Its me with the power supply again

[MmmPedals]

I built the PS from tonepad. I wired the 2 lugs from a dc jack to the 2 12v ac pads on the board. I plugged in a 9v Panasonic adapter (I know it call for 12v but the 9v adapter reads 12-14v) into my noisiest pedal, a mosfet booster witch hums obnoxiously loud when powered from a wall wart and it was still really loud. only a very minor improvement. i tried a few more wall warts and i got the same result until i got to a Sony adapter. This was the only one of 5 or 6 that made any real improvement. Only small problem is the sony wall wart only measures 11V and drops to 8.8v or so after the lm317. PS the Sony adapter without the filtering was also LOUD.
What could make one power supply work with the filtering and others not?
Is there any way i can improve the filtering to work with the other wall warts?

[JKowalski]

You need 2-3 volts drop across the LM317 (from input to output) to make it do anything. Even though your pedal adapters read 12-14v, they are not good enough for a 9V output because you'll find that they drop down to 8-10 volts when you put a load on them.

Also, different wall warts have different amounts of filtering already. And I am confused - are you plugging in DC wall warts or ac wall warts? If you plug in a DC wall wart you should bypass the rectifier diodes. They would work with the DC like that but would put diodes in series with the power line.

Also remember that diodes give a voltage drop so you need to consider that when you are trying to get 2-3 volts higher then the output of the LM317 on the input.

[joethugs]

why not try the huminator by Dano

http://www.beavisaudio.com/Projects/Huminator/index.htm



think it would solve the filtering problem for your wall wart power supply...

[MmmPedals]

HMMMMMMMMMMMMMMMMMMMMMMMMMM
I HATE the hum
I perfed the bevis filtering. The filtering on the tonepad PS is MUCH better.... But not good enough
I just wanna run my mosfet booster on wall power without hum 

[joethugs]

you sure it's not from the guitar? check your guitar cable.. or try isolating your effects..

[petemoore]

  Joethugs approach...eliminate this/that. Find where noise happens.
  put battery as comparator to eliminate possibility of AC input from supply.
  If 'pure DC' [battery] helps...
  Get a supply Wall Wart with DC= *2v+ what you want for your supply voltage, use a *regulator and filtering. Your DC is now 'solid' ripple free.
  *Regulators generally require 2v 'xtra' before they start operating.

[MmmPedals]

You need 2-3 volts drop across the LM317 (from input to output) to make it do anything. Even though your pedal adapters read 12-14v, they are not good enough for a 9V output because you'll find that they drop down to 8-10 volts when you put a load on them.

Right on. I realized this after i tried it.

And I am confused - are you plugging in DC wall warts or ac wall warts? If you plug in a DC wall wart you should bypass the rectifier diodes. They would work with the DC like that but would put diodes in series with the power line.

Doh (smacks his hand to his forehead unusually hard) So, i should connect the DC wall wart to after the diodes or get an ac wall wart, correct?

[petemoore]

  Read power supplies for effects at GEO.
  AC and DC...not to be mixed up !
  DC for effects power, is used to amplify AC input from Guitar.
  AC, 120v wall current, can be converted to DC for various applications incl. amplifiers, the alternative is batteries.
  AC is 'signal' if it's withing human hearing range, which includes 60hz [sometimes unfortunately called humbuzz], or input from guitar.
  The circuit has audio inputs at the power supply as well as the 'input'.
  Ripple free DC [ah] has no AC riding on it, if it was only perfect or easy to make close to perfect, amplifiers would be so much easier to manage.
  Anyway, I didn't see mention of anything I could follow, or reference to schematic, or reference to FWR [in relation to AC] or other except 'diodes' and connecting 'stuff'. Not being in the schem-guessing mood, warning against applying AC to a DC circuit is all I know for sure, other than specifying clearly [to what?] in relation to 'connect to'.
 
 
 

[JKowalski]

And I am confused - are you plugging in DC wall warts or ac wall warts? If you plug in a DC wall wart you should bypass the rectifier diodes. They would work with the DC like that but would put diodes in series with the power line.

Doh (smacks his hand to his forehead unusually hard) So, i should connect the DC wall wart to after the diodes or get an ac wall wart, correct?

Yeah, exactly. The diodes are arranged in a "full wave rectifier" configuration, usually easily spotted by the 4-diode diamond shape layout. When you put an AC signal into this rectifier, it "flips" the negative going peaks of the AC signal around to make them positive too. Take a look at this simulation to see how the diodes block current and end up with the positive only output in the end. The AC source pushes current one way then the other way, but the diodes make sure that current "push" goes to the same side of the load each time, and always leaves a way for it to return to the source.

If you imagine a DC voltage added to the AC inputs, you can trace how this would work. The current would go through the right upper diode, through the load, and back through the bottom left diode. (or the opposite diodes if you hook it up upside down) It's like the AC signal except it never flips and only two of the diodes are ever conducting. So it works, but you now have two diodes in your DC voltage path, giving voltage drops.

If you just hook up the DC voltage after the rectifier diode, it would work perfectly (unless you have too little voltage for the regulator LM317). The filtering capacitor after the rectifier diodes is less important then, but leave it since it might help a bad wall wart that may have too little filtering by design. The rectifier diodes can be left in as well since they can't conduct with the voltage hooked up across them like that.

But you might as well hook up a AC wall wart since thats what the circuit was designed for 

[amptramp]

If you want to be able to predict what you are going to get from a power supply, use the download on this page:

http://www.duncanamps.com/psud2/index.html

It gives you a spice simulation of a power supply that you design.  You have to supply the ESR value for the capacitors, but that can be estimated.

[JKowalski]

That looks like it is focused on tube amps, though - unregulated supplies. This one is well regulated, and the filter capacitor value is not critical since the low voltage implies a wide range of inexpensive usable caps. Thanks for pointing it out though, I might use it in the future.

Besides, he already has it built  

[MmmPedals]

AH the sweet sound of silence. I was considering my next move, was thinking of just ordering an AC wall wart when it hit me. A while bought i bought a computer bag for a few bucks as a pedal board bag. It came with a PS for a laptop, AC of course. Dug it up and it was 16V (center positive but it dosent matter) hooked it up, adjusted the trim pot for 9.5v and BINGO.
Thanks all for the help

[JKowalski]

It came with a PS for a laptop, AC of course.

You mean DC? Laptop power supplies are always offline SMPS (no mains transformer) and produce DC output.

Some SMPS (switch mode power supply) units are very noisy at high frequency and may induce a high pitch whine into the signal path, so if you get problems there then you'll know. However, a properly designed SMPS with good filtering is overall much better then a linear power supply (mains transformer like a wall wart) because it is more effecient/less wasteful, much smaller, and much lighter. Some people say never use a SMPS for audio but that's just a "stereotypical" view (I.E. saying all of them are bad since one gives you problems).

[MmmPedals]

Yeah im an idiot, its DC. I got confused because it was in a drawer with some hard drive PS which are AC. Anyway it works great. I did get that squeal when i was testing one of my pedals. i thought it was oscillation from the pedal since i had it pretty loud. Just turned it down a bit and it went away.

[petemoore]

  Audio circuits require DC.
 IF ac adaptor is required, the first thing it sees is probably a FWR, which is then filtered to make DC for the audio circuit.
 AC applied to a DC circuit generally results in heat/poof/smoke.

[MmmPedals]

  Audio circuits require DC.
  IF ac adaptor is required, the first thing it sees is probably a FWR, which is then filtered to make DC for the audio circuit.
  AC applied to a DC circuit generally results in heat/poof/smoke.

Take a look at the project. the diodes convert it to DC so i need an AC wall wart.