Re-wiring a powered Subwoofer

[sirboh]

Hi, I know this is my first post, and I'll understand if you tell me where to go ;-) but I'm hoping someone can help me with this,

I had a JVC TH-A10R AV surround system, the controller recently died and I believe is uneconomical to repair. I certainly don't have the skills to diagnose and repair this myself, I'm happy enough finding dud caps and changing these out but that's probably as far as I could go. Anyway, back to the subject I need some help with:

The system comes with a powered subwoofer that contains the audio amp and speaker connections for the controller, the subwoofer is connected to the controller by an 8 pin din cable, the subwoofer has its own mains power cable. I would like to use this subwoofer as a stand alone powered subwoofer with a new AV receiver. The pins on the cable are as follows:

Pinout : 0



Pin Name Direction Color Description
1 Left Left
2 Right Right
3 SL Surround left
4 GND Ground
5 SR Surround right
6 SubWoofer SubWoofer
7 Control Control
8 Power on 12 + Power on 12 +

Would it be possible to butcher one one of the cable to allow me to connect this to a standard AV receivers sub out connection?

I'm assuming I'd need to somehow trigger the power on circuit in the subwoofer (pin8?, bypassing this so the subwoofer needs to be manually powered on wouldn't be a problem and may be a simpler option) then wire pins 6 and 4 to an RCA connector to provide the audio signal form the AV receiver.

I have the full schematics for both the subwoofer and the controller is any more detail is needed.

Thanks in advance for any assistance you might be able to provide.

 

[Arouse1973]

Yes please post the diagrams here.
Adam

 

[sirboh]

Yes please post the diagrams here.
Adam

Hi Adam,
Thanks for the reply,
Not sure which parts of the diagrams would be relavent, the output stage is on page 62 of this pdf:

http://j.mdownload1.free.fr/Schemas/JVC/TH-A10_TH-A10R.pdf

The Subwoofer schematics are o page 63.

Thanks

 

[kickit2]

That control wire runs off to control three seperate circuits. It looks like one of those controls the gains of the all the amps within the system, and another enables / disables output to the speakers / sub via a relay. I'd say you need to figure out what signaling was being used on that control wire as well - I don't imagine it working without that.

I would imagine that this system expects a fixed, line level (preamp) input and handles gain levels (volume / amplitude) via commands though that control wire. Being that the first thing the signal lines do is run though buffer amps, I'm assuming this is the case. I'm really not sure what would happen if it was fed speaker levels directly.

I might be completely off base - but that's my 5 minute look over.

 

[sirboh]

Thanks Kickit2, I guess it's not a simple as I was hoping.

 

[KrisBlueNZ]

I think you were right the first time. That signal is used as a power source. It goes to several places - it controls a front panel LED, it goes into the mute circuit, and it goes into the protection circuit - but none of those circuits use it in any clever way. I think it's just a standard +12V supply from the main unit to the powered subwoofer.

Pin 7 doesn't seem to have any "control" function either. According to the markings on the schematic, it's "FC" - front centre channel audio.

 

[sirboh]

So the only tricky bit would be to trigger the sub to come on via pin8, maybe take a +12v source from within the subwoofer and wire it to a toggle switch? I'm thinking the control pin allowed the (now dead) av controller to send volume signals to the amps, Am I right in thinking this won't be necessary if I use an AV receiver?

Thanks again, I'm finding this all very interesting.

Edit, interestingly on the AV receiver I'm going to use (an old ARCAM AVR200) there's a 12v trigger out that might simplify this whole project!

 

[KrisBlueNZ]

Right, I think a +12V rail from inside the subwoofer or from your AV receiver would do the job.

Re pin 7, it has no control function. It just goes through the same type of circuitry as the other five audio signals. I don't think there is any gain-control signal.

Edit: It looks like the powered subwoofer has four more amplifiers for other speakers. Is that right? So it has the amplifiers for all or most of the other speakers in the system? That's pretty handy!

 

[sirboh]

Hi, yes the amps for all of the speakers are in the Subwoofer, I'm only interested in the sub itself though, I would think it might complicate things enormously if I used these amps to power the rest of the speakers, in effect turning it into a power amp and making the AV receiver a pre amp.

 

[sirboh]

So, the actual wiring then, The existing cable has 1 wire for the subwoofer signal (pin 4) Am I right in assuming this is the positive, and the ground cable is used as the negative? Also, would I use the same ground cable for the negative side of the 12v trigger, or will I need to create another ground (negative) for the 12v trigger from one of the other (now unused) wires in the cable?

