Morning fellas,
I hope
mdconnelly doesn't mind if I tag along my own mini review of the BOSC Class D GaN amplifier monoblocks. I had the pleasure of listening to them a few days ago for several hours before shipping them off to the next person in the tour. For those of you who know me, I am extraordinarily picky about amplifiers, particularly with regards to measurement criteria. Prior to accepting these monoblocks I had a look at the measurements provided by Leo, because it isn't worth my time to review a product unless it actually has the 'potential' to make the grade. I am not saying that measurements are the end all be all, but I am saying that over the years I have been able to separate the wheat from the chaff so to speak. Given the flat THD versus frequency and extraordinarily low THD and IMD measurements it appeared worthy. My main 2ch amplifiers are designed by Tom Christiansen, the Modulus 286, all SMD designed, 4 layer boards and again, extraordinary measurements. They are my references.
Other gear in my system include:
- Roon with everything upsampled to DSD 256
- Auralic Aries G2 streamer
- Matrix Audio X Sabre Pro (MQA) - output voltage of 4.5V RMS
- Poseidon's Voice/Bent Audio TAP-X (fully differential silver autoformer based preamp)
- Poseidon's Voice Moksha/GedLee NA12 loudspeakers (96dB efficient)
- Behringer DCX 2496 w/AMB Kappa DCX modifications for a quad set of subwoofers
- The room is fully custom, fully treated, and of course the entire system has been measured and optimized using REW, etc....
The noise floor of the room is low. Using a NIOSH app on my iPhone XR, with C-weighting, it rests at about 28 dB. So yes, details are heard in galore.
System details:
https://www.audiocircle.com/index.php?action=systems;system=11843 amps were used for the evaluation:
A DIY Sony VFET Class A design (15-30 watts/ch Class A, overall gain of 16dB) - on loan.
Modulus 286 (~60-100 watts/ch Class AB, overall gain of 20dB)
BOSC Class-D GaN monoblocks (150 watts Class D, overall gain of 16.8dB, this is the 8 ohm version)
Gain differences between the 3 amplifiers were completely accounted for by the 1dB volume settings on my TAPX. In addition, gain settings were accounted for the multiple sub configuration as well.
I would like to echo nearly everything said by mdconnelly. This is an extremely good amplifier, something I could live with easily if I didn't own the Modulus 286. The noise floor is very low, and you hear tiny details into the background on many recordings. The amplifier is very similar sounding to the Modulus 286 which is a major compliment! Big, bombastic dynamics, excellent tight very well delineated bass and yes, ethereal high end. Soundstaging was wide, and performers were well placed, such that you could easily distinguish the differences between them. At no time was power a problem, and this is really because my main speakers are very efficient, they loaf at 10-20 watts. I was listening at 80-100dB spl's without a hint of strain, and my listening position is about 12 feet away.
The major difference between Modulus 286 and BOSC Class-D GaN monoblocks are:
- BOSC is a bit more 'forward' sounding. This isn't a negative per se, and is quite system dependent.
- BOSC bass although well delineated was slightly less impactful than the Modulus 286. Interestingly enough, they both have very similar damping factors as well as measurements, so this may be all in my head.
Would I be able to tell the difference in a blinded situation? Probably not.
How about the PASS DIY Sony VFET? Sadly this amplifier fell in last place. Although very good sounding in its own right and actually, more detailed than many of Pass' DIY designs, there were major differences in bass detail, realism, imaging density and overall believability. Relative to the other 2 amplifiers, there was smearing and bleeding of images within the soundstage instead of fine delineations. You could easily walk away from the system with the Pass amps whereas with the Modulus 286 or BOSC amps you were fastidiously held in the listening seat. You could say that the Modulus 286 and BOSC designs gobsmack you immediately. They are that good. Mind you, that the finely delineated stages exhibited by the Modulus and BOSC amps are not at the expense of TONALITY. Tonality is quite neutral and very natural.
A few observations and nitpicks. I think it is important that audiophiles understand and particularly Leo understands the importance of good system integration here. Note that the input impedance of these BOSC amps are 5k ohms and 7k ohms for the 8 ohm and 4 ohm versions respectively. So no tube preamps or passive preamps with high output impedances need to apply. In addition, do take into account the overall closed loop gain of these amplifiers; they are somewhat on the low side of 14-17dB. They will most likely EASILY work in a system with fine DACs that have adequate voltage swings along with sensitive speakers. But if you have the 4 ohm version of the BOSC, along with Magnepans, guess what, you will most likely need a preamp with some gain, and low output impedance. In addition, for you vinyl enthusiasts, you will most definitely need a preamp and phono preamp of course. The final nitpick is that the amplifier has no power switch whatsoever. You just plug it into the wall, and you need to be careful about making sure your preamp or DAC is on first and that speaker cables are already connected to the amplifier prior to plugging it into the power outlet.
All that being said, the sonics of this amplifier are truly excellent to spectacular. I put the BOSC amps in the league of other greats like the Modulus 186, 286, 686 series, the Benchmark AHB2, Hypex NCore designs, etc...
Leo is a fine audio engineer and has definitely done his homework. Sonically, I have little to no concerns. From a reliability standpoint, and given how small the chassis is, I would like to see measurements on how hot the chassis gets with high powered situations as I was a little surprised with how heat can be dissipated even after taking into consideration how efficient Class D amps are. So some measurements at 8 ohms, 4 ohms , and/or an FTC 1974 torture test. 1/3rd of rated power for an hour, then five minutes at full power. That would be interesting to see. I understand that these amplifiers are designed for music systems and not sinewave generators, but reliability is just as important as sonics in my opinion.
Thank you Leo for lending your amplifier design. It was a sonic splendor and I feel that it is an even better effort than my PecanPi streamer! Best of luck to you in this new venture!
Best,
Anand.
