Hello all.
I have built a SIT (VFET) headphone buffer for low impedance (24ohm) Sony MDR-Z1000.
Sony 2SJ18 source follower with a CFB LDO regulator can provide noise free, clear and natural sound.😀
As SIT has low Rd( Drain resistance), Power supply noise reduction is a must when using SMPS.
I installed a CFB LDO reguator (http://www.diyaudio.com/forums/power-supplies/273688-current-feed-back-power-ldo-regulator.html
To improve crosstalk caused by headphone cable L-R common wire, crosstalk canceller (bridging resistor between L-R output) is added.
Zobel is tuned for optimal transient response.
Gate resistors are to prevent oscilation when VR is minimum.
Gain 0.557
residual noise 5.3 uv (30Khz BW)
THD+n 0.1% (10mW, 24ohm)
1% (100mW, 24ohm)
f. response 10-100Khz (-0.5db)
Power 600mA 15V
Weak point is pop(bang) noise on power on, I wait few second after powering up.
I have built a SIT (VFET) headphone buffer for low impedance (24ohm) Sony MDR-Z1000.
Sony 2SJ18 source follower with a CFB LDO regulator can provide noise free, clear and natural sound.😀
As SIT has low Rd( Drain resistance), Power supply noise reduction is a must when using SMPS.
I installed a CFB LDO reguator (http://www.diyaudio.com/forums/power-supplies/273688-current-feed-back-power-ldo-regulator.html
To improve crosstalk caused by headphone cable L-R common wire, crosstalk canceller (bridging resistor between L-R output) is added.
Zobel is tuned for optimal transient response.
Gate resistors are to prevent oscilation when VR is minimum.
Gain 0.557
residual noise 5.3 uv (30Khz BW)
THD+n 0.1% (10mW, 24ohm)
1% (100mW, 24ohm)
f. response 10-100Khz (-0.5db)
Power 600mA 15V
Weak point is pop(bang) noise on power on, I wait few second after powering up.
Attachments
> To improve crosstalk caused by headphone cable L-R common wire, crosstalk canceller (bridging resistor between L-R output) is added.
So what is the output impedance of each channel ?
And what is the common ground cable impedance of the Sony headphone ?
Thanks in advance,
Patrick
So what is the output impedance of each channel ?
And what is the common ground cable impedance of the Sony headphone ?
Thanks in advance,
Patrick
Cross talk cancelling
The output impedance of channels Zout are around 2 ohm.
As measuring low impedance precisely is very difficult, I measure voltages level instead.
When I cancel the crosstalk, I measure the crosstalk level by driving one channel and disconnect other channel output, measure the output level of this open channel by HP8903B audio analyzer . this is the crosstalk generated by ZC. The level was -38.8db/1Khz for MDR-Z1000 with long cable.
The cancelling Resistor might be around 200ohm (2*100). Then I prepared 500 ohm VR to cover this range. Then set up the circuit and minimized the differential Voltage to get the crosstalk down. the cancelling point was very critical. I finally set to 220 ohm.
This could imrove the crosstalk around -15db.
The output impedance of channels Zout are around 2 ohm.
As measuring low impedance precisely is very difficult, I measure voltages level instead.
When I cancel the crosstalk, I measure the crosstalk level by driving one channel and disconnect other channel output, measure the output level of this open channel by HP8903B audio analyzer . this is the crosstalk generated by ZC. The level was -38.8db/1Khz for MDR-Z1000 with long cable.
The cancelling Resistor might be around 200ohm (2*100). Then I prepared 500 ohm VR to cover this range. Then set up the circuit and minimized the differential Voltage to get the crosstalk down. the cancelling point was very critical. I finally set to 220 ohm.
This could imrove the crosstalk around -15db.
Attachments
Don't you think you should short the one labelled "no input" to ground instead of leaving it open ?
Patrick
Patrick
This Spice file illustrates the principle.
Of course the output impedance is not a fixed value, and the cable impedance is difficult to measure.
But if you can trim as follows :
1. Ground one input A, and put a 100Hz signal on the other input B (say 1Vrms).
2. Measure AC voltage across the headphone at the driver A using a DMM.
3. Trim the cancellation resistor until the voltage across driver A is 0.
Then you should have the right value at that output level.
And of course you can also listen instead of using a DMM.
Clever idea. Never thought of that ..... 😉
Only works for that particular headphone though ....
Patrick
.
Of course the output impedance is not a fixed value, and the cable impedance is difficult to measure.
But if you can trim as follows :
1. Ground one input A, and put a 100Hz signal on the other input B (say 1Vrms).
2. Measure AC voltage across the headphone at the driver A using a DMM.
3. Trim the cancellation resistor until the voltage across driver A is 0.
Then you should have the right value at that output level.
And of course you can also listen instead of using a DMM.
Clever idea. Never thought of that ..... 😉
Only works for that particular headphone though ....
Patrick
.
Yes, This is dedicated to SONY MDR-Z1000.
Different headphone needs different crosstalk cancelling resister.
Adjust it by hearing is I think difficult.
Different headphone needs different crosstalk cancelling resister.
Adjust it by hearing is I think difficult.
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