Is 100 - 150mV peak-to-peak ripple acceptable for pedal power supplies?

[Chance92]

Hello everyone!
I am thinking about using four PCB mount AC-DC converters (Multicomp Pro MP-LD20-23B09R2) to provide four 9V 2.2A isolated output. However, according to the datasheet, these converters have a peak-to-peak ripple of 100mV typical and 150mV maximum. The datasheet does suggest using 1uF and 100uF at the output to filter the noise, but I am not sure how much improvement they will make. Is this something usable for powering guitar pedals?

Link for the converter: https://uk.farnell.com/multicomp-pro/mp-ld20-23b09r2/power-supply-ac-dc-9v-2-2a/dp/3584003

[iainpunk]

that really depends on the pedal using it. if its a Fuzz Face or something similar, you'll be deafened by the buzz, but a lot of digital pedals don't mind as long as its input power is higher than 6-ish volt

cheers

edit: 150mv, thats about as much as a guitar produces (its more complicated than that but its a good ballpark for the note sustain, the attack can be just over double that, but hotter pickups can get as loud as 1.4v on the sustain)
Edit 2 : nevemind, that's about half what a guitar produces, since its peak to peak instead of zero to peak

[Chance92]

that really depends on the pedal using it. if its a Fuzz Face or something similar, you'll be deafened by the buzz, but a lot of digital pedals don't mind as long as its input power is higher than 6-ish volt

Thanks for your reply. Yes I think I will be using this to power digital multi-effect most of the time, but I do want it to be able to power analogue pedals as well. Maybe I should try it out first. Do you know if there's any cheaper alternative of Fuzz Face?

[vigilante397]

150mV p-p is a little high in my opinion, but that's stated max, which means filtering can get it lower. You can always add more filtering to drop the ripple.

[antonis]

Typical and Maximun ripple voltage refer on Max current (2.2A here..)

Unless you DO need 2.2A, you don't have to worry about those values..

[Chance92]

150mV p-p is a little high in my opinion, but that's stated max, which means filtering can get it lower. You can always add more filtering to drop the ripple.

Thanks. I definitely need to add some filters. May I ask how much ripple is normally considered acceptable?

[antonis]

Not a plain answer available..

Better consider acceptable Ripple Rejection Ratio higher than 60dB..

P.S.
Just noticed 45A inrush current (for 230VAC) which might be an issue for PCB tracks..

[bushidov]

The only issue I've seen on those style of converters that bit me in the butt one time is the ramp up speed. Probably not going to matter with analog guitar effect pedals, and also not likely to be an issue with digital, but I had an issue with a GPS IC not getting its voltage "fast enough" so it locked up. I have to change over to a Murata one that had a faster ramp up speed, and then it worked. But that's wireless transmission for ya.

[Chance92]

Unless you DO need 2.2A, you don't have to worry about those values..

2.2A x 4 is probably too much isn't it . I probably need to dial it back a little bit.

[antonis]

IMHO, in conclusion, get 12V respective converter (1.67A though) and feed a 7809 voltage regulator (1.5A)

You can wire in parallel 2 voltage regulators for double the current or use a series pass transistor..
(for the later, you can even use 78L09 100mA regulator..)

[Chance92]

Better consider acceptable Ripple Rejection Ratio higher than 60dB..

Well that's a new term for me. I need to look it up.

Just noticed 45A inrush current (for 230VAC) which might be an issue for PCB tracks..

Thanks for the heads-up. I do have a 5D-9 NTC on the input side as suggested by the datasheet, but since I have four modules, I probably need to make sure it can handle that much current.

[Chance92]

IMHO, in conclusion, get 12V respective converter (1.67A though) and feed a 7809 voltage regulator (1.5A)

You can wire in parallel 2 voltage regulators for double the current or use a series pass transistor..
(for the later, you can even use 78L09 100mA regulator..)

