FILTERING 9VDC

Frequently asked questions regarding powering your pedal.

FILTERING 9VDC

Postby StopDViolins » 21 Jan 2009, 17:37

I'm working on a BYO boost, and I'm trying to find out if there's any way I can filter the dc power jack for any noise that might originate from my wall warts. Any ideas?
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Re: FILTERING 9VDC

Postby moltenmetalburn » 21 Jan 2009, 18:07

you could try this minus the led, led resistor. built right in to the supply.

http://www.beavisaudio.com/Projects/Huminator/index.htm
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Re: FILTERING 9VDC

Postby Fuzzer » 21 Jan 2009, 18:54

The Freestompboxes Forum search function is soo great, use the search function..., the S E A R C H function.
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Re: FILTERING 9VDC

Postby moltenmetalburn » 21 Jan 2009, 20:03

can you please explain the advantage to the regulator?
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Re: FILTERING 9VDC

Postby Fuzzer » 21 Jan 2009, 21:44

Sure, in my experience, using a regulator with a nice filtering gets rid of any Supply noise you could get in pedals.

The simple reason is because those cheap Supplies (which dump noise in the circuit) are just rectified and then heavily filtered. But that doesn't get rid of all the ripple in the signal. Adding any extra filtering will be pretty insignificant for that scheme.

On the other hand, a linear voltage regulator keeps the voltage level steady even with changes in ts input; off course, they have some current limits, and if the input voltage gets too low, they will shut down, but for effects pedals, I think they are appropriate.

This is just my opinion, indeed, others might have some more refined solution.
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Re: FILTERING 9VDC

Postby moltenmetalburn » 22 Jan 2009, 16:21

Thanks!
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Re: FILTERING 9VDC

Postby earthtonesaudio » 22 Jan 2009, 17:35

"Normal" linear regulators are everywhere and cheap... but have some shortcomings. For 9V effects the biggest one is voltage drop. To get 9V regulated output, you might need 12 or more volts of unregulated input. If the pedal draws more current than the (unregulated) 9V wall wart is rated for, it's output voltage will decrease, making the external regulator basically unable to do it's job.

For pedals that don't draw much current (most pedals would fit in this category), you don't really have to worry about this.


Also you might want to check out "low dropout regulators" or switching regulators, both of which are typically more efficient.
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Re: FILTERING 9VDC

Postby Fuzzer » 22 Jan 2009, 20:42

hmm, in the homebrew world I think switching regulators are the last thing to look (for me), but thanks for the recommendations and additional info. :thumbsup
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Re: FILTERING 9VDC

Postby Entrant_21 » 25 Jan 2009, 17:49

my pedal power gave out (very gold garage at band practice wrecked something in the circuit) so im building a L200c voltage & current regulator based power supply using some parts from a cheap variable voltage 500mA unregulated wall wart. quick and easy :)
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Re: FILTERING 9VDC

Postby danlotano » 19 Sep 2014, 08:05

Hello, can someone explain me how to put a regulator in a layout (or maybe just one in front of the whole chain) to get rid of noises? I have the same problem on almost every distortion pedal I've built, but never had any one for modulation effects, like delays or envelope filters! Thank you! :)

P.S.: Hello everyone, this is my first post on FSB! :D
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Re: FILTERING 9VDC

Postby Nocentelli » 19 Sep 2014, 17:48

How many different dirt circuits? What layouts? Exactly the same amount of noise, or varying amounts but noticeably bad?

Any noise from the power supply will be massively amplified by high gain levels within fuzz/overdrive/distortion pedals, so is much more noticeable than with modulation fx that tend to just buffer the signal at unity gain, and then maybe split it in two and modulate one of those two signals before recombining them at unity level (e.g chorus+phase) or just modulate the straight buffered signal (e.g many tremolo circuits). If your diy dirt pedals are much worse than commercial equivalents, with the usual cap + resistor (i.e. 100r or so resistor from +9v leading to a 100uF or so electrolytic cap to ground, with the 9v to the circuit coming from the top of the cap.

If the noise is still bad with decent filtering, and the DC adaptor is known to be good and noise is not blighting other dirt pedals, it is possible the layout or wiring of a DIY build is contributing to the noise: This would obviously not affect different pedals in the same way, but it is easy to check wiring by opening the pedal and moving the input and output wire around a bit - If the input is running near the output or some certain part of the board, it may amplify noise but the noise will change as you wiggle the wires. Layout noise is hard to pinpoint, but rare and would also not affect several pedals in the same way unless they are all clones built with identical layouts.

I have used a +9v regulator with a a 9.2v supply, and it worked but I'm not suere it made any difference to the noise floor, plus they usually need a 12v supply to be totally reliable. TO-92 regulators are just like transistors, but one pin is for "in", one to ground, and one to "regulated out": They are usually filtered with a cap to gound on the in and out pins, with a higher cap on the in.
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Re: FILTERING 9VDC

Postby danlotano » 19 Sep 2014, 21:57

There are 3 different dirt circuits (OD1, BM Rams Head and Blowerbox, but I use only one every time) and I've tried to put a 220R resistor in series between the DC jack and the +9V on the board: it seems it reduced the noise a lot, but I can still hear it. I'm not using an high quality adaptor, I bought a generic one, but it worked very well for my Zoom B2.1u. Moreover if I use a battery there is no kind of noise coming out from the pedals.

What should be the value of the caps on the regulator? Can I still use a 9V adaptor or should I use a charge pump to 12V?
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Re: FILTERING 9VDC

Postby FiveseveN » 19 Sep 2014, 22:46

danlotano wrote:I'm not using an high quality adaptor, I bought a generic one, but it worked very well for my Zoom B2.1u.

Ah, there's your problem! Always use regulated PSUs, at the very least for boost/od/drive/fuzz pedals. The Zoom was fine because it regulates internally (and probably to different voltages for the digital and analog side).
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