Common negative on LM3875?

troystg · 13th May 2004, 01:57 PM

Hi All-

I was wondering if I could use a common ground headphone jack with the output of BrianGT's LM3875 gainclone?

I am constructing my office desk unit now and would like a headphone jack on the front for private listening.

I searched and found lots of stuff saying it was overkill

, but nothing saying I couldn't combine the two negative leads from the separate chips to the headphone jack.

Thanks in advance,

Troy

troystg · 13th May 2004, 03:20 PM

TTT

officeboy · 13th May 2004, 03:29 PM

I don't see how it would be a problem, it's just a ground for AC. So be sure your grounding stars are all grounding to each other, for both channels.

Just don't be hooking negative leads up together, There is an OUT pin. the other side of the connection is the ground.

HDTVman · 13th May 2004, 04:16 PM

I'm a little confused here. The question was

"
I was wondering if I could use a common ground headphone jack with the output of BrianGT's LM3875 gainclone?

I am constructing my office desk unit now and would like a headphone jack on the front for private listening.

I searched and found lots of stuff saying it was overkill , but nothing saying I couldn't combine the two negative leads from the separate chips to the headphone jack.

"
It's this part about the "two negitive leads from the separate chips" part that has me confused. If you mean the Negitive Power Supply rail then the answer is NO. If your talking about the signal/power supply common / Ground other wise known as the speaker negitive, then the answer is YES. You can connect the two channels together. I would suggest resistors in series with the headphone jack to reduce the signal level to the phones. 220 to 330 ohms should be fine. With out these you will be buying lots of new headphones and hearing aids before long.

Have fun BZ

troystg · 13th May 2004, 04:33 PM

Sorry for the ambiguity.

I was hoping to use a 3 connection headphone jack(TRS) and use the tip as right spkr +, ring as left spkr + and sleeve as COMMON spkr -.

Would that pose any problem for the separate chips?

Thanks again to those who replied!!

Troy

officeboy · 13th May 2004, 05:05 PM

Should be no problems, Just be sure that the "sleeve as COMMON spkr -" is ground, and NOT a negative connection.

And yeah, major overkill for headphones.

troystg · 13th May 2004, 05:36 PM

Well, its MAIN purpose is as a desk amplifier for a small line array.

But for those quiet days I would like to jack in my phones.

Thanks again!!

Troy

Edit: spelling

Alcaid · 13th May 2004, 06:06 PM

I would suggest to lower the gain. The chips are stable down to a gain of 10 I think, and for headphones, that would be a good place to start.

officeboy · 13th May 2004, 06:35 PM

You could also just add a switch to shunt some signal to ground.
Kind of a headphones level thing, use it to drop your signal 20-30dB.
It would at least help to give your volume control a more usable range when your using the headphones.

troystg · 13th May 2004, 09:00 PM

Thanks all for the help, now this thread can be achived for future searches..

Death to the thread!!

Troy

P.S.- I'm really a positive person.

13th May 2004, 01:57 PM	#1
troystg diyAudio Member Join Date: Apr 2004 Location: Lousy Anna	Common negative on LM3875? Hi All- I was wondering if I could use a common ground headphone jack with the output of BrianGT's LM3875 gainclone? I am constructing my office desk unit now and would like a headphone jack on the front for private listening. I searched and found lots of stuff saying it was overkill , but nothing saying I couldn't combine the two negative leads from the separate chips to the headphone jack. Thanks in advance, Troy

13th May 2004, 03:20 PM	#2
troystg diyAudio Member Join Date: Apr 2004 Location: Lousy Anna	Tickle, or bump... TTT

13th May 2004, 04:16 PM	#4
HDTVman diyAudio Member Join Date: Aug 2001 Location: Chicago area	I'm a little confused here. The question was " I was wondering if I could use a common ground headphone jack with the output of BrianGT's LM3875 gainclone? I am constructing my office desk unit now and would like a headphone jack on the front for private listening. I searched and found lots of stuff saying it was overkill , but nothing saying I couldn't combine the two negative leads from the separate chips to the headphone jack. " It's this part about the "two negitive leads from the separate chips" part that has me confused. If you mean the Negitive Power Supply rail then the answer is NO. If your talking about the signal/power supply common / Ground other wise known as the speaker negitive, then the answer is YES. You can connect the two channels together. I would suggest resistors in series with the headphone jack to reduce the signal level to the phones. 220 to 330 ohms should be fine. With out these you will be buying lots of new headphones and hearing aids before long. Have fun BZ __________________ What ever makes the tunes flow

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13th May 2004, 03:29 PM	#3
officeboy diyAudio Member Join Date: Nov 2003 Location: NW Washington	I don't see how it would be a problem, it's just a ground for AC. So be sure your grounding stars are all grounding to each other, for both channels. Just don't be hooking negative leads up together, There is an OUT pin. the other side of the connection is the ground.

13th May 2004, 04:33 PM	#5
troystg diyAudio Member Join Date: Apr 2004 Location: Lousy Anna	Sorry for the ambiguity. I was hoping to use a 3 connection headphone jack(TRS) and use the tip as right spkr +, ring as left spkr + and sleeve as COMMON spkr -. Would that pose any problem for the separate chips? Thanks again to those who replied!! Troy

13th May 2004, 05:05 PM	#6
officeboy diyAudio Member Join Date: Nov 2003 Location: NW Washington	Should be no problems, Just be sure that the "sleeve as COMMON spkr -" is ground, and NOT a negative connection. And yeah, major overkill for headphones.

13th May 2004, 05:36 PM	#7
troystg diyAudio Member Join Date: Apr 2004 Location: Lousy Anna	Well, its MAIN purpose is as a desk amplifier for a small line array. But for those quiet days I would like to jack in my phones. Thanks again!! Troy Edit: spelling

13th May 2004, 06:06 PM	#8
Alcaid diyAudio Member Join Date: Nov 2003 Location: Klepp	I would suggest to lower the gain. The chips are stable down to a gain of 10 I think, and for headphones, that would be a good place to start.

13th May 2004, 06:35 PM	#9
officeboy diyAudio Member Join Date: Nov 2003 Location: NW Washington	You could also just add a switch to shunt some signal to ground. Kind of a headphones level thing, use it to drop your signal 20-30dB. It would at least help to give your volume control a more usable range when your using the headphones.

13th May 2004, 09:00 PM	#10
troystg diyAudio Member Join Date: Apr 2004 Location: Lousy Anna	Thanks all for the help, now this thread can be achived for future searches.. Death to the thread!! Troy P.S.- I'm really a positive person.

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