Very simple passive mixer driving me nuts. Please help.

Bobhof · 28th May 2006, 09:43 AM

Hi all,

I am trying to make a simple passive mixer to sum the outputs from my computer (minijack) and my DVD player (RCA out) and send them into my sub (RCA inputs). I also need the output to be cut off when I plug my headphones into to a switched jack. Diagram is attached.

Here's the problem: it works perfectly when going out to the sub (whether I plug the sub into the RCA or the jack out) but when I plug in my headphones the sound is hardly audible. I have tried various phones with the same effect. It's driving me nuts! Surely if there is sound coming out it should work for either headphones or the amp?

Any help would be greatly appreciated.

Rob

tschrama · 28th May 2006, 10:34 AM

You are trying to feed your headphone through 10K resistors, correct? This might attenuate the signal to much for 32 Ohm or even 150 Ohm headphones...

Bobhof · 28th May 2006, 11:11 AM

Yeah, but the level is fine when going to the amp. Should I just remove the resistors or do I need them? Sorry, really don't know much about this stuff.

lndm · 28th May 2006, 12:53 PM

The amp will have a relatively high input impedance. The 10k resistors will not be significant here, they will be significant to the headphones.

Bobhof · 28th May 2006, 02:08 PM

I see. Is there any reason not to take the resistors out of the circuit? I just put them there because I read that that was how to sum inputs.

tschrama · 28th May 2006, 02:33 PM

Yes, you need those 10K resistors for the mixing. But nor the RCA output of a DVD nor the line out of a PC is meant to be used for a headphone. You need a headphone amp for that.

Bobhof · 28th May 2006, 03:47 PM

But the line out from my pc is a headphone out. Works fine if I plug the phones into my pc. What do you think I should do?

tschrama · 28th May 2006, 06:06 PM

replace the 10K with 470 Ohm and see if that helps...but it might be that the dvd RCA output will not be suiteble for driving a headphone...

gl,
Thijs

Bobhof · 28th May 2006, 06:47 PM

Thanks for all your help.

Nigel Goodwin · 28th May 2006, 08:58 PM

You really need an amplifier to feed the headphones, what you're trying to do is WRONG - which is why it doesn't work!.

28th May 2006, 08:58 PM	#10
Nigel Goodwin diyAudio Member Join Date: Jul 2005 Location: North Derbyshire	You really need an amplifier to feed the headphones, what you're trying to do is WRONG - which is why it doesn't work!. __________________ Nigel Goodwin

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28th May 2006, 10:34 AM	#2
tschrama diyAudio Member Join Date: Jul 2001 Location: The Netherlands	You are trying to feed your headphone through 10K resistors, correct? This might attenuate the signal to much for 32 Ohm or even 150 Ohm headphones...

28th May 2006, 11:11 AM	#3
Bobhof diyAudio Member Join Date: Apr 2006 Location: Cape Town	Yeah, but the level is fine when going to the amp. Should I just remove the resistors or do I need them? Sorry, really don't know much about this stuff.

28th May 2006, 12:53 PM	#4
lndm diyAudio Member Join Date: Mar 2006 Location: nsw	The amp will have a relatively high input impedance. The 10k resistors will not be significant here, they will be significant to the headphones.

28th May 2006, 02:08 PM	#5
Bobhof diyAudio Member Join Date: Apr 2006 Location: Cape Town	I see. Is there any reason not to take the resistors out of the circuit? I just put them there because I read that that was how to sum inputs.

28th May 2006, 02:33 PM	#6
tschrama diyAudio Member Join Date: Jul 2001 Location: The Netherlands	Yes, you need those 10K resistors for the mixing. But nor the RCA output of a DVD nor the line out of a PC is meant to be used for a headphone. You need a headphone amp for that.

28th May 2006, 03:47 PM	#7
Bobhof diyAudio Member Join Date: Apr 2006 Location: Cape Town	But the line out from my pc is a headphone out. Works fine if I plug the phones into my pc. What do you think I should do?

28th May 2006, 06:06 PM	#8
tschrama diyAudio Member Join Date: Jul 2001 Location: The Netherlands	replace the 10K with 470 Ohm and see if that helps...but it might be that the dvd RCA output will not be suiteble for driving a headphone... gl, Thijs

28th May 2006, 06:47 PM	#9
Bobhof diyAudio Member Join Date: Apr 2006 Location: Cape Town	Thanks for all your help.