A high quality audio system build with basic tools!
Size matters! What loudspeaker size and amplifier power suits your needs? It all depends on how large your listening room is, your preferred listening level and type of music. However, size matters when it comes to sound. And so does the audio quality of each of your components. This build will play any music, low or loud, with nice and deep bass, perfectly clear and transparent mids and highs.
Step 1: The Amplifier
Here is the circuit board list for this custom 6 channel High End Bluetooth Home Theater amplifier :
-Stereo 420 + 420 Watt RMS Bridged TDA8954 THD 0.03%
-Center channels 210 + 210 Watt TDA8954 THD 0.03%
-Rear channel 100 + 100 Watt Bridged TPA3116 SNR 102dB
-Surround delay circuit using PT2399
-Differential and Tone circuit with OPA2134 with only 0.00008% THD!
-Remote Volume PGA2311 120dB dynamic 0.5dB step 0.0002% THD
-Headphone amp TPA6120A2 SNR 128dB THD+N -108dB 1300V/µs Slew Rate
-Bluetooth 5.0 DA converter 24Bit using AD823 108dB THD
-Startup delay and speaker selector (custom mute function)
-Led VU meter, unfortunate DOA and I'm waiting for a replacement
Using class D amplifiers with above 90% effectivity gives you high output power with the use of small heatsinks.How eer, it does get hot, so I suggest mounting a fan. Class D are ultra linear and with good audiophile characteristics.
When buying your circuit boards it's a good idea to look up the datasheets for the amplifier components used. Check that the operating voltage for the selected circuits fits your power supply. For the best sound you should pick amplifier components with as little THD% (audio distortion) and highest possible SNR dB (signal to noise ratio).
Step 2: The Skeleton Amplifier Cabinet
Making your own cabinet is easy and great fun. Using two pieces of steel or aluminium sheet. I have chosen perforated steel for the bottom half, its rigid, lets air through and keeps electromagnetic noise out. It's also easier to bend using only your bare hands and a piece of wood for folding the corners around. To make it even easier, no cutting is needed for sheets that comes in 50x50cm. Simply bend at 12.5 cm and the bottom half is done.
Framed aluminium mesh is used for the top part and power supply cover,. Both the mesh and the aluminium profile frame is easily cut with a metal scissors. The front panel is 12.5x50cm aluminium sheet. Glued corner profiles and decor.. Mine has approximately 3000 gold flakes, one by one, but you can be creative with other materials. On top as a dust cover and in the front panel, plexiglass is used. Plexiglass is easily cut by firstly marking with a sharp knife then snap it over a sharp corner using a piece of wood to press equally along the edge.
Ones the chassis is ready you can mount the parts. Start with the power supply. For easier installation, make a wire diagram and connect wires to circuit boards before installing them.
To avoid noise and hum, make all ground connections to one star point. The more circuit boards your amp has the more complicated the grounding will be. Inside the cabinet shielded cables are grounded only on the receiver end. Each board normally has two ground connections. One for power and one for signal ground. If you connect both you will probably get a ground loop in your system. In some cases it's better to solder ONE ground cable to a star point in the circuit board instead of using the connectors. Where possible, try separate power ground, digital ground and signal ground paths.
Step 3: Loudspeakers:
Main stereo speakers: Two 12” Peerless 300W woofers in a shared sealed 96l cabinet with no bass-reflex for quicker cleaner bass that goes well below 30hz -3dB. The midrange box has double insulated walls and triple front panel holding a 6.5" 150W midrange with ultra stiff kevlar membrane and phase plug. The stylish midrange box finish is simply glued wallpaper (same used for the stereo cabinet). High power silk dome tweeter mounted in stylish plastic housing stuffed with insulation material as well.
I prefer having stereo in my centre. Mainly used for movies, TV, live concerts etc. Boxes made to fit the hex design of the speaker element by hand planing 12,5 degrees off each side of the 2x10cm wooden beams creating a volume of about 36l. High power, high sensibility 96dB/1W PA element for mid low connected directly with no filter. This nice speaker element has a perfect response curve for speech and a nice upper rolloff taken over by the top mounted tweeter filtered with a simple 6,8uF/250V polypropylene condenser. Note: All speaker elements tend to have more distortion in the higher frequencies of their curv, so for audiophile listening I suggest adding a 12 or 18dB/oct filter a bit tower than the highest frequency mentioned in its specs. No visible cables. Signal connection is made through the support bolts in the two feets.
The surround speakers use the same carbon fiber element as the 6.5” midrange with no filter at all reproducing 100 - 7KHz.
Placing your speakers.
Every room has its different acoustics. So the placement has to be tried out. The distance to the main speakers should be bit larger than the space between them. For optimum bass response, place one speaker in your listing position, then listen near the corners of your room where you hear most bass. That's where you place your main speakers or bass speaker. The front center and side speakers must be aligned on the same line or you might get a phase out. With the PT2399 circuit you can adjust the time delay for your rear speakers so that they sound as the same distance as your front speakers. If your listening position is in the middle of the room, you don't need to delay the rear signal. Simply using a single differential op amp for the signal decoding.