@AKLegal - Yes, what Jaytor said. The AMB Alpha 24 is a very flexible opamp based preamp that is dc coupled using some of the finer opamps out there, fully biased in class A. DC Offset isn't an issue either.
The AMB Alpha 20 is a different animal altogether. It is a discrete design, and has a push pull output stage that needs some bias to stay in Class A for most output loads. Only 30mA is required but you can bias it much higher. I use about 50mA. I have found that at higher gains (10X or more) the DC offset can vary a bit, but it isn't too big of a deal. This is common with JFETs which as discrete devices do vary in matching. The closer matched they are, the better, and that is the issue with *any* discrete design. With opamps, the matching is quite exacting, as such DC offset "drift" is very rarely seen. With the Alpha 20 discrete preamp, the small amount of dc offset even at the 10X gain (20dB) isn't an issue in my setup because the next stage is capacitor coupled (my MOFO stage). If it troubles you, use a very high quality capacitor on the output of the Alpha 20 preamp (sized enough so that it can pass low frequencies, like 10Hz or so) and you should be fine; or else design a DC servo, etc...
Here is my Class D build:
Front panel with push button switch that glows a very subtle blue when on:
Rear panel, which uses Furutech binding posts, IEC and XLR's. The writing in Cyrillic says: Ayzenshtat Class D which pays homage to the designer, Leo Ayzenshtat who is the owner, and proprietor at Orchard Audio.
Here are the innards. It uses Neurochrome Audio's SMPS-86 supplies (dual mono), set to +48V. It has it's own soft start, surge protection, and Pi Filter on the output of the MeanWell power supplies and is also compatible with any AC power grid from about 100V to 240V AC. The audio signal wiring is all Neotech. I purchased the Orchard Audio "BOSC" boards as blank boards and had to order and populate the parts myself, all very small SMD! As such, we had to order an SMD stencil to accurately place the parts on the board. Fun stuff. Nowadays, you can order just the boards, fully built which is much easier for the end user, since it is fully tested as well.
The unit is very light, about 8 lbs, and easily pumps out 100 watts into 8 ohms with astonishingly low distortion figures. I have comfortably listened to the amps hooked up to my system and achieved SPL levels of 85-95dB at my main listening position of ~ 4 meters. At these SPL levels, I have measured about a minimum of 6watts and max of 20 watts (my impedance varies from 4.8 ohms to 20 ohms from 100Hz on up). Bear in mind that I use a distributed multisub setup for frequencies below ~ 200Hz.
Here is a measurement at 10 watts:https://www.audiosciencereview.com/forum/index.php?attachments/e215338b-09ca-40e7-8f29-1246f2635a8d-jpeg.83025/
@Jaytor - I will at some point post pictures of my Modulus 686 build which puts out more power and is very amenable to more difficult loads like 3 to 4 ohms. It is a phenomenal amplifier in its own right and the finest Class AB amplifier I have heard.