Balanced CMOY

[JammyBStard]

Is this possible?

I have an external Soundcard (firebox) with balanced outputs, I've been wanting to try-out balaced headphones for a while to see what the crack is with it so my thought turned to my old nemsis the CMOY headphone amp, I've buil two already (one even works) so I'm thinking better the devil you know.

Is there any reason why this wont work, I'm sure there is or someone would have done it before me but would pairing an identical inverting amp circuit with the usual non inverting not make a good balanced headphone amp???



Hope my ranting makes some sort of sense.

[Atilla]

You've a balance signal coming in. The - is the inverted version of the +. You pass that trough an inverting amplifier and you get ... the original version again.

This config will give you the equivalent of total silence over anything you connect at the output.

Also - this thing at the bottom is not an inverting opamp configuration anyway.

[gfiandy]

If you want to feed the signal to the headphones as a bridged mode (i.e differential) then since you have +ve and -ve signals from your preamp both amplifers need to have the same polarity.

So if you have already built a working heaphone amp you could test to see if this will work well by wiring up the +ve and -ve inputs to the two channels then using the output to drive just one headphone (ether left or right).

However there is a problems with this. Most headphones do not have a seperate ground return for each channel. The ground is shared for left and right. In this situation you cannot drive the headphones using a bridged amplifer as the two amplifers driving the -ve side will both be driving the same ground and will "fight" with each other.

Regards,
Andrew

[JammyBStard]

Cheers guys

Originally posted by Atilla
You've a balance signal coming in. The - is the inverted version of the +. You pass that trough an inverting amplifier and you get ... the original version again.
This config will give you the equivalent of total silence over anything you connect at the output.

yeah, that was a bit daft of me cheers for spotting that.

[i]However there is a problems with this. Most headphones do not have a seperate ground return for each channel. The ground is shared for left and right. In this situation you cannot drive the headphones using a bridged amplifer as the two amplifers driving the -ve side will both be driving the same ground and will "fight" with each other.[/B]

I thought the ground wouldn't be connected to the drivers, just on the connector for screeing, my scrible only shows a single channel! are you saying my left and right channels would need seperate grounds?

CHEERS
j

[Rainwulf]

Originally posted by gfiandy
If you want to feed the signal to the headphones as a bridged mode (i.e differential) then since you have +ve and -ve signals from your preamp both amplifers need to have the same polarity.

So if you have already built a working heaphone amp you could test to see if this will work well by wiring up the +ve and -ve inputs to the two channels then using the output to drive just one headphone (ether left or right).

However there is a problems with this. Most headphones do not have a seperate ground return for each channel. The ground is shared for left and right. In this situation you cannot drive the headphones using a bridged amplifer as the two amplifers driving the -ve side will both be driving the same ground and will "fight" with each other.

Regards,
Andrew

yea, this annoys me as well.
I guess its just single ended!
I am going to use a TDA7375 as a headphone amp.

[Atilla]

I don't see what the problem is when you've got balanced inputs already - both channels are already quite separated and every headphone is driven, essentially, by bridged amplifiers. I see no reason why this wouldn't work as a concept, but maybe I'm missing some detail?

Ah yes, of course, you're going to have to wire the headphones properly for that type of operation, if they aren't made that way. You can NOT simply use the usual 3-wire cable - L,R,G, this will result in spectacular failure. You do need a balanced cable going to each separate headphone. Since we're talking balanced connections here, I kind of assumed this is implied. (Note to self, do not assume)

[pacificblue]

That is the point. You would need two 3-pole connectors instead of one. Or better one 5-pole connector to avoid plugging them into a normal headphone jack.

BTW, if you are ever going to build an inverting amp, like the lower op amp in your sketch, remember that the gain setting is different for the inverting circuit. The feedback resistor would have to be 11k for a gain of 11 to match the non-inverting half.

Why don't you just feed the balanced signal to a single op-amp? You have an inverting and a non-inverting input there. http://www.nrgkits.co.uk/workshop/ba...vice_versa.htm

[angchuck]

Just make two cmoys boards, one for each channel. Can leave out ground for headphone side.

[JammyBStard]

Originally posted by Rainwulf

yea, this annoys me as well.
I guess its just single ended!
I am going to use a TDA7375 as a headphone amp.

Sounds good, you got a circuit for that?

[gfiandy]

If you are looking for something a bit better than a single opamp this app note from Burr Brown might be interesting.

http://focus.ti.com/lit/an/sboa031/sboa031.pdf

You don't need to use a bur brown opamp, the concept will work with almost any voltage feedback amp. The NE5532 would be a good cheap choice.

Andrew