Power supply test

Grolschevik

There was a discussion a while back about the merits of various power supply units, and mention of the Maplins Power Block came up. I've since acquired one, and thought you all might be interested in how it fared.

First of all, it's heavy, with a hard wired mains lead, and it's about twice the size of the Dunlop DC Brick. I've never tried the DC Brick, but I A/B/C'ed the Power Block with a standard Boss PSA (with daisy chain) and with batteries on a chain of a few of my pedals. For the analogue chorus and digital delay, there was no noise difference between the Boss unit, the Maplins unit or batteries. This changed when I added a distortion pedal.

Powered by the Maplins unit, the distortion pedal had significantly more noise than with the Boss PSA. Interestingly, it seemed to me that there was no noise difference whatsoever between battery powered distortion and Boss powered distortion.

So, the upshot is, the Maplin unit seems ok, until you use it to power (at least my) distortion pedal. It's batteries or Boss PSA for that pedal...

Don1

The buzzing is due to the fact that cheaper AC/DC adapters only reverse one half of the sine wave to give a reasonable DC flow. It ends up looking like a mountain range basically. It buzzes as the voltage output is going from 0 to 9 and back around 100 times a second. The distortion magnifies the hell out of this.
A battery will give a clean (the cleanest if you can afford them) constant 9V ouput. Hence no buzz. The Boss PSA-240a gives almost perfect 9V out also by adding an icke capacitor to smooth out the peaks and troughs on the sine wave. It charges when the votage is rising up to around 9 and discharges when it starts dropping and this carries the output over until the voltage reutrns to start chrarging again. (if you see what I mean)

In short the PSA-240 and other similar units win hands down over budget items although I can't understand why that wee capacitor costs so much!

Thomas_S_Hunterson

Don1 wrote:

In short the PSA-240 and other similar units win hands down over budget items although I can't understand why that wee capacitor costs so much!

It's thwe transformers that are the expensive components, the capacitors are realtively cheap. As you move into higher output transformers, the cost rises sharply. Also the more expensice supplies will have voltage regulation circuits as well as the capacitors, and these all add to the cost unfortunately

Eoin Madsen

Even the cheapest adaptors have filtering capacitors after the rectifier, a DC circuit wouldn't really function without it. The difference is that more expensive adaptors will also have voltage regulators. The cost is really down to the additional unit assembly time, as even the semiconductor in a regulating circuit has a pretty low value.

Afaik, the filtering on most PSUs will struggle as you near the current capacity of it.

There is no "Maplins unit" - they do about 20-30 different PSUs, some regulated, some unregulated, some switched-mode, some with universal primaries, lots of different secondary voltages, some fixed voltage, some multi-voltage, and with current capacities ranging from 200 milliamps to 6 amps.

Grolschevik

Eoin Madsen wrote:

There is no "Maplins unit" - they do about 20-30 different PSUs, some regulated, some unregulated, some switched-mode, some with universal primaries, lots of different secondary voltages, some fixed voltage, some multi-voltage, and with current capacities ranging from 200 milliamps to 6 amps.

I meant the one pictured here:

Johnny Storm

With all due respect, Grolshevik, all those double adaptors look like something I saw on the Simpsons onetime, just before it burst info flames

PS apart from my contribution, this has been a very informative thread.

Eoin Madsen

Grolschevik wrote:

I meant the one pictured here:

Link it on the Maplin website.

Grolschevik

Eoin Madsen wrote:

Link it on the Maplin website.

I tried to, but couldn't find it on Maplin.co.uk. It was there a few weeks ago, though, but I can't remember the technical stuff: think it puts out about 400mA. I'll have another look...


Edit: just found this: http://www.maplin.co.uk/Free_UK_Delivery/Power_Bank_31292.htm

The unit doesn't appear to be listed where you'd expect it on their site, certainly not where it was a few weeks ago (under "music accessories"). I found this page using Google.

Grolschevik

Johnny Storm wrote:

With all due respect, Grolshevik, all those double adaptors look like something I saw on the Simpsons onetime, just before it burst info flames
QUOTE]

I agree, but it's not my board. It was just the first pic of the power supply unit I could find...