Hi everyone,
Recently I constructed a fet based pre amp for my guitar. The sound performance seems good and overall I am happy with it. However, I was somewhat disappointed initially with the background noise it produced - almost a white noise/hissing sound.
On a hunch I swapped the power supply (its one of those multi-voltage ones where you can select a number of different voltages from 1.5-12V) for a 9V battery and the noise disappeared. Good times.
However, I would like to continue to use my DC power supply and perhaps others which could be just as noisy. I would like to keep the circuit as simple as possible, therefore my question is this: How can I clean up a power source using non-regulated techniques initially then if this doesn't work what regulated circuits have people used?
Thanks!
Recently I constructed a fet based pre amp for my guitar. The sound performance seems good and overall I am happy with it. However, I was somewhat disappointed initially with the background noise it produced - almost a white noise/hissing sound.
On a hunch I swapped the power supply (its one of those multi-voltage ones where you can select a number of different voltages from 1.5-12V) for a 9V battery and the noise disappeared. Good times.
However, I would like to continue to use my DC power supply and perhaps others which could be just as noisy. I would like to keep the circuit as simple as possible, therefore my question is this: How can I clean up a power source using non-regulated techniques initially then if this doesn't work what regulated circuits have people used?
Thanks!
It probably comes from the switching regulator. Does the adaptor look something like this?
MW 2006GS | GES-ELECTRONICS
Then it is a SMPS and some LC filter should help get the noise down.
MW 2006GS | GES-ELECTRONICS
Then it is a SMPS and some LC filter should help get the noise down.
Thanks for the messages!
Conrad, I have a capacitor but no series resistance. Am I right I thinking that this creates a low-pass filter? If this is the case then I believe my cut-off is too high (the capacitor is only 10uF) hence why I can still hear the noise.
If I were to use a resistance of 100ohms and a capactor of 100uF then this would set the cut off at about 15Hz?
Kubeek, yes its very similar. Say I use a 100uF cap, would I be correct in saying that using an LC filter could produce the cut off required without needing the such a high series resistance? In my comment above I said I could use 100Ohms which seems a little high?
Conrad, I have a capacitor but no series resistance. Am I right I thinking that this creates a low-pass filter? If this is the case then I believe my cut-off is too high (the capacitor is only 10uF) hence why I can still hear the noise.
If I were to use a resistance of 100ohms and a capactor of 100uF then this would set the cut off at about 15Hz?
Kubeek, yes its very similar. Say I use a 100uF cap, would I be correct in saying that using an LC filter could produce the cut off required without needing the such a high series resistance? In my comment above I said I could use 100Ohms which seems a little high?
LC means inductance with capacitance, which will be far better. If you don´t have access to a suitable inductor, you can use RC filter.
You don´t say how much current does your amp need, but the 100ohm resistor would limit the current to 120mA. I would use something smaller, like 10ohms, which with the 100uF cap will make a 160Hz low pass filter, which will attenuate -42dB at 20kHz and that should be enough.
If it is not, you can split the resistor into two 5 ohms and make a two-stage filter with two caps, connecting it R-C-R-C, which will yield -70db attenuation. If you got different caps, use the larger as the first one, preferably with a 100nF ceramic one in parallel.
You don´t say how much current does your amp need, but the 100ohm resistor would limit the current to 120mA. I would use something smaller, like 10ohms, which with the 100uF cap will make a 160Hz low pass filter, which will attenuate -42dB at 20kHz and that should be enough.
If it is not, you can split the resistor into two 5 ohms and make a two-stage filter with two caps, connecting it R-C-R-C, which will yield -70db attenuation. If you got different caps, use the larger as the first one, preferably with a 100nF ceramic one in parallel.
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