Does any of that make sense?

 

[KrisBlueNZ]

Yes, pin 4 is the audio signal for the subwoofer. It's not "positive", but it is ground-referenced. Ground is the reference for the signals, and the negative return for the +12V supply.

 

[sirboh]

Ok, so I use the same ground reference wire for both the rca jack and the 12v trigger? I need to read up on ground reference. Would this be the same thing some people refer to as a "common" ground?

 

[KrisBlueNZ]

Yes. Ground, 0V rail, common, return, ...

 

[Wolfgang Knight]

Hi There! I'm trying to do basically the same, with another model of JVC powered subwoofer. Thank you so much for the guidelines! I have a question a (probably) silly question, if you have the time. When you say 12V to the power on pin, is it DC or AC?
Thank you so much for your time and your help!

 

[KrisBlueNZ]

Hi Wolfgang and welcome to Electronics Point

Hi There! I'm trying to do basically the same, with another model of JVC powered subwoofer. Thank you so much for the guidelines! I have a question a (probably) silly question, if you have the time. When you say 12V to the power on pin, is it DC or AC?

It's DC.

 

[Wolfgang Knight]

Thank you KrisBlueNZ! I was able to turn the powered subwoofer on. Should I pre-process (using a preamp) the input signals before feeding it into the left, right, and sub input terminals (I'm trying to use it as a 2.1 system)? I apologize for the newbie questions, audio related electronics was never my strong. Thank you again for your help!

 

[KrisBlueNZ]

It depends what kind of signals you have.

The functions of a preamp are:

1. Boost (amplify) the signal level, so a signal with low amplitude (low voltage) can drive the amplifier to maximum volume;
2. Provide easy user adjustment of the volume;
3. Provide multiple inputs with an input selector switch to choose between them;
   
4. Provide tone controls (treble/bass or sometimes a graphic equaliser);
5. Provide processing to create extra output channels - for example, a subwoofer output channel;
   
6. For phono preamps for turntables, provide a lot of gain and the required RIAA equalisation to undo the filtering that was used when the vinyl was manufactured.

If your signal comes from a CD player, it may already have a high enough level to drive the amplifier to maximum output, so you don't need function 1.

If you only want to use one source, you don't need function 3.

If you don't need treble/bass control, you don't need function 4.

If you don't have a subwoofer, or you don't mind wasting a bit of power, you don't need function 5 - you can feed the subwoofer channel from a mix of the left and right channels using two resistors to mix the channel signals together;

If you're not using vinyl records, you don't need function 6.

So you might be able to get away with just connecting a volume control potentiometer between the signal source and the power amp. I used this arrangement with my own system for a long time. But if you need those other features, you really need a preamp.

 

[Wolfgang Knight]

Wow, excellent explanation, thank you so much! I tried feeding the left and right channel using the headphone output from an old iPod, but I got absolutely nothing from the speakers (no sound at all). Do you think I should have gotten some kind of response? (I'm asking this because I don't know if maybe I connected something wrong, or the output of the iPod is not high enough, or simply the powered sub woofer is just not working.
Thank you again!

 

[KrisBlueNZ]

The headphone output from an iPod or iPhone should be able to drive the amplifier to reasonable volume. If you don't hear anything from it, there is a problem. Either you connected it wrong, or something is broken. Post a diagram of what you did, if you like.

Edit: Make sure the volume setting on the iPod is turned up!

 

[Wolfgang Knight]

According to the schematics, the 8 pin (9 if you count the ground outer ring) input is the same as sirboh posted at the beginning of this thread.

So I connected:

Positive 12V DC to the Power On Pin (pin 8)
Negative 12V DC to the Ground Outer Ring.

After this connection, I can hear 2 relay when I plug it the system, one immediately and another one around fours seconds later.

Then connected:

The Left Channel signal cable from the Ipod output to the Left Left input (pin 1)
The Right Channel signal from the Ipod output to the Right Right input (pin 2)
The Ground (the third cable) of the Ipod output to the GND Ground input (pin 4)

For this connections, I used this diagram
http://robrobinette.com/images/Audio/TRS_Pinout_4_Wire.jpg

connecting to Tip for Left, Ring for Right, and Sleeve for Ground (pin 4)