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The DIY 2.1 amplifier. Should I build it? Would you buy it?

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  • tyger23
    replied
    Re: The DIY 2.1 amplifier. Should I build it? Would you buy it?

    I didn't mention it above, but I could really use some support reviewing the schematics from you op-amp guys. The sallen-key filters on a single supply rail provide a challenge, and I may have missed something.

    Leave a comment:


  • The DIY 2.1 amplifier. Should I build it? Would you buy it?

    OK guys,

    This thread is evolving out of my thread listed here. I wanted to separate this thread since the project took a decided turn away from a flexible base board to a design that focuses simply on the 2.1 amplifier project.

    I took the time today to generate a first cut of schematics (see attached) and a proposed BOM for the 2.1 amplifier. The idea behind this is to be able to buy TWO of those TDA7492 boards, mount them on top of a "base board", fit them into the larger SURE case sold here at PE, and voila - a 2.1 amplifier in a reasonable case. The base board will provide the crossovers and volume controls, but nothing like BSC or EQ. I'm assuming that the EQ and BSC are handled in the speaker design. This choice reduces the costs and complexity of the board significantly.

    When assembling the board, you'll have your choice of op-amps, crossover frequencies, and so on. The board is designed to provide LR4 crossover slopes, and the schematics show values for 80Hz. The frequency is adjustable by changing the resistor or capacitor values around the sallen-key filters.

    There are 5 op-amps required, and the op amps can be anything that supports about 20mA or greater of short-circuit current. The current requirement comes from the fact that one op-amp is used to supply the midrail bias voltage. I'd recommend an NE5532 or better. The TL052/72 parts won't have enough current and the noise performance won't be that great. An LM4562 would be awesome, but adds about $10 in cost to the board and probably won't buy you that much. The TDA7492 board will probably be a more limiting factor than the op-amp. R1 is the the master volume control that will be on the front of the amp. R12 is an adjustable gain for the subwoofer. This will protrude from the back of the amp and allow for easy adjustment of the subwoofer volume.

    I'm choosing a 2.5mm by 5.5mm DC jack to accommodate a wide range of power supplies. The jack will support 10A, which is far more than the normal DC jack, but it's required for a design like this.

    A few challenges exist with the design:
    1. The back panel of the amplifier will need to be drilled out for 2 extra binding posts and the extra subwoofer volume control.
    2. The volume knob is a funky size and hard to source. There's some options on eBay and one at Mouser, but not much.
    3. The hole for the binding posts is an odd size. One might have to drill out that hole larger depending on the binding posts chosen.
    3. Power supplies for this aren't cheap. Also, there's different voltage recommendations for 8-ohm or 4-ohm. Overall, I'd recommend using a 150W laptop supply at 19V. An Asus compatible power supply will work and costs around $22 shipped from Asia. This provides a good in-between for 8 and 4-ohm loads. Technically, 150W isn't going to actually allow the chip to get to full power, but I'm willing to bet that it has a more than enough headroom and volume for a desktop design or even a bedroom design.

    I did manage to make all the components through-hole, so hopefully anyone can solder it.

    Now for the nitty-gritty. Buying all the required components from Digi-key, the amp boards, case, and binding posts from PE, the powersupply from eBay, and the PCB from me the total cost would come out to just about $130. That's a complete project! You'd be responsible for assembling, but it should be very easy. There are several ways to save money such as buying several parts from eBay (amp boards are $7 cheaper each, pots are $2 cheaper, op-amps can drop $3 or more), but there are inherent risks with this option.

    With this in mind, I need to know just how many PCB's you'd be interested in buying. Basically, if we get anywhere north of about 20, I'll try and complete the project.

    Amp Base Board.pdf

    Thanks!
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