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RJM Audio Sapphire Desktop Headphone Amplifier
RJM Audio Sapphire Desktop Headphone Amplifier
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Old 13th January 2019, 04:12 AM   #1461
rjm is offline rjm  Japan
Richard Murdey
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RJM Audio Sapphire Desktop Headphone Amplifier
What impedance of the dt990, 250 ohms?

Open loop or closed loop Sapphire? What gain and bias current?

I have used K702 with my Sapphire with no obvious issues, though it was an earlier variant of the circuit the output drive characteristics haven't really changed much.
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Old 13th January 2019, 02:45 PM   #1462
blackdod is offline blackdod  Europe
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No issues with my K701 or DT990 (600 Ohms). You need to turn up the volume but nothing alarming
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Old 14th January 2019, 12:49 AM   #1463
khuongtran is offline khuongtran
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Hi, I managed to detect the problem, it is due to bad quality switch for the gain switch that make them sound weird. I bought the better gain switch know and get the fanstastic result. I would love to know you guys opinion for upgrading the sound. Would it get good result with replacement of two input cap, right now I am using M cap Mundorf 4.7uf. Or is there anyone here experiment on changing transistor bc337 to another and better transistor.
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Old 14th January 2019, 09:57 AM   #1464
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Richard Murdey
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RJM Audio Sapphire Desktop Headphone Amplifier
I really don't think you need to mess around with it further. The Mundorfs are already very good, and frankly a transistor is a transistor. The only think you may want to experiment with is the closed loop vs open loop choice.
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