Headphone jack out as a line out

[wf1318]

Hello!

Please take a look on the following picture first.

Recently I had build 2 of this amp circuit for my family's PC as a headphone amp.
This little amp work OK when connected to headphone.
After that I have an idea is that I want to use the amp headphone jack output as a line out to drive a 3W cheap power amp,
just want to see what kind of sound will come out.
However there is no sound come out.

Therefore I check the circuit again, and then I connected it back to the headphone, and it work fine without any problem.

I don't know what happen, why it works fine with a headphone but not OK as a line out.

After that, I connect these 2 amp circuit as the following setup just want to find out what the is problem:



I use a Headphone Jack Splitter connected to Amplifier 1,
and then this Headphone Jack Splitter is conneced to a headphone and also a audio cable is connected to Amplifier 2.
As the result there is no sound come out from the Headphone.
However, when I unplugged the audio cable, the sound is back to the headphone!

So, what is the problem with this amp?

Can I add / modify the component that I can make this amp can connect to other power amp?

Oh, sorry for my poor english....

Anyway, thank you.

 

[BradtheRad]

If it puts out a strong enough signal for the headphones, then it ought to be sufficient for the amplifier.

Did you try feeding another sound source to the plug? Did that work?

 

[wf1318]

I study the circuit again.
I found that the output terminal of this circuit is using positive (+) with the output signal, not like other normal audio device using Ground (-) with the output signal.

So, how can I convert a positive (+) output signal to Ground (-) output signal ????

Can someone suggest some simple circuit to convert it?

Thank you.

 

[godfreyl]

I study the circuit again.
I found that the output terminal of this circuit is using positive (+) with the output signal, not like other normal audio device using Ground (-) with the output signal.

Yes, it is a strange circuit, and not very good.

So, how can I convert a positive (+) output signal to Ground (-) output signal ????

Can someone suggest some simple circuit to convert it?

The easiest way is to connect a capacitor in series with the output. 1uF or higher is OK for line out. 100uF or higher will be needed for headphones. A resistor to ground after the capacitor is a good idea too.

If you use 100uF and 1K, it will be good for headphones and line out.

 

[ALERTLINKS]

R2,R3 and capacito C4 provide +ve biasing and bootstrapping.
https://en.wikipedia.org/wiki/Bootstrapping_(electronics)
Connect another capacitor in series with speaker like this to connect with -ve ground.

Similar approach,

 

[wf1318]

Thanks for "godfreyl" and "ALERTLINKS" suggestion first.
I follow the method they provided to modify the circuit a little bit.
Finally it work perfect without any problem!!!

Thanks again!!!