Home Forums DIY Amplifiers and Electronics Building a 5.1 Amp or 7.1 amp to power the Kartesian system

  • Building a 5.1 Amp or 7.1 amp to power the Kartesian system

  • ajc9988

    March 21, 2021 at 4:06 am

    So, since already biting the bullet on DIY, I am starting to think about how to power the system I want to build. I am thinking of making this a pre-amp/amplifier combo.

    I will fully learn board design if need be, but I am leaning toward tying in pre-made boards. Here is my thoughts so far:

    1) Get the bluetooth board like this one: https://www.parts-express.com/5-VDC-Bluetooth-4.2-FM-Radio-MP3-WAV-FLAC-Audio-Preamp-Board-with-Remote-320-347

    2) You would need a DTS HDMI decoder that could otherwise also take RCA in from other devices. The best I currently can find is a ZY-DTS8 DTS AC3 7.1 Channel Decoder Board. http://www.lillyelectronicsllc.com/controller-electronic-boards/7-1-channel-decoder-board-dts-ac3-decoder-board-3959 (they also have a link to Ali-express, or you can find these boards on Ebay). Yes, it is only HDMI 1.4, but I do figure this is for sound, not for HDMI throughput, so I can make due (although I think it says it has an HDMI out). But, otherwise, the way I would do it is buy one of the HDMI 7.1 decoders, split it open, and take that to place inside of my amp (like this: https://www.amazon.com/AllAboutAdapters-Analog-Surround-Decoder-Version/dp/B07J2VZ8DL (not preferred but just started looking)).

    2.5) if a person wanted something more upscale, like Dolby Atmos, they could always buy something like this from Texas Instruments: https://www.ti.com/tool/EVMK2G ; https://www.ti.com/tool/AUDK2G#order-start-development (Audio daughter card to pair with the first card, together is $1200; they also mention power supplies and point to an LCD you can pair with that board)

    3) 3-5 amplifier boards. Since no single board I’ve found fits my needs at 5.0 or 5.1 for amplification, that means I would need at least 3 boards: 1) one powerful enough to run two front floor standing speakers at 350-370W (meaning wanting likely 500W@8Ohm so that it does not run too hot ever), 2) an amplifier with about 120W for the two bookshelf speakers to as much as 170W (so maybe 250W@8Ohm), and 3) either a mono 1.1 or a 2.1 amp with enough to support at least 500W to a sub and support 120W to a center channel. Now, if planning to expand to a 5.2 or a 7.1 or 7.2 system, you may want a couple more boards. For 5.2 or 7.1, you need 4 boards, at least. For two subs (either left/right or front/back), you would need a powerful amplifier that could run at least 500W continuous (like the first amp), or 1000W even, over two channels. You may even need two amps to accomplish this, depending on your plans. And if doing Dolby Atmos… Now, unless you find an audio processor able to do .2, you will just be doubling the signal through both channels for the two subs. Not the best/most elegant solution, but serviceable. If you could find or create a circuit to take the lower hz range from either the surround channels left and right or the front channels left and right (or put in a switch to physically choose between front and surround to pull that from, but that is WAY too complicated for my build), then you could accomplish the goal. But back on point, you need an amp that can run those subs. And for 7.2, you would need the first three amps, another amp like for the surrounds, plus the amp to drive the subs. (side note, if available, look for Amp RMS to figure out what it can do without too much stress.

    4) Then you would need the PSU to power ALL OF THOSE AMPS. Not for the light of heart.

    Now, I still need to learn more on how to order things, how to set the gain per amp to make it so they cannot send out more than the RMS, then setup either a master volume after a phase in between the 7.1 and the signal going off to the different amps. Basically, the FM tuner with bluetooth would go first and feed into the 7.1 decoder. From there, the 7.1 decoder would feed the signal out to the amps (with whatever needs introduced between them put into place). Then, that would feed out to the speakers. The 7.1 decoder has a 5.1 in, along with coax and digital. At least with the RCA plugs, those can be soldered off and moved to the back of the case easily if need be. Also, if you have a preamp/receiver, this is easier as you could skip the first items and get the amps and setup the inputs labeled on the back for what is coming in to the specific amp to hand that channel. Since the signal processing for the 7.1 or 5.1 decoding is handled by the pre-amp or the receiver, then this is just to send the signal to the appropriate channel of the appropriate amp.

    Still rolling this around in my mind and trying to figure out how I want to approach this. Any thoughts or advice is welcome.

  • 123toid

    March 23, 2021 at 4:52 am

    Sounds like a hard build, but awesome!  I think I would go for the HDMI stripper to analog.  I was considering this myself.  But chose not to. 

    Building a 5.1 Amp or 7.1 amp to power the Kartesian system

  • ajc9988

    March 24, 2021 at 8:13 pm

    @123toid – yeah, I’m going to pick up some books on amplifier design. I think getting a better grasp on the design process will help with how ambitious this project will be.

    I haven’t done calculus in nearly 18 years (so have to dust off that cap for some of the limit and integral stuff from some of the equations, both for this and the speakers). I also always sucked at reading schematics! So I have a book for helping with schematics, I have the loudspeaker cookbook on the way, then will need to buy the engineering textbooks for designing amplifiers, one dedicated specifically to class D amplifiers and CMOS integration.

    My other hobbies are calibrating displays and building and overclocking computers. From that I’ve seen some cheap places to pickup prototype PCBs. So I figure if I learn enough, figure out the layout I want, etc., I could pay to have the PCB prototype and then just have to solder down the surface mount components.

    That and it is cheaper to get started by picking up an old used receiver that does at least 100W+ per channel. That will buy time to develop the skills needed to do it right. Also, if I treat this like grad school, I should be able to read through the books quick enough to pick up what I need.

    Stay tuned because I will be filling this thread in as I learn more and get my design down.

  • lionhrt9

    March 25, 2021 at 1:27 pm

    Very interesting post! I was just thinking about this but as I kept reading getting an avr that’s got most of what I want or the ability to customize into what I want sounds way more realistic at my skill level. Lol. I do love the idea and think it would be an awesome project to follow along if you attempt it. 

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