Godlyke power-all: extra power supply filtering

[scaesic]

I use the godlyke powerall switched mode supply daisy chained to power multiple pedals. I got to wondering about how necesary it was to put power supply filtering in every single pedal i use, instead, couldnt i just add a simple box at the end of the powerall and before the daisy chain with this sort of circuit inside.

                                        100ohm
              + -------¬---------|__|--------------------------¬---------
                           |                        |                              |
                           __   1000uF       |                              |
Godlyke  >           __                  __                             __              > Daisy chain
                             |                    __  2000uF               __  0.1uF
                             |                     |                               |
                             |                     |                               |
                - -------------------------------------------------------------

I'm not sure if this would a concern as the output of it should be loaded by several effects pedals, probably +8. Would an op-amp buffer be a viable solution?

[R.G.]

There are a few other considerations that you should make.

The powerall is probably a switching power supply, and as such has regulation and filtering inside. Adding a lump of filtering at the power supply won't add all that much to it, as it's already pretty good at low frequencies. It may cause stability problems with the regulation, although most modern regulators are pretty good about that these days.

In addition, the pedals will still have several feet of wire between them and the power supply. The inductance of these leads is significant at high frequencies, so filtering at the power supply won't help.

The circuit you show won't work. The ??100uF?? 1000uF?? cap in series at the input blocks the DC you're trying to get to your pedals. They won't be powered at all.

Finally, unless you are remounting your pedals in one huge enclosure so the power supply is the only way to power them, what happens if you decide to remove a pedal with no filtering in it and power it some other way? It now has no internal filtering, and so it's going to have all those no-internal-filtering problems pedals used to have.

It's a matter of choice. I tend to do belt-and-suspenders. I try to make each pedal as durable to external forces as possible, so I would put filtering into each pedal. But that's only my opinion.

[scaesic]

the first cap was meant to be in parallel, drawing schems using fonts can be frustrating :s

it's meant as a sort of smoothing cap before the lpf, i hadn't thought about long leads being a problem for the power supply, i'd only connected that with signal leads for some reason. ohwell, thanks anyway!

[Mark Hammer]

I think that's a badly drawn (oh, the limitations of the ASCII set!!! ) 100R resistor, with the goal of making a 100R/2000uf LPF.  That may or may not achieve the objectives, but it *should* provide power to something.

I'm wondering about the issue of buzz when powering several digital pedals from something like that.  I still have a problem trying to run two of my Tone Cores off the same supply.

[scaesic]

yeah that was supposed to be a 100 ohm resistor

that's a good point though, the instruction manual for the godlyke does mention that you shouldnt run more than one tonecore in the daisy chain. It's not too much of a problem for me, i don't run any digital type pedals, apart from digital delay...

[R.G.]

Gotcha.
Yes, as redrawn, the 1000uF cap and series 100R resistor will provide power OK. That then gets it down to the following issues:

1. Voltage drop in the 100R resistor.
2. What happens if you move a pedal off to another power supply?
3. Possible - although unlikely - stability problems on the power supply.
4. Is it any real benefit?

It won't hurt, other than the voltage drop on the 100R. Have you thought about changing that 100R to an inductor rated for about 1A? That would be much preferable to the resistor, and much better filtering.

As a matter of personal choice, I would still put some filtering in my pedals for reason #2.

I'm wondering about the issue of buzz when powering several digital pedals from something like that.  I still have a problem trying to run two of my Tone Cores off the same supply.

It may or may not help. The Tone Cores especially have problems with external power supplies. It appears that the Tone Cores have some kind of internal switching power supply that interacts with some external power supplies to cause buzz, whine, and hum problems. Not all of them do, but some. It can be a problem. I suspect that they're pulling pulses of current out of the power supply at ultrasonic rates, and have insufficient filtering to suppress these down to the DC level as seen by the power supply.

When any two switching devices run from the same power supply there is a potential for the difference of the two rates to be heard in the audio unless the devices are carefully thought out. Is your power supply a simple linear regulator or a switching type? It would be interesting to know if two Tone Cores interact with themselves on a simple linear power supply, not just a switching one. That would be a real problem in the TC design.

I ... think... that you could use an CLC pi filter on each Tone Core to suppress their pulse demands and keep them quiet. But I haven't tried that out, as I don't have access to two TC's. If I did, I'd design the filter as a plug in to go on the back of the TC, have a zillion of them made, get rich selling them to TC owners, get TC to buy me out, retire to the Carribean, [slap]

... oh, OK. Thanks, Cartwright. I needed that.   

[scaesic]

Gotcha.
Yes, as redrawn, the 1000uF cap and series 100R resistor will provide power OK. That then gets it down to the following issues:

1. Voltage drop in the 100R resistor.
2. What happens if you move a pedal off to another power supply?
3. Possible - although unlikely - stability problems on the power supply.
4. Is it any real benefit?

It won't hurt, other than the voltage drop on the 100R. Have you thought about changing that 100R to an inductor rated for about 1A? That would be much preferable to the resistor, and much better filtering.

The reason i chose the resistor to be 100 was because of the voltage drop. I thought the benefit would be that the power supply would be much cleaner with some extra filtering and it also meant lesser comonents needed for my particular board.

2. What happens if you move a pedal off to another power supply?

I understand this but i don't expect i'd ever be using it without my power supply on my effects board as it's for personal use, either that or battery, where filtering isn't a concern. i get where you're  coming from though, it's just a case of component parts vs. rigged design.

What's this buisness of using a 1A inductor? do you mean like a pi section filter?

[scaesic]

Is your power supply a simple linear regulator or a switching type? It would be interesting to know if two Tone Cores interact with themselves on a simple linear power supply, not just a switching one. That would be a real problem in the TC design.

he says it's the same one as mine, so it's switching.

[R.G.]

What's this buisness of using a 1A inductor? do you mean like a pi section filter?

Yes. Making a pi section filter from ceramic or film caps and a series inductor would cut the RF parts of the spectrum a lot. Electrolytics, especially bigger value electros, have poorer characteristics at above-audio frequencies because their parasitic series inductance keeps them from bypassing.

he says it's the same one as mine, so it's switching.

Oh. Duh.

I understood that to mean "I still have a problem trying to run two of my Tone Cores off  a single power supply of unspecified nature." instead of "I still have a problem trying to run two of my Tone Cores off a Godlyke power supply just like yours."

It's this pesky English I can't understand. Numbers I get OK.   8-)

[scaesic]

Electrolytics, especially bigger value electros, have poorer characteristics at above-audio frequencies because their parasitic series inductance keeps them from bypassing.

thats why there's a smaller cap in parralell with the large one in the lpf, big electro sets the roll off freq, and smaller ceramic catches the highs whilst increasing the overall capacitance further. The first capacitor before the rc filter is used to smooth out any ripples or large spikes. It was really to clean up the power supply, i hadn't taken into acount interference picked up on the wire.

I understood that to mean "I still have a problem trying to run two of my Tone Cores off  a single power supply of unspecified nature." instead of "I still have a problem trying to run two of my Tone Cores off a Godlyke power supply just like yours."

oh yeah! you could be right there! looks like neither of us understand english.

[Mark Hammer]

English is easy.  Numbers are easy.  Women?  Now THAT's hard.

[scaesic]

some women are easy too!

[scaesic]

some women are easy too!

*note* i had to try really really hard not to make a "your mum" joke there to avoid insulting anyone*