I came across this circuit and I was wondering about its benefits, and how it could be integrated into a headphone amplifier.
But before we start, I want to clarify one thing: is a standard 4-pin cartridge a differential output device? I suppose the answer is "it depends on how you connect it". In a 3-pin dynamic microphone, you certainly have an explicit GND pin since the moving coil is center-tapped, so it provides two 180 degrees out of phase signals. But in a voice coil with two pins, such as your standard phono cart, the signals are balanced depending on how you wire it?
In the case of the circuit I posted, I understand the input is referenced to GND via R7/R8. Normally, one end would be tied to GND and the other end would be treated as a single-ended input. In the posted configuration, the differential signals are referenced to GND via the R7/R8 resistors. I suppose those resistors have to be precisely matched to avoid distortion, but if they are, the common-mode noise will be rejected better.
First question is: does this configuration provide better rejection against common mode, in comparison with the usual single-ended configuration?
Then we have the gain stage. A headphone amp chip such as the TPA6112A2 has differential inputs, and it would be straightforward to just feed this preamp, with its differential outputs, into the gain stage. This should provide a very clean signal path and lots of headroom.
so the second question is: is this assumption correct?
Finally, IMO, any preamp really needs some sort of tone control. I understand some people will prefer a "flat response" but this is an argument I don't want to go into. I'd like to have some sort of tone control. But I'm confused as for how to implement such a thing
I haven't found any differential tone control circuits. I wonder if it's even possible to implement such a thing or if i'd basically just need two controls, one for each leg of the differential path. Which i think would be a disaster. It would be impossible (or very expensive) to eq both signals exactly the same.
So the practical way to do this would be to have a single-ended opamp, which will basically render the initial circuit (balanced output) moot. Might as well just use a single-ended output opamp and keep the differential input, and everything else single-ended
final question: is there a practical way to implement a balanced (differential) tone control?
But before we start, I want to clarify one thing: is a standard 4-pin cartridge a differential output device? I suppose the answer is "it depends on how you connect it". In a 3-pin dynamic microphone, you certainly have an explicit GND pin since the moving coil is center-tapped, so it provides two 180 degrees out of phase signals. But in a voice coil with two pins, such as your standard phono cart, the signals are balanced depending on how you wire it?
In the case of the circuit I posted, I understand the input is referenced to GND via R7/R8. Normally, one end would be tied to GND and the other end would be treated as a single-ended input. In the posted configuration, the differential signals are referenced to GND via the R7/R8 resistors. I suppose those resistors have to be precisely matched to avoid distortion, but if they are, the common-mode noise will be rejected better.
First question is: does this configuration provide better rejection against common mode, in comparison with the usual single-ended configuration?
Then we have the gain stage. A headphone amp chip such as the TPA6112A2 has differential inputs, and it would be straightforward to just feed this preamp, with its differential outputs, into the gain stage. This should provide a very clean signal path and lots of headroom.
so the second question is: is this assumption correct?
Finally, IMO, any preamp really needs some sort of tone control. I understand some people will prefer a "flat response" but this is an argument I don't want to go into. I'd like to have some sort of tone control. But I'm confused as for how to implement such a thing
I haven't found any differential tone control circuits. I wonder if it's even possible to implement such a thing or if i'd basically just need two controls, one for each leg of the differential path. Which i think would be a disaster. It would be impossible (or very expensive) to eq both signals exactly the same.
So the practical way to do this would be to have a single-ended opamp, which will basically render the initial circuit (balanced output) moot. Might as well just use a single-ended output opamp and keep the differential input, and everything else single-ended
final question: is there a practical way to implement a balanced (differential) tone control?