More noise than normal from DMG-CPU-06 (Page 1 of 2)

If the noise is constant when adjusting the volume pot even on the prosound then we're talking interference from the power regulator board or maybe the CPU. A prosound with the volume turned all the way down is basically the same as shorting the mixer input to ground. The noise must be picked up along the stretch of wire inside the Gameboy.

Thinking about it, the lack of noise right after the loading screen suggests that this has to do with what is displayed on the screen. I can make you a test ROM to test this hypothesis. Also, before I do that, try and see if the noise goes away or gets lower if you adjust the contrast to the extreme positions, so the image gets completely white or completely dark.
(Btw, just because the problem might be in the display, doesn't mean that's the actual source of the interference. Varying power load from the CPU and display will change the operating frequency of the power regulator and can cause interference.)

But ultimately, I think this boils down to an interference problem. You have either
1) connected the ground cable to a bad ground point. As any good electrical engineer will tell you, not all ground points are equal. A ground lead, like any other electrical lead, will vary in potential (voltage level) between different points when there goes a current through it. The ground point on the pot is a good point. The negative battery terminal is probably a decent choice. The ground point on the 4-wire connection coming from the regulator board is a bad choice. If you've tried a point on the 4-wire and have gotten the wrong one so you're using e.g. the -18V point instead of ground, you're certainly in for a noise problem. You'd still get sound, but also a louder click on startup, as well as a lot of noise.
2) laid down the actual cables near things that cause interference, mainly the power regulator board. Maybe you placed the PS jack on the left side on the noisy one, and right to the side of the regular jack on the one that's not noisy?

Oh wow thanks for all that! I'll give this ROM a go ASAP!

Interference sounds very plausible and my next objective was to remove my Pro-Sound mod to see if that changes things. I'll tackle both of these today. I have to fix my LCD configuration anyway since I accidentally moved around the backlight while replacing all those caps under the LCD cabling

The good news is that my travel headphone amp appears to attenuate the high pitches noises to the point it almost becomes bearable, so if I can't fix things completely, that may be an option for now while I'm composing. I'm not sure exactly how it's doing that (other than it having a hi pass filter on it) unless it's a grounding issue there as well.

So I tried changing the contrast and the ROM. The contrast only helped very marginally. The ROM also didn't change the high pitched noise in any of the screen configurations that it cycles through. The patterned screen does create more noise than the others, but it sounds more like an addition to high pitched noise itself. I will try removing the Pro Sound mod today but will have to wait until this afternoon most likely.

I tried the ROM on my other GB as well and you can faintly hear a high pitched whine on what I think is the patterned screen. I can't tell because I have to put my ear right next to the speaker and can't see the screen Otherwise the normal noise from my good GB is basically constant (mostly some hiss and a faint buzz).

I am still banking on interference being the potential cause, though.

nitro2k01: did you make a mode that turns the screen off?
m00dawg: you can also download and try the mGB rom from http://code.google.com/p/arduinoboy/dow … B1_3_0.zip
and hit Select + A to turn off the screen, I guess the noise would go away then. The high pitch wine reminds me of the GBC's screen wine issue.
You might not hear the wine after removing the prosound mod, but that may be just because the noise level is so high it will hide it.

The resistors shouldn't need to be changed on the leds, but the 6v from the batteries might be too many volts (6v max from there), though it probably will be fine.

Wow well the problem instantly went away as soon as I blanked the screen in mGB. Sounds like awesome now. But since the LEDs are still active, that means there's less of a chance it's the LEDs, or is it?

As in, now that I know screen blanking works...it doesn't seem like there is much I can do about that?

EDIT: At least until I start using mGB Which still requires I finish up my ArduinoBoy (it's taking a break right now whilst I work on my MidiBox stuff)

Last edited by m00dawg (Nov 10, 2011 7:33 pm)

Ok, I'm entering science mode again. You will always get some noise from the headphone output. That's just to be expected, and why people prosound their boys in the first place. Newer versions of LSDj also don't have the power save option, but always go into a new auto mode. This mode should give only a minimal amount of the power save noise (basically interference from the CPU turning on and off) when LSDj is idle or playing a song. However, when moving the cursor, or changing screens etc, you may still hear some noise. This is normal. Here are some things to test.

On the headphone out, does the noise sound the same when you're not doing something and you're doing something? Or is there additional noise when you do something?
What happens if you create an empty chain with an empty phrase in it and press play. Any difference in noise?
What happens if you create a chain with a phrase with an pulse instrument with volume 08 (yes, silent) but otherwise unchanged settings in a new song, and press play? What's the difference in noise compared to nothing playing? Compared to the empty phrase?

Hey nitro2k01! Sorry I never saw your update when I last posted and have been away for a week. I ended up just moving the pro-sound mod to my GameBoy that is much more quiet. The noise appears to have nothing to do with the backlight mod but something on the LCD board itself and was constant (Pro-Sound, headphone, power-save or not, always the same high pitched noise at the same volume) which is why I think replacing other components apart from the caps might help.

My good GameBoy sounds great with the only downsides being that it is not backlit and the LCD screen itself looks a bit off-center with the Chipmusic in Stereo cover for some reason. I used it all last week and it works like a champ so I'm going to call it good for now. I'd still like to see if I can fix the sound issues on my other GB at some point, but for now I have a functional solution at least.