I would like to build an headphone amplifier based on the well known opa + buf634 pair configured as seen on the datasheet, but i would also add an input buffer before the pot to have a better impedance interface with various sources.
My questions are:
1) is this correct or i have to add series and/or parallel resistor between the first opamp and the pot and/or between the pot and the second opamp?
2) which is the correct value for the pot? (i have one 20K and one 100K ALPS)
Ciao
Andrea
My questions are:
1) is this correct or i have to add series and/or parallel resistor between the first opamp and the pot and/or between the pot and the second opamp?
2) which is the correct value for the pot? (i have one 20K and one 100K ALPS)
Ciao
Andrea
Attachments
May be there is a misunderstanding.
I meant,
Yes youre right, there will be no input impedance swing if you use just a potentiometer on input.
However, I adviced a parallel resistor to middle pin of the pot to gnd. So in this case you will have a variable input impedance. But this is a need I think. Because as my experiences, if an opamp works without an input load resistor then it becomes unstable situation. And if your potentiometer fails while running without a parallel resistor then your headamp may oscillate and you may say goodbye forever to your precious headphone..
I meant,
Yes youre right, there will be no input impedance swing if you use just a potentiometer on input.
However, I adviced a parallel resistor to middle pin of the pot to gnd. So in this case you will have a variable input impedance. But this is a need I think. Because as my experiences, if an opamp works without an input load resistor then it becomes unstable situation. And if your potentiometer fails while running without a parallel resistor then your headamp may oscillate and you may say goodbye forever to your precious headphone..
Ok.. If you plan to measure the noise and compare with some others then youre right.
I've designed and made (also published in this forum) a class A biased headphone amplifier with really cheap components. In the beginning it had 2x gain and by the time I needed more gain for especially a 250R headphone. Then I have changed its gain to 4.3X...
So, it has a OPA134 opamp in front with 4.3X gain and there was no input load resistor before it but a 100K potentiometer. It was also a DC coupled headamp and there was no Ci or Cin.. The DC offset was only 4mV at all time. And believe me;
I have never heard anykind of noise, I have never noticed that it was working or not working even while its input was open!
Anyway,
The buffer is not necessary, remove it and go with just one OPA and a buffer, IMO...
I've designed and made (also published in this forum) a class A biased headphone amplifier with really cheap components. In the beginning it had 2x gain and by the time I needed more gain for especially a 250R headphone. Then I have changed its gain to 4.3X...
So, it has a OPA134 opamp in front with 4.3X gain and there was no input load resistor before it but a 100K potentiometer. It was also a DC coupled headamp and there was no Ci or Cin.. The DC offset was only 4mV at all time. And believe me;
I have never heard anykind of noise, I have never noticed that it was working or not working even while its input was open!
Anyway,
The buffer is not necessary, remove it and go with just one OPA and a buffer, IMO...
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.