If I put my notes here, I might be able to find them again later!
Orb JADE-1 headphone amplifier and DAC : review
This is a headphone amplifier with digital inputs, not a DAC with a headphone jack. Though technically given equal board space, the headphone amp, with hot-running single-ended class-A output stage, is surely the centerpiece of the design. (The Asahi Kasei DAC, with MUSES01 for the I-V, is no slouch mind you.)
First impressions. It is large, solid, and very nicely made, but - after seeing the inside - rather simple, spartan even. From the DAC output to the headphone jack is just two op amps and two transistors, the op amps being shared between channels. A third op amp most likely just buffers the analog line output. Apart from the headliner MUSES01 op amp none of the parts are especially expensive, though many were clearly carefully chosen for sound quality - the 2SC5196 for example. The TE7022 USB receiver is a disappointment, as is, to be honest, the single set of power rails and the use of dual op amps shared between channels.
On a positive note, the front panel is gorgeous, if understated. The volume control knob is a work of precision machining. The controls and layout are excellent (I especially like the position of the headphone jack bottom-right, well away from the volume knob.) Too bad there is no way to adjust gain - I would have taken that over the direct/comfort switch function any day. About that, though: the "comfort mode" is not, as I had feared, a treble cut filter but appears instead to be a crossfeed. It narrows the sound stage and puts in more in front rather than inside your head. As these things go it is restrained but more of a curiosity than something I'd feel a need to use.
After some testing I've settled on listening to this connected by TosLink to the computer motherboard, with the analog outputs connected to my Sapphire3 headphone amp. I'm switching back and forth between connecting the headphones to the JADE unit and the Sapphire3.
The sound of the JADE-1 headphone output is much as expected for a single-ended output coupled through 1000 uF, i.e. Szekeres type circuit: smooth, plenty of mid-bass, subdued highs. It is nicely tuned to balance the DAC section, which has some hardness or glare in the upper midrange but is otherwise blameless apart from perhaps the slightly folded-in soundstage. The Sapphire3 has an unfair advantage of having a high gain optimized for my headphones. Still, it sounds more lively and clear. Unfortunately it also highlights the synthetic quality of the JADE-1 DAC.
I think I prefer the subtractive combination of the native Orb headphone amp, but it is a very close thing. Perhaps the most surprising thing to come out of this is how similar the JADE and Sapphire headphone amps are tonally. Both are basically transparent and allow me to hear the DAC for what it is. It's just that the Sapphire does this more rigorously.
chassis
2.5 mm aluminum top and bottom sheets, steel back plate, front panel is actually milled from a thick block of solid aluminum.
Heavy steel partitions between power supply, audio, and front panel controls.
The circuit boards are all mounted on a steel baseplate.
Milled, satin finish aluminum volume knob and buttons.
Volume control is the standard Alps blue velvet potentiometer.
power supply (analog +12 V, -12 V, and digital)
Custom R-core transformer from Kitamura Kiden (Single secondary, probably 12-0-12 VAC and 40-50 VA) Actually manufactured by Pheonix, R40 size.
JRC 7812A 7912A regulators with heatsinks.
Four very large filter capacitors, about 10,000 uF ea.
A separate small switching module powers the digital and control circuits.
digital
Tenor TE7022L USB receiver - bleh
Asahi Kasei AK4113VF receiver
[note complete board isolation between receiver and DAC]
Asahi Kasei 4382AT DAC (2 channel, 24/192 delta-sigma, 112 dB)
MUSES01 JFET dual op amp - DAC IV conversion and LP filter as per DAC datasheet, a good part of the BOM got spent on this part alone.
analog
MUSES 8820 bipolar dual op amp (NE5532A equiv.) - I'm guessing this is the buffer for the analog line output, following MUSES01.
LF412CN JFET dual op amp - the input / gain stage of the headphone amplifier, following the volume control.
2SC1815 NPN transistor, TO-99 - this is probably the driver stage of the headphone amplifier
2SC5196 NPN Toshina "triple diffused type" 40W 6A 80V - this is the output device for the headphone amplifier
68 ohm power resistor (5W?) - emitter resistor for the output stage.
Nichicon KW 1000 uF - the output coupling capacitor.
The rated output power (1100 mW/16ohms, 30mW/600 ohms) defines an envelope of 262 mA and 4.24 V ac rms output, which for a single-ended follower, sets the supply voltage to 12 V (2.8*4.24). The resistor is connected from the transistor base (+5.4 V) to the negative supply (-12 V). 68 ohms gives a bias current of 264 mA.
