headphone audio control PCB help on a Kenwood DP-R4430 multi cd changer

[circuitman1989]

I have an old Kenwood DP-R4430 cd changer that I stripped the guts out of to make a HTPC. I want to make the factory headphone jack and volume control a functional part of the HTPC using the front panel headphone output from the computer motherboard. There are only five wires coming from the main PCB of the cd changer to the headphone PCB. I know that one wire should be "ground", one wire should be "left channel +", and one wire should be "right channel +". But what are the other two wires and which wire is which? I've looked all over the internet to find a technical schematic but I can't afford $50.00 for a one time thing. If anyone has the digital copy of the technical schematic for a Kenwood DP-R4430 multiple cd, please let me know. Thanks in advance,

John

 

[dumpsterdiver]

Did the original deck cut off the outputs when phones were plugged in? If so then those two extra wires are the right and left returns. The headphone jack probably has a switch contact that opens when phones are plugged in.

 

[circuitman1989]

*correction* there are six wires. the wire in the red square was screwed to the metal chassis, but the no other parts of the cd changer or even the chassis itself were grounded. the five wires in the yellow square are the five wires I was talking about.

 

[Blueteeth]

Looks to me like that 'headphone' PCB has a fair few parts on it. Resistors, caps, and what looks like a SIL IC (probably an amplifier?). Looks 'active' to me, so I'm guessing one of those wires will be power Another may be a mute fuction for the on board amp. And of course, probably since wires either directly connected to the jack to sense when something is plugged in, or feedback from the chip to indicate the same thing.

Your best bet is to trace out that little PCB Hopefully the chip will still have a part number on it (they sometimes remove it). once you have that, working out whats what will become a hell of a lot easier. The jack pinout can be worked out with a continuity tester, or even a battery and some headphones! (bzz bzz).

Now, if you're *really* stuck, take a macro shot of the top and bottom of the PCB, and I'll see if I can trace it out. I have no job at the moment, so I need somethign to stop my mind going to mush.

 

[circuitman1989]

Ok, I took my digital multimeter and did some continuity tests and found that the ground wire that went to the metal chassis also grounds the main PCB through one the other five wires. I also found the left and right positive for the headphone jack. I think "Blueteeth" is right about the amp because there is a volume control next to the headphone jack. Yes, the part number is still on the chip so I'll look that up. I just need to find what the voltage to the amp is.


*edit*
I typed into google the part number on the chip, which is NJM4565L. I found the datasheet, which I've attached to this post. If I'm reading the datasheet correctly I can power it anywhere between 4 to 18 volts at 4.5mA... and I asume that is DC current and not AC. I now know which wires are + and - for the amp from tracing the PCB, so I've now figured out all of the five wires

 

[circuitman1989]

I want to know what would be easier... Modifying the original headphone jack and volume control board to accept the amount of current and 12volts for a desktop pc power supply... Or taking the volume control and headphone jack and cutting through the contacts of the PCB but still leave them attached to the board. Then making a new custom headphone amplifier to accept 12volts at whatever the current is that the the 12V side of the power supply?

 

[Blueteeth]

Well, tahts always a tricky one.... modify existing modules.... or making entirely new ones? The first requires that you know exactly how the circuit works, so 'tap' it for signals that you need, or remove parts off the PCB, and add wires to extend them (so your headphone jack can go anywhere on your PC case, and isn't attached the the PCB). You can always discard the original jack, and wire up the one on your PC's front panel to it. Just make sure you get the pinouts correct. Front panel jacks in PC's have 5, sometimes 6 wires, but you only need three. L, R and GND.

The second is a lot of work, with the only real advantage that you have complete control over what goes where, and how it works.

I skimmed over the datasheet, and it just looks like a nice stereo power amp. If you look at the recommended supply voltage... its bipolar, that is +V and -V. Now many can work with a single supply, that is 0V (GND) and +V (your 12V) but that mens the output of the amp 'sits' at half the supply voltage (6v). If order to filter out this DC component, you'll see many headphone amps with large capacitors on the outputs .. which I don't see on your PCB.

So I'm guessing the ribbon cable that supplies that module provides +V, GND as well as -V (with the other two being L and R audio channels). From that I think its safe to assume that the audio inputs to the PCB are AC, that is, the signal is centred around 0V (GND). This means that theoretically it should be fairly straight foward to build your own headphone amp - one that will happily run off a single supply (12V in your case).

As an FYI, as you pionted out the chip requires +/- (yes, that means plus AND minus) 4 to 18V. You are correct in assuming thats DC, few semiconductors are powered by AC But the current (4.5mA) is what the chip will draw when the voltage is within its supply range, and when its not driving anything on the output. Give it the right power voltage and it'll draw whatever current it requires, as long as your power supply can provide it. If you have a a +/- 12V supply that can kick out a thousand amps....the chip will only take 4.5mA.

If I were you, I would just extend the volume pot and headphone jack with wires So the PCB can sit anywhere you wish. I assume you're using the whole 'device' (the thing thats attached to this headphone amp), so that will provide lal the votlages already, and you wouldn't have to redesign anything. Of course, now you have a fair idea of whats going on - good detective work on your part - you have the option of replacing the amp with something you prefer, perhaps a lower noise chip, or one that runs off a lower voltage.

APologies for a massive post, but its always good to keep things clear eh?