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

[tyger23]

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

As an FYI - I've been talking about the TDA7492 board, but the design is agnostic to the actual amplifier board. There's several out there that would plug and play just as well:

TPA3116:
http://www.yuan-jing.com/ClassD-T/tp...rice&order=ASC

http://www.ebay.com/itm/TPA3116-50W-...item35db922e9d

http://www.ebay.com/itm/2-x-50-Watt-...item20e9b81d77

http://www.ebay.com/itm/1PC-TPA3116-...item19eb84bd19

TP2050/TK2050:
http://www.yuan-jing.com/ClassD-T/tp...rice&order=ASC

http://www.ebay.com/itm/TP2050-Class...item19f0e6ee2f

STA508:
http://www.ebay.com/itm/digital-ampl...item5b04695014


And probably others...

[evilskillit]

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

Basically, I would just be selling the board only, and at cost to me. I'm not looking to make money - only friends ;). The PCB would be about $5-$15 depending on the total quantity the community commits to. You could put it in a case or in anything else you want. It will be fairly big, though, as the case it will be designed for is slightly larger than 4"x6".

Ahh I'm pretty tired, I didn't quite understand the first time. For $5-$15 heck yeah. I'll put it with the pile of boards I ordered from Elliot Sound Productions and never built. But hey I'm not that old, I may build some of them before I die. ;)

[tyger23]

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

Sounds pretty awesome $130 isn't impulse purchase money for me so I can't commit to buying one right now. Seems like a really solid idea tho. If you end up following through on this would people have the flexibility of getting it without the case? The case is very pretty but it sounds like there's a lot of fiddly extra stuff that needs to be done that might not make it a goood value for everyone at $20.

Basically, I would just be selling the board only, and at cost to me. I'm not looking to make money - only friends ;). The PCB would be about $5-$15 depending on the total quantity the community commits to. You could put it in a case or in anything else you want. It will be fairly big, though, as the case it will be designed for is slightly larger than 4"x6".

[tyger23]

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

Total price puts this in the maybe category. If the x-o is remote for the mains, I’d only need an x-o for the sub. Maybe this could reduce the cost.

The way the board is designed, you could populate any or none of the crossover components. It's flexible.

Not that I know what I’m saying, but can you use a master volume and then just a trim pot for the sub? I guess if you had really efficient mains you could consider a trim pot for the mains. I want the sub to track with the main volume.

The board is designed to do exactly what you want. There's a volume control that will affect the sub and the mains, and there is a separate trim for the sub.

[tyger23]

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

The outputs are at 1/2 of VCC and the outputs should be cap coupled unless you float the supply with respect to the actual ground and connect the virtual ground of the crossover directly to actual signal ground of the system.

You are correct - but the amp board has series caps built in. I didn't want to have caps in series, so I left them off of the base board.

I don't know about using an op amp as the regulator and hanging a 220 uF cap on the output without a pass transistor.

I'm not sure about your main concern here - can you explain more? The circuit I designed in has been used in several applications in the past, but I'm up for learning new tricks.

VCC had better be specified as well. Most op amps would probable like to see 10 volts or more for VCC.

Yes - 12V minimum, up to 26V max (the limit of the amp board)

Get of a pot and put it at the output of U4a.

I don't understand this, can you help explain more?

If you use JFets input op amps you can make the caps in the low pass filter smaller values and the resistors large values.

Agreed, but I was trying to accomodate Jfets and bipolars. I personally don't like the sound Jfets compared to bipolars. Call me different, if you wish.

I would work of the virtual ground circuit a bit more.

I'm open to any and all suggestions.

[tyger23]

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

Please disregard if this was covered before, but is there an ability to have an auto-on function? This isn't critical since I could rig something up using the speaker bar power output from my monitor, just thought it would be a nice to have.

I hadn't thought about it, but there should be room to build in an option for that (you could choose between a switch or auto-on). Let me think about that....

FYI - the class D should take very little current when not playing audio, so it could probably always stay on without much concern.

[tyger23]

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

Tyger, what would be the approximate cost of the PCB?
What would be the output VRMS?
If I were to just run the PCB, what are the PSU requirements?

With that asked, I would be interested in getting 2-3 PCBs

Cost of the PCB depends on how many ordered. However, I think about $10-15 each. It could go as low as $5 if we get upwards of 50 total.

