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
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
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. Just cut above the "y". ;-)
Cheers! Rich
There's a 4 conductor 1/8" plug used on Nokia cell headsets, if that helps...
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Is it possible to process the two signals before amplification so that one leg of each amplifier output carries the same signal? Then conventional headphone connections could be used.
Chris
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
Headphones with the 4 pin DIN headphone connectors usually have separate wires.
Paul
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!
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,
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.
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.
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
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.
Chris
In which case you contact some firms about an offer to produce them the way you want them.
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 snipped-for-privacy@eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com)
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Fair enough for driving high impedance 'phones. The power supply current might get a bit high though when there's any significant difference audio components when the loads on two of the amplifiers are effectively short circuits (through the internal 50 ohm resistors). Rather limited output power into low-Z 'phones though, with those 50 ohm resistors that can't be bridged out.
As the data sheet
Chris
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Indeed, and the question is then what is the identity of that IC?
Mention has already been made of Maxim's 'DirectDrive' scheme that creates a synthetic negative rail using a charge pump
Anyone know what Apple use in their iPods and suchlike ... is there a separate audio output IC?
Chris
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 snipped-for-privacy@eskimo.com Googleproofaddress(account:mzenier provider:eskimo domain:com)
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