As I know pcb still isn't released. Headphone amp:
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I should just make the headphone amp and use as either a preamp or headamp.
How much power into 60ohms is possible?
How much power into 60ohms is possible?
You can buy used amp for $100 but with 100VA transformer, plastic speaker terminals, 100g heatsinks, about 6800uF caps... or you can diy $1000 amp 😉
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Maybe 6 channels of FX8 😀 which is exactly what I am building so am looking for a case. 🙂
Btw, the Apex headphone described earlier with the BD139/150 output stage, what kind of power can that drive?
I guess those BD139/140's are 1.5 amp capable and with 24 volt rails, that is a lot of watts actually. Could probably drive a small set of speakers nicely. 🙂
Hmm... what is it that limits the impedance of the load on the output? I recently made a JLH class A head phone amp with a pair of TIP41's on the outputs and it seems to drive 8ohm speakers pretty nicely, but only up to 1.6w.
I have an signal line input transformer, I would like to try out.
So far I have on the delete list: 10uF, 2k2,22k,100pf.
So far I have on the delete list: 10uF, 2k2,22k,100pf.
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So the trafo allows removal of all those components via balanced inputs with no DC? Let us know how it sounds. Is this the FX8?
Thats the beauty of a trafo, It blocks the DC.
More over, removing the R & C from the signal chain, improves the SQ immediately, high input capacitance is no good. Which is why the K1058's are a good choice, they also have lower input capacitance when compared to some other MOSFETS.
5cm Square FX8 First Sound
The Hitachi lateral FETs came in today. I installed a pair of 10ohm safety resistors in series with the power rails so that I can measure the quiescent bias current. I set the pot at about midpoint. Flipped the switch and observed about 550mA bias so quickly adjusted the pot down to 100mA current. The offset voltage was -15mV and there is no adjustment for that other than matching the LTP stage (which I forgot to do). -15mV is very livable though. I am using a Dx PSU with 250VA 25V toroid for 35.6v rails.
Removed the safety resistors, hooked up the speaker and gave it input from my CD player (laoded with a Suzanne Vega track) headphone out (like a pre-amp to control volume). Flipped the switch and sweet music plays! 🙂 Sounds real nice, very clear, no sign of distortion.
The heatsinks feel average warmth for a class AB at 100mA bias (probably circa 45C at moderate volume). Seems like a good place to be. The BD139/140's do feel a bit hot - probably needs a small heatsink as was shown on the silkscreen.
Anyhow, this is a nice compact amp, I really like it and will build up 5 more units for a 6 channel active amp.
The Hitachi lateral FETs came in today. I installed a pair of 10ohm safety resistors in series with the power rails so that I can measure the quiescent bias current. I set the pot at about midpoint. Flipped the switch and observed about 550mA bias so quickly adjusted the pot down to 100mA current. The offset voltage was -15mV and there is no adjustment for that other than matching the LTP stage (which I forgot to do). -15mV is very livable though. I am using a Dx PSU with 250VA 25V toroid for 35.6v rails.
Removed the safety resistors, hooked up the speaker and gave it input from my CD player (laoded with a Suzanne Vega track) headphone out (like a pre-amp to control volume). Flipped the switch and sweet music plays! 🙂 Sounds real nice, very clear, no sign of distortion.
The heatsinks feel average warmth for a class AB at 100mA bias (probably circa 45C at moderate volume). Seems like a good place to be. The BD139/140's do feel a bit hot - probably needs a small heatsink as was shown on the silkscreen.
Anyhow, this is a nice compact amp, I really like it and will build up 5 more units for a 6 channel active amp.
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