BadBert's GBZ Build

[BadBert]

OK... i had some time to work on the GBZ, things i got done:

• Wire up udb DAC (remove the bulky connectors first)
• Wire up the audio amp (stereo)
• Wire up the 3,5mm jack
• Wire up the volume pot
• Wire up the teensy to the usb hub

it is not usefull to take pictures of every step now... but a few pics:
So removed all bulky connectors of the USB DAC and added wires:


And here everything for the audio is wired up

As you can see, i already used the tip from @Wermy on the stereo audio using the resistors

Only thing left for the audio is hooking up the amp to the power strip

New todo list:

• Mounting audio parts.
• Wire up the external USB to the usb hub
• last little bits of soldering (power strip)
• Glue in the screen protector
• close the gbz up
• set everything up (screen size/position, font size, load roms etc)
• ENJOY PLAYING

[BadBert]

After reading and looking some more, i realise i have made a mistake...

i wired the audio like this:
USB DAC -> AMP -> POT (after market) -> gb jack and speaker

So i'll change that to:
USB DAC -> POT (after market) -> AMP -> gb jack and speaker

[Zero]

Why would you need the amp to boost the headphones? Shouldn't it go ... USB dac > headphone jack > amp > speaker.

[RxBrad]

Actually, have you tested it with the amp totally removed from the circuit? The USB DAC has an amp built in. You might not need it.

Also, note that the PAM8403 amp you're using is basically TWO amps that do not share a common ground. If you're merging the negative output from the left and right channel, you're basically hooking two amps into each other. From what I've gathered online, if the left channel is outputting louder audio than the right, it might conduct a current INTO the right channel and fry the amp.

Here's a blog post by a guy who tried to find a good way to merge the grounds. I tried the first and second methods he listed. I agreed with him on the first method -- it sounded bad. The second method sounded great; and I'm okay if there's a little bit of crosstalk between the L and R channels. In my case, I used two 10ohm resistors, and two 100nF capacitors that I desoldered from the original DMG PCB. Instead of simply merging the R(-) and L(-) into a single output, I recommend doing what's pictured below when wiring out of the R(-) and L(-) terminals: (Someone please correct me if I have the cap polarity backwards. It's never called out anywhere that I can find, but this seems how it'd go.)

[BadBert]

Actually, have you tested it with the amp totally removed from the circuit? The USB DAC has an amp built in. You might not need it

I have not... But if i read your whole story... I think I'll let the amp out then, way simpler...

Why would you need the amp to boost the headphones? Shouldn't it go ... USB dac > headphone jack > amp > speaker.

Wermy also has it going from the amp to.the jack, and then to the speaker.

Thanks guys

[BadBert]

Actually, have you tested it with the amp totally removed from the circuit? The USB DAC has an amp built in. You might not need it

I have not... But if i read your whole story... I think I'll let the amp out then, way simpler...

Why would you need the amp to boost the headphones? Shouldn't it go ... USB dac > headphone jack > amp > speaker.

Wermy also has it going from the amp to.the jack, and then to the speaker.

Thanks guys

[alien0matic]

Actually, have you tested it with the amp totally removed from the circuit? The USB DAC has an amp built in. You might not need it

I have not... But if i read your whole story... I think I'll let the amp out then, way simpler...

Why would you need the amp to boost the headphones? Shouldn't it go ... USB dac > headphone jack > amp > speaker.

Wermy also has it going from the amp to.the jack, and then to the speaker.

Thanks guys

Wermy didn't use an USB dac but the GPIO pins. They need boosting.
The USB dac I used wasn't strong enough to power the speaker but was good for headphone use. So I added the amp behind the headphone jack to only power the speaker.

[BadBert]

Wermy didn't use an USB dac but the GPIO pins. They need boosting.
The USB dac I used wasn't strong enough to power the speaker but was good for headphone use. So I added the amp behind the headphone jack to only power the speaker.

Ok, thanks.

I'll first try it without the amp, if that does not work, i'll use one channel of the amp to the speaker

[PolletjeNL]

Does this also apply for a USB audio card instead of the DAC?? I am using a Audio out / Mic in combo card with it's own volume buttons.

Link to the USB Sound card

Actually, have you tested it with the amp totally removed from the circuit? The USB DAC has an amp built in. You might not need it.

Also, note that the PAM8403 amp you're using is basically TWO amps that do not share a common ground. If you're merging the negative output from the left and right channel, you're basically hooking two amps into each other. From what I've gathered online, if the left channel is outputting louder audio than the right, it might conduct a current INTO the right channel and fry the amp.

Here's a blog post by a guy who tried to find a good way to merge the grounds. I tried the first and second methods he listed. I agreed with him on the first method -- it sounded bad. The second method sounded great; and I'm okay if there's a little bit of crosstalk between the L and R channels. In my case, I used two 10ohm resistors, and two 100nF capacitors that I desoldered from the original DMG PCB. Instead of simply merging the R(-) and L(-) into a single output, I recommend doing what's pictured below when wiring out of the R(-) and L(-) terminals: (Someone please correct me if I have the cap polarity backwards. It's never called out anywhere that I can find, but this seems how it'd go.)

[RxBrad]

@PolletjeNL - you won't need to worry about any of the stuff to merge grounds. That's just for that particular amp.

As far as needing an amp at all: it depends on how much power output that particular USB card has. I'd say it's a safe bet you won't need an amp between the soundcard and the headphone. You may still need an amp between the headphone jack and speaker though. Try it without an amp first and see if the speaker is loud enough.