Blodgett Desktop Audio... I've never had a speaker setup for the Blodgett Desktop; it's always been headphones only. This had made sense with even open air headphones bugging other house members. My headphone system there is stellar Schiit Mjolnir2, Schiit Gungnir MB, and Mr Speakers EtherC Flow closed plannar magnetics or Sennheiser 600 open cans. Nonetheless, I like speakers better in general these days so why not toss a pair below my monitor for near-field listening in the study. I'll just need to pick my listening times properly.
GaN FET Class-D... I am watching the progress in the power, efficiency, and quality of "chip amp" audio amplifiers. I've owned, and used, and sold, and mothballed many of these inexpensive and efficient amps over time. These included Toppings, NADs, PopAmps, and other brands of "Class-D (digital)" amps and they were OK but nothing compared to my finer transistor or tube gear of classic linear amplification circuit designs. But I'm intrigued with the latest high speed class D variants in gallium nitride (GaN); they are even more efficient, even clearer & flatter, and still not expensive or large.
Class-D PWM Amplifiers... These convert analog audio input into high-frequency pulses using a technique called pulse-width modulation (PWM). Transistors (MOSFETs and increasingly GaN FETs) switch between power rails creating a pulse train (versus classic transistor amps using linear gain techniques). A low-pass filter is applied to eliminate very high frequencies and EMI from output. Efficiency is increased substantially in employing transistors fully on or fully off, 100%. Switching amps have been around since the 1930s but only relatively recently have gained the quality and performance status sought by audiophiles and music pros.
Mid-Fi Class-D... My dive on the category yielded numerous entries from $70 - $7000. The high end is not for me and I can't believe they'd be worth it compared to comparably priced classic SET, Class A or Class AB designs, much less SET tube designs for home audio. Many good products are raw boards for integration with powered speakers or in plate forms for PA systems, but I wanted a boxed variant. And, I prefer a unit with a pre-amp for volume control. The entry-level is littered with Chinese gear of varying sonic and reliability levels but one needs a bump in price to get GaN FETs and higher quality. After reviewing SMSL, Hypex, Purifi, atma-sphere, Nord, Buckeye, Crown, and others I decided on the Chinese entry-power level SMSL PA200. It's GaN stereo with 85W/ch into 8Ω with "no" THD for ~$400. Awesome on paper, and the reviews were 4.8/5.0 stars.
Install & 1st Impressions... The amp arrived quickly from Amazon. I'd retrieved a pair of "retired" NHT SB1 bookshelf speakers from the Nest that I repurposed to be the near-field transducers for this updated desktop system. Viola; it was all quickly installed and cooking. The audio path employs source flac files spun from my server through macOS via JRiver MC (or YouTube vids), then through my fine Gungjir R2R Multibit DAC over USB, and onto the SP200 amp from SE-out (single ended) via unbalanced RCA cabling; the last run to the speakers is via 16 gauge zip cord terminated with banana jacks. Listening demonstrated wanting low end so I need to work on a sub, but down to 100Hz it was stellar. Else the Blodgett Desk system is really clean and true and fun. Of course I measured the system raw at this point; measurements are taken @ listening position ~3ft away @ 1.5x the mains separation.
Subwoofer Trial... I own a closed SVS SB 1000 subwoofer deployed in the Blodgett Fam Rm theater. I borrowed it for a trial with the NHT SB1 mains for a 2.1 system to fill the low end. One failing of the SMSL PA200 is the lack of a sub-out... to solve this I added a combiner to the 2nd SE-Out of the Gungjir DAC. I did not optimize the sub location; I just plopped it on the floor beneath my desk. I tuned it a smidge and this is the Blodgett Desk Audio 2.1 SPL sweep. I twidled the sub crossover & output volume for good integration. So much nicer. The full range 2.1 off the Gungjir MB DAC is nice but I wanted to see if I could smooth out some peaks.
EQ Baby... I found other aberrations, beyond lack of low end, in the 2.0 sweep and so employed my miniDSP 2x4HD to flatten for the speakers and the room. I rue the moment I converted my sweet R2R built analog back into 24bit/48KHz via USB in the miniDSP, but I did. Raw was good, DSP EQ was maybe better. Time will tell. I eliminated the Gungjir MB and used the miniDSP directly via USB from macOS, as DAC and PEQ, and drive both the mains and the sub exclusively from the miniDSP, with less perturbations and fine results. I measured again with REW, then created PEQ/biquad filters and saved the file ~ I loaded the file into proper slots in the miniDSP. Here are the Gungjir raw (orange) and miniDSP EQed (green) final integrated sweeps. Nice, a new fine mid-fi audio, system is born.




























