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.
Update 04Sep26 ~ New Kanto Subwoofer & New Sweeps & Filters... The trial with the borrowed subwoofer worked very well but I returned it to its rightful place in the Blodgett Fam Rm system. So, I bought an entry level sealed sub (preferred for tighter musical bass) with decent reviews, a Kanto SUB8VMB for $350. It's smaller than the SVS but fine for the desktop audio low end. I again spun the dials testing crossovers and gains, measuring them each time. I ultimately chose a 100Hz crossover point and created a new filter set for the sub itself. And, to be most accurate, I remeasured the NHT SB1s and built filters off the new measurement for them and reloaded into the miniDSP 2x4 HD. The new Blodgett Desktop audio system sounds great. It is used sparingly in waking hours but useful in preparing monthly Music Appreciation entries when in COS.
Remeasuring NHT SB1s ~ Here are the filters and then the raw vs EQed SPLs; clear improvement but displaying the need for a subwoofer.
Kanto Sub Integration ~ Here are comparisons of Kanto Sub8 and mated miniDSP crossover settings for the sub, with the baseline NHT SB1 wanting low end. I settled on the Kanto set at 70Hz crossover (not really as the integrated xover is not very effective) and a 100Hz low pass filter in the miniDSP (more effective). The Sub8 can get loud but gets pretty distorted. The gain on the sub's Class D amp is probably ~25% here to produce 75dB, as my SB1s are doing. At final setting THD is ~11%! And, it loses steam from 20Hz-30Hz. I'd go to the SVS if I could but it is 2X the price of the Kanto. There was a little bump at 100Hz I could tame in the miniDSP and so I built a biquad for it.
Final Integrated SPL Sweep & Listening ~ Once everything was completed I re-swept the integrated system (compared to original raw) and started listening in earnest. This is a decent result for lower end gear chosen specifically for this location... I'm pleased. I wanted to hear the bass thump and listened to Miley's latest drop of pop, "Bass Persuades;" wow, and so it does. I moved on to more complex stuff from Elephant Survival, AJ Lee, & Cat Clyde and the kit is very smooth ~ I was concerned for harshness from the GaN amp but none, just clean. The distortion from the Kanto SUB8 was not a problem.
