Tapping to Head Unit PCB for Lineout

[neilpaulx]

Good day to all,

First post but have been reading this forum for a long time...

Just like to ask a guide here where I can tap in the schematic shown below for the line level out. I like to install an external amp to my Clarion Head Unit but this model don't have line level out. So instead of adding LOC, I plan to take the line signal in the PCB before it reache the amplifier section.

In the schematic attached, I'm assuming that I can tap in Pin 17, 20, 24 and 27. May anybody here can advise me if this is right?

Thanks

[Perry Babin]

The output level probably won't be enough. There may be other issues also. Can you send me the full schematic?

babin_perry@yahoo.com

[neilpaulx]

Thanks Perry,

Files sent to your email..

[Perry Babin]

At the point (volume control position) where the internal amp is driven to clipping, the volume control IC produces ~1/2v. If that is near the maximum volume on the head unit, that's probably the most you can get from the IC.

I couldn't find a datasheet on the volume IC but I doubt that it has any internal protection. It may be possible to damage the volume IC (static discharge, contact with an external voltage source...). It's also impossible to know the output impedance of the IC without the datasheet. It may be too high. An op-amp buffer would solve both of these problems but would make it more complex. There may be better options.

What amp are you going to drive with this?

[djQUAN]

you would need a op amp based preamp after the volume IC. most of them cannot drive enough current and voltage to get reasonable frequency response off long cable runs.

to keep things simple, you can use a NJM4560 dual op amp, add a bit of gain and run them off the 8V analog supply and analog ground. that would have around 2Vrms output depending on gain...

[1moreamp]

You could also use a simple line driver off the shelf. Its input loading would be minimal and the output would be adjustable and it uses a internal bi-polar supply for that high end touch. And they usually isolate the input from the output enough to protect all the radio internals from any serious issues that may come from any auxiliary gear you might attach...I have done this and it worked out wonderful and the client was stoked with the SQ and adjust ability...

Muting of the signal may become a issue, but between J-fets and relays and delayed turn on of the line driver their are simple ways around this also. You can also loom for the input electrolytic caps on the output amp chip and tap in at that point also. And by using a off the shelf line driver you save time and trouble fabricating most of what you will need to get the job done as the Line Driver will already have all the needed DC blocking on its input anything you might add would need...

Hope this is helpful, we were doing this sort of thing all the way back to the early 90's and especially to stock HU's like Lexus and what not....

[neilpaulx]

Thank you very much guys for the replies...

Now this gets complicated than I thought and losing the mute means losing my steering remote.

I might just add a resistor after the HU amplifier to drop the voltage. The pin out in my first post will go to TA6276H Bipolar Linear IC and out a 6.1V to the speaker. My amp is Boston Acoustics GT series which can handle 200mv-8v input signal but I don't know the input impedance. Can I just use a resistor of 10K in series to + side and xx R accross? Anybody know the value of xx R? Thanks.

[Perry Babin]

The 200mv-8v is AC voltage. The 6.1v on the schematic is DC voltage.

I think you can get good sound quality from a good line output converter.

The output on the TA8276 will swing from 0v to 6v when the head unit is switched on. This may cause a loud pop in the amp even if you use one or more resistors. The LOC has a transformer that prevents the 6v of DC from causing a pop when switching the system on or off.

[neilpaulx]

Thanks Perry. Well I will just buy LOC then and avoid trouble. Thanks guys for the input.

Lot's of things to learn.....