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RJM Audio Sapphire Desktop Headphone Amplifier
RJM Audio Sapphire Desktop Headphone Amplifier
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Old 26th January 2018, 05:53 AM   #1351
ammel68 is offline ammel68  United States
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RJM Audio Sapphire Desktop Headphone Amplifier
Quote:
Originally Posted by TypodCrow View Post
Hey @rjm, any chance you have some measurements of this amp design? I'd like to compare it to the Objective2 - doing a custom amp build and would like to know which amp will provide the best "reference" listening experience.
LOL...comparing Richard's discrete design to an op-amp design is like comparing apples to oranges.
I've built and listened to both, personally.
In the real world, measurements and sound quality usually have little in common when it comes to your search for the best "reference" listening experience.

The Objective 2 will sound a little more "sterile" than Richard's Sapphire as a result of noticeably weaker bass.
If you don't mind the weaker bass of the Objective 2, then you may consider it the best "reference" listening experience on the planet.

Good luck!
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Old 26th January 2018, 07:01 AM   #1352
rjm is offline rjm  Japan
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In any event comparative measurements between headphone amplifiers is highly suspect.

I use measurements to check & confirm, never to judge.
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Old 8th February 2018, 02:51 AM   #1353
felipeunix is offline felipeunix  Germany
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@rjm

How did you test in lineout mode?

The positive output signal from the DAC directly into the Sapphire input? Suppressing any opamp in the signal path? How do you recommend?

Best Regards
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Old 8th February 2018, 04:15 AM   #1354
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I used the soundcard line out to the Sapphire input, the Sapphire output back to the soundcard line in.

This will be fine if your soundcard can exceed the Sapphire's distortion performance. That's not a given though, so check the results without the Sapphire in the loop first, then compare with the Sapphire. If no change then you are looking at the sound card performance not the Sapphire and you'll need to find a better soundcard or measurement setup.
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Old 8th February 2018, 05:37 AM   #1355
felipeunix is offline felipeunix  Germany
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Sorry, I mispronounced. My question is not regarding your Sapphire performance test, but about using it as a lineout rather than headphone amplifier.
Do you directly connect the positive output of the converter to the Sapphire input?
How do you suggest this connection?
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Old 8th February 2018, 11:08 PM   #1356
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You mean as a line preamplifier? Or as the output stage of a DAC? That's not the same thing exactly.

Please be a little more specific to describe the application you intend.
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Old 8th February 2018, 11:43 PM   #1357
felipeunix is offline felipeunix  Germany
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Quote:
Originally Posted by rjm View Post
You mean as a line preamplifier? Or as the output stage of a DAC?
Output stage of a DAC, unbalanced.

The output of the DAC is balanced, and commonly used op amp to unbalance. How do you suggest using Sapphire at this stage, and eliminate the use of op amp in the signal path?
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Old 9th February 2018, 06:05 AM   #1358
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So the problem there is most DAC output stages have three op amps per channel, two I/V converters, one for each phase, and then one more to filter the signals and convert to unbalanced output.

I don't know how you'd go about integrating the Sapphire into that circuit, though if you can find an output circuit that uses a CFA opamp, you should be able to substitute the Sapphire for that op amp.

I suggest consulting SNOA364c and SNOA365c.
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Old 27th February 2018, 08:34 PM   #1359
mswann is offline mswann
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I am choosing cases for my Phonoclone and Saphire builds and I would appreciate any input.
I only use headphones; other than getting rid of a set of interconnects and sockets, would there be any advantage housing all the circuits in one case?
Could I disregard the output caps on the Phonoclone ?
Would there be any potential issues, such as earthing?
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Old 28th February 2018, 03:25 AM   #1360
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I have no direct experience putting everything in one chassis but there is no reason it shouldn't work, per the usual caveat that the transformer should be as far away from the phono stage as possible.

It is best if you keep both the Phonoclone output cap before the volume control, and the Sapphire input cap after it. The phonoclone output cap prevents ticks and pops when changing volume, the sapphire input cap prevents the output offset voltage varying with volume.
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