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RJM Audio Sapphire Desktop Headphone Amplifier
RJM Audio Sapphire Desktop Headphone Amplifier
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Old 22nd August 2019, 04:13 AM   #1511
DRONE7 is offline DRONE7  New Zealand
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Boards assembled and working... offset set at 5mv but can go lower.

Testing on the bench with a discman and Lightspeed attenuator .

I did use thermal paste because....why not..

I note that the Q14/15 pair runs noticeably warmer than the Q13/16 pair.....just the finger touch test but the same for both boards...

I am about to take them inside to the main system and will raid the medical cabinet for the digital thermometer and recheck..

Otherwise....sounding great and no hiss clicks pops hum sparks or worries of any sort...!!

Having built the Emerald Phono stage and now the Sapphire I have to say that these are the most diy friendly projects I have ever encountered.
The build guides are comprehensive and the "Design Manual" provides great insight and options...and best of all they power up and work first time.
Thank you Richard for sharing and supporting !!
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Old 22nd August 2019, 09:31 AM   #1512
Mixi is offline Mixi  Europe
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Glad to see that the "Design Manual" idea gets so much traction.

Thanks for the quick reply, Richard! I think this has to be my next DIY project. I'll now try to understand the circuit. I've built a few opamp based designs, no discrete circuitry so far. ....apart from an ACA and B1 I guess but that is super simple.
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Old 23rd August 2019, 01:59 AM   #1513
rjm is offline rjm  Japan
Richard Murdey
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RJM Audio Sapphire Desktop Headphone Amplifier
Quote:
Originally Posted by DRONE7 View Post
I note that the Q14/15 pair runs noticeably warmer than the Q13/16 pair.....just the finger touch test but the same for both boards...
That's strange. With 30 mA bias neither pair of transistors, nor the heatsinks, get appreciably warm. The heat dissipation of each pair is less than 1 W total.

Check the voltage drop across R17 and R18. They should be equal and the current, computed as I=V/R, should be the expected value for the bias current setting.

Richard
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Old 23rd August 2019, 04:26 AM   #1514
DRONE7 is offline DRONE7  New Zealand
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Fingers are such sensitive things....

I remeasured with the thermometer and Q14/15 pair is only 4 degrees C warmer than Q13/15.
Voltage drop across R17 and R18 measures the same for each.

Bias current measures 39 mA and highest heatsink temp is 42 degrees (20 above ambient) so all appears as expected and normal.

Last edited by DRONE7; 23rd August 2019 at 04:31 AM.
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Old 23rd August 2019, 12:24 PM   #1515
rjm is offline rjm  Japan
Richard Murdey
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RJM Audio Sapphire Desktop Headphone Amplifier
That sounds about right!
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Old 20th September 2019, 12:05 AM   #1516
withmatt is offline withmatt  South Korea
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Default Mini Sapphire 4

My mini version Sapphire 4 implementation.
(Sorry for Korean)

SCU-SAP4 : 네이버 블로그
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Old 20th September 2019, 12:32 PM   #1517
rjm is offline rjm  Japan
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Well that is incredibly cool.

I'm most impressed how you managed to condense the transistor stack like that and put two channels on a single board without going to SMT. I realize you moved the regulators off, but still... great job!
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Old 23rd September 2019, 04:09 PM   #1518
withmatt is offline withmatt  South Korea
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Default mini Sapphire Gerber.

For those how requested Gerber.
Attached Files
File Type: zip SCU-SAP4_2019-05-16.zip (151.9 KB, 21 views)
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