9 Volt power supply/battery replacement

[JohnX]

I looked all through this site for a post on this topic and did not find any. I am hoping that it’s OK to post this here.

I thought it might be handy to create a universal 9 V power supply for some of the guitar pedals that we have which are “battery only”.

Some pedals really eat batteries and it just gets annoying having to change them constantly. This theoretically would’ve solved that problem.

Here is what I tried:
I took a standard Boss 9 V power supply for stomp boxes & replaced the traditional center negative jack with a 9 volt battery terminal - polarity reversed so that the opposite terminals (of the battery terminals inside the pedal) would align correctly. (terrible diagram attached.)

Although I can get this simple hack to work with numerous other devices, when I try to use it on the actual guitar pedals, it powers the devices perfectly but I end up with some serious noise. Almost sounds like a nasty grounding buzz.

Yes, the polarity is correct. Please don’t ask.

I have tried this three times with two different power supplies and three different sets of battery terminals. Same result every time.

I found someone on Amazon (screenshot attached) selling a similar product and when I read the reviews, the responses from the guitar players indicated exactly the same results with stomp boxes. His design is better and easier.

Can anybody point me in the direction of what might be causing the excessive noise in the pedals? I am assuming that I must be overlooking something simple and counting on one of you to point it out immediately.
Thanks in advance

 

[ccaudle]

Batteries are relatively low noise, so if the pedals do not have power supply inputs they may not have as much power supply filtering as a pedal with a jack for use with an AC power supply might have. The first thing I would try is just solder a capacitor across the power connector. That will likely be too inconvenient for permanent use, but might let you see if that may be all that is needed.

 

[JohnX]

The first thing I would try is just solder a capacitor across the power connector.

thanks

when you say across the connector, are you suggesting to connect the red + and black - with a capacitor?
is there any random estimation of a capacitor value I should try?

 

[ccaudle]

are you suggesting to connect the red + and black - with a capacitor?

Exactly. Perhaps you could find a phyisical arrangement that would fit into a normal battery compartment, so maybe something to keep in mind when thinking about how to arrange the terminals during soldering (e.g. fit some shrink tube, some kind of physical support to prevent breaking the solder joints, etc.).

any random estimation of a capacitor value I should try?

I would just grab something you already have and see if it helps. I would start with 1uF and go up from there. Too large of a value might cause the power supply to have problems trying to start up (a capacitor with 0V charge will have a low impedance as the power supply tries to jump up to 9V right away, with the current determined by capacitance multiplied by the rise time of the power supply output as it goes from 0V up to 9V). Because of the large current spike at turn on I would not start with 1000uF, start small and work your way up to larger values, maybe 1uF, 10uF, 47uF, 100uF to see if there are noticeable improvements as you add capacitance. Maybe the problem is something else, but hopefully you find that a reasonable size cap is all you need to cut down the buzz.

 

[JohnRoberts]

Batteries are DC output so no AC ripple or hum. A battery powered stomp box is expecting a battery clean DC supply.

A cheap wall wart lump PS will likely have ripple if it is a DC supply (check that). If it is an AC supply you will need to add a rectifier too.

Adding capacitance should help. I would start with hundreds of uF. Be sure to observe proper polarity if using polar electrolytic cap.

JR

 

[usbdevice]

Could you tell us what pedals you are trying to power? And also what power supples (you mentioned 2) you are using? Boss has produced several different ones over the years.
The newer Boss PSA series adapters look like switched-mode power supplies and it could be excessive noise/ripple from a switched-mode power supply that is running below minimum load (I'm thinking of simple fuzzes with high gain and less than 1mA of current draw). I've experienced this first hand (not with a Boss power adapter though).

 

[Newmarket]

Questions:
Is s the psu you are using a regulated supply ?
Is the specified max current of the PSU sufficient for the specified current demand if the pedal(s) being powered.
In fact it should be comfortably above the specified current. I very recently had a pedal that wouldn't work properly with a supply specified at 500mA despite it's specified current demand being 500mA.
No surprise tbh given tolerances and likely higher current demand on power up (digital pedal). Run from a lab type power supply set to a higher current limit = work no problem.

 

[Tubetec]

I have a bunch of the old Boss linear regulated supplies I like to use ,
Multiple SMPS feeding devices on a pedal board is asking for trouble .

 

[PermO]

Get a linear regulated one, Electro Harmonix still sell these.

It could be this... I had this happen, when you don't put a sufficient load on a switchmode psu it can enter "hickup mode" and puts out a lot of hash...

