My brother and I have build two Nelson Pass Aleph P Class A preamplifiers, and we are very pleased with the sound. The preamp is controlled by a PIC18F4620 micro controller.
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The new attenuator pcb, with 5 relays giving approx. 1.7 dB pr step. The new attenuator is originally designed by a Dutch engineer Jos Vaneijndhoven.
The electronic files