It all started in 1999.
47 Laboratory (Junji Kimura) introduced the 4706 Gaincard amplifier, which produced 25 Watts per channel from a single IC chip amplifier per channel.
The special features of this amplifier design were:
- A ‘high-end’ dual-mono amplifier designed around a single power IC (per channel)
- The world’s smallest number of parts in an amplifier (9 per channel)
- The world’s shortest signal path length (32mm including parts lengths)
- The world’s shortest negative feedback loop (9mm)
- Smallest possible Power Supply filter capacitance (1,000uF) combined with a high capacity power transformer
STEREOPHILE magazine in 2004 said:
” …a sense of transparency: a crystalline clarity that seemed to extend from the lowest bass to the highest treble. The resolution of fine detail was quite extraordinary… The sound had a directness, a feeling that music was being reproduced with a minimum of artifacts getting in the way. “
The 47 Laboratory Gaincard amplifier subsequently inspired and spawned numerous ‘Gainclones’.
One of the most well-known is by AUDIOSECTOR (Peter Daniel), who offers PCB kits.
Jeremy Young’s project here is based on an AUDIOSECTOR ‘Premium’ LM3875 amplifier kit.
This kit consists of 2 x amplifier PCBs with 2 x LM3875 power amplifier chips (Texas Instruments), resistor components, PSU smoothing capacitors, 1 x PSU PCB with rectifier diodes.
The Premium LM3875 kit price is US$98 and is upgraded with gold-plated PCBs, Kiwame and metal film resistors.
The Classic (basic) LM3875 kit price is US$68. Both kits are supplied with Panasonic FC PSU caps and MUR ‘ultrafast recovery’ rectifier diodes.
Power output is around 50 Watts per channel (depending on supply voltage), into 4 – 8 Ohms.
To the above kit, you need to add:
- Power transformer
- Volume control 25k – 50k Ohms
- Input and output socket hardware
- Mains power input connection parts
Jeremy elected to build into a Walnut wood case again.
The heatsink design for this LM3875 amplifier required quite a few hours of CNC machining:
CNC-engraving the front panel escutcheon rings:
See more at – JEREMY YOUNG DESIGN
Right from the first piece of music – wow!
This LM3875 ‘Gainclone’ sounds REAL good – hooked up to Spendor SP1 loudspeakers (87dB/W). So transparent, so clear, clean, effortless, ‘direct’ and ‘natural’.
Wide subjective bandwidth with ‘oodles’ of harmonic richness and ‘decay’.
Bass is delivered with deep extension (when it exists in the recording) and power.
Stereo ‘imaging’ is ‘out-of-the-speakers’ and ‘open’. And with absolutely zero hours of ‘running-in’.
Upper frequencies – jury is still out until we can hook this up into the big system with a variety of source material. So far, very elegant, uniform tone, no complaints.
There’s a lot to be said for simplicity and minimal signal path.
For US$98, I’m shaking my head.
I’m looking forward to hooking up this Gainclone LM3875 amplifier to my big Compound Mid-Bass Horn loudspeaker system.
I feel that this modest little amplifier will create a sound quite different (but equally interesting) compared to my Output transformer-coupled 6SN7 linestage with 2A3 triode push-pull power amplifiers.