Power supply for under 100€ with 10 true separate outs

[JeroMa]

Hey hey,

My first post on this forum so I'm stoked to see the reactions!

My goal is to build a power supply for my pedal board.
When building my pedal board I was on a limited budget and had te make a few compromises.
Offcourse, the power supply unit was one of them. I bought the cheapest one I could find (and somehow believed it would work) and voila: There is a lot of noise in my chain.

Now that I am ready to move on from the el-cheapo to a good-one, and I want the best. But sadly some of them cost over 300€! So I started looking at wat was inside them, and started doing a rough calc on TME.eu regarding the parts.

I truly believe I can significantly reduce my cost and go below a 100€ for a power supply like a Strymon or a Cioks.

The goal:
10 channels out
5 x 9v  0.5A  =  22.5W
3 x 9v  2.0A  =  54W
1 x 12v 0.4A? = 4.8W
1 x 18v 0.4A?  = 7.2W

Total power consumption: 88.5W
I will use a 7809 DC/DC convertor.
An external 230VAC to 24VDC convertor.

Some about me:
I have 2 kids, a fulltime job as an engineer, and a band to play in (so it might take me a while to build it). Apart from that I have some electronic experience, but not that much, we'll see how this goed 


So, who is in for the ride?

[antonis]

Hi & Welcome.. 

Could you plz elaborate this..??
3 x 9v  2.0A  =  36W

[JeroMa]

nice one! adjusted the original 

[antonis]

nice one! adjusted the original 

Well done.. 

Now, could you plz elaborate this..??
7809 DC/DC convertor.

[JeroMa]

What would you like to know?
It is a DC/DC convertor.
It is a voltage regulator, you have a input voltage range and a stable fixed out with a max power consumption.
check this datasheet: https://www.tme.eu/Document/d2fb08f5ab52ac9c7fa07aea3823d998/amsri-78-nz.pdf

[antonis]

 

A 7809 (without any prefix lettering) calls for ordinary voltage regulator..

P.S.1
Could you plz elaborate the need for using switching regulators..??

P.S.2
Late night here so a bit of gossip/lark is imperative..

[JeroMa]

Easy to implement, not too many other components needed, affordable.

As I underdstand from your reaction you do not think it is a good idea?
What is your suggestion? How would you do this?

[stallik]

Welcome.

I'm interested to know which 3 of your pedals consumes 9v @ 2A?

[GibsonGM]

Welcome.

I'm interested to know which 3 of your pedals consumes 9v @ 2A?

I think that one is called "The Transmitter", and contains a linear amplifier....      Welcome, JeroMa! 

[JeroMa]

which 3 of your pedals consumes 9v @ 2A?

Some pre amps and real tube distortion pedals tend to consume a lot.
Admitted, not 2A of current draw.

Try to compare it to your car. It probably can drive 220km/h.
If you would drive that fast all the time, it will not only shorten the lifespan of the car significantly, altough the car can drive that fast (and is 'build' to go that fast), the handling of it at those speeds will be pretty unpredictable and probably end in a fatal crash.

To have some overhead, I'll oversize the outputs.
But to think of it, it might be a bit too much 

[antonis]

As I underdstand from your reaction you do not think it is a good idea?
What is your suggestion? How would you do this?

I've nothing against switching regulators other than efficiency and noise.. 

Now, for 9V/500mA, 12V/400mA and 18V/400mA respective LMs (7809, 7812 & 7818) should be OK..
(although, a 7815 should be suggested between 24VDC and 7809 to share Vin - Vout / 0.5 power dissipation..)

For 9V/2A, LM350 (preferably TO-3) adjustable voltage regulator should also be OK..

[ElectricDruid]

https://www.tme.eu/Document/d2fb08f5ab52ac9c7fa07aea3823d998/amsri-78-nz.pdf

Welcome JeroMa!

That's an interesting device. Have you played with one? What does the output voltage look like? Is it noisy?

Some of the figures on the datasheet worry me a bit (50mV noise, 250mV output variation with 25% load transient) but without knowing what that's like in the real world, it's a bit hard to guess.

Personally, if I was going to use a switching converter, I'd probably use two, one for the higher voltage supplies (12V and 18V) and one for the lower voltage supplies (all the 9Vs) and then follow them with linear regulators. Using two different input voltages for the regulators would help to keep the heat down, since if you ran the lower voltage regulators from the higher supply, you have to burn the extra volts as heat.