I got myself a 1spot pro PSU to power all my pedals, can recommend that unit.

 

[Newmarket]

Harley Benton Junior is a good option for most analogue pedals. Make sure it's the Junior though as the non Junior has a common 0V.

 

[JohnX]

I would just grab something you already have and see if it helps.

Do you think something like the attached diagram would work?
As you can see, I have to reverse the polarity going to the battery terminal so that it will re-align when it connects to the battery terminal inside of the pedal.

NOTES TO OTHERS WHO HAVE REPLIED:
Since posting this question earlier, I have had the opportunity to do a little bit more testing.

The wall wart that I’m using is the newer stock BOSS power supply. PSA 500 mA. (screenshot attached) The one that is used on most of their pedals and is center negative. BOSS PSA adapter

If I test the “battery replacement rig” on other Boss pedals, it works fine.

I have a number of pedals - some battery only and some width power supply input. I plan to test this on quite a few more of them so that I will be able to give you a more accurate list of what works and what doesn’t. What I am seeing is inconsistent behavior. I am only testing this on devices which use 9 V batteries.

I have one of those small cigarette pack smoky amps. Very basic. It does not like the “battery replacement rig”. It made a horrible noise for about 15 seconds and then stopped working completely. We also have a beautiful cigar box amp which is 9V battery powered. The unit powers up and achieves exactly the same volume as it does with a 9 V battery in it, but the buzz is horrendous.

 

[JohnRoberts]

Keep in mind that trying to power multiple floor efx boxes from a single DC power supply can result in audio ground contamination and noise issues.

JR

 

[JohnX]

Keep in mind that trying to power multiple floor efx boxes from a single DC power supply can result in audio ground contamination and noise issues.

JR

Thanks so much. I haven’t had the opportunity to do the deep dive with all of the pedals yet, but I tried a few more last night and it seems to be about 50-50. Either it works perfectly, or it’s absolutely horrible.

So far, every BOSS pedal that I have tried has worked perfectly. Unfortunately, they all have power supply jacks so this is unnecessary. The 2 “battery only” amp boxes do not like this at all. I also tried it out with some digital Japanese toys/noisemakers. It worked great for those.

What I am seeing is that although this is a useful hack, it will not be usable in every scenario.

 

[Ike Zimbel]

Do you think something like the attached diagram would work?
As you can see, I have to reverse the polarity going to the battery terminal so that it will re-align when it connects to the battery terminal inside of the pedal.

NOTES TO OTHERS WHO HAVE REPLIED:
Since posting this question earlier, I have had the opportunity to do a little bit more testing.

The wall wart that I’m using is the newer stock BOSS power supply. PSA 500 mA. (screenshot attached) The one that is used on most of their pedals and is center negative. BOSS PSA adapter

If I test the “battery replacement rig” on other Boss pedals, it works fine.

I have a number of pedals - some battery only and some width power supply input. I plan to test this on quite a few more of them so that I will be able to give you a more accurate list of what works and what doesn’t. What I am seeing is inconsistent behavior. I am only testing this on devices which use 9 V batteries.

I have one of those small cigarette pack smoky amps. Very basic. It does not like the “battery replacement rig”. It made a horrible noise for about 15 seconds and then stopped working completely. We also have a beautiful cigar box amp which is 9V battery powered. The unit powers up and achieves exactly the same volume as it does with a 9 V battery in it, but the buzz is horrendous.

It would be really helpful if you could give us a better description of the noise. For example, if the "buzz" is 120Hz hum, that speaks to the problem being poor filtering in the wall-wart supply. That issue should benefit from adding capacitance, as mentioned in several earlier posts. If the noise is more like an actual buzz, or white noise etc., those point to different issues and different solutions.

 

[JohnX]

It would be really helpful if you could give us a better description of the noise.

I’ll try to record some of it for you, but it sounds like a nasty grounding buzz. Although there is some high frequency information, it’s more than likely just distorted harmonics coming through the speaker.

 

[ccaudle]

Although there is some high frequency information, it’s more than likely just distorted harmonics coming through the speaker.

Switching power supplies (like your Boss) have a lot of high frequency noise on the output, not just 120Hz and a few additional 60Hz (or 50 in other parts of the world) like linear supplies.

So far, every BOSS pedal that I have tried has worked perfectly. Unfortunately, they all have power supply jacks so this is unnecessary. The 2 “battery only” amp boxes do not like this at all.

