stereo earphones with 4 conductors?

[Bill]

Hi,

Does anyone know of stereo earphones with a connector with four
conductors? (ie., they don't share the ground node). I would like to
drive them in a bridge-tied load (BTL) configuration, to save the
coupling capacitors.

Thank you

 

[Kalman Rubinson]

Hi,

Does anyone know of stereo earphones with a connector with four
conductors? (ie., they don't share the ground node). I would like to
drive them in a bridge-tied load (BTL) configuration, to save the
coupling capacitors.

I do not know but I suspect that all earphones and headphones with
separate leads to each piece can be rewired to keep the leads
independent.

Kal

 

[Rich Grise]

Does anyone know of stereo earphones with a connector with four
conductors? (ie., they don't share the ground node). I would like to
drive them in a bridge-tied load (BTL) configuration, to save the
coupling capacitors.

Sure. Just cut above the "y". ;-)

Cheers!
Rich

 

[David Lesher]

Hi,

Does anyone know of stereo earphones with a connector with four
conductors? (ie., they don't share the ground node). I would like to
drive them in a bridge-tied load (BTL) configuration, to save the
coupling capacitors.

There's a 4 conductor 1/8" plug used on Nokia cell headsets,
if that helps...

 

[Paul Keinanen]

Hi,

Does anyone know of stereo earphones with a connector with four
conductors? (ie., they don't share the ground node). I would like to
drive them in a bridge-tied load (BTL) configuration, to save the
coupling capacitors.

Headphones with the 4 pin DIN headphone connectors usually have
separate wires.

Paul

 

[Bill]

In a normal bridge-connected amplifier the load is connected between the
outputs of a pair of amplifiers each with a gain A, the input signal Vi is
fed to one amplifier and is inverted and fed to the other as -Vi. The
voltage across the load is the difference AVi-(-AVi) = 2AVi.

In the stereo case, if the input signals are Vl and Vr the output signals
from the two pairs of amplifiers are 2AVl and 2AVr.

If the circuitry is changed a little so the input signal for the opposite
stereo side is added to the input of each amplifier then:

for the left channel the pair of output signals would be 2A(Vl+Vr) and
2A(-Vl+Vr) giving a (difference) output signal of 2AVl as before;

for the right channel the pair of output signals would be 2A(Vl+Vr) and
2A(Vl-Vr) giving a (difference) output signal of 2AVr as before;

but one leg of each carries the same voltage so their connections could be
paralleled, or a single amplifier used for left and right channels, and only
three headphone connections would be required whilst retaining the low
supply voltage advantage of the BTL configuration.

Where's the flaw? Any mismatching of amplifier gains would introduce
crosstalk, but a little of that may not be such a bad thing for headphone
listening.

Chris

I think that the idea is excellent. One drawback is that the output
power capability is reduced (the dynamic range is lower, because now
the signal that does not have to saturate is A*(Vl+Vr), instead of
A*Vl. So, half the voltage, and 1/4 of the power, which is a lot.

Even that, there are cases in which you have plenty of output power
capability (and you could live with 1/4 of it), and this idea would
help save you two (relatively) big electrolytic capacitors. I've
searched for ICs implementing this idea, but haven't found any, and
I'm surprised. Ok, in case of high power speakers, it makes no sense,
because they never share any node, in any connector. But for
ear/headphones, with so many 3-node connectors out there, I think
there would be market. Maybe I'm missing something else.

Thanks!

 

[Bill]

I do not know but I suspect that all earphones and headphones with
separate leads to each piece can be rewired to keep the leads
independent.

Kal

Sure, but we need to buy earphones and include them "as they are",
with our product. We can't modify each earphone, in mass production.

Best,

 

[Holloway,Graham \(UK\)]

I think that the idea is excellent. One drawback is that the output
power capability is reduced (the dynamic range is lower, because now
the signal that does not have to saturate is A*(Vl+Vr), instead of
A*Vl. So, half the voltage, and 1/4 of the power, which is a lot.

Even that, there are cases in which you have plenty of output power
capability (and you could live with 1/4 of it), and this idea would
help save you two (relatively) big electrolytic capacitors. I've
searched for ICs implementing this idea, but haven't found any, and
I'm surprised. Ok, in case of high power speakers, it makes no sense,
because they never share any node, in any connector. But for
ear/headphones, with so many 3-node connectors out there, I think
there would be market. Maybe I'm missing something else.

