The 300B Thoress input sensitivity is 3.25 V and input impedance is 100K ohm. According to the manual, the amp needs a preamp with more than 2.71 V total.
I tried with my Allnic L3000 preamp (output voltage: 15V, voltage gain:+20dB, output impedance: 150 ohm) and the sound has no dynamics at all and has very low volume even if I turn the preamp volume knob higher and higher... I don’t understand why it doesn’t work because the Allnic specifications should match the Thoress specifications.
I searched for the Thoress line stage specifications, but there is no information about output in the manual and anywhere. So I can’t know what the manufacturer made with his preamp in order to to compare with other similar preamps.
In a Stereophile review, Art Dudley connected a Shindo Masseto in the Thoress 300B. According to Shindo website (
http://www.shindo-laboratory.co.jp/English/Masseto.html), the Masseto has Output/ Impedance:5V/600Ω.