Good. I think I have the output circuit worked out now: two NPN followers with simple resistive current sources, connected to the positive and negative rails. Some bias network to put the input up to around +6 V so the output coupling capacitor does not reverse polarity.
Product homepage: https://www.orb.co.jp/audio/jade.html
First impressions. It is large, solid, and very nicely made, but - after seeing the inside - rather simple, spartan even. From the DAC output to the headphone jack is just two op amps and two transistors, the op amps being shared between channels. A third op amp most likely just buffers the analog line output. Apart from the headliner MUSES01 op amp none of the parts are especially expensive, though many were clearly carefully chosen for sound quality - the 2SC5196 for example. The TE7022 USB receiver is a disappointment, as is, to be honest, the single set of power rails and the use of dual op amps shared between channels.
On a positive note, the front panel is gorgeous, if understated. The volume control knob is a work of precision machining. The controls and layout are excellent (I especially like the position of the headphone jack bottom-right, well away from the volume knob.) Too bad there is no way to adjust gain - I would have taken that over the direct/comfort switch function any day. About that, though: the "comfort mode" is not, as I had feared, a treble cut filter but appears instead to be a crossfeed. It narrows the sound stage and puts in more in front rather than inside your head. As these things go it is restrained but more of a curiosity than something I'd feel a need to use.
After some testing I've settled on listening to this connected by TosLink to the computer motherboard, with the analog outputs connected to my Sapphire3 headphone amp. I'm switching back and forth between connecting the headphones to the JADE unit and the Sapphire3.
The sound of the JADE-1 headphone output is much as expected for a single-ended output coupled through 1000 uF, i.e. Szekeres type circuit: smooth, plenty of mid-bass, subdued highs. It is nicely tuned to balance the DAC section, which has some hardness or glare in the upper midrange but is otherwise blameless apart from perhaps the slightly folded-in soundstage. The Sapphire3 has an unfair advantage of having a high gain optimized for my headphones. Still, it sounds more lively and clear. Unfortunately it also highlights the synthetic quality of the JADE-1 DAC.
I think I prefer the subtractive combination of the native Orb headphone amp, but it is a very close thing. Perhaps the most surprising thing to come out of this is how similar the JADE and Sapphire headphone amps are tonally. Both are basically transparent and allow me to hear the DAC for what it is. It's just that the Sapphire does this more rigorously.
chassis
2.5 mm aluminum top and bottom sheets, steel back plate, front panel is actually milled from a thick block of solid aluminum.
Heavy steel partitions between power supply, audio, and front panel controls.
The circuit boards are all mounted on a steel baseplate.
Milled, satin finish aluminum volume knob and buttons.
Volume control is the standard Alps blue velvet potentiometer.
power supply (analog +12 V, -12 V, and digital)
Custom R-core transformer from Kitamura Kiden (Single secondary, probably 12-0-12 VAC and 40-50 VA) Actually manufactured by Pheonix, R40 size.
JRC 7812A 7912A regulators with heatsinks.
Four very large filter capacitors, about 10,000 uF ea.
A separate small switching module powers the digital and control circuits.
digital
Tenor TE7022L USB receiver - bleh
Asahi Kasei AK4113VF receiver
[note complete board isolation between receiver and DAC]
Asahi Kasei 4382AT DAC (2 channel, 24/192 delta-sigma, 112 dB)
MUSES01 JFET dual op amp - DAC IV conversion and LP filter as per DAC datasheet, a good part of the BOM got spent on this part alone.
analog
MUSES 8820 bipolar dual op amp (NE5532A equiv.) - I'm guessing this is the buffer for the analog line output, following MUSES01.
LF412CN JFET dual op amp - the input / gain stage of the headphone amplifier, following the volume control.
2SC1815 NPN transistor, TO-99 - this is probably the driver stage of the headphone amplifier
2SC5196 NPN Toshina "triple diffused type" 40W 6A 80V - this is the output device for the headphone amplifier
68 ohm power resistor (5W?) - emitter resistor for the output stage.
Nichicon KW 1000 uF - the output coupling capacitor.
The rated output power (1100 mW/16ohms, 30mW/600 ohms) defines an envelope of 262 mA and 4.24 V ac rms output, which for a single-ended follower, sets the supply voltage to 12 V (2.8*4.24). The resistor is connected from the transistor base (+5.4 V) to the negative supply (-12 V). 68 ohms gives a bias current of 264 mA.
Good. I think I have the output circuit worked out now: two NPN followers with simple resistive current sources, connected to the positive and negative rails. Some bias network to put the input up to around +6 V so the output coupling capacitor does not reverse polarity.
Product homepage: https://www.orb.co.jp/audio/jade.html
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