9v supply for 'pedals'

[untune]

Hi all,

Just pondering how best to approach this;  I have created something of a patchbay for a mixer, and I have a bunch of effects that are essentially very simple stompbox and guitar pedal circuits - single transistor boosters, blenders, fuzz etc

I have the capacity to have perhaps 10-20 of these circuits (I plan to build a few more complex ones alongside the simple stuff) so that I can patch and chain different effects and experiment with sounds.  They're generally standard 9v - some might be 18v for more headroom.  I've put a little 2 pin 9v/gnd header on each board so I can just plug it in.

I need a way to power these efficiently, keeping things clean and quiet as much as I can.  I'm thinking I either make a supply from scratch - something that will deliver 9v to each effect, and I could utilise charge pumps to step up to 18v for circuits that need it.  I'm thinking a very simple Eurorack-style busboard that I can feed from a single supply then distribute everything from there.

What I'm unsure about is how best to go about making something like that from scratch - whether things need to be 'isolated' or whether effctively daisy-chaining a bunch of circuits in such a way will be an issue.  My other option would be to go out and buy a pre-built guitar pedal psu and just gut and modify it to use my 2 pin board connectors instead of dc jacks.

How would people approach this?  Tons of pedal PSU schematics floating around but I don't really know what to look for.  I have enough stuff lying round in the bitsbox (loads of LM317Ts doing nothing) but it might just be reinventing the wheel.

Any advice appreciated!

Cheers

 

[JohnRoberts]

Not easily.... I suspect most pedals are not designed to connect together and run from common power source.

A possible source of trouble is a common audio ground (most pedals are tip-sleeve), and common power supply ground.

You will need to try them, and see how sensitive they are to being connected together. I expect some new pedals are better in that regard than old stuff that is probably simpler and didn't anticipate playing nice with others.

JR

 

[Bo Deadly]

The way I would do this is to get a bunch of these MeanWell SMPS which are ~$5 USD each:

These are small (37x24x15 mm) AC/DC switchers. You can "stack" these to make positive and negative voltages. Then use a common mode choke and cap to remove high frequency noise and then regulate down to the target voltage. Make two PCBs: one for the SMPS module, choke and cap and one for one or two regulators with solder jumps to configure for pos or neg. Then you can make all sorts of voltages (using separate regulator if desired) by just wiring things together differently (maybe make a 3rd PCB that is a simple wiring "bus" to assist with the wiring).

For example, you could use 3 IRM-03-12 and stack them to make -12V, +12V and +24V. Now you can regulate to -9V for germanium circuits, +-9V for op amp circuits (or get a 4th SMPS and do +-15V proper), +9V for most pedals and +18V if you need it.

 

[JohnRoberts]

I killed a bunch of brain cells trying to replace multiple wall warts last century but this seems easier (maybe).

I'll try to scribble something out after beer o'clock tonight (if I don't get distracted).

It seems to power a bunch of 9V DC pedals without ground interaction via a common power supply should be possible.

Imagine a floating 9V regulator, that takes it's 0V (ground cough) reference from whatever you connect it to. The top of this 9V regulator is fed through a current sense resistor that detects the positive current draw, and then sucks the exact same current from the low 0V side. 

You could probably manage the + side from a 12V supply, the minus side a bunch less voltage. If these pedals run from 9V batteries I ASSume they don't draw much current. Typical 9V batteries are around 240 mAH total.

As long as the + and - current is in balance there should be minimal interaction if multiple 0V reference nodes are connected together.

Maybe.....  8)

JR

 

[PRR]

> I suspect most pedals are not designed to connect together and run from common power source.

In the last 20 years, "most" are. This comes from products like One-Spot which is a good 9V supply and a daisy-chain power cord.

For more fun, most pedals wire the polarity *reverse* from most non-pedal 9V plugs.

Many pedals can play-nice on a shared supply, but some *won't*. There are other multi-pedal supplies with several or all outlets isolated.

IMHO, even as a DIY-head, this is one field better bought than built.

 

[CJ]

Get yourself a  12 volt gel cell motorcycle battery and build a charger which contains a transformer, a diode, and a resistor.

those effects sound better under battery power.  you can even add a "dead battery' circuit (some fuzz box stuff sounds better with a drained battery)  Fulltone has this feature on their pedal supply but it is big bucks.

of course leave the charger off while using the effects and that battery better have a fuse or else you could be in for a real tripped out experience of the non enjoyable kind. 

 

[abbey road d enfer]

> I suspect most pedals are not designed to connect together and run from common power source.

In the last 20 years, "most" are.

That's what I figured out too.

Many pedals can play-nice on a shared supply, but some *won't*.

