The Poseidon's Voice NPXP is an amp that I had aspired to build for quite some time. At it's core it's basically a foundation to experiment with the multitude of Pass inspired designs. The front end is composed of Neurochrome's THAT RX:: Mono circuit along with Neurochrome's Guardian-86 ahead of the speaker output. The main power supply is composed of a Furutech IEC, a massive 800VA custom Toroidy with 4 pairs of 20V secondaries (for ease of wiring) and dual XRK Audio SLB supplies, populated with Mundorf E-lytics. A soft start is provided by Neurochrome's ISS board and a Bulgin momentary switch is used on the front panel. Neurochrome's THAT RX::Mono circuit is an extremely well designed differential to single ended converter with 0dB gain and operates on a bipolar regulated supply. In my case I decided on Jan Didden's excellent Silent Switcher V3 which when provided a 5V DC to 10V DC supply, pumps out a very clean +/- 15VDC @ 150mA (min) at vanishingly low ripple levels. A Mean Well supply provides the requisite 5V DC with 6A (30W) to spare. The dual SLB supplies provide a rock solid +/- 24VDC at 1-2mV RMS ripple.
The main amp module used in this premier round is the Aleph J. Building this board was fairly easy, thanks to member Dennis Hui who was kind enough to provide me with matched IRFP 240 Mosfets and 2SJ108V JFETs. I had VH Audio's 1uF ODAM capacitors on hand which I pressed into service as the input capacitor. For this build I have elected to use the Aleph J as a single ended input only, even though the input stage is composed of a differential pair and can accommodate XLR sources. At some point, I may experiment with bypassing the THAT::RX Mono module, although I frankly doubt the sonics will improve. The THAT::RX is based on the THAT1200 chip and Tom Christiansen's very elegant implementation/layout (hints of which are available in the THAT 1200 data sheet). In previous amp builds, this module has completely surpassed the sonics as well as measurements of my previous reference (Lundahl amorphous core transformers). The CMRR is maintained over a wide range of source impedance imbalances. Moreover the distortion levels of this module is several orders of magnitude lower than any diy Pass or Pass inspired amp circuit I have seen at typical dac output voltage levels (2V to 5V RMS). Given that the THAT::RX is discontinued, I would encourage folks to look at the Neurochrome Universal Buffer or other competitors like AMB Audio's α24 or XRK's BTSB if a differential input is desired. If you look carefully in the photos, I have drilled holes to mount AMB Audio's α24 which gives me the option of gain settings (from 6dB to 20dB) if needed. On the output, we have Neurochrome's Guardian-86. This is a speaker protection module and my choice here was easy. Many speaker protection modules unfortunately raise the distortion levels of the amp module that they are paired with. The Neurochrome Guardian series has been tested with their own Modulus 686 which is one of the lowest distortion amplifiers I have ever encountered. Given that the Guardian isn't an impediment to the Modulus 686, I was sure they wouldn't be an impediment to any of my Pass experiments.
So in summary, the ingredients are:
More pics in the next post!
Contents:
Aleph J vs Aleph J Zen subjective commentary
The main amp module used in this premier round is the Aleph J. Building this board was fairly easy, thanks to member Dennis Hui who was kind enough to provide me with matched IRFP 240 Mosfets and 2SJ108V JFETs. I had VH Audio's 1uF ODAM capacitors on hand which I pressed into service as the input capacitor. For this build I have elected to use the Aleph J as a single ended input only, even though the input stage is composed of a differential pair and can accommodate XLR sources. At some point, I may experiment with bypassing the THAT::RX Mono module, although I frankly doubt the sonics will improve. The THAT::RX is based on the THAT1200 chip and Tom Christiansen's very elegant implementation/layout (hints of which are available in the THAT 1200 data sheet). In previous amp builds, this module has completely surpassed the sonics as well as measurements of my previous reference (Lundahl amorphous core transformers). The CMRR is maintained over a wide range of source impedance imbalances. Moreover the distortion levels of this module is several orders of magnitude lower than any diy Pass or Pass inspired amp circuit I have seen at typical dac output voltage levels (2V to 5V RMS). Given that the THAT::RX is discontinued, I would encourage folks to look at the Neurochrome Universal Buffer or other competitors like AMB Audio's α24 or XRK's BTSB if a differential input is desired. If you look carefully in the photos, I have drilled holes to mount AMB Audio's α24 which gives me the option of gain settings (from 6dB to 20dB) if needed. On the output, we have Neurochrome's Guardian-86. This is a speaker protection module and my choice here was easy. Many speaker protection modules unfortunately raise the distortion levels of the amp module that they are paired with. The Neurochrome Guardian series has been tested with their own Modulus 686 which is one of the lowest distortion amplifiers I have ever encountered. Given that the Guardian isn't an impediment to the Modulus 686, I was sure they wouldn't be an impediment to any of my Pass experiments.
So in summary, the ingredients are:
- Modushop 5U/400 mm deep chassis with UMS heatsinks customized using Front Panel Express.
#frontpanelexpress #frontpanel - Neurochrome Audio ISS
- Toroidy 800VA w/120V primary and a quad pair of 20V secondaries
- XRK Audio's Smooth Like Butter supplies (SLB, dual rail)
- Meanwell MPM 30-5-ST
- Linear Audio Silent Switcher V3
- Neurochrome Audio THAT RX::Mono (pair) [discontinued]
- Neurochrome Audio Guardian-86 (pair)
- DIY Audio Store Aleph J (pair) w/matched pair of 2SJ108V JFETS & quad matched IRFP-240’s mounted on ceramic thermal insulators
- Various wires from Neotech, VH Audio, DH Labs and generic mil-spec wiring.
- Cardas XLR input and Cardas Rhodium binding posts
- Furutech FI-10 IEC




More pics in the next post!
Contents:
Aleph J vs Aleph J Zen subjective commentary
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