Hi:
This is my first post here, so I hope you'll bear with me.
I'm attempting to connect a sound board (built around a WT588D sound module) to an amp powered by a TDA7297 Dual Bridge Amplifier, but the resulting sound is very overmodulated.
I offered to help an acquaintance install an electronic kit into a Ghostbusters Proton Pack he's building. The kit includes a sound board built around a WT588D-U voice/sound module. The module has several sound effects programmed into it, along with the Ghostbusters theme, trigger by various switches. This sound board runs off of 3 volts, so I'm powering that with 2 AA batteries for now. The board has + and - outputs you're supposed to connect to an amp (not included in the kit). I had him buy this amp package, built around a TDA7297 amplifier.
https://www.amazon.com/DROK-TDA7297...ocphy=9032849&hvtargid=pla-647203956957&psc=1
The amp runs off a 12V Li-ion battery. I have a pair of 50W Boss 4 ohm speakers connected to the amp. When I connect the sound board to the amp (via alligator clips clipped to a 3.5mm plug and cable plugged into the 3.5mm jack on the amp) the resulting sound is very distorted. Turning the amp's pot almost all the way down makes the sound quieter, but you can still hear the distortion.
I think this accurately represents how the sound module is connected to the amp:
As a test I routed the outputs of the sound board into the 3.5 mm AUX inputs of a Bluetooth speaker and an old boom box, and in both cases the sound is perfect, no distortion on those devices even with the volume cranked up all the way.
As another test I plugged an iPhone (and then iPad) into the amp using the 3.5mm cable and played the Ghostbusters theme with the iPhone and iPad volume cranked to maximum, and the audio sounded fine, no distortion with the amp audio turned up to the point of being uncomfortable.
So these two individual units appear to work just fine when connected to other amps or sources. It's only when I connect this sound board to this amp that the audio is distorted. Research on the GBFans forum indicate others have had issues with this particular sound board outputting distorted sound.
I've also tried this method of connecting the sound board to the amp, tying together the + PWM output to the wipers of both input pots on the amp and the - PWM to the ground sleeve of the plug (and thus the ground of the amp). That's just as distorted:
My only guess is that the sound board is outputting its signal in a way that the amp can't deal with. I know enough about electronics to read and build simple schematics, but I don't have a great understanding of the underlying electronic principles of how everything works together. I have a 40-year-old Radio Shack multi tester.
Here's a link to a PDF data sheet of the WTD588-D sound module:
https://www.dropbox.com/s/zc323uo3f8583uf/WT588D-U Voice Module 28 pin.pdf?dl=0
And here's a link to a PDF data sheet of the TDA7297 amp chip:
https://www.dropbox.com/s/d6aktgd3qgdngim/tda7297.pdf?dl=0
Perhaps someone smarter than I can look at these spec sheets and tell whether there's some incompatibility between the sound module and amp that can be corrected with different wiring or adding in some simple, additional components. Like would I get a better result tying the DAC output of the sound chip to the amp (with common grounds)? That's not how this sound board has been wired, though. Something else?
If it came to it we could buy a different amp, but I don't want to just randomly buy another type and risk that that wouldn't work either.
Thank you!
Shawn Marshall
Portland, OR
This is my first post here, so I hope you'll bear with me.
I'm attempting to connect a sound board (built around a WT588D sound module) to an amp powered by a TDA7297 Dual Bridge Amplifier, but the resulting sound is very overmodulated.
I offered to help an acquaintance install an electronic kit into a Ghostbusters Proton Pack he's building. The kit includes a sound board built around a WT588D-U voice/sound module. The module has several sound effects programmed into it, along with the Ghostbusters theme, trigger by various switches. This sound board runs off of 3 volts, so I'm powering that with 2 AA batteries for now. The board has + and - outputs you're supposed to connect to an amp (not included in the kit). I had him buy this amp package, built around a TDA7297 amplifier.
https://www.amazon.com/DROK-TDA7297...ocphy=9032849&hvtargid=pla-647203956957&psc=1
The amp runs off a 12V Li-ion battery. I have a pair of 50W Boss 4 ohm speakers connected to the amp. When I connect the sound board to the amp (via alligator clips clipped to a 3.5mm plug and cable plugged into the 3.5mm jack on the amp) the resulting sound is very distorted. Turning the amp's pot almost all the way down makes the sound quieter, but you can still hear the distortion.
I think this accurately represents how the sound module is connected to the amp:
As a test I routed the outputs of the sound board into the 3.5 mm AUX inputs of a Bluetooth speaker and an old boom box, and in both cases the sound is perfect, no distortion on those devices even with the volume cranked up all the way.
As another test I plugged an iPhone (and then iPad) into the amp using the 3.5mm cable and played the Ghostbusters theme with the iPhone and iPad volume cranked to maximum, and the audio sounded fine, no distortion with the amp audio turned up to the point of being uncomfortable.
So these two individual units appear to work just fine when connected to other amps or sources. It's only when I connect this sound board to this amp that the audio is distorted. Research on the GBFans forum indicate others have had issues with this particular sound board outputting distorted sound.
I've also tried this method of connecting the sound board to the amp, tying together the + PWM output to the wipers of both input pots on the amp and the - PWM to the ground sleeve of the plug (and thus the ground of the amp). That's just as distorted:
My only guess is that the sound board is outputting its signal in a way that the amp can't deal with. I know enough about electronics to read and build simple schematics, but I don't have a great understanding of the underlying electronic principles of how everything works together. I have a 40-year-old Radio Shack multi tester.
Here's a link to a PDF data sheet of the WTD588-D sound module:
https://www.dropbox.com/s/zc323uo3f8583uf/WT588D-U Voice Module 28 pin.pdf?dl=0
And here's a link to a PDF data sheet of the TDA7297 amp chip:
https://www.dropbox.com/s/d6aktgd3qgdngim/tda7297.pdf?dl=0
Perhaps someone smarter than I can look at these spec sheets and tell whether there's some incompatibility between the sound module and amp that can be corrected with different wiring or adding in some simple, additional components. Like would I get a better result tying the DAC output of the sound chip to the amp (with common grounds)? That's not how this sound board has been wired, though. Something else?
If it came to it we could buy a different amp, but I don't want to just randomly buy another type and risk that that wouldn't work either.
Thank you!
Shawn Marshall
Portland, OR