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2009-10-14 - It has been more than a year since I have worked on this project. I am now getting back around to it now that winter is coming and I will have lots of time indoors. I ordered two more dual mono LM3886 kits for building up my amp count to six channels. Soon I will have a full home theater surround sound setup. 

2008-12-26 13:28 - So I finished the first prototype. I am listening to it now and I think I like it. I need some more time to get used to it. I am driving a pair of old Pioneer HPM-150s which are six ohm loads. This is not optimal for the amps as they do best with a four ohm load, but it sounds good. I managed to fit it all in that old Shuttle aluminum case. I used the drive bay for mounting the amp modules above the power supply modules. The toroids are on the the bottom in front so that all the power connections could be in one place. Amazingly enough I built the thing and it worked first test in. How nice! Initial testing was done last night with the case 

open so I could monitor it and check for excessive heating. I watched about two hours of Lost. My first impression was this amp was quite a bit more detailed compared to my Pioneer SPEC-2 amplifier. It is also very sensitive, as I could only use about the first five or six notches out of thirty two(!!!) on my pre-amp volume knob. I may have to change the gain resistor on the amp boards to see if I can make it a little easier to work with. Although sometimes I use my MP3 player with the amp, so maybe having that extra oomph would be good. I will have to think about a gain knob for the amp I guess (I originally did not think I would need it). The amp barely got warm after some rather loud explosion scenes and 

the transformers and power supplies where cool cucumbers, so I am very happy about the power/heat envelope. Today I have it all buttoned up after some tightening adjustments to the binding posts and RCA jacks. I have listened to Toby Mac Portable Sounds, Nora Jones Come Away With Me, Allison Krause & Union Station New Favorite, and Jars of Clay Good Monsters. The grungy sound in some of T-Mac's tracks felt extra harsh with this amp (although the HPM-150s with those crazy tweeters on top have always felt too bright), but I will see how it goes after a couple of weeks of use. Nora Jones and Alison Krause sound wonderful and very balanced. Very detailed but not too bright, with excellent middle range extension. This amp controls the bass much better then the SPEC-2 amplifier. It is not as strong as the SPEC-2 but I would guess that is due to the power differences. The SPEC-2 is rated at two hundred fifty watts per channel, where as my amp is rated at 150 watts per channel (these are peak ratings). The vocals and guitars in Jars of Clay are a little too bright some times. Again that same harsh feeling. I just remembered the cross over network in the speakers. A little tweak in the upper mids and highs and its better! I will have to come around and listen to my test CDs again with these changes. We shall see, but anyhow my amp is plenty loud. Now to save up for the other four channels and the aluminum enclosures. I am still thinking about the best way to drive a sub woofer as it is recommended to use about one hundred twenty watts of power for a single eight to twelve inch sub woofer. There a couple of dual bridged LM3886 designs out there that I might try to tackle. Once I decide I like these LM3886 amps (and I am well on my way) I will save up for the other four channels and the aluminum enclosures. :-)

2008-12-24 11:26 - So I managed to get quite a few things done over the last few days. First I load tested the transformers to make sure they would handle the load without too much trouble. The rule of thumb I have found is that a transformers secondary voltage should not sag when loaded to specification past five percent of the unloaded voltage. So the first test was unloaded voltage which in the case of these transformers is fifty five volts across the secondary (these transformers have a single center tapped secondary). After loading the secondary with one hundred sixty watts of one hundred ten volt incandescent bulbs the secondary sagged by about four percent. I did not leave the load on for a significant period of time so I do not know what kind of sag would occur with heat present but it does appear to show these transformers have a very conservative 100VA rating with plenty of reserve. This is good since this power amp can only push about one hundred fifty watts peak for a very short time, so these transformers should be more than enough to run the amp. I finished building the power supply and amplifier modules as well. This required some thinking as I do not have dual secondaries on these transformers. I found a few references to using a center tapped transformer in a power supply and found that I did not need two full bridge rectifiers and that I could use half the diodes and still get two full wave DC rails that are out of phase with one another. So I built the power supplies minus four diodes and bridged the two AC live rails together and the AC reference rails together. Last I went hunting through my parts looking for a prototype enclosure to put everything in until I get something better for the final version. I found a mostly aluminum Shuttle XPC case that looked good. I spent the afternoon grinding, sanding, and moving things around in the enclosure to make room for all the components. I also chopped a piece of steel (I tried to find some aluminum in town but I could not find any sixteenth inch scrap sheet, only eighth inch which is too big) up and riveted it to the inside of the back side of the enclosure to provide a mounting surface for the inputs, outputs, and power jacks. The only problem piece is that part of the front of the enclosure will be open for little fingers to get into. Oh well it should be fine. I may have some old panels around to mount in the front, we will see. On to mounting the components in the enclosure and wiring it all up. I might even get to test it today.

