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RJM Audio Sapphire Desktop Headphone Amplifier
RJM Audio Sapphire Desktop Headphone Amplifier
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Old 17th June 2020, 09:59 AM   #1571
Adam Lukas is offline Adam Lukas
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Originally Posted by rjm View Post
There are two obvious issues. Without C1 you have a DC amplifier. Any DC offset on your input signal will end up on the output, multiplied by the gain. Second, the trim pot. which is used to adjust the DC output offset to zero no longer functions. So even if you don't have any DC on the input signal, you may likely have a large DC offset on the output regardless, and no way to counter that.

Thanks Richard. You explained it beautifully. Now I know what to expect. I think I'm lucky, because the output offset without a connected source is 5mV, and with a connected 20mV. I don't use C1 because it soothes transients in music.
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Old 17th June 2020, 10:27 AM   #1572
withmatt is offline withmatt  South Korea
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Quote:
Originally Posted by Adam Lukas View Post
Thanks Richard. You explained it beautifully. Now I know what to expect. I think I'm lucky, because the output offset without a connected source is 5mV, and with a connected 20mV. I don't use C1 because it soothes transients in music.
You may need to carefully measure output DC transient while power up/ down also if your input source does not have output coupling capacitor.
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Old 18th June 2020, 01:25 AM   #1573
rjm is offline rjm  Japan
Richard Murdey
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RJM Audio Sapphire Desktop Headphone Amplifier
Quote:
Originally Posted by Adam Lukas View Post
I think I'm lucky, because the output offset without a connected source is 5mV, and with a connected 20mV.
I really can't recommend you operate it like this. The offset might have been 20 mV when you measured it, but you have no guarantee that it will stay at 20 mV. It will be dependent on the configuration of the output circuit of the component you have plugged into the inputs.

However, that said, there is little risk of actual damage to anything because the headphone impedance is high enough to withstand even very high offset voltages. To be absolutely clear though: That does not make it any less wrong.
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Old 3rd July 2020, 02:00 PM   #1574
Photosthanh is offline Photosthanh
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Originally Posted by rjm View Post
I really can't recommend you operate it like this. The offset might have been 20 mV when you measured it, but you have no guarantee that it will stay at 20 mV. It will be dependent on the configuration of the output circuit of the component you have plugged into the inputs.

However, that said, there is little risk of actual damage to anything because the headphone impedance is high enough to withstand even very high offset voltages. To be absolutely clear though: That does not make it any less wrong.
I did it but it every hot at two Bd135 and two bd136. what wrong Mr RJM?. how to fix it? and when i try to adjust bias i don't know where is bias because i new member. thank you so much
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Old 5th July 2020, 01:06 AM   #1575
rjm is offline rjm  Japan
Richard Murdey
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RJM Audio Sapphire Desktop Headphone Amplifier
The bias current is set by the resistors you use, it is not adjustable, nor should it need to be adjusted.

Without further information about what you did and what the measured voltages are, I can't provide any useful advice.

Those transistors will get a little warm in the normal version, and quite hot in the high bias current build. There are many mistakes you could have made that could cause the currents in the circuit to rise above normal. I suggest emailing me to discuss further.
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Old 5th July 2020, 02:53 AM   #1576
Photosthanh is offline Photosthanh
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can you show me your email? i need talk with you. Thank so much.
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Old 6th July 2020, 03:42 PM   #1577
rjm is offline rjm  Japan
Richard Murdey
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Old 27th July 2020, 02:15 AM   #1578
Peleus is offline Peleus  Taiwan
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Hi, Guys,

I finished the Sapphire headphone amp, Finally.
I order the kit of Sapphire, It is easy to build with very well designed board.
So, I successfully done the kit once, without any mistake.

My Sapphire is different from the original.

First, I change the PSU. What I use is the GR regulation that is designed by a Taiwanese. The GR regulation use a highly precise and ultra-low noise voltage reference IC and a op amp for error amplifier.

The last, the VR is Alps RK-50, it is located in another case.

The sound is awesome. With my ATH AWKT, it sound smooth and clear, with good punch. I like it.
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Old 28th July 2020, 02:29 PM   #1579
rjm is offline rjm  Japan
Richard Murdey
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Thanks for sharing your build. The Sapphire is open to power supply mods, though the Z-reg built in to the main boards is quite sufficient for the purpose. You can even run it from unregulated supplies, like you would a power amplifier. It really comes down to what sound you prefer.
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