For one..You can find a quality built less TDH rated amp with under rated/more than often unregulated supplied power and good power for a dirt cheap price compared to todays mainstream over rated amps.Built so much better with quality parts, and in most cases can be easily replaceable compared to todays micro boards.I still run several old school Zed made amps from the late 80s and 90s that still perform and sound absolutely fantastic compared to alot of newer amps Ive bought to replace, and go back to due to the SQ difference. My Autotek BTS and Mean machine series seem to always shell out excellent power and sound fantastic.My Mean Machine 99s,66s,44s,40-90 mxis,BTS 7050s,7100s,7150s,7300s,7204s,and My Hifonic Vii,Viii series Cyclops, Vulcan,Hercules,Gemini,Thor,Odin,Pluto,and some of the cleanest sounding Alpines even to date of the Duo-b 35 series pure SQ with some balls as well 3522,3523,3525,3527, 3548,ect.JBL gtq series/concord(rare),Concord/Harmon K.series,Special Editions/PPI series,SStream USA,SS Granite series,. More than I can list that were built like Tanks! that are pretty much indistructable that can be slammed on all day long and built to last for years,and components inside can be easily replaced.To meet most of these that Ive mentioned that can be had used seem to run in the market of todays amps that most do not want to spend the money for in my opinion.Alot of todays amps run in the range of TDH 0.05%and upwards and rms values are rated @14.4 v unless specified as alot of old amps range from 0.01%TDH and up to 0.05 from 11.9v on up,and some without any current limits up to 16v.I can deff hear the difference in an A/B,A amp compared to a Class D or from an old A/B to a new A/B amp.The depth as well as the clarity.Its just like anything these days..you want quality,your going to have to pay for it.I honestly think that todays amps have an Hour playing limitation such as the new TVs that we have/light bulbs ect. within the electronics world compared to the old tube TVs and old amplifiers,electronics myself? Every Old Zed Made/Steve Mantz Made amplifier Ive bought over the years has always performed,and never let me down.Built Like Tanks!