Slight sound distortion with 3.3v regulator.......

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zenloc
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Slight sound distortion with 3.3v regulator.......

Post by zenloc »

So something weird happend yesterday. Everything was working fine but now suddenly the sound is distorted.. Tested this on 2 n64 both have the same problem. Used 3 different regulators and all of them have the same issue. So I thought it would be the n64 sound chip beeing messed up. Connected the original power supply and the distortion was gone. Then I only connected the 12v line from the original power supply and powered the rest from the 3.3v regulator also no distortion. Then only connected the 3.3v from the original power supply and used 7.4v from the psone adapter + powering the psone screen ofcourse also no distortion!!! but when I connect the 3.3v line and the 7.4v line it has distorted sound... only slightly tough but still....

So It's not the psone screen that works fine. The n64 also works fine with orginal power supply. The only thing I can think of is that the psone adapter would not have enough amps which is bull since the n64 and led modded screen don't use up 3 amps. Also tested this with a battery of 7.4v 4 amps and get the same distortion :? I get the feeling this has to be some grounding problem but don't know what else to try.

I have absolutly no clue as to what it could be... any thoughts on this... :?:
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marshallh
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Re: Slight sound distortion with 3.3v regulator.......

Post by marshallh »

Your switching regulators are producing a ton of back-EMF. Basically, the regulars work by pulsing the input voltage on and off very quickly (several khz usually). The average output of this is the output voltage.

For example, if you took a 10v source, and pulsed it on and off very quickly, you would read 5 volts. This is with a 50% duty cycle (which looks like a square wave). The output votlage is varied by changing the duty cycle.

You have two problems created with this method. You need a device to buffer the current between the regulator input and its power source. A decent sized inductor (coil) will work here. The next problem is that when the switching regulator is turning itself on and off, everytime it turns itself off it creates back-EMF which will damage the coil. This is solved by putting a diode in parallel with the coil.


TL;DR put a coil in series with the input power to the reg, also wire a diode in parallel with the coil.
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zenloc
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Re: Slight sound distortion with 3.3v regulator.......

Post by zenloc »

Hmmm that's worth a try. It's like this diagram here right? but only with my own regulator
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Thanks for the info I'll try it out and let you know if it worked right. For the inductor coil could I use this one?
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Can the diode with a higer voltage rating let's say 10v be used for a 7,4 power supply? The battery fully charged is like 8v.
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marshallh
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Re: Slight sound distortion with 3.3v regulator.......

Post by marshallh »

Oh wow, lol. I completely forgot I even made that diagram. Yes, you can use a diode with a higher voltage rating. Try to find a smaller choke if you can. I used one that size and it caused problems (too high inductance)
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timmeh87
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Re: Slight sound distortion with 3.3v regulator.......

Post by timmeh87 »

Is there no input capacitor? Thats the first thing you should add.
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zenloc
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Re: Slight sound distortion with 3.3v regulator.......

Post by zenloc »

the cap is already in place. Marshall what about these?? I have a couple of gc regulators lying around and most likely i can use the components on them. just not sure which would be the inductor coil.
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if it's not on any of these then i'll just buy one. Could you post an example of the sze it should be?
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Re: Slight sound distortion with 3.3v regulator.......

Post by marshallh »

In the first pic, the black square under the 2R7 coil.

YOu actually have quite a few coils in those pics. They are labeled with "L1, L2, etc" on pcbs.

I see lots of 100uH coils and a couple 2.7uH coils (that say 2.7). Try a 100uH for now. It may be too much, I dont remember
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timmeh87
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Re: Slight sound distortion with 3.3v regulator.......

Post by timmeh87 »

zenloc wrote:the cap is already in place.
To clarify then, you have TWO capacitors next to the regulator one on either side... right?
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zenloc
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Re: Slight sound distortion with 3.3v regulator.......

Post by zenloc »

Only 1 cap is necessary on the input. I put one on the output aswell just to try but didn't do anything. According to the datasheet you only need to put a cap on the output if the draw changes during use. Since the n64 draw about the same amount of amps all the time it isn't necessary. I'm using a PTH08000W by the way.

I tried the 100uH coil and a diode but didn't do anything either... If I would buy a coil how much uH should it be?
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