How to intergrate headphone amp into my power amp.

[Boscoe]

Just wondered how i go about this as I want the volume to be control by the power amp volume control but do I use the power amp outputs with a resistor network in with the headphone output?

I will be using Carlo's DX Class A design with two lots of the 2sc3281/2sa1302's in stereo.

Thanks
Boscoe

EDIT- How do I disable the speaker outputs when i have the headphones plugged in?

 

[jaycee]

Yes, you basically just use some power resistors to pad down the level for headphones.

To disable the speakers, you'd use a relay in line with the speakers (and while you're at it, add a DC protect circuit), and simply open the relay contacts when the headphones are plugged in.

 

[Boscoe]

Okay for the power to the coil can I do something in the way of when you plug the headphones in, with some electronics basically put the relay on say the left and ground terminal to energise it?

Have any idea of what sort of values I need for the resistors and the electronics needed? I did kind of think of something last night but it's early and can't remember what it was!

 

[AndrewT]

the TRS socket has the facility to break the feed to the speakers.
I cannot vouch for the quality of that make and break but it does work.

If your amp produces 50W into 8ohm and you add a 16ohm resistive ladder then that ladder must be able to cope with 25W of potential short term overload.

I'd suggest you aim for ~100r for the resistive ladder.
100r feeding 10r to ground. Tap off across the 10r gives a -20dB signal to feed the headphones. The 100r wll have a worst case overload power of about 4W so a 2W to 5W resistor would do for the dropper resistor.

If the 10r is too loud for your headphone listening, just add a second 10r in parallel and you get -26dB to feed the headphones.

 

[Boscoe]

Thanks, would be possible at all to do a small schematic!!! I know I sound stupid, just didn't quite get it that's all. Much appreciated!

 

[AndrewT]

two resistors in series does not need a schematic.