Thanks!

If it's any use, I've tried the TI/Burr-Brown DRV134's to drive headphones.
Just tied the left -ve output of the balanced output to the right -ve. Works
fine.


Graham H.

 

[Bill]

I've just known of approaches like the DirectDrive by Maxim (to be
able to use stereo earphones with connectors with 3 nodes). Not bad,
but they use switched capacitor charge pumps, and I have to avoid
noisy circuitry like that.

 

[Michael Black]

Hi,

Does anyone know of stereo earphones with a connector with four
conductors? (ie., they don't share the ground node). I would like to
drive them in a bridge-tied load (BTL) configuration, to save the
coupling capacitors.

Thank you

And then you end up with not being able to use just any headphones simply
because you don't want the capacitor. Headphones are the thing that's
likely to break first, and you've ended up with a situation where the user
will then end up not being able to use the gizmo since they have to order
the headphones from some single source in New Jersey.

I have a headphone jack on the car radio that I use as a bedside radio. I
put the capacitor on it so I could use a single output of the car radio to
feed the headphones. I sure didn't need the extra power of balanced
output, and the capacitor was hardly "large". You should have been around
forty years ago, then a 10,000uf capacitor at 17v was the size of a coke
can. Now, it's not any extra size.

Since this sort of thing is dealt with all the time in commercial
equipment, you've made the issue more complicated than necessary. They
live with the usual headphones, and thus they must live with the "nasty"
output capacitor. On the other hand, my Sansa Fuze is small enough that
there must be miniscule capacitors at the needed capacitance, since all of
the unit complete with batteries and LCD screen is jammed in that tiny
package.

Michael

 

[Kalman Rubinson]

Sure, but we need to buy earphones and include them "as they are",
with our product. We can't modify each earphone, in mass production.

OK. You did not so specify. If you are buying them in
bulk, you should query the manufacturers directly since you
will also have to deal with the specification of the
connector. The standard connector is tip-ring-base and only
accomodates 3 lines.

That said, it is possible that any earphone with a
tip-ring1-ring2-base plug is, or can be, suitable.

Kal

 

[Bill]

Since this sort of thing is dealt with all the time in commercial
equipment, you've made the issue more complicated than necessary. They
live with the usual headphones, and thus they must live with the "nasty"
output capacitor. On the other hand, my Sansa Fuze is small enough that
there must be miniscule capacitors at the needed capacitance, since all of
the unit complete with batteries and LCD screen is jammed in that tiny
package.

No, they must not live with the output capacitors. You can avoid them
with a dual supply (or with charge pumps if you run from an explicit
single supply). I'd bet that's what they do in tiny MP3s, etc.

It's only that I don't want to use noisy circuits like charge pumps,
and I don't have a dual supply.

Best

 

[Sjouke Burry]

Sure, but we need to buy earphones and include them "as they are",
with our product. We can't modify each earphone, in mass production.

Best,

In which case you contact some firms about an offer to
produce them the way you want them.

 

[Mark Zenier]

You're right, it throws away the output power advantage of the bridge
configuration. It was getting a bit late when I wrote that!

A simpler arrangement providing the same output power and using no more
parts would use conventional push-pull amplifiers for left and right, and a
third amplifier fed with no signal to provide a stiff half-rail node to
which both loads would be returned. That doesn't have the same crosstalk
issue.

Which appears to be what some $10-20 radio/cassette players use for
the audio output amps in their one IC. The "ground" in the earphone
jack is at 1/2 the battery voltage. (The jack is mostly plastic).
There's only a + and - connection at each end of the three volt supply,
so it's a derived virtual ground.

Mark Zenier [email protected]
Googleproofaddress(account:mzenier provider:eskimo domain:com)

 

[Mark Zenier]

Indeed, and the question is then what is the identity of that IC?

Looking at my notes and digging out a screwdriver and just looking
showed part numbers of LAG668F, LAG665CB and LAG665F. A google
search for LAG665F indicated the manufacturer is Mitsumi. (They're
only good for about three hard drops, so I have plenty of corpses to
autopsy).

Mark Zenier [email protected]
Googleproofaddress(account:mzenier provider:eskimo domain:com)