9v supply for 'pedals'

[Brian Roth]

I vote for this concept!  Total ground iso so oddBALL stompboxes don't screw up the entire system.  Linear regulators so that a bunch of switching regs won't introduce hash, and beat against themselves.

Bri

This sounds like what you are looking for:

http://geofex.com/article_folders/oldspyder/oldspyder.htm

The referenced transformer is still available for $25 from Weber: https://www.tedweber.com/wpdlxfmr-2

It gives you eight 11VAC secondaries each rated at 300mA, which means you can put a simple rectifier and and 9V regulator on each output, and have eight isolated 9V regulated outputs.

 

[Matador]

Datasheet mentions the possibility to connect in parallels for more current or in series for more voltage.

Indeed...on closer inspection, there's also a 9VAC @2A rail that could probably be coerced into a 9V supply, provided a low dropout regulator was used.

The other side benefit of this transformer-per-output approach is that the outputs can be stacked for 18v supplies, or split with a shared 'ground' for symmetric supplies.

 

[Bo Deadly]

The switching supply clocks are not synchronized to each other so they will create beat frequencies, when two almost identical switching frequencies interfere...

That's not my experience. My channel strip supply uses two identical MeanWell LPC-35-1050 30V SMPS and I never saw any "beat frequencies".

 

[abbey road d enfer]

That's not my experience. My channel strip supply uses two identical MeanWell LPC-35-1050 30V SMPS and I never saw any "beat frequencies".

My 500 Lunchbox uses 5 smps, all free running and I never heard or saw any sign of them beat frequencies; I must say I have extra CLC filtering.
However, many wall warts are not as quiet. A few years ago, I tested about 6 or 7 9V wall warts, only two or three did not create interference. And they all had issues when powering the Line 6 Echo Park with another pedal.

 

[Gus]

You can often use one supply for many pedals.

I would use a 18VDC and 9VDC supply and try it. 

 

[JohnRoberts]

I believe it is possible to design floating 9V supplies that could be used positive ground or negative ground without interacting. To support different grounding would require a +/- 12V supply, that the 9V regulated floats within.

BUT..... I will wait for the OP to report actual problems when trying to operate multiple pedals from single supply. 

Don't fix it if it ain't broke.

JR

 

[abbey road d enfer]

I believe it is possible to design floating 9V supplies that could be used positive ground or negative ground without interacting. To support different grounding would require a +/- 12V supply, that the 9V regulated floats within.

It could probably be done with a THAT1646. Interesting lab curio; however, with a good dose of marketing BS and the infinite gullibility of many guitar players, it could sell.

 

[dp]

I'm with PRR on this one... I would use this and be done with it...

https://truetone.com/cs12/

I actually do use it to power my pedalboard. It has boatloads of current available, everything is isolated and you can choose  different voltage options easily.

But of course, designing and building your own is fun too!  8)

 

[Matador]

How can it advertise galvanic isolation for every output with a single power transformer?  They could use a flyback design with optical feedback, but that thing has a dozen outputs and I can't tell from the interior shots if there are that many flyback transformers.

 

[Bo Deadly]

I see one PT and what looks like two SMPS transformers. Each could have multiple secondary windings. Not sure about feedback but that does give each out galv. isolation.

 

[untune]

Hi everyone,

Thanks again for the contributions - looks like things could be potentially more complex than envisioned.

Just to clarify here the setup a little bit in case anyone has picked up halfway through; so technically I'm not powering 'stompboxes' in the traditional sense. Imagine if you will that you took a bunch of your pedals, took the guts out of each, eliminated the footswitch and just had the bare circuit with an in and out jack.  You put all those circuits in a box, then you can patch them together from outs to ins in whichever way you wish. Now this box is going to sit between a sampler and a mixing desk, with up to eight separate signals running through any number of those circuits between the line outs and mixer ins.

The ones I've built so far as mentioned are very simple boosters and fuzzes - tiny circuits with (I expect) very little current draw.  I plan to make a few blenders and buffer/inverters to correct polarity etc but the general idea is that this will be modular, much like a Eurorack system, so I can add new little circuits as I go along and try news ones out.

I have a 9v bog standard Boss wall-wart style adapter that I can experiment with first -  essentially just running the output of the adapter to a bus board of linked 2 pin headers in place of separate DC jacks.  I imagine this will be the most basic option I could go with and it has been suggested a couple of times.  From there I can hook up each individual circuit to the supply and test them to see how they interact in terms of noise.

My reasoning was that because these circuits would be interacting slightly differently than they might in a traditional guitar pedalboard situation, and using multiple signals rather than one, they might need a bit more isolation to prevent any noise or hum issues creeping in.

But yes, for now I'll start simple - test a single daisy chained/busboard type supply and if I have problems, I'll look into the other options.

Interesting discussion though, thanks for everything so far

 

[abbey road d enfer]

  From there I can hook up each individual circuit to the supply and test them to see how they interact in terms of noise.

Interaction is essentially a matter of power supply decoupling, ground stiffness and capacitive coupling.
You want to have proper rail decoupling, with a capacitor of large enough value (that depends on the current draw, typically 1-10uF per mA), low value isolation resistors ( calculated to introduce minimal voltage drop), a very stifff "ground" bus (since you have multiple access, hierarchical ground is not practical), of course the PSU should be of adequate capacity, as for capacitive coupling, you should provide adequate distance between circuits that carry different signals.

 

[JohnRoberts]

Power Supply interaction should be easier to manage that way...

You could still get some interactions depending upon what you patch in where, but you will figure that out.

Guitar pedals typically expect single ended, relatively high impedance sources (like a guitar pickup). Patching in low z line level sources should be easier, but if you are only sending line level to the EFX maybe consider active differential inputs to improve signal/ground integrity.

JR