AMB Gamma3 DAC Build

Discussion in 'DIY' started by Jh4db536, Jun 11, 2016.

  1. Jh4db536

    Jh4db536 Friend

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    Not going to repeat my AMB build log, not going to cite any measurement/specs, but I will highlight and summarize a few things, and then show build progress for people who never even heard of it. These are pictures from my actual build.

    This is the most complex DIY project i have taken on to date (yes i could've easily just gone out and bought an off the shelf Yggdrasil or a DA11, but that wouldn't be any fun). I had built an OpusDAC prior which is basically a desktop version of the Gamma2 that came out in like 2006 so i am familiar with the sound signature beforehand. There's a LOT of through hole, there's some SMD (not much more difficult than a AMB Mini^3's SOIC opamps), and only 1 fine pitch the SRC4392 48pin quad. With a decent iron, the right tip, and solder flux it's actually not that bad.

    The Gamma3 is a DIY only, full feature, desktop class DAC (12x12x2" twin enclosure w/ separate PSUs) based on a popular DS Wolfson DAC chip just like the Gamma2 (Compact) DAC, EAR DAC, and OpusDAC. It's an expensive project and focus was made on the implementation input through output.

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    Start with 3 high-performance power supplies - Sigma11's and Sigma22 single and dual rail LPS. The same gadgetry that powers and regulates the AMB Beta22, Beta24, M^3, etc. This DAC has more balls than my 4channel Beta22 (until i upgraded it) and M^3 combined. Keeping the AC and transformers in a separate box is an effective method to ensure that the DAC is unaffected by noise (obviously adds a lot of cost and it's not optional - no compromises were made on power conditioning..even the power cord inlet is a filtering type). To fit all this in a single box would be ridiculously large and require a lot of shielding. This is a LARGE step up from the Gamma2 or the OpusDAC which are basically powered by a single Sigma11 or wallwart.

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    Gamma3 "motherboard" (mostly complete in this photo). What you get here is isolation of the digital inputs (audio signal and digital controls) and outputs (see the 'bridges' over the dark line). The USB (noise/jitter) is on the outside obviously and the signal must go through digital isolators before it gets to the DAC. Any digital inputs (SPDIF noise/jitter) are also completely isolated. The entire (outside) isolated section including Zeta1 USB receiver has its own dedicated power. Priority was put on optimization of signal traces, layout, galvanic isolation of all critical components, and using all available real estate to put the noisy stuff far away.

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    Gamma24 DAC module is a module that contains the essential core functionalities (DAC chips, the precision oscillator, additional power regulation for each sub component, digital receiver chip, asynchronous sample rate converter with integrated digital audio interface receiver and transmitter - this unit allows the Gamma3 to serve as a (clean) USB or SPDIF receiver for other digital sources outputting additional SPDIF). The DAC chips only cost $40 out of the $1,500 in electronic components. It's modular, maybe AMB will come out with a R2R module or when a better DAC chip comes out. Who knows.

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    Dual Alpha24 modules serve as fully-differential output stages (for voltage amplification of a voltage ) and final stage LPF to ensure rejection of any HFreq noise coming from DS modulators. The topology is a modified instrumentation amplifier: a high-CMRR input buffer/gain stage, followed by a balanced-to-unbalanced converter with 2x gain. This module provides for balanced-to-unbalanced or unbalanced-to-balanced conversion. [Mostly copied from AMB site] The Gamma2 and OpusDAC do not have output stages at the same level.

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    Who says DIY had to be bland? Gamma3 has a LCD screen, digital volume controls, IR/remote control (required to setup), personalization/programmability, and motorized pot. There's about a hundred fifty bucks in bells and whistles, most of the money was allocated towards the very important stuff...but it is still feature rich. Consider that the Academy Audio solution used by Bob Katz in his M^3 build was double to triple the price of the AMB LCDuino.

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    Last edited: Jun 11, 2016
  2. Jh4db536

    Jh4db536 Friend

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    Soldering was the easiest and least stressful part of this whole project (had very little SMD experience prior to this). Enclosing is a beast of DIY and something i am not good at, but getting better and more confident with each project. Still, I do not enjoy this part at all. To make up for this, AMB provided awesome documentation of the actual build, parts list with different pathways, alternative parts to cut costs, BOM with vendor part numbers, reference build, even the FPD files, and custom bridge boards i.e. epsilon 31.

    Enclosure/CNC cost for the y3 is expected to be about somewhere between 25-30% of the passive component cost, which actually isn't that bad. i.e. my M^3 enclosure cost approximately 67% and a Mini^3 is almost 100% ($40 front plates plus hammond probably cost more than mini3 finished board)

    FPD for default y3 build is downloadable off the AMB website. It's spot on and the only change i had to make was for the diameters of my Vampire RCA outlets and inlets.

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    Drawing of layout/floorplan - i copied AMB's but you still have to do your measurbating in FPD and actual.

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    Execution of floor plan with my black and decker drill and harbor freight drill bits/countersinking bits. A CNC, laser cutter, or even a Mill/Drill press would make my life a lot easier.

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    When things don't fit right (filtering IEC module)...well you have to do something about it. Take out a hammer or a dremel/pneumatic metal nibbler.

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    Almost done with the DAC side.

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    Last edited: Jun 17, 2016
  3. Jh4db536

    Jh4db536 Friend

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    Current Status - Front Panels shipped today, Finishing SSR Trigger on PSU, determining whether i'm going to proceed with the illuminated switch hack on the Gamma3.

    A smidgen of progress today. Can't really do anything until the mailman brings my parts. Worked a little bit on the beta22 upgrade (fabricating a rear attenuator mount), that could be another thread in itself since I have two big projects going on at the same time and three if a mainline and/or T3 kit come in ;).

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    Tidying up the internal wiring harnesses
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    Last edited: Jun 17, 2016
  4. Jh4db536

    Jh4db536 Friend

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    ALL the front panels came in...there's still some metal work to do. I have to cut up the frames a little bit to get all the Neutrik jacks to fit on the DAC rear plate per AMB build instructions..

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    Another side project i have going on hehe...

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    Last edited: Jun 23, 2016
  5. Jh4db536

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    Function tested - pass.
    Still have to tidy things up and put in LEDs, neons, bells, whistles, and ricer stuff.
    Haven't tested UAC2 mode yet since my work laptop doesn't let me run anything including drivers.

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    Last edited: Jun 26, 2016

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