Help~ only one channel sounds

[wanggogh]

I newly completed a truepath and have 2 bugs.
1) only left channel sounds and right channel remains slient.
2) when I turn it off, a "jit" sound last for 1 sound, quite loud

What can I do? Please help, thanks so much!

[thomaseliot]

First check DC voltage on outputs of both channels, when muted and when unmuted.

Check the output inductor in the bad channel, maybe the enamel is still there.

Next step is to post pictures, search in the Truepath forum and search again for bad soldering on the PCB.

[wanggogh]

thanks for reply.
I checked the followings:
Normal (left) channel output during unload:
muted stage: +2.6V DC
unmuted stage: +6mV DC
Shut down stage: -195mV DC

Slient (right) channel output during unload:
muted stage: -2.6V DC
unmuted stage: +2mV DC
Shut down stage: +195mV DC

There is a 0.9V AC pop up for a very shot time when I shut down, I think that's why there is a "jip" sound.

Resistance is 0 between the totoid/ join points, the enamel should be cleared.

[wanggogh]

I am so careless. I reversed the +ve & -ve of input and output of the silent channel.
But after I corrected it, there is no sound!

[thomaseliot]

The pop at shut down is normal. Mute the amp before turning off.

Your amp unmutes regularly, because you have DC down to 2mV on the silent channel. So the chip is OK. Check again the signal path
before and after the chip for components in wrong places.

[wanggogh]

Thanks thomaseliot, I found the bug finally. There is no contact between input and C100 capacitor, I short them by a lead and problem is solved. Now both channels are singing.

I now have 2 concerns:
1) There is a background low frequency noise that I can hear is 10cm away from the speakers. I will try to use metal board to isolate the main board later.

2) Although I can mute the speakers every time I turn off the truepath to eliminate the "jit" pop up sound, it's too inconvenience since the mute botton is located at the back of the case. Is there any better method to protect my speakers?

[thomaseliot]

Noise is always a bad soldering problem. Annoying, but the only way is check connection an resolder.

I use Velleman K4700 for speaker protection and silent power on/off.