Wire up old amp with 6 pin DIN

[jmurphy]

I’m trying to re-purpose a small 1979 Hitachi HA-M1 MKII stereo amplifier.  My goal is to use it with an analog HiFi-Berry in my small workshop to drive 2 bookshelf speakers.  I found the schematic online but I’m not sure how to wire up the left and right channel RCA outputs from the HiFi-Berry to the single 6 pin DIN input connector on the Hitachi amp.

[MarkF]

I can't tell which is the 'right' and 'left' channel inputs.
However, pins 3 and 5 are the audio inputs and pin 2 is ground (also pin 1 is GND).

CAREFUL with pin 4.  I can't figure out if it is an input or output.
It looks like some kind of power pin. 
Edit:  It looks like 12VDC power output.

[jmurphy]

Thanks Mark.  I assume pin 3 is the right channel because of all the R's after the component markings.  Maybe pin 4 is used to power an external tuner.

[MarkF]

Thanks Mark.  I assume pin 3 is the right channel because of all the R's after the component markings.  Maybe pin 4 is used to power an external tuner.

Yes.  I missed that.

Pin 3 is the 'right' channel.
Pin 5 is the 'left' channel.

I now think pins 4 and 1 are 12VDC power and GND respectively for an external device.

[jmurphy]

I now think pins 4 and 1 are 12VDC power and GND respectively for an external device.

Cool, I can use external power for the HiFi-Berry with a 5V step down.  I'm off to the surplus store to see if I can find the matching 6 pin male DIN plug.

[jmurphy]

Unfortunately, it looks like the output on pin 4 is 15V AC.  It's a shame because the amp has large toroidal transformer that would probably provide cleaner power to the HiFi-Berry than a wall wart.
Also the 12V DC barrel output on the back doesn't appear to work when running off the mains.

[MarkF]

I don't see how that can be.
According to the schematic you gave, pin 4 is the DC power for the whole amplifier.

[jmurphy]

I don't see how that can be.
According to the schematic you gave, pin 4 is the DC power for the whole amplifier.

I agree.  I don't know how I was getting that value on the scope.  I tried again and now I'm getting 0V on the pin.  The amp seems to work fine otherwise.  Both channels sound good.
If it's not too difficult, I'll try to pull the board.  I'd really like to get access to the 12V DC out.

[jmurphy]

I pulled the pcb and it looks like there has been several bodges.  The trace to pin 4 of the J501 DIN connector has been cut and jumped.
Not sure why, but none of the 12V outputs work now.

[MarkF]

Also, the 12V jack wiring as shown on the schematic is wrong.
The wiring of the jacks as shown will short out the power.

Edit:  I guess this is correct.  The intent is that the 12VDC input is
       connected to GND if no DC power is connected. 

[MarkF]

Careful what you connect to the internal 12VDC.
It is very possible to inject noise into the amplifier through the connection.
I also would not try to pull a lot of current and starve the amplifier output drive.

[MarkF]

After studying the PCB, it looks like the DC power jacks are wired as below:

[jmurphy]

Thanks Mark for taking the time to color the schematics and all the advice; I got everything working!  I think the bodge wires were bypassing fuse F601 which was blown despite everything working except the DC output on pin 4.  I replaced the fuse and the DC power out is working on the DIN jack.

I press the power on the amp and it automatically turns on the Raspberry Pi and the HiFi-Berry DAC.  This starts a hotspot so I can control everything from my phone.  The amp drives 2 Polk Atrium bookshelf speakers and it sounds great in my small workshop.  There is a little bit of noise on the line when nothing is playing but it goes away when the music starts.

[MarkF]

Good

I wouldn't be surprised if the noise is from the Raspberry Pi.
Maybe a little choke on the power lines.

Enjoy.