Output power is dependent on several things - the power supply used and the thermal capabilities of the design. Remember that the amplifier design is already BTL, so summing to mono only increases the amount of current the amplifier can provide to the speaker, and not the amount of power out of the amplifier. What this means is that the amplifier can drive a lower resistance load, but it can't drive a mono speaker any harder than a stereo load if the power supply is limited. Thermal is another concern, but I can't comment on that until I get the design built. I don't expect it to be an issue....

With the power supply I was calling out (19V) and an 8-ohm load, the system would provide about 20W per channel before distortion starts to become audible. Into a 4-ohm load, it would provide about 30W per channel. The mono output would be the same wattage, but the mono allows you to drive down to a 2-ohm load. At that load, you would probably get about 70W. Note that's out of the mono channel only. The stereo channel can only support 4 ohm loads minimum.

Since the mono channel is parallel-BTL and can support the extra current, you should be able to run the whole thing off of 24V supply. With that voltage, 8-ohm loads would produce about 30W and 4-ohm loads would be about 50W-60W. A 2-ohm load at 24V might cause some thermal issues, but it should produce close to 100W. Note that you should NOT exceed 22V if running 4-ohm loads on the stereo amplifier.

So, PSU requirements are dependent on your loads:

• If 8-ohms on the stereo amp and 4-ohms on the mono amp, then 24V should work well. A 2-ohm sub would likely work at 24V, but that's getting close to the limits.
• If 4-ohm loads on the stereo amp, then I'd probably stick to 19V maximum.
• Power requirements for the PSU also vary for the loads and voltage. Let me know what you are planning, and I can help you figure it out. Generally, though - for the two scenarios above, I would want 120W or 150W minimum, respectively.

[S7910]

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

Sounds pretty awesome $130 isn't impulse purchase money for me so I can't commit to buying one right now. Seems like a really solid idea tho. If you end up following through on this would people have the flexibility of getting it without the case? The case is very pretty but it sounds like there's a lot of fiddly extra stuff that needs to be done that might not make it a goood value for everyone at $20.

I may have misread the OP but I think the $130 is total for all the parts + board, not the board. If so I'd be interested in one, maybe two, I can always pick up the case and fiddly stuff later.

[evilskillit]

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

Sounds pretty awesome $130 isn't impulse purchase money for me so I can't commit to buying one right now. Seems like a really solid idea tho. If you end up following through on this would people have the flexibility of getting it without the case? The case is very pretty but it sounds like there's a lot of fiddly extra stuff that needs to be done that might not make it a goood value for everyone at $20.

[fdieck]

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

The sub will track with volume with this circuit

[jhollander]

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

Total price puts this in the maybe category. If the x-o is remote for the mains, I’d only need an x-o for the sub. Maybe this could reduce the cost.

Not that I know what I’m saying, but can you use a master volume and then just a trim pot for the sub? I guess if you had really efficient mains you could consider a trim pot for the mains. I want the sub to track with the main volume.

[fdieck]

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

The outputs are at 1/2 of VCC and the outputs should be cap coupled unless you float the supply with respect to the actual ground and connect the virtual ground of the crossover directly to actual signal ground of the system. I don't know about using an op amp as the regulator and hanging a 220 uF cap on the output without a pass transistor. VCC had better be specified as well. Most op amps would probable like to see 10 volts or more for VCC. Get of a pot and put it at the output of U4a. If you use JFets input op amps you can make the caps in the low pass filter smaller values and the resistors large values. A 10k pot is going to have a maximin output impedance of 5k at the mid point setting. Assuming you do use the negative supply as the ground reference, you are putting half of the noise on VCC into circuit with your filtering cap bypassing scheme at audio frequency range. While may reduce turn on thumps, it really degrades the signal to noise of the circuit. I would work of the virtual ground circuit a bit more.

[NickS]

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

Am I incorrect or should your input & output grounds be connected to VGND to keep the output from being at 1/2 VCC. Or should the outputs be capacitor coupled?

[superspeeder]

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

Please disregard if this was covered before, but is there an ability to have an auto-on function? This isn't critical since I could rig something up using the speaker bar power output from my monitor, just thought it would be a nice to have.

[Silver1omo]

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

Tyger, what would be the approximate cost of the PCB?
What would be the output VRMS?
If I were to just run the PCB, what are the PSU requirements?

With that asked, I would be interested in getting 2-3 PCBs