earth, and that tingle, albeit at a very low current, is enough to cause audio issues.

 

Look for switchmode supplies that actually have an earth connection. Although that doesn't actually guarantee that it's used!

 

Here's Rapid Electronics PSU section:-

 

Rapid electronics PSUs.

 

The cheap ebay PSUs should be avoided like the plague. Their electrical regulation and isolation between the mains and low voltage side makes them totally unsuitable for any use let alone something you are handling like a guitar.

 

Does your equipment really use a lot of current? Maybe a traditional linear supply is a good option.

[dirkenstein]

The biggest issue with the switchmode power supplies is that they usually don't use the earth connection, and apart from capacitive coupling across the windings, there's also a capacitor physically between the low and high voltage side for RF suppression reasons. On most of these unearthed supplies you can get a tingle from the output to earth, and that tingle, albeit at a very low current, is enough to cause audio issues.

Interwinding capacitance plus suppression capacitor. I have been looking for a resonable explanation of why this happens, given that the secondary is galvanically isolated from the primary.

 

This is also why the problem often goes away when you separately earth the 0v secondary side of the PSU, but not always.

 

Probably going to stick to linear PSUs for now, as the extra-light replacements only make sense for a hand-carried gig bag.

I'll try a 3-pin SMPSU for the one thing that actually needs more than about 100mA or just get one of those dedicated multi-output pedalboard PSUs.

 

Now if only somebody made electrically quiet aftermarket laptop PSUs. What did I do with my special USB isolator again?