The EML20A is an excellent choice for a single stage preamplifier that can satisfy the most exigent audiophile. This DHT has enough gain to use it with line output transformer and it is indeed, as stated by Emission Labs, one of the lowest distortion tube ever built.
The preamplifier has a separate power supply, which is a great practice inn order to make a quiet DHT preamp.
The power supply uses all Lundahl power transformers and chokes for the high voltage section. It is a CLC supply with the Ludahl chokes in common mode for lower noise. The rectification is hybrid, using two TV dampers 6CJ3 on the positive and SiC 1200V on the negative.
The power supply is connected to the main preamp chassis through a 6 feet umbilical cord using a MIL spec Amphenol connector. The umbilical cord is carrying only DC and it is screened with copper mesh, which a good practice to have a good S/N ratio.
The low voltage supply for the filaments of the EML20As is on a separate board with its own transformer. There is a third DC supply for the Volume remote control and shunt output delay circuit.
The main preamplifier uses the excellent high gain EML20A mesh in a self biased setup and loaded on a Monolith Amorphous Core LTA 01/25mA line output transformer (wired 4:1).
The cathode bias resistors are Mills MRA-5 and the decoupling capacitor is Elna Cerafine.
The input is DC coupled and the output is transformer coupled. There are no coupling caps for input or output, an no negative feedback ( global or local).
The volume control is ePOT V3 mini by Tortuga Audio using either LDR module or 60k discrete steeped attenuator module. The display is Oled and remote by Apple.
This is one of the simplest one stage preamps that is using an excellent sounding DHT and extremely low distortions, second harmonic being dominant. The gain is 14dB ( 5x) and with a 2Vrms source will provide 10Vrms at a Zout of 375 ohms. Measured THD was 0.02% at 10Vrms output ( 50Vrms on the plate).