2008-12-19 14:20 - My second batch of parts arrived. This includes the all important 100VA torroidal transformers. Turns out the transformers I purchased are not 25 volt dual secondaries, but a 50 volt center tapped secondary. At first I thought this would be a problem but after thinking it through and studying some circuits I think I can make it work. I also received the power switches, power jacks with integrated fuse receptacles, speaker wire terminals, and the RCA input jacks. Only other bummer is that I do not have the correct fuses for the project. This is not a show stoppper, but it means I will need to go find the right fuses before I put this amp into everyday use. I pretty much have all the parts to assemble my amplifiers. The only thing left is now to come up with some way to house each amplifier. I am thinking I may just stuff it all in an old PC case for the time being and then save  up for the aluminum cases. We shall see. Oh and the Apex Jr. guy also shipped my things to me via USPS priority mail. Overall shipping is about $25,00 so far. Not bad with sourcing from two different suppliers. Now if everything sounds good I hope I will be able to pickup four more of these toroids as they are pretty close to perfect for this project. Here is to hoping there are some left at Apex JR. in a month or so.

2008-12-17 17:11 - My first batch of parts arrived. This included the PCBs for the amp and the power supply. I also received the amp ICs, caps, resistors, and other miscellaneous parts.Here you can see everything inventoried and checked by meter. Everything is looking good. You can  see the big capacitors sitting on the manila envelope everything came in. Those parts are about eight dollars a piece. Lets hope they sound good. You see two sets of everything for a stereo amp. This is because I am building what is called a dual mono-block design. This means that each channel (left, right, center, etc) are discreet circuits with discreet power supplies and transformers. This makes for the cleanest possible sound and more expensive too. Boy am I excited to start assembling it. I am still waiting on the chassis components like speaker posts, RCA jacks, and power jacks. Also to come are the transformers. Hopefully they show up soon. I am still looking for an aluminum chassis to house it all in. So far I really like the extruded aluminum split profile cases but they would cost almost sixty dollars plus shipping for a stereo pair of amplifiers. Not quite inexpensive. You can see another amp project here that uses aluminum cases. Maybe I can assemble it all up and test it before I get the chassis, maybe even give it a listen! Looks like I may have been shipped a few extra parts. Not that I am complaining but I might have to go back and study the PCB layout and the schematic and see if I missed something. Well I am off to practice some soldering with my new iron before I touch these components.

2008-12-11 12:26 - So I am one of those do it yourself kind of guys. I do not know why, maybe because I grew up in Alaska and Alaskans are pretty independent. So when I started building my home theatre (with mostly left over, second hand, and used components since I am cheap too), I decided that I wanted to build my own amps for driving the surround sound system. So I went to Google and started my research. Low and behold there are lots of other people like me (scary isnt it?). I ran across several websites with interesting information about other people building amplifiers. Since my electronics knowledge is rusty at best (I took a couple of correspondence courses when I was a teenager), I decided on the simplest design I thought I could build. This led me to amps built around the LM3886. These designs are frequently called gain clones, due to being based on a design called the Gaincard. This amazing little chip only requires a handful of components and puts out an amazing 50 to 60 watts of power. Many designs also used a simply toroidal transformer/unregulated power supply configuration that I was positive I could build (but could I do it safely?).  So today I purchased a set of PCBs and components kit from chipamp.com after a couple of polite and helpful emails from Brian Bell (the guy who runs the website and puts together the kits) about what I would need. I also ordered the toroidal transformers (one of the more expensive components) and various odds and ends from another online retailer called Apex Jr which is run by a guy named Steve Slater who was willing to ship stuff to me USPS (this saves a ton to Alaska!). What a deal. So I am set for a Christmas vacation project that will hopefully end up with a working stereo amplifier to drive my pre-existing speakers. Some more interesting information about amp/power supply building and another LM3886 design at Elliot Sound Products. More to come later!