In most cases, I've found that it's due to improper "stiffness" of the PSU. So far I've found only digital pedals suffer this. I had a Line6 Echo Park that refused to play with others, also a lousy Intellitouch wireless receiver. My current pedalboards run on single supplies; I had to eliminate a few candidates from the selection.

There are other multi-pedal supplies with several or all outlets isolated.

IMO, unless justified by the need for a different voltage or polarity, this should not be necessary. Non-compatibility between pedals is the result of a flawed conception.

 

[abbey road d enfer]

I have a bunch of effects that are essentially very simple stompbox and guitar pedal circuits - single transistor boosters, blenders, fuzz etc

As long as they are of the same polarity/voltage, they should work from a single supply. If not, there's a flaw.

  I could utilise charge pumps to step up to 18v for circuits that need it.

I used charge pumps to power wireless receivers that were of inverted polarity and different voltage. I was not sure about noise but it turned out to be a non-issue. 

whether things need to be 'isolated' or whether effctively daisy-chaining a bunch of circuits

IMO isolated PSU's are a palliative that does not solve the problem, just like lifting safety ground on an amp that buzzes. 

 

[untune]

Hi all,

Thanks to everyone who has weighed in on this! There's a lot of discussion and a lot of great ideas, and I may be leaning towards PRR's 'better bought than built' idea with this, as there are plenty of relatively affordable solutions for this that will do the same job; all I'd need to do is modify a few cables and maybe create some small boards with headers on.

Since they will all be using the same polarity 9v and are all analogue as opposed to digital, there should be no conflict.  The UK branch of Joyo audio is a five minute walk from me, they do a cheap multi output isolated supply for 60 quid with an 18v as well as a bunch of 9v and even a 12v - I reckon that would work and I could always re-use it for actual pedals if the need arises.

 

[JohnRoberts]

In my first post I suggested trying and see what happens.

I could ask an old friend who has his own pedal company, but I'm pretty sure his will work well with each other.

I did scribble up a very rough schemo for floating 9V regulators powered from common PS, but it doesn't make sense to invest more effort until we determine that there is an actual problem.

Might be different using old legacy pedals mixed in among the newer modern stuff...

JR 

 

[Matador]

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.

 

[JohnRoberts]

Back in the late 80s/early 90s I made an AMR/Peavey product to replace something like 6x 16VAC @ 1A wall warts with a single transformer.

It was expensive to make and didn't sell well... It filled a 1U rack space so I put lamps in it to light the face plates of other SKUs racked in below it.  People loved it, but not enough to buy them...  :

an 8x 11VAC at 300mA seems cheap... Is it UL?

JR

 

[Audio1Man]

What not to do is use multi switching supplies as they typically FREE RUN and the mix down beats will drive you nuts. Also note some pedals may have + or – common battery polarity.

Buy a BIG STOCK OF 9 volt batteries or PS that has many single floating outputs.
Duke

 

[Bo Deadly]

What not to do is use multi switching supplies as they typically FREE RUN and the mix down beats will drive you nuts.

What does "FREE RUN" and "mix down beats" mean?

 

[Matador]

an 8x 11VAC at 300mA seems cheap... Is it UL?

No idea - it's rated at 45VA, however seems sizable (difficult to fit in a 1U rack).  Most of the comments seems favorable.

It won't drive a pedal with high current requirements however.

 

[Matador]

These are another possibility: 2.5VA rated, 12.6VAC @200mA, one square inch of PCB space for each transformer:

https://www.mouser.com/datasheet/2/410/media-263435.pdf

Only $5 a piece.

 

[abbey road d enfer]

It won't drive a pedal with high current requirements however.

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

 

[abbey road d enfer]

Back in the late 80s/early 90s I made an AMR/Peavey product to replace something like 6x 16VAC @ 1A wall warts with a single transformer.

It makes sense perfectly since wall-wart powered products have different ways of managing grounding, but gtr pedals that use the Boss standard are compatible in terms of grounding/reference. The only remaining issue is conducted emissions; not an issue with all-analog products.

 

[moamps]

What does "FREE RUN"

not synced

and "mix down beats" mean?

You can hear the difference in oscillators frequencies as a beat.
http://hyperphysics.phy-astr.gsu.edu/hbase/Sound/beat.html

 

[JohnRoberts]

What does "FREE RUN" and "mix down beats" mean?

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

Old story but I was chasing down a LF (maybe 1Hz) rogue noise in a junior engineer's lab... It turned out to be a beat frequency from his computer terminal raster, beating against the computer terminal in the next office, inches away.... crazy LF because they were free running very close.

JR