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RJM Audio Sapphire Desktop Headphone Amplifier
RJM Audio Sapphire Desktop Headphone Amplifier
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Old 1st January 2019, 08:51 PM   #1451
blackdod is offline blackdod  Europe
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Two Triad 25VA 2x12VAC

You can find it in RJM BOM
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Old 1st January 2019, 08:57 PM   #1452
Lbcyclist is offline Lbcyclist  United States
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Quote:
Originally Posted by blackdod View Post
Two Triad 25VA 2x12VAC

You can find it in RJM BOM
Thank you. Yes, I know that it is listed, but Iím trying to avoid buying new transformers for this project.
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Old 1st January 2019, 09:27 PM   #1453
blackdod is offline blackdod  Europe
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You could use some more power but I would not use more than 12V
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Old 2nd January 2019, 03:12 AM   #1454
rjm is offline rjm  Japan
Richard Murdey
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RJM Audio Sapphire Desktop Headphone Amplifier
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Originally Posted by Lbcyclist View Post
Hi,

I finally got around to stuffing my boards [4.1t] and want to finalize the power supply. I have the DBRB board and diodes, so the rectifier is taken care of. For transformer I have a 2x15V, 100VA [Triad VPT30-3330]. Will that work?
The transformer spec is "two 12 V secondaries". The recommended minimum transformer pwoer spec is "single 50 VA, or two 25 VA if dual mono".

15 V secondaries will bring the V++ up from 17 V to about 22-23 V. The BD135/136 regulator transistors will get a bit warmer, but other than that it will be okay I think as long as you stick with the regular 35 mA bias current build.

/R
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Old 3rd January 2019, 03:49 AM   #1455
Lbcyclist is offline Lbcyclist  United States
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Many thanks Richard, I’ll give it a try.
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Old 11th January 2019, 04:18 AM   #1456
sthcoaster is offline sthcoaster  United Kingdom
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RJM Audio Sapphire Desktop Headphone Amplifier
Nearly ready to finish this bad boy!! Got some drilling to do and wire up the HP jack (temporary one for now but will fit Neutrik NJ3FP6 eventually)

1500uf and 100uf Panasonic FM
Mundorf Supreme Silver/Gold/Oil
Elma A47 25k series attenuator
Case same as RJM

4.1t Boards fabbed by PCBWay - I thought white would be fun but regret it now - too many different colours happening! should have gone black as per RJM boards or green to match little rectifier boards. At least internal aesthetics will be moot once the lid goes on!!

I have enough BOM for a second set of boards which I'll do with NOS Elna Starget 1000uf (they're a bit big but I think I can make them work) and a Russian PIO for C1 duties.

I'll see you next week with final pics and help on the bias if needed. Looking forward to hearing this compared to my O2 and SSMH. Listening through Sennheiser/Massdrop HD6XX.

Cheers! RJM thanks for supporting this community.
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Last edited by sthcoaster; 11th January 2019 at 04:23 AM.
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Old 11th January 2019, 12:55 PM   #1457
rjm is offline rjm  Japan
Richard Murdey
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RJM Audio Sapphire Desktop Headphone Amplifier
Kewl. I think white+white works.

More importantly one thing I should really address is the way C1 blocks the input screw terminal strip. For the moment I recommend soldering the wires in directly.

Honestly for that case you are using I'd go with a shared power transformer and diodes. Dual mono gets too crowded, I regret going that route on my build. Think about it anyway, if you haven't already drilled the holes.
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Old 11th January 2019, 02:33 PM   #1458
sthcoaster is offline sthcoaster  United Kingdom
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Originally Posted by rjm View Post
More importantly one thing I should really address is the way C1 blocks the input screw terminal strip. For the moment I recommend soldering the wires in directly.
Yeah - it's tight/fiddly. At the moment I have the input terminals facing towards the variable resistor so I can get at them. However, once I am settled on which open/closed loop options; different C1 caps etc. I plan to remove the terminal strips across the board and directly solder inputs/outputs/rectifier. The Molex connectors will stay only until I'm done playing.

Quote:
Originally Posted by rjm View Post
Honestly for that case you are using I'd go with a shared power transformer and diodes. Dual mono gets too crowded, I regret going that route on my build. Think about it anyway, if you haven't already drilled the holes.
I've looked at yours plenty and I think the C-core trafos are generally smaller than your nice medical grade toroids so I think I will have more free space than you do. (I'd need to buy a more powerful trafo if I dropped dual mono). I stagger the alignment of the trafos and boards rather than align them through the centre, which means there is about 1 inch clearance passed the trafos for the input and the same on the other side where the AC goes up to the front switch. I'm using mini coax for the inputs so that should provide shielding if the physical separation is not great enough.

Hope to have time Sunday to finish up!!
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Old 11th January 2019, 10:42 PM   #1459
rjm is offline rjm  Japan
Richard Murdey
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Originally Posted by sthcoaster View Post
(I'd need to buy a more powerful trafo if I dropped dual mono)
No, really not. That single R-core shown in the photo is more than large enough. I assume it's 50 VA, but even 25 VA would be OK.

/R
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Old 13th January 2019, 02:39 AM   #1460
khuongtran is offline khuongtran
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I finished mine and loving the sound come out of it. Smooth and transparent I would say. Very neutral and balanced headphone amplifier. I recently have encountered one weird issue. I plugged my dt990 and my AKG Q701 to the Sapphire they sound very weird. The Dt990 lose signal on the right channel and the AKG Q701 sound very narrow. I have tried other headphone like the HD 6XX and Hifiman 400i, they sound right smooth. I am not pretty sure if anyone here have the same issue as mine.
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