[JeroMa]

Some of the figures on the datasheet worry me a bit (

Is this not something typically solved with a filter on the output? Also the switchin freq is far above the audible spectrum.
I was thinking in using one 78x for each out.
These figueres also justify my choise on not pushing the limit of the components. One of the reasons (see my car reference below) to my choise for 0.5A and 2A outputs.

I have not tested them yet, but will so on a breadboard before assembling.

What type of linear regulator do you have in mind? Why not use them directly? The ones I find, lack enough power.

I'll use an external tranformer to provide the 24V DV to feed the board.
something like:
https://www.tme.eu/be/nl/details/cld-9024-t2-e25/desktopadapters/cellevia-power/

P.S.1
Could you plz elaborate the need for using switching regulators..??

I am still curious on what solution you would find ideal, as in: the best.   
I was also thinking about a simple ringtranfo with separate secondaries and rectifiers + filter. any toughts on that?
Apart from that, how would you do it?

[Unlikekurt]

 Just to toss another couple pennies at this; how will this device provide isolated supplies?  ie: isn't this quite open to ground loops still and thus all sorts of associated noises?

[iainpunk]

Just to toss another couple pennies at this; how will this device provide isolated supplies?  ie: isn't this quite open to ground loops still and thus all sorts of associated noises?

i was just about to post this exact concern as well.
i big problem in daisy chain isn't the shared power rail, its the shared ground connection. i have seen people use pedal patch cables with one sided ground disconnect for use with daisy chains and non isolated power supply's

the expensive units use rectification straight after the mains in. they use high frequency DC switching for the use of smaller transformers, making it possible to make 10 parallel outs, without shared ground, in such a small form factor.

cheers, Iain

[ElectricDruid]

Some of the figures on the datasheet worry me a bit (

Is this not something typically solved with a filter on the output? Also the switchin freq is far above the audible spectrum.

Yes, you could probably add more filtering. But that's more parts, PCB area, and trouble for something that doesn't *have* to be there. Noise above the audio spectrum tends to show up as hiss in your circuit nonetheless. It's particularly bad with digital circuits in my experience. The digital processing might be noise free, but unless the voltages that run the ADC/DAC are spotless, the signal is full of noise - and there's no such thing as "above the audible spectrum" with a sampled system since higher frequency elements will simply alias back down to where you can hear them.

I was thinking in using one 78x for each out.
These figueres also justify my choise on not pushing the limit of the components. One of the reasons (see my car reference below) to my choise for 0.5A and 2A outputs.

Agree, not pushing the components too hard is usually a good idea.

What's the advantage that you see in using these switching regulators rather than "normal" ones?

What type of linear regulator do you have in mind? Why not use them directly? The ones I find, lack enough power.

These ones, the ones that that thing you found is claiming compatibility with:
https://www.mouser.com/datasheet/2/149/LM7812-461970.pdf
https://www.sparkfun.com/datasheets/Components/LM7805.pdf

These are 1A regulators, but there are 1.5A and 2A versions available as well. Note the noise figure given is 40uV - a big drop from mV!

I don't really see what benefit you get by using the switching regulators rather than the linear ones. Although the efficiency might be better and they probably stay cooler, the performance doesn't seem to be as good.

I'll use an external tranformer to provide the 24V DV to feed the board.
something like:
https://www.tme.eu/be/nl/details/cld-9024-t2-e25/desktopadapters/cellevia-power/

That's another switching power supply, not a transformer. It does the same job, of course, but describing it as a transformer is misleading.

You're going to be running one switching power supply into lots of little switching regulators. That sounds like a recipe for lots of noise to me. I'd swap the switching regulators for linear ones, and I'd have two separate power bricks providing the input (or find one with dual outputs) so that the 9V regulators don't have to run from 24V. They *can*, but they'll get hot doing it. They only need slightly more than 11V (the "dropout" voltage is 2V, so they need the output+2 volts at the input), so a 12V supply would be enough. Finding a dual output 12V/24V power brick shouldn't be too hard.

HTH,
Tom

[iainpunk]

What's the advantage that you see in using these switching regulators rather than "normal" ones?

higher efficiency and way less heat, the disadvantage is that ''stacking'' switching regulators might cause a bunch of problems, mainly noise and matching current peaks that kill chips. either a HUGE amount of overkill filtering should be applied or one of the regulator "layers" should be replaced by linear devices.

cheers, Iain