apríl 14, 2007
One more loud.
I have been promising pictures of my latest amp for a while. It is based around the very popular 'BrianGT' kit available at chipamp.com. This is a Gainclone, or a 'chip amp', based around a 'common amplifier on a chip', the LM3886 from National Semi conductor.
The reason be hind the 'clone' in Gainclone is that it is a knock off of the Gaincard, a semi mystical amplifier built by the Japanese audiophile company Sakura Systems about which there are volumes of spurious claims and plain ol' audiophile bullshit. The Gaincard also costs US$1500, plus another US$1800 for the power supply (But they recommend that you purchase two power supplies, one for each channel), but all this expensive magic is produced using US$10s of dollars of parts.
The BrianGT kit costs US$85 with two power supply modules. A suitable transformer will cost you NZ$80-120, or 2xNZ$70 for dual independant transformers.
Thus the real, no hype advantages of Chipamps is that they are cheap, quick to build (I finished soldering the 4 modules while watching a 45 minute TV show), and they offer an extremely clean sound with very low distortion.
For this build, I have stolen something from the aesthetic of tube amps, with all the components being mounted on a metal plate. I wanted to be able to mount this plate in a wooden frame for use/display at home, and I wanted it to be portable, so I could take the amp to parties etc without damage I sized the plate to be a perfect fit for an old Canon camera hard case that I have had for years and always thought that I should do something neat with.
I opted for an encapsulated toroidal transformer from Radio Spares. These transformers are 'potted', or encased in a block of resin, so that they have absolute stability of output and very low hum. Hum is caused by the wires in the transformer vibrating as electrical current flows. Sealing it all in a solid block of plastic fixes that. Being potted, it doesn't radiate heat as well, so I have specced the transformer conservitavely at 300VA, so overheating shouldn't be an issue.
Being bolted to a 4mm thick plate of marine grade aluminium helps too. The wee amp chip beasties don't like being heated past 150 deg or so, so the attached heatsinks keep the entire amp at a 'barely warm' operating temperature.
The power switch is at the back, near the case hinge, as is the iec jug cord input. This prevents the lid of the case from being closed while the amp is powered on (see above).
The BrianGT/chipamp.com kit can be ordered with a single power supply module to drive the two mono amp boards if you intend to build it in a single chassis, or you can purchase it with dual power supply boards if you intend to build the amp as two separate monoblock amps.
In the intest of future utility, I ordered the dual supply kit, and have made the unusual decision of running to mono amp setups from a single transformer. I mainly did this so the build looked symmetrical. ;)
TBC....