EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: matb on June 19, 2024, 09:44:33 am
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Hi I thought I would ask my dumb questions in the beginner section.
I never worked with battery powered devices.
I play guitar and bass gigs in France (~15 ish gigs per year no rockstar here) and I have 2 pedalbords (1 for bass 1 for guitar).
The guitar one doesn't have a dedicated power supply just multiple wall warts, so that's where my noise comes from I guess.
I sometimes play on really crappy earth wiring and also micro cuts.
Internet wise people recommand isolated power supplies (which I think means isolated from the AC powergrid ?)
My idea would be to make a 9v UPS of a couple watts (don't know how much we are not speaking kW here) in hope that noise wise there would be none.
The box would always be powered from some kind of wallwart and I'm hoping the noise coming in from the wallwart would disappear after the battery circuit.
What do you guys think ? Does it exists, am I day dreaming ?
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What about a decent size 12V lead acid battery and regulate it down to 9V? Complete isolation from the mains so no earth loops.
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Yes, that should work fine with a Linear LDO 9V Regulator, or use 3~4 LiON 18650 cells and a LDO.
Best,
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Might be worth while double checking the polarity of the signal earth on your pedals ,most connect signal earth to the battery -v,however there is the occasional odd ball that do something different that can end up with quietness or smoke when the 2 get joined to the same power supply
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There are two very different types of noise. The white noise hiss will always be present and will vary based on how much pre gain distortion you include and how many pedals are in your chain. You have probably found out and understand that part. Now, the A.C. line noise and interference from SMPS powered devices and the old triac dimmer packs as well as V.F.D. drives for fans and compressors in the venues where you play. That has been a difficult issue to solve since instruments became electrified. If you want to go with battery power from a single source that would be do-able but two things should be considered. First, make sure all of your FX pedals use D.C. and that the negative is also bonded to the common 'sleeve' 1/4" connections of each pedal!! If the pedals are internally wired differently like a floating +/- 4.5 volts with your power negative return not bonded to the chassis there could be a problem trying to use a single 9v supply. You could use a single 12 volt 7.2 amp hour gelcell. These are very common and very cheap. Use a single power switch in the +12 supply and decide if you may want to use a single 7809 linear regulator per FX pedal. Since most of those pedals only draw 50 milliamps the efficiency loss using linear regulators won't be horrible and will be the most noise free solution. Be aware that those huge multi-function pedals like the BOSS guitar pedal use more like 1 amp and may be 12 volt or even A.C. input. Another possibly simpler solution is to plug all of the wall wart inputs to a single cord and supply that cord through a small isolation transformer. Probably something in the 150 V.A. to 250 V.A. range would be more than enough. We often use isolation transformers to eliminate ground loop hum. I have several in my sound equipment trailer and they do get used!!
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My suggestion of the 7809 regulator may be flawed as there may not be enough voltage 'headroom' to maintain regulation as the battery voltage drops. I don't have a part number at hand but you will need a 'Low Drop Out' LDO version of a 7809 or an LDO who's output voltage can be adjusted with a pair of resistors.
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Thanks for the replies appreciate it.
I looking for something portable which for me 12v batteries are not.
I'm not looking for a battery powered pedalboard just to smooth out incoming noise created by the AC line.
Maybe an isolated power supply is the best solution ? To be clear I'm not looking for a 200€ solution to get no noise or something. Just wondering if a cheap solution could be found that no manufacturer want to do as it's cool to sell 250€ isolated power supplies. https://www.thomann.de/gb/harley_benton_powerplant_iso_2_pro.htm?shp=eyJjb3VudHJ5IjoiZ2IiLCJjdXJyZW5jeSI6NCwibGFuZ3VhZ2UiOjJ9&reload=1 (https://www.thomann.de/gb/harley_benton_powerplant_iso_2_pro.htm?shp=eyJjb3VudHJ5IjoiZ2IiLCJjdXJyZW5jeSI6NCwibGFuZ3VhZ2UiOjJ9&reload=1) Regarding this one they are not all isolated only 3 → 8 are ?
I guess my question would be could I use for example a 12V DC wallwart and just build a board that regulates the voltage using an LDO to 9V ? This is a mystery to me :-//
@CaptDon what is a "small isolation transformer" do you have a link
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A cheap switching power supply giving of 12V is generally isolated from the mains with the use of a small transformer. Most of them are not even grounded on the primary side, let alone on the secondary side.
The problem with these supplies is the switching noise that needs to be filtered, and for that a simple linear regulator and a couple of capacitors will do the trick.
See the "Practical Example for Regulator Circuits" on this page (https://circuitdigest.com/electronic-circuits/voltage-regulators).
An extra bigger capacitor before and after the regulator gives a bit more stability, but don't remove the small ones, because they prevent oscillations.
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Just wondering if a cheap solution could be found that no manufacturer want to do
To be honest,by the time youve made something road and roadie proof the price of that thoman offering or even the more expensive fuel tank starts looking pretty reasonable
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Isolated supplies are for preventing ground loops - not just with external equipment, but also between pedals themselves - the ground of the guitar signal is also the ground of the power. This is of course not an issue running on batteries since each pedal only has one ground connection to its neighbour - via the patch leads - but when they're all powered from the same power supply, theres two grounds - power and signal, its the difference in these two that can cause ground loops, hum, and also some pedals produce noise on the power lines which is then shared by all the other pedals.
The "noiseless" part mostly comes from that, but also with fairly clean linear supplies. Some pedals don't really mind noise on the power lines (digital delays, flangers etc..), where-as others will just amplify any noise there (transistor based high gain distortions etc..). Batteries are what are considered the cleanest but of course are a hassle.
I would just get one of those power supplies with multiple isolated 9V outputs. Most can easily provide 100mA per channel with an extra 500mA one for larger pedals (strymon digital stuff, or even multifx) and these are all isolated from each other, and generally low noise - I believe they all have a LC filter and linear regulator per channel.
Forgot the portable part. Most of these isolated supplies run off 12V from a wall plug PSU - you can use a Portable lithium 12V supply for this - even though these can be somewhat noisy I doubt the noise from that will make it through the internal converters each channels linear regulator/filter. Note, this won't be particularly efficient - these pedal power boards aren't made for efficiency since they're mains powered, but a largish lithium 12V power pack should last a few hours at least unless you're running rackmount stuff or multiple multieffects unit (which no-one does).
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You can, as suggested by others, a mutiport supply run off a 12V LA will work great as long as you carry a charger about.
Big LA and Li batteries come with a fire risk of you short them out or damage them.
They'll happily melt your wiring and your pedal under adverse conditions.
If you dont want to buy power pack off the shelf, build your own.
Fully isolated outputs are a good idea. Some pedals are split supply and others can catch you out with a +Ve ground.
I'd go for 230v 50Hz and isolated linear regulators. I'd use split bobbin pcb transformers for lower CM noise and better insulation.
Triad PC Mount Split Pack look like a vfm choice. The two separate secondaries can be used to create a pair of fully isolated outputs.
Add jellybean bridge rectifiers a few LEDs, smoothing caps and LM317 regulators. Say $5 per channel + pcb+ case and fused IEC mains filter.
Filter the incomming mains. I prefer Schurter or Shaffner filtered IEC input blocks.
Use a metal box, mains ground it but don't connect to isolated DC grounds