Don’t forget the early Koss estats! The ESP 6, 7, 8, 9, and the 10. I have the ESP 6, ESP 9b, and the ESP 10, all sealed. I am sure this new one will seriously out perform all my Koss headphones.
I would love for you to do a write up the D amps. I use one of 3 amps with mine. The Golden Tube SE40, the Aragon 8008, and a Carry Rocket 88 are my usual suspects for amplifying headphones. I do have a few other amps that I could use but they need repair.
I am glad you told me that, I would not want to buy bogus transistors. So with that in n mind, I will continue to use my SRD-7 Pro and my SRM 212, and save up for a better amp.
Yes the older Stax amps do offer a way into the Stax world. But be weary that many have parts that are no longer available. I have a
Buyer beware on older Stax amps. Many have parts that are no longer available. I have a SRM 1/ MK2 that I tried to refurbish but some of the transistors are not to be found at any price. I know the Stax SRM1 is loaded with obsolete discontinued parts. If you were to look at this point of view, Topping at least has modern and available parts. Design wise the topping is iffy at best.
Maybe Birger and Mr Gilmore can give us a list of Stax amps that have replacement parts issues so others can make better informed decisions.
Look up online the owners manuals of Koss ESP7,8,9 and they have a oscope printout of a 400 hz square wave. It looks as bad as the Topping. These models of the ESP all use an external transformer box (the ESP6 had its transformers in headset, heavy and uncomfortable)
hfe_koss_esp-7_en 2.pdf
Get a Stax SR003 and the cs1 kit. Isolates very well
If you are taking it somewhere there is the SR002 iem portable. I have the SR002 and an adapter so I can use it with a SRM 212. The little battery operated amp is actually pretty good.