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RJM Audio Sapphire Desktop Headphone Amplifier
RJM Audio Sapphire Desktop Headphone Amplifier
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Old 21st July 2017, 05:51 PM   #1251
withmatt is offline withmatt  South Korea
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Join Date: Sep 2016
Location: Seoul
Update :
Power test : works fine.
LEDs are too bright, I need to add some resisters.
Will finish/listening test soon.

Click the image to open in full size.

Last edited by withmatt; 21st July 2017 at 05:54 PM.
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Old 26th July 2017, 04:30 PM   #1252
withmatt is offline withmatt  South Korea
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Location: Seoul
Had problem with output impedance, just solved.
I ordered takman 4.7ohm but, it was 4.7k ohm
Now it works charm.
I temporarily put it in cookie box
Click the image to open in full size.
I used 10k ladder attenuator from allo,
Mundorf supreme 0.68uF,
Nichicon KG super thru 2200uF,
Nochicon KZ Muse and fine gold.
Mix of takman and PRP metal film resisters.
Mogami OFC cable, BC550C and BC560C without matching, but filtered odds.
BYV27 for rectifier, and RS-component transformer, which is actually Talema's OEM.

Comparing to my previous project - Lehmann clone with discrete OPAMP, Alps RK27, Mundorf AG 4700uF, Silmic II, Clarity Cap ESA for coupling, all takman metal film - Sapphire has even clearer sound and wider stage with same depth of bass. I'm very impressed.

I have tested one transformer configuration vs separate transformer configuration, unfortunately I noticed nothing difference.

I have tested both of open loop and close loop,
Open loop gave me more dynamics, more bass, and much tighter bass. Awesome for pop songs, but ears get easily tired.
Close loop provides wider stage and clearer high tone. It's bass is comfortable. Much more reference sound.
I can't say which one is better, but I still can enjoy both sound color, and which is good thing.

I need to spend more time to define my feeling, but my first impression is very positive and far better than lehmann's diamond buffer.
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Old Yesterday, 02:09 AM   #1253
rjm is offline rjm  Japan
Richard Murdey
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Location: Kyoto
RJM Audio Sapphire Desktop Headphone Amplifier
Thank you for posting your build notes and listening impressions. I get the feeling we are homing in on the closed/open loop sound difference now with several people reporting fairly consistent opinions.

I imagine other people might be interested in your power supply boards. Would you mind posting the gerber/brd files?

Lastly do you have a link to the allo attenuator? I haven't seen that model before.
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Old Yesterday, 02:50 AM   #1254
withmatt is offline withmatt  South Korea
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Join Date: Sep 2016
Location: Seoul
Attenuator link :
Allo.com - Stepped Attenuator

It came with gold plated Chinese switch, I measured each resister value as below.

L-Ch R-Ch

9.98k 0.5 9.99k 0.4

9.98k 2.4 9.99k 2.3

9.98k 4 4 9.99k 4.3

9.98k 7.4 9.99k 7.3

9.98k 13.4 9.99k 13.3

9.98k 22.4 9.99k 22.3

9.98k 40.5 9.99k 40.4

9.86k 70.8 9.86k 70.7

9.86k 113.1 9.86k 113.2

9.86k 177.9 9.86k 177.8

9.74k 249.0 9.74k 249.0

9.63k 353.0 9.63k 353.0

9.51k 493.0 9.51k 493.0

9.29k 698.0 9.29k 698.0

8.96k 989.0 8.96k 989.0

8.54k 1.403k 8.54k 1.404k

7.94k 1.978k 7.94k 1.978k

7.48k 2.51k 7.49k 2.51k

6.79k 3.14k 6.79k 3.15k

6.03k 3.95k 6.03k 3.95k

4.98k 4.97k 4.98k 4.97k

3.69k 6.31k 3.69k 6.31k

2.04k 7.93k 2.04k 7.93k

0.5 9.96k 0.5 9.96k

You can share gerber of power board, since it was based on your board outline design
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