So... would anyone be able to point me to some measurements of the effect of current driving on headphones' distortion performance (as done by Meriläinen on speaker drivers)? The effect would have to be much smaller than with speaker drivers since power levels just aren't the same (and I mean, good cans will hit 0.1% at 100 dB at mid-high frequencies even in voltage drive), but there should be something, right?
To do so, one would need to have :
1) a palanar magnetic headphone of a certain quality;
2) a calibrated headphone measurement system that can detect distortion to say better than -90dB.
Unfortunately, I have neither.
And basically you are then measuring the headphone under current drive.
AND not the transconductance amplifier itself.
Patrick
1) a palanar magnetic headphone of a certain quality;
2) a calibrated headphone measurement system that can detect distortion to say better than -90dB.
Unfortunately, I have neither.
And basically you are then measuring the headphone under current drive.
AND not the transconductance amplifier itself.
Patrick
Perhaps Table 1 in this reference has the answer you are looking for :
https://hal.archives-ouvertes.fr/hal-01112181/document
2 more interesting links :
Current-Driving of Loudspeakers
Current-Driving of Loudspeakers
Patrick
https://hal.archives-ouvertes.fr/hal-01112181/document
2 more interesting links :
Current-Driving of Loudspeakers
Current-Driving of Loudspeakers
Patrick
Sorry Patrick, had another project
(no Hifi-Project)Yes, I'm still interested.
Greetings Arnd
Proto Board Building Notes
.
As the three of you will be ready soon for building using the proto boards, here are a few related details.
Please take time to read through.
There is a small error in the proto PCB.
The bottom pad of R34 is missing, a software conversion error.
It can be easily fixed by using a piece of 0.3mm copper to connect R34 bottom end to the neighbouring R32.
Do not use a large diameter copper, as it will put strain on the resistor.
I use one copper strand removed from a stranded wire.
If you wish to reduce bias a bit (170mA is a bit high for 50R load), you can increase the value of R30.
If you wish to optimise the circuit for 50R load (at 20dB gain), you can change R7,8 to 1.3k.
You should always attached a load (50R) for testing.
The amp does not work properly without a load connected at the output.
For the 50R dummy load for testing, any 2W 51R metal film resistor will do.
Unless you want to measure distortion with that, then you need a low distortion resistor as well.
You can make one up using 4x 200R Dale RN60 in parallel. 20x RN55 1k would of course also do.
Once you finish with all the measurements you want to do, you must remove the dummy.
Else the amp has to drive the 50R and your headphone (another 50R) in parallel.
In operation, you should always have a phone plugged in when you switch the amp on.
The SHPP will protect the phone for any switch on transients by shorting the phone V+ to Gnd.
Also it takes a few minutes before DC offset current stabilises (unless with DC servo).
So SHPP Trans is a must.
Patrick
.
As the three of you will be ready soon for building using the proto boards, here are a few related details.
Please take time to read through.
There is a small error in the proto PCB.
The bottom pad of R34 is missing, a software conversion error.
It can be easily fixed by using a piece of 0.3mm copper to connect R34 bottom end to the neighbouring R32.
Do not use a large diameter copper, as it will put strain on the resistor.
I use one copper strand removed from a stranded wire.
If you wish to reduce bias a bit (170mA is a bit high for 50R load), you can increase the value of R30.
If you wish to optimise the circuit for 50R load (at 20dB gain), you can change R7,8 to 1.3k.
You should always attached a load (50R) for testing.
The amp does not work properly without a load connected at the output.
For the 50R dummy load for testing, any 2W 51R metal film resistor will do.
Unless you want to measure distortion with that, then you need a low distortion resistor as well.
You can make one up using 4x 200R Dale RN60 in parallel. 20x RN55 1k would of course also do.
Once you finish with all the measurements you want to do, you must remove the dummy.
Else the amp has to drive the 50R and your headphone (another 50R) in parallel.
In operation, you should always have a phone plugged in when you switch the amp on.
The SHPP will protect the phone for any switch on transients by shorting the phone V+ to Gnd.
Also it takes a few minutes before DC offset current stabilises (unless with DC servo).
So SHPP Trans is a must.
Patrick
DC Servo
.
The Alpha tester built his version with the DC servo.
It works first time and you do not have to worry about start-up DC.
But even if you were to use the servo, you should still try to trim CCS1/2 such that the voltage across R3,5,4,6 are identical.
To do that, remove R23 so that the servo is not getting in the way. Use a 50R load at the output.
Patrick
.
The Alpha tester built his version with the DC servo.
It works first time and you do not have to worry about start-up DC.
But even if you were to use the servo, you should still try to trim CCS1/2 such that the voltage across R3,5,4,6 are identical.
To do that, remove R23 so that the servo is not getting in the way. Use a 50R load at the output.
Patrick