Bluetooth/Class D Amplifier

[Jehannum]

I'm about to wrap up what is (for me) a fairly exciting project on my 240Z, and I thought it would be nice to share, as it's not something I see discussed here very often.

The goal: retain AM radio function in my Series 1.5 (5/71, so series 1 drivetrain and dash, but no hatch vents) 240z, while being able to pair with my phone and stream music over bluetooth.

My materials: a class D one-board amp (bought from a guy who calls them "Shiznit", hence "U_Shiznit" in the wiring diagram), 50Wx2, a handful of relays, a line-level bluetooth board, two Match M5X speakers, and a spare speaker bracket from another 240z.

My modifications: I created a switched output from the Hitachi TM-1081ZB by soldering an additional wire (I chose purple, to differentiate from the existing harness colors) to the switch side of the L10 choke coil (the Hitachi service manual is available online), and then running that out the bottom of the deck through the remaining open hole.

The drawbacks: Limited to 5.25" speakers that fit in the stock hatch locations, I'm not going to win any sound quality or SPL competitions.  I also had to crack open my AM unit to add the switched 12V, which can be nerve wracking.  Honestly, my Z is pretty loud (2.5" exhaust, triple webers, rumbly cam), so the goal is really just to have intelligible audio in a stealthy package.

Wiring diagram:

Pre-relay testing configuration:

So far, I've only mocked up the connections, but I'm running the wires soon (the entire thing should fit under the lid of the driver's side storage bin) for final installation.

Edited December 15, 2016 by Jehannum

[hr369]

You've got ballz That's an expensive radio you're modifying.  I'm curious how you're going to switch from radio tuner to your amp. You're using a relay for that right? Are you going to turn off the tuner or just disconnect

it from the amp via relay?

 

You ever think of adding a fm tuner into the mix? Perhaps bluetooth fm receiver?  

I think it would be much easier to just switch between your amp and the radio via a bluetooth or a physical switch.

Cool project. I like to see these kind of mods that improve the old stock radio's functionality and sound quality.

 

Edit: just looked more closely at your schematic and i must say thats an interesting but complicated way of doing things. It answers my questions about tuner power.

It looks like you're using the tuner logic signal to actuate the relay. Is that going to be kosher longer term?

 

 

Edited December 15, 2016 by hr369

[Jehannum]

1 hour ago, hr369 said:

You've got ballz That's an expensive radio you're modifying.

Edit: just looked more closely at your schematic and i must say thats an interesting but complicated way of doing things. It answers my questions about tuner power.

It looks like you're using the tuner logic signal to actuate the relay. Is that going to be kosher longer term?

I took a deep breath before I touched soldering iron to the board, that's for sure.  The radio itself is pretty well documented in the service manual, so I'm confident I could repair it, if need be.  I just couldn't get where I needed to go without pulling the logic output (the switched +12V) out of the radio.  On the bright side, there is a 4th hole in the bottom socket of the radio, so I didn't have to cut anything.

I had one additional constraint laid on by the guy who built the amp - it can go into overheat protection if you turn it on without a load attached to both outputs, so I needed all 3 relays.  One to power the amplifier (RY1, SPST), one to switch the speakers (DPDT, RY3), and one to trigger both at the right time (SPDT, RY2).

[Jehannum]

Could someone move this to the Z electrical section?  I'm clearly a dumbass.

[ajmcforester]

ON the single speaker your attaching the radio and the amp to, what is stopping back feed from the amp to the stereo thru the wire?  You might want to add a switch either one that uses the current or a manual switch.

[Jehannum]

1 hour ago, ajmcforester said:

ON the single speaker your attaching the radio and the amp to, what is stopping back feed from the amp to the stereo thru the wire?  You might want to add a switch either one that uses the current or a manual switch.

It's protected by the DPDT relay.

[ajmcforester]

OK I saw it in the picture but I thought that was just a connector block

[Mike]

13 hours ago, Jehannum said:

Could someone move this to the Z electrical section?  I'm clearly a dumbass.

Ok, I'll move it.  No problem.

Looks like an interesting project!  I'd love to see how it turns out.

[Jehannum]

Final packaging.  I changed the scheme because I realized that the amp/bt combo would be on whenever the radio's off, including when the car's off, so I added a 4th relay to switch power to the whole shebang.

 

 

 

Mounting location, after pulling all the wires through, and testfitting the amp itself.

 

The antenna harness now carries the radio switched and ignition switched triggers to the back of the car.  In doing so, I can now run a modern antenna without modification.

 

Blue wire is the traditional blue wire - switched on when the radio's on.  It's attached where the power switch attaches to the main board.

 

There was a 4th hole for passing cable through on the radio, so I didn't even have to modify the case.

Edited December 17, 2016 by Jehannum

[Jehannum]

I smoke tested the radio after the modification, and it puts the antenna up just fine, and makes AM radio noises when its on, so I didn't screw it up

[Jehannum]

And from the "inviting the stereotype" department, this is straight out of the service manual for the Hitachi radio.

[Captain Obvious]

My local far east supermarket has on the shelf in the meat dept "Beef for stir-fly". I was gonna say something, but didn't want to risk pissing someone off.

Nice work on the radio stuff. I gotta ask though... Couldn't you have come up with something a little less conductive than building that whole thing on a piece of sheet metal?     I know the stock radio chassis is sheet metal too, but didn't they at least put a piece of insulating material in there between the back of the board and the chassis?