The SMPS-powered Gainclone
Gainclone projects have been described extensively in the past and there is no point in repeating what is written elsewhere.
The new aspect of this implementation is the power supply. I used the SMPS300RE Power supply Module 300W +/-30V for my Gainclone.
As you can see I did not use a PCB for the amplifier part but one small tag strip per channel. All parts are directly soldered from the tag strip to the pins of the LM3875. The schematic I used is the standard one from the LM3875 datasheet but omitting Ci thus building a DC-amplifier. I have got a maximum offset voltage of 10mV. However, other samples of that chip may not achieve this low value.
For Cs I used 10µF / 50V Black Gate capacitors bypassed with 47nF Siemens KP capacitors. The 4 resistors used are Audio Note 1/2W Tantalum types. Tantalum resistors are one of my preferred resistors to work with the other less expansive ones being Takman Metal Film resistors.
The SMPS300 module provides regulated output voltages with sufficient current drive ability for apair of LM3875. The module uses LLC Series Resonant Converter Topology. There is no audible noise in my Lowther TP1 speakers. From my point of view there is no reason to avoid switch mode power supplies in Class-A or Class-A/B power amplifiers. You actually save a lot of weight and money using them. I guess that nobody will ever call my Gainclone sounding harsh or “digital” (whatever that means).
I have never heard Gainclone implementations with a conventional power supply in my system but this one does compare very favourably with any of my tube amplifiers. It sounds best when paired with my modified Schiit FREYA + preamp. The description of my mods will be published soon in the gear section.
When you pair a DC-power amplifier with a tube preamp it is reassuring to use a DC-protection especially when you use expansive drivers like my Lowther PM-2A. I use a uPC1237-based ready-built module for this purpose.
The wiring is straight forward. I have used silver wiring almost everywhere. The case is from a company called Daub in Wenden / Germany.