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1.3V DC offset on computer audio output causing severe distortion at low volume
1.3V DC offset on computer audio output causing severe distortion at low volume
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Old 3rd September 2019, 09:05 PM   #11
phofman is offline phofman  Czech Republic
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Thanks. DC? How did you measure the original DC 1.3V offset, between which points?

Which points on the schematics did you short that 9V battery?
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Old 4th September 2019, 02:32 AM   #12
Dextrin is offline Dextrin  Grenada
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I measured the original DC 1.3V offset using a 4 pin 3.5mm jack between the Tip (pin1) and Pin 3. I got 1.6V a offset between the Tip and Pin 4.
This represents the Jack pins
______
< = = =|_____|
1 2 3 4

Also i have to add that the distortion can also be reduced if i use the waves maxx audio software to set the jack to Headset mode instead of Headphone mode ( for devices with the 4 pin connector) but pins 3 and 4 must be shorted for it to work [ shorting pins 3 and 4 can be done by using an ordinary 3 pin connector instead.]
but headset mode disables the microphone on the computer.

The 9V supply was from a linear power supply without a voltage regulator (cheap power supply for electronics ) that plugs into ~ 110 - 240V ac.
The positive rail of the supply was shorted to the Audio Ground of the headphone jack.
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Old 4th September 2019, 06:17 AM   #13
phofman is offline phofman  Czech Republic
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Quote:
Originally Posted by Dextrin View Post
The positive rail of the supply was shorted to the Audio Ground of the headphone jack.
While the negative rail was connected to what part?
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Old 4th September 2019, 06:18 AM   #14
phofman is offline phofman  Czech Republic
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I agree with Charlie - get a USB soundcard, most likely you will not be able to fix the onboard problem anyway.
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Old 4th September 2019, 01:32 PM   #15
Dextrin is offline Dextrin  Grenada
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I cant remember what the negative rail was connected to, but most likely audio ground.

Ill just have to get A USB soundcard
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Old 4th September 2019, 03:26 PM   #16
nigelwright7557 is offline nigelwright7557  United Kingdom
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Its possible you have fused a track on the motherboard for audio ground.
Connecting to USB ground bypasses it.
You can pick up usb DAC's for next to nothing on ebay.
Or spend a bit more and get better quality.
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PCBCAD51 and PCBCAD360 out now >>> https://www.murtonpikesystems.co.uk
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Old 8th September 2019, 01:53 AM   #17
MAAC0 is offline MAAC0  Portugal
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Bear in mind computer sound cards have a bias voltage on the mic inputs for connecting condenser mikes. It usually doesn't harm connected equipment.
On some computers when You select line in instead of mic via software, this bias is disabled but on most it is fixed... Oh and then there are many variations of 4 pin jack connections...LRGM LRMG MRLG for example.
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