Thanks for you advice. I was actually thinking about using a 12V or 15V converter together with a DC-DC converter like this (https://uk.farnell.com/xp-power/tr2024s09/dc-dc-converter-9v-2a/dp/3295738?ost=tr2024s09) because they seems to have smaller ripple (75mV p-p in this case). Are these essentially the same as 7809? Which one is better? By the way how can I reply to a specific member?

[Chance92]

but I had an issue with a GPS IC not getting its voltage "fast enough" so it locked up. I have to change over to a Murata one that had a faster ramp up speed, and then it worked. But that's wireless transmission for ya.

Thanks for sharing. I wonder if it is some sort of protection feature or just a design flaw.

[vigilante397]

Generally speaking linear regulators like the L7809 do great for keeping a nice low output. As for how much is acceptable, as was mentioned above there isn't a solid answer besides "it depends." When I designed power supplies for my day job I was told if anything is over 50mV p-p then it's too noisy, but that may be overkill for pedals. Aim as low as you can then plug it in and see if you can hear the noise

[antonis]

I was actually thinking about using a 12V or 15V converter together with a DC-DC converter like this (https://uk.farnell.com/xp-power/tr2024s09/dc-dc-converter-9v-2a/dp/3295738?ost=tr2024s09) because they seems to have smaller ripple (75mV p-p in this case).
1. Are these essentially the same as 7809?
2. Which one is better?
3. By the way how can I reply to a specific member?

1. Not at all..
They are DC-DC converters (switching regulators)..
IMHO, good for many applications but not for audio ones..
You also can see the 4 extra caps and 1 choke for EMI filter.. 
(linear regulators don't need them..)
2. See above..
3. Either by quoting him/her or via P.M.

[Chance92]

1. Not at all..
They are DC-DC converters (switching regulators)..
IMHO, good for many applications but not for audio ones..
You also can see the 4 extra caps and 1 choke for EMI filter.. 
(linear regulators don't need them..)

I was checking out the 7809 and it seems like a much better solution, but the application circuit confused me. I believe it requires two decoupling capacitors. As far as I know some pedals ground the negative. If I turn on the power supply, then plug in the pedal, I will be short-circuiting all the capacitors at once, right? is that suppose to happen?

[Rob Strand]

If you don't know what it takes to build mains powered products safety you shouldn't use mains powered devices. 
Use a Wall-Wart/Plug-Pack/Power-adaptor, it's much safer.

It's not really possible to tell if an adaptor will be noise free upfront.  You need to test it on a number of different types of pedals.

[Chance92]

If you don't know what it takes to build mains powered products safety you shouldn't use mains powered devices. 
Use a Wall-Wart/Plug-Pack/Power-adaptor, it's much safer.

It's not really possible to tell if an adaptor will be noise free upfront.  You need to test it on a number of different types of pedals.

Thanks for your advice Rob. Don't worry, everything is still on paper at the moment. I am just trying to find out the best way to do it. Using a wall-wart is definitely a safer option, and I am considering it as well. I will definitely get a certified person to take a look at the design before making it, and get it tested before plugging it into the wall.

[vigilante397]

I was checking out the 7809 and it seems like a much better solution, but the application circuit confused me. I believe it requires two decoupling capacitors. As far as I know some pedals ground the negative. If I turn on the power supply, then plug in the pedal, I will be short-circuiting all the capacitors at once, right? is that suppose to happen?

What do you mean shorting the capacitors? It's common practice for regulators to have both bulk and decoupling capacitors (depending on the level of filtering needed) on the input and the output, and on a single supply (+9V as opposed to ±9V) negative terminals of everything go to ground. I'm not sure I understand your question.

[Chance92]

What do you mean shorting the capacitors? It's common practice for regulators to have both bulk and decoupling capacitors (depending on the level of filtering needed) on the input and the output, and on a single supply (+9V as opposed to ±9V) negative terminals of everything go to ground. I'm not sure I understand your question.

Sorry for the stupid question. I don't know why I saw it that way yesterday. I guess I need to have a more regular sleep pattern now.