My amp plays everywhere Except the PC

[thebadtall]

Hello. I ve recently build a 36W 2 ch amplifier. Works great.
However, when I connect it to my computer audio out, it doesnt sound at all.
It plays everywhere but the computer.

The computer plays great to a 2.1 Hercules audio system Ive got..

It has to do with resistance of my amp ? Does it need a preamp ?

thank you

 

[betwixt]

Most likely you have a sound system in the PC that has multi-function sockets. They look at the current flowing from them to try and work out what you have plugged in. Try wiring a 1K resistor across the wires going to the PC and ground, this should make it think an amplifier load has been connected.

Brian.

 

[thebadtall]

I used a T splitter for audio out from the pc, and the Hercules 2.1 system plays ok, whereas the other amp doesnt play :/
and both get signal from same cable

 

[ahsan_i_h]

T splitter is faulty.

 

[thebadtall]

splitter is not faulty, i measured it, its ok, and i connected it with crocodile cables the same..
cannot understand !

 

[ahsan_i_h]

To confirm, interchange the output connection of the T splitter and then check again.

 

[thebadtall]

i checked. T is ok. maybe the pc output is low ? do I need preamp ?

 

[ahsan_i_h]

You should not need preamp.

---------- Post added at 23:25 ---------- Previous post was at 23:20 ----------

May be, your hercules volume control knob is maximum, and in your PC, volume level is minimum.

---------- Post added 25-05-12 at 00:41 ---------- Previous post was 24-05-12 at 23:25 ----------

May be your PC amp's(in the mother board) output capasitor has a leak. Due to that leak, a DC component is there with the AC signal at your PC's output.
Now that DC component is making trouble with your amp. That DC component is not making trouble with hercules,because the input dc blocking capasitor of the hercules is perfect. Now your amp's input dc blocking capasitor has also leak or it is not present(sometimes dual supply amp do not necessarily need that). The DC component at input of your amp makes your amp to saturate. It will not harm your speaker because probably you have a output capasitor at your amp.
If it is true, then you will get a DC voltage if you connect your digital volt meter(set the selector in DC voltage range) at your PC's output when playing sound.
To solve this, connect a 1k resistor at your PC's output(parallel connection) to bypass any leakage current to ground.

 

[thebadtall]

Ahsan you speak correct. I have no courage at this time to check that.
Anyway, I connect my 12au7 tube preamp and works great, but tube life runs out fast!! .
Now I shall sleep, and tomorrow I'll check again, and maybe I'll connect 1K R
Thank you all for your help, if problem continues i'll keep asking sollutions !!

 

[tpetar]

PC sound cards should have up to 1vpp-1,5vpp signal on output. Show us circuit of your amplifier.

 

[betwixt]

I still suspect this is one of the 'clever' sound cards that can use it's sockets as inputs or outputs depending on what it thinks is plugged in. I'm guessing it thinks the amplifier is a source rather than a load and isn't routing the audio output to the socket at all. Other possibilities: is the amplifier DC coupled? if so, is there a DC offset from the sound card that is upsetting the voltage levels?

12AU7 should last for years - why does it have such a short lifetime?

Brian.