TDA8946AJ headphone amplifier
I built this up to see how the TDA8946AJ DC-controlled volume element sounds. According to the datasheet and comparing the figures with those for the same amp minus the volume control (TDA8946J) there's some additional THD so I was curious to hear how transparent it is.
There are transformers both on the input and the output of this. On the input to match levels (4:1 step down) and to do unbal-bal conversion. On the output again for the same reasons, except bal-unbal to drive my phones which I've not modified for 4 wire operation. The trafos are ferrite (=very cheap) RM10 for the input (under the board) and RM12 for output (behind the board). In order to be able to match a variety of phones, I've wound 4 identical secondaries so they can be combined in series or parallel.
From the pic you'll see the customary array of caps - I need to order up some lowESR (preferably NCC) 1800uF caps to do better justice to the rails. Last night I experimented with some ceramics across the rails and for the first time didn't much like what I heard, so I went back to 'lytics, just more of them. The chip takes only 40mA from the 15V rails hence doesn't need a heatsink - I have mounted it at the edge of the board though as I might just play with CCSs on the outputs to get classA....
If anyone is interested in building one of these and wants to know the details of the trafos, just ask.
Update - my contact on Taobao turned up some amazingly low ESR caps for me which aren't a listed type on Nichicon's website. HZ series - 1800uF at 16V comes in a 10*25mm can and turns in an eye-watering 6.5mohm ESR. This ESR equals polymer caps but with much higher available capacitance and they're much cheaper. Breaking them in now.....
There are transformers both on the input and the output of this. On the input to match levels (4:1 step down) and to do unbal-bal conversion. On the output again for the same reasons, except bal-unbal to drive my phones which I've not modified for 4 wire operation. The trafos are ferrite (=very cheap) RM10 for the input (under the board) and RM12 for output (behind the board). In order to be able to match a variety of phones, I've wound 4 identical secondaries so they can be combined in series or parallel.
From the pic you'll see the customary array of caps - I need to order up some lowESR (preferably NCC) 1800uF caps to do better justice to the rails. Last night I experimented with some ceramics across the rails and for the first time didn't much like what I heard, so I went back to 'lytics, just more of them. The chip takes only 40mA from the 15V rails hence doesn't need a heatsink - I have mounted it at the edge of the board though as I might just play with CCSs on the outputs to get classA....
If anyone is interested in building one of these and wants to know the details of the trafos, just ask.
Update - my contact on Taobao turned up some amazingly low ESR caps for me which aren't a listed type on Nichicon's website. HZ series - 1800uF at 16V comes in a 10*25mm can and turns in an eye-watering 6.5mohm ESR. This ESR equals polymer caps but with much higher available capacitance and they're much cheaper. Breaking them in now.....
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