AC power creates unwanted noise

Frequently asked questions regarding powering your pedal.
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McHuge
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Post by McHuge »

Hi all,

I've finally finished this treble booster and it sounds awesome with a battery but as soon as I plug in my power supply, it makes so much background noise, its unusable. Any clues as to why??

Thanks for your help
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McKenzy
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Post by McKenzy »

You need to supply 9V(DC) to the circuit not AC. Also those unregulated DC supplies can be pretty noisy and horrible for pedals.

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bajaman
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Post by bajaman »

I think he is using a DC power supply :wink:
try adding a series 100 ohm resistor with the power supply input and then drop a 220uf /16v electrolytic capacitor from the circuit DC input to ground (negative terminal to ground) - that will get rid of the noise for you :wink:
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McHuge
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Post by McHuge »

bajaman wrote:I think he is using a DC power supply :wink:
try adding a series 100 ohm resistor with the power supply input and then drop a 220uf /16v electrolytic capacitor from the circuit DC input to ground (negative terminal to ground) - that will get rid of the noise for you :wink:
cheers
bajaman
How would this be wired into the circuit? Forgive my asking but this is my first ever build.

It is a dc supply by the way do'h!!

Thanks again

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Zen Arcade
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Post by Zen Arcade »

If you want to hack the series resistor and cap to ground in, without changing the rest of the layout, you could try something like this. Note the cut underneath the resistor.

What this resistor and cap do is create a low-pass filter with a cutoff frequency of around 7 Hz. This means any signal with a frequency higher than 7 Hz (like the 50 or 60 Hz hum coming from your wall power and polluting your circuit with noise) will get attenuated.
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McHuge
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Post by McHuge »

Thanks so much for that, I really appreciate it.

One question though, will it do anything to the overall tone at all??

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McHuge
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Post by McHuge »

This is the same noise I'm getting by the way...

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Nocentelli
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Post by Nocentelli »

McHuge wrote:One question though, will it do anything to the overall tone at all??
Power filtering with a series resistor and cap should not alter the tone: If you used a much larger series resistor, it would drop the voltage well below 9v and would have a "sag" effect on the circuit like people sometimes deliberately do with fuzzes - 100ohms would not have a noticeable effect. In deliberately tone-mangling noise-fuzz circuits, a filter cap can sometimes interfere with the self-oscillation that is "designed" in to the effect, but that is not relevant for your booster circuit.
modman wrote: Let's hope it's not a hit, because soldering up the same pedal everyday, is a sad life. It's that same ole devilish double bind again...

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McHuge
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Post by McHuge »

Thanks for your advice. I believe I understand it.
I will post the results :D

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McHuge
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Post by McHuge »

Ok, I've done the mod and it is a lot better. There is still a bit of noise but I figured if I used a 120 resistor it may completely get rid of that. (Is that correct?)
The other thing is its now got a high pitched whistle when I use it on a gain channel of my Marshall DSL 2000, even at very low volumes. I'm using a bc109c transistor and I thought it maybe an overdose of gain so I put a 2n5088 in and all that did was create a spluttery sound like it was going through a heavy noise gate. I checked the pinout of the 5088 and I had installed it correctly according to the specs. To be honest though, I do like the extra omph the bc109 gives and I'd prefer to keep it.
What do you suggest??

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Post by bajaman »

are you using a well regulated DC power supply :?:
You should be :wink:
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