anyone ever look at power supply voltages with a scope

[lcipher3]

So I've been messing around measuring the effects of load on various 9V power supplies I have. Most are switching mode power supplies but I've looked at the old school transformer ones too.

Looking at the voltage with a scope is interesting to see the switching artifacts. The BEST by far is the BOSS power supplies. Very smooth.
What do you think of some of the images below? Seems like spikes are common - seems like a problem, maybe not for digital that have their own regulation inside? Comments?

The one on the left is what I typically see for various SMPS - 9V 12V etc. The Boss seems to have added some way to filter pretty well.
Various pedal board power supplies can look like either depending on the port and manufacturer. I have not looked at enough variety to know if this is typical (the noise). Would be interested in hearing similar tests or experiences?

 

[lcipher3]

Would really be interested to see what the "1 SPOT" (original) looks like. It looks like the generic SMPS but I know they can be made very quiet. I have a random "DVE" 12V power supply that I think is for a network switch and it's as flat and smooth as the boss. Most look like the TRIO type power supply spikes.

 

[vigilante398]

Are these measurements taken with a pedal connected? SMPS often have very different output characteristics depending on the load on the output. I'm now curious enough to measure a couple of my supplies with and without a pedal connected.

 

[GAStan]

Try putting a filter cap on to see the effect. 10u to 100u should be good. Electrolytic between v+ and ground.

 

[lcipher3]

Are these measurements taken with a pedal connected? SMPS often have very different output characteristics depending on the load on the output. I'm now curious enough to measure a couple of my supplies with and without a pedal connected.

They're with a resistive load. Doesn't change the spikes any. I have a test switch box to go from 0 to 100mA, 200mA etc resistive load.
Changing load affects the volts (more / less depending on the supply) but the switch pulse stays pretty much the same.

 

[lcipher3]

Try putting a filter cap on to see the effect. 10u to 100u should be good. Electrolytic between v+ and ground.

Wont work on these high freq spikes (I tried). There are articles that discuss SMPS but its not easy. I dont know what BOSS and DVE are doing but they're a lot better. The spikes get past a linear regulator too if I put a LM7809 after a 12V SMPS with spikes.

If you use a RC *filter* that might work but you're going to take a drop across the resistor etc.

 

[lcipher3]

Seems like there are "good" supplies - I imagine a lot of the pedal board power supplies as switching. This is a DVE power supply 12V into an LM2596 to get 9V - actually better than the $40 BOSS supply.

*typo on the first plot should be DVE and 9V regulation (actually set to 9.3)

 

[GAStan]

If you use a RC *filter* that might work but you're going to take a drop across the resistor etc.

For tube amp pwr supplies an LC filter typically is used, have you tried an inductor in conjunction with a cap? For 60hz ripple 3-4mH coil with ~100uF cap before coil and 20-30uF after.

Or perhaps a ferrite bead for the HF noise in the last two pics posted?

 

[KreoPensas]

I put an LC filter on a lot of things that prove touchy about switching power. Cap, coil, cap, coil, cap, tuned as needed.

I've built 4 amp 24v linear power supplies because some 100 watt class D projects never behaved with any SMPS and any attempts to filter.

 

[lcipher3]

I put an LC filter on a lot of things that prove touchy about switching power. Cap, coil, cap, coil, cap, tuned as needed.

That's what a lot of the app notes imply. You can do LC but then you potentially have a tuned oscillator dependent on loads.
But like my last post shows - they can be made pretty smooth. Or not. Depends on what was asked for by the PS designer I guess.

Linear are much more straight forward. But when you get to high current you're into heatsinks, lots of size, waste etc. For low current linear is prob the way to go.

The higher current stuff (usually digital) pretty much stuck with SMPS. I just haven't found any real info on what the pedal power supply guys do for design in terms of "smoothness". Like I said - if anyone has a 1SPOT and a scope I'd love to see the output.

From what I'm seeing - the BOSS claim to "use only their power supply" may have some merit. I suspect most of the cheap "9V 2A" power supplies you can buy are pretty darn noisy (not to mention bad on 9V regulation vs load). Does it matter? who knows....

 

[schoeps]

Have you tested a Cioks power supply?

 

[andrewsrea]

IMHO, the artifacts of a decent regulated and filtered supply, rarely present themselves as audible noise floor. I could see a logical argument for it affecting linearity of amplification of an effect (clarity and evenness), which would be quite overcome by a boost or dirt pedal.
I build my own analog regulated supplies and only use the (+) sends, with exception of one pedal (typically a power-hungry digital pedal) with the plus and return, thus using the signal ground to avoid eddy currents.

 

[lcipher3]

Have you tested a Cioks power supply?

Don't have one.

Have an old Vitoos DC8 supposed clone. Powered by a 12V 2A SMPS (with spikes) that it feeds two 1000mA (isolated from each other) which both use a LM2956 to get the 9V. Then there are 5x300mA non isolated (regulated). The 1000mA ports are "clean" the 300mA pass the noise from the wall wart. Using a "clean" 12v supply cleans up the 300mA (the 1000mA are already clean).

I suspect a lot of power supplies are like this - with the "wall wart" type SMPS feeding the pedal for filtering and/or regulation etc.

 

[vigilante398]

I have a Cioks and a OneSpot, and an oscilloscope, just not free time Maybe I'll remember to pull it out in the next day or so and take some curiosity measurements.

 

[lcipher3]

I have a Cioks and a OneSpot, and an oscilloscope, just not free time Maybe I'll remember to pull it out in the next day or so and take some curiosity measurements.

Which Cioks do you have? DC7? Would REALLY REALLY be interested in what that looks like. Thinking about getting one.

 

[KreoPensas]

I have a DC7 and a DC4 but not scope that takes pretty screen shots

 

[lcipher3]

I have a DC7 and a DC4 but not scope that takes pretty screen shots

how do you like your DC7? Expensive -but worth it? ... I have a lot of 200 series Boss pedals a GT1000core and hate all the separate power power supplies.

 

[vigilante398]

how do you like your DC7? Expensive -but worth it? ... I have a lot of 200 series Boss pedals a GT1000core and hate all the separate power power supplies.

I have a DC7 and a DC4. Tube pedals are my main thing and they take a ton of current, which many "brick-style" supplies can't handle. Cioks delivers a ton of current (660mA @9V per output) and it's low noise and reliable. And all that while still being slim and sexy so I can mount it under my board. So absolutely worth it for me.

I don't sleep much on weekends, I'll try to remember to grab some scope pics tonight or tomorrow. I know I still have a 1Spot somewhere, I'll try to find it as well.

 

[KreoPensas]

I *think* they were worth the money. I know there are some serious quality components in those bricks.

For the most part, if a device came with a power supply, I'll use it unless it proves to be garbage ( looking at you TC E )
Edit: Digitech Whammy 4th gen is one of the few pedals that works better on it's own supply than it does on the Cioks. Too thirsty, I reckon.
Boss IR-200 was the only 200 series I bought that came with a power supply.

I would like to see if the scope detects any difference under load using the DC4's USB input power function.

 

[KreoPensas]

The Eurorack "community" has a lot of info to share about SMPS vs linear. Low cost options use SMPS and attempt to silence it, but the vast majority avoid SMPS completely to avoid misery. I would say that analog synthesizer circuits are as touchy as high gain tube circuits.
I use a Hammond 187E12 and linear regulators for every 3-4 amps of power I need. That transformer would make one hell of a pedal board power supply.