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RJM Audio Sapphire Desktop Headphone Amplifier
RJM Audio Sapphire Desktop Headphone Amplifier
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Old 19th October 2017, 02:50 AM   #1321
Stan63605 is offline Stan63605  Canada
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RJM Audio Sapphire Desktop Headphone Amplifier
Quote:
Originally Posted by rjm View Post
...input switching, ... mute, mono, and R/L invert switches, recording buffer, headphone output, phono preamp, as well as remote control functions to consider. It is quite dizzying.
Yes. I guess these are the reasons there are so many uninspiring preamps out there in vacuum land!
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Old 29th October 2017, 04:33 PM   #1322
wanders is offline wanders  United States
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Richard,

I built the Sapphire in mid to late 2015. I housed it in the same chassis as shown in your #1 post on this thread. However, I don't use it much and I've now decided to move it to another chassis. I have an audio rack in my listening room. The rack cannot accomodate the Sapphire in its current box. The only location alternative is near the phonostage, but that results in noise. Also, I built the Sapphire using a temporary chassis (aluminum cake pan). The amp was essentially noise free at that point. However, after moving it to the permanent chassis, I picked up noise - not horrible, but not great either. (The Sapphire was one of my earlier builds. I've got more tools and more experience now and should be able to get the Sapphire performing closerer to spec.)

I've ordered a 2u, 19" rack-mountable enclosure from Asia and plan to reorganize my stack and include the Sapphire. The larger chassis will enable me to separate the power supply components from the circuit boards, to re-do the wiring, and to upgrade the attenuator(s).

It will probably be a month before I get the new chassis and start this project, but I thought I'd ask a few preliminary questions. First, since 2015, have you made any project upgrades that I should consider? Second, what are your views on volume control; I used only a modest Alps pot in the Sapphire. Last year I built a 6SN7 preamp and used two gold point 47 step attenuators ($300 +/-). The 6SN7 sounds fantastic, but I'd appreciate your views on upgrading the Sapphire to that extent.

I'll doubtlessly have other questions as the rebuild progresses.

Thanks in advance
Warren
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Old 29th October 2017, 11:30 PM   #1323
rjm is offline rjm  Japan
Richard Murdey
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RJM Audio Sapphire Desktop Headphone Amplifier
Hi Warren,

You probably have the Sapphire 3, rev. 30 or 31 boards. The latest version is a fully discrete circuit with adjustable gain and open/closed loop alternate configurations. It's called the Sapphire 4 and you can read the story of its development by scrolling through the last few pages of this diyaudio thread. As you'll see, 3->4 is well worth the upgrade.

I use Goldpoint for my volume control in both my Sapphire 4 builds (preamp and headphone amp) and highly recommend them if you can spare the cash. Something like my Gitzo tripod (.....), its something you only ever need to buy once, so its worth getting the best.

Noise can be a connection issue (ground loops) or it can be an interference issue (from nearby transformers). Feel free to pm/email me, hopefully we can sort it out.
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Old 12th November 2017, 12:50 AM   #1324
felipeunix is offline felipeunix  Germany
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Did you occasionally come to test the output with two pairs (bd139/140)? Maybe for some improvement in thd, as for balancing the temperature.
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Old 12th November 2017, 09:24 AM   #1325
rjm is offline rjm  Japan
Richard Murdey
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The Sapphire 3 had five BC337/327 output pairs, the 4 has just one BD139/140 pair.

I don't think there is much need to add more than a single pair. THD is limited by the input stage not the output, and nothing gets warm anyway.
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Old 22nd November 2017, 12:12 AM   #1326
wanders is offline wanders  United States
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Richard,

I mentioned that the sapphire 4.1 I'm working on is going to be housed in a 19" rack-mount chassis. So it won't be practicable to open the unit to change the gain with the jumpers. I'd like to mount a toggle switch on the front panel. I'm thinking that a three position dpdt switch should suffice but I don't know how to wire it. Help appreciated.

Warren
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Old 22nd November 2017, 12:30 AM   #1327
rjm is offline rjm  Japan
Richard Murdey
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Assuming the switch has a stop in the middle (neither switched) this will work, but it's a bit weird - middle will be low gain, up (or down) will be mid, down (or up) will be high.

Maybe there's a better way. Well, best would be relays on the board... but I didn't go that road. I'd be careful wiring to the switch ... keep leads short.

/R
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Last edited by rjm; 22nd November 2017 at 12:32 AM.
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Old 26th November 2017, 06:11 PM   #1328
wanders is offline wanders  United States
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Maybe a 3 position rotary switch mounted between the boards - with a shaft extension to the front panel - to minimize wiring.
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Old 26th November 2017, 07:08 PM   #1329
wanders is offline wanders  United States
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Default Grounding v4

Not clear on grounding for the new version. VPM has a ground wire, so perhaps that (those) grounds to IEC instead of chassis ground to IEC (as v3). Looks like that in the picture.
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Old 26th November 2017, 11:03 PM   #1330
rjm is offline rjm  Japan
Richard Murdey
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I'm sure something useful could be implemented with a rotary switch. Exactly how best to do it would require some additional thought.

Grounding the Sapphire 4 is the same as all previous versions. Either the chassis is connected via OUT- at the headphone jack by virtue of the panel jack making that connection automatically, or, if isolated, then the chassis connects to the GND pads.

From my testing it doesn't really matter which.
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