Build Your Own Clone Message Board

I quite often build power supplies and my friend asked me why you couldn't use a switchmode power supply for a guitar pedal
first off if you have a buffered bypass pedal (the best kind - but I won't go into that) a switchmode can potentially interfere with the switching circuitry especially when it is CMOS based - some of those tricky pedals use a clunky switch but actually switch with a CD4011 IC because people have complained that the pedal sounded bad, not knowing it was the buffer that gave it some of the boost power.

anyway the way a switchmode power supply works is by basically switching power on and off - this passes through an inductance/capacitor setup which stores the power on the off time which is in the order of nano seconds. so why can't you use this with a pedal?
well switching problems aside, you can do, in fact MARKBASS provided their (very expensive) filter pedal with one however it suffered a hell of alot from noise issues because essentially a switchmode power supply is an oscillator controlling the on and off times of transistor which uses an op-amp and sense resistor/divider to set the voltage which doesn't translate that well when plugged into a high gain amplifier and they did this because switchmodes are cheaper and they assumed the only bassists would use the pedal with no distortion which in my opinion is poor product design and bad forward thinking.

Battery's - no noise issues you'd think, you're wrong haha - Batteries do actually give out noise because electrons move otherwise power doesn't go anywhere so there is noise and I will show you a scope image of that noise however if you want to test for yourself set your DMM to AC and attach your probes to a battery and you'll see a few milivolts of noise as the display goes up and down a bit

so I hope you battery users do your bit for the environment and start using a Linear PSU to power that pedal board because there are no advantages to using batteries over Linear supplies and of course stay away from switchmode supplies with your pedals. here are scope pictures of each type of supply...

How can I (easily) tell which type I've got? Just look for fluctuations on my mm?

Those spikes are evil nasty ho's

if the box looks too small to house a transformer or doesn't weigh very much then it will be a switchmode, however it's quite rare to get a switchmode with a pedal which is why I was quite shocked (pardon the pun) to find one with the MARKBASS

Visual Sound appears to have been successful with the 1 Spot, which from reading RG's posts on other forums, is an SMPS. I don't own one, so I haven't disassembled to verify type or scoped the output of one. Can you give some details on your test setup, like current load, scope point, etc? Judging by the irregularity of the noise, I'd be suspicious that it's a failed PSU, but having read experienced tech's troubles with repairing SMPSs, I don't think repairing would be high on my list.

can't that noise be (mostly) filtered out by caps?

it's a 1 amp constant current dummy load (set at the switchmodes highest current rating before voltage drop occurs) I made - I posted a layout to it on this site.
it is set at 200mV/2.5nS divisions which is normal function for switchmodes - the scope has a pause/record and magnify function so it looks worse than it is, the point is more about there is greater noise and it really comes through on analog type electronics especially plugged into high gain amps. I sorted the noise out by making myself a new power supply for it in which I went a bit mental with regulators - I had a 317 outputting 24 volts to a 12v regulator with filter caps in between and so on

the noise on the battery picture is also very amplified but it is just to show you the noise because people never believe that batteries are noisy.

@captain p. there's a risk of oscillation if you use too much capacitance so I doubt it would have been viable and I think MARKBASS were using off the shelf asian market SMPS to cut costs