I've been meaning to build a power amp for some time now, but never managed to get around to it. You know, life...busy...

Well, my priorities changed recently, when my Technics SA-GX505 receiver blew its output stage. I've found a renewed excitement for diving into my long-missed hobby of electronics. Listening to built-in television speakers just isn't the same. :(

So I did what I always do when I get excited about something. I bought a book on amplifier design - "High Power Audio Amplifier Construction Manual" by G. Randy Slone. Excellent read by the way.

More recently I revisited www.diyaudio.com. I read some of the forums last year, and was delighted to find new forums on Chip Amps. Looks just like what I'm looking for! What a great bunch of people hanging out there, full of knowledge and willingness to offer advice when called upon. The posts in the diyAudio forums inspired me to build a GainClone, and to update my website with some project pages!

I would love to make something that looks nice, like ones by Peter Daniel and Pedja Rogic. Time will tell if I succeed. :)

I started a thread on diyAudio.com. Click here to view it!

I have just about all the parts I need to get started! First part I ordered was the transformer. It is a 300VA Toroidal transformer from Plitron. It has two 115V primary windings and two secondary 25V windings. I went with this rating so I could get the full power rating out of the LM3875 chips. Some people on the diyAudio forum say that running at this voltage will generate a lot of heat off the chips, so I'm going to see how my heatsinks do. I'm also going to put a switch on the Plitron's primaries that will allow me to run them in series or in parallel, so I can run the amp at half-voltage. From what I read, a gainclone running at a lower voltage sounds better and runs cooler, but it doesn't put out as much power. My speakers are pretty sensitive though, so this should work well for most listening.

There are some useful parts in a used computer power supply I got which had a seized fan. The enclosure is a perfect size to house this transformer, and it has some useful mounting hardware for TO-220 devices (screws and washers). It also has a number of wires that could be used to connect the amp to the power supply. Here is a photo for size comparison:

Here is an aerial view of the parts that will be used in my gainclone. At the top-left are the fuse holder and power switch. The white package to the right of them are the insulating pads that will go between the chips and the heatsinks. They are made of Bergquist's "K10" material which is very thin and good at conducting heat. Below the package is one of the LM3875 chips with the unused pins removed. I have 3 more to the right of it. In the ZipLoc bag are the feedback resistors. They are 1/4W 210K 0.1% tolerance metal films. Beside them are two bridge rectifiers for the power supply. Take a look at the heatsinks! They are part of a car amp enclosure. I'm going to use these enclosure parts to house the amp.

This is a closeup of the remaining parts. The light blue devices are the input resistors, 1/2W 10K 1% carbon films by Riken. Beside them are four 1000uF 50V Panasonic FC caps for power supply filtering. Above those are a pair of BlackGate 4.7uF non-polarized input caps. And finally, the bannana plugs and jacks for speaker connections.