I think that does continue to point to lack of power filtering in the battery-only pedals.
Take the Boss pedals apart and see what kind of filtering they have at the power input jack, that would give a really good starting point. My guess is a 100uF electrolytic cap, but might also include a ceramic cap, and/or an inductor, depending on how fastidious they were trying to be about cleaning up the input power.

 

[JohnRoberts]

Thanks so much. I haven’t had the opportunity to do the deep dive with all of the pedals yet, but I tried a few more last night and it seems to be about 50-50. Either it works perfectly, or it’s absolutely horrible.

So far, every BOSS pedal that I have tried has worked perfectly. Unfortunately, they all have power supply jacks so this is unnecessary. The 2 “battery only” amp boxes do not like this at all. I also tried it out with some digital Japanese toys/noisemakers. It worked great for those.

What I am seeing is that although this is a useful hack, it will not be usable in every scenario.

When designing for battery or single PS sources it is easier to keep signal grounds isolated and clean. When tying PS grounds together in SKUs that were not designed for that application stuff happens.

[TMI Old Peavey Story] Back last century when I designed a common power supply to replace a rat's nest of too many wall warts in back of (Peavey/AMR) equipment racks, to brute force the common power supply ground issue, I designed a big dog transformer with 6x1A output windings to perfectly replace 6 wall warts. It worked nicely, but was too expensive for the mass market to embrace. [/TMI]

Alternately there are possible ways to manage signal ground if such applications are anticipated (like Boss probably did for some of those pedals). Making multiple different pedals work together nicely after the fact may be more difficult than the effort is worth. Good luck.

JR

 

[scondon]

Which pedals doesn’t it work with? IIRC some PNP fuzz boxes (most germanium if I’m remembering right) need -9v and will not work by inverting a 9v supply.

 

[JohnX]

Which pedals doesn’t it work with?

We’ve probably got hundreds of pedals here. As I mentioned earlier, the BOSS pedals work fine. So did the electro harmonix & the Dunlops. The crybaby wah seemed OK but our digitech wah did not. There are a few boutique pedals that it also does not work on. The result is generally the same: Nasty buzz that is not unlike grounding issue. It completely blew the chip on my small smoky cigarette box amp almost immediately. I’ve got it working again, but I certainly won’t be trying this out on it.

I don’t think this thread needs to get too much deeper because what I’m finding is enough inconsistency between devices that I do not believe there will be a single solution that is going to create a 100% functional 9V battery substitute. It’s likely that some of these devices are intended to be “battery only”. As some have mentioned earlier, it’s a much cleaner, simpler circuit.

Even if adding a capacitor makes this work on certain models, more than likely it’s not going to make it work on all of them. It may make the most sense to chalk this up to being a limited use hack with an approximate 60% chance of usability.

 

[JohnRoberts]

We’ve probably got hundreds of pedals here. As I mentioned earlier, the BOSS pedals work fine. So did the electro harmonix & the Dunlops. The crybaby wah seemed OK but our digitech wah did not. There are a few boutique pedals that it also does not work on. The result is generally the same: Nasty buzz that is not unlike grounding issue. It completely blew the chip on my small smoky cigarette box amp almost immediately. I’ve got it working again, but I certainly won’t be trying this out on it.

I don’t think this thread needs to get too much deeper because what I’m finding is enough inconsistency between devices that I do not believe there will be a single solution that is going to create a 100% functional 9V battery substitute.

Last century I actually killed some brain cells thinking about a universal solution. I didn't find one that would be cheap enough for Peavey to sell profitably, but there is a way. Visualize a pair of high compliance current sources and perhaps terminate across them with a 9V zener (and maybe a cap) to deliver the desired supply voltage. For this to work in all conditions the current sources would probably need to support tens of volts above and/or below ground. I didn't bother to make a prototype since it seemed like a very high hurdle to work for all conditions.

I can imagine a simpler version working from say an only +15 to +20V rail, using a PNP power transistor to dump current out and an op amp using NF to vary the current drive. The 0V end of the 9V supply could have a build out resistor to prevent ground contamination.

This would be relatively simple for low current pedals... IIRC back last century when Peavey was messing with digital pedals they made some real battery killers (>100mA).

If you want to make a multiple output power supply each would need independent floating outputs, and separate control NF networks.

To repeat I never reduced this to a working design.

JR

It’s likely that some of these devices are intended to be “battery only”. As some have mentioned earlier, it’s a much cleaner, simpler circuit.

Even if adding a capacitor makes this work on certain models, more than likely it’s not going to make it work on all of them. It may make the most sense to chalk this up to being a limited use hack with an approximate 60% chance of usability.