About 15 years ago the Gainclone amp was the new best thing in the DIY audiophile world. The history starts with a very expensive commercial amp whose name I do not recall. The actual circuit used two inexpensive microchips and only a few other discrete components (that was the genius of it), and a high end supply. The sound reproduction was excellent. DIY’ers designed and built many examples usually with the best capacitors, maximized power supplies, and beautiful enclosures to produce truly stunning amplifiers.
I had never heard one and was curious. I did not need high power output and had decided at some time that mono sounded as good as stereo to me, so I decided to build an amp with an LM1875 chip, put it in a utilitarian, but clean, enclosure and see what I thought.
My initial attempt to build it from scratch failed so I purchased the K 50 kit from Paia.com. A thread titled Beginner’s Gainclone, HiFi LM1875 on Diyaudio.com (http://www.diyaudio.com/forums/chip-amps/) indicated that the Paia product could be improved so I modified a number of components. (I will post the schematic when I find it and scan it, but several schematics are posted in this Diyaudio thread).
Since my source is stereo and my amp is mono a simple resistor mixer network is needed at the audio input to avoid soundwave cancelling. It is not a big deal to build and does make a difference in sound quality.
I decided to set this up in the basement (man cave) and bought a 8 Ohm Infinity bookshelf speaker from Amazon.com. The speaker is very good, but directional and audio is best heard when the listener is at a distance, but in front of the speaker. I don’t suppose anyone needs to know that.
The chip uses a split power supply: V+ 0V (ground) V-. I was not interested in building a power supply because it would be heavy, require a larger case, and be expensive (the transformer) so I made my own.
I purchased two regulated wall power transformers from Jameco.com which were rated at 12 VDC and 2 Amps. I cut off the plugs and used a box cutter to separate the two wires on each unit, stripped off the insulation for 1/2 inch.The wires are marked so one can distinguish positive and negative visually. I chose the positive from one unit and the negative from the other wall supply and wrapped these together and soldered them. This is 0V. Then I applied solder to the other two leads separately to strengthen them. The idle supply current at +/- 12 VDC is ~55 ma, so I have an overbuilt power supply too.
I have read that the amp sounds better using an unregulated power supply, but I don’t know any more about that.
Next the amp was mounted in the box and the chip back was isolated from the case with a mica insulator and mounted to the enclosure which serves as the heat sink. Since my amp is mono and low power this works fine.
The relation of voltage input and power output is linear with a steep slope. The full power amp uses +25v 0V -25V or 30-0-30and puts out 20 or 30 watts. Mine puts out about 6-7 watts.
This barely readable schematic contains my mods to the www.paia.com K50 schematic on their site.
My pedestrian enclosure–>
The case is spray painted with hammered silver paint.
The knob is for the volume control and the toggle switch disconnects the speaker for <mute>. The volume control is stereo and I used it only because I had it available.
The back shows stereo speaker connectors, the on/off switch, power input, and audio input.
The item on the left of the last picture is a headphone buffer amp that I use as a pre amp. It adds current and makes the speaker output fuller. I thought the sound was a little thin until I added the buffer.
CONCLUSION: The build became straightforward once I went to a kit. Some knowledge of electronics is necessary, but one does not need a lot of knowledge. Certain building tools are needed too to assemble the circuit, make the case, etc. But that is part of the fun, eh?
The internet has all the information one could want.
The sound is quite good (No it isn’t! It’s great!) although I may be biased since I built it.