Yamaha A-S2000/A-S2100 Integrated Amplifier:
-
http://i.nextmedia.com.au/avhub/pdf_yamahaas2000hfnov08.pdf?128701600396577735
Probably above your desired budget, but it's 100% balanced inside and with floating ground (amp's ground is not tied up to case's ground, so lower background noise, no ground-loops possible and less distortions at full power vs. similar amps with similar power specs).
A-S1x00/S2x00/S3x00 measures the same way and is also sharing the same internal schematic, only the no. of output transistors differ and, of course, output power and PSU/transformer are more powerfull as well.
A-S1x00/S2x00/S3x0 are using
Circlotron technology and are using MOSFET in output buffer (overheating cause auto-decreasing the output power, so less worry about overheating defects); also, using several linear PSUs inside and lot of reservoir caps. Also, there's included a dedicated high-quality headphone amplifier around transistors and with 10uF input cap; separate PSU for the headamp as well. Several protections inside: DC-output for speakers, thermal protection for most power bridges, transformer, output transistors for each heatsink, over-current etc. Also, firmware upgradable not only for the inside DAC (on A-Sx100 models), but also for the microcontroller that takes care of the protection circuits and the relays inside.
Yamaha A-S700/A-S701/A-S800/A-S801 Integrated Amplifier:
-
http://i.nextmedia.com.au/Assets/Yamaha_AS-700_Amplifier_Review_LoRes.pdf
-
https://audio.com.pl/testy/stereo/wzmacniacze-stereo/2786-yamaha-a-s801
-
https://audio.com.pl/testy/stereo/odtwarzacz-cd-wzmacniacz/2676-yamaha-cd-n301-a-s701
-
https://audio.com.pl/testy/stereo/odtwarzacz-cd-wzmacniacz/1510-yamaha-cd-s2100-a-s2100
A-S70x/A-S80x measure the same way and is also sharing the same internal schematic. Also
https://www.audioholics.com/amplifi...1-amplifier-review/yamaha-a-s801-measurements worth a read. These amps are using BJE/bipolar transistors in output buffer and dual PSU for entire amplifier, but separate smaller PSUs for DAC, preamp etc. Like most amp in this price-range, there's no dedicated headamp inside, just couple or resistors that creates a
resistive divider, connected to the 6.3mm output jack. Several protections inside: DC-output for speakers, thermal protection for most power bridges, transformer, output transistors for each heatsink, over-current etc. Also, firmware upgradable not only for the inside DAC, but also for the microcontroller that takes care of the protection circuits and the relays inside.
BTW, if you like a bit of DIY, then you could have a look over
https://www.neurochrome.com/lm3886-done-right/ and how well it measures (almost 100dB between fundamental and its 2nd harmonic!). Also,
https://www.neurochrome.com/product/modulus-286-2-2/ and recommended PSUs, plugs wires and case might be even better.
P.S.: I do own A-S701 and I'm enjoying it. It can push over 2x130W RMS with less than 0.1% distortions on my 4-16 Ohms speakers, that would be over 100dB in my living room, so quite powerful.