Hey!
I'm planning to build a wireless Bluetooth-speaker using a TDA7492P amplifier. I want to power it with a 10Ah USB -Powerbank using a step-up converter to 12V.
Since I don't know how much current the amplifier needs, i am not sure if my powerbank can provide enough current (3.1 A max at 5V).
I'm using 2 8 ohm speakers...
Has anyone got some experience with the TDA7492P and can tell me if this will work?
Sorry for bad english,
Tobi 🙂
I'm planning to build a wireless Bluetooth-speaker using a TDA7492P amplifier. I want to power it with a 10Ah USB -Powerbank using a step-up converter to 12V.
Since I don't know how much current the amplifier needs, i am not sure if my powerbank can provide enough current (3.1 A max at 5V).
I'm using 2 8 ohm speakers...
Has anyone got some experience with the TDA7492P and can tell me if this will work?
Sorry for bad english,
Tobi 🙂
Hi,
P (Watts.) = V (Volts.) x I (Amps.)
In your data:
5 Volt. x 3.1 Amps = 15.5W. That's all the juice you have, for both channels at max.
Now begin to subtract inneficiencies... Amplifier is not 100% efficient, as the step up converter, ...
I think you should seek for more juice or other less hungry amplifier 😉
I'm not saying it won't work, but surely not at its best performance.
P (Watts.) = V (Volts.) x I (Amps.)
In your data:
5 Volt. x 3.1 Amps = 15.5W. That's all the juice you have, for both channels at max.
Now begin to subtract inneficiencies... Amplifier is not 100% efficient, as the step up converter, ...
I think you should seek for more juice or other less hungry amplifier 😉
I'm not saying it won't work, but surely not at its best performance.
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12V 8Ohms?
Hmm, lets see.
Is BTL? Yes!
12V*0.7=8,4Vrms
8,4Vrms*8,4Vrms/8Ohms=8.8Wrms per Channel.. ideally but consider Rdson of the amps output stage = 2*0.2Ohms so:
8,4Vrms*8,4Vrms/(8Ohms+2*0.2Ohms)=8.4Wrms more or less.
So having 8.4Wrms per channel or 16.8Wrms in total, does ~34Wpk worst case.
34Wpk != 15Wpk of your power bank.
Quiescent current of the amp is ~25mA + some mA for the rest of the board, let's say 40mA in total. Considering the musics crest fractor of of 5:1, the average output power seen by the power input is 1/5 of 34Wpk = 6.8W at high volume. Lets say, you wont run at full volume, but on half volume, this results in 1/10th in power -> 680mWpk or 57mA. Together with your 40mA quiescent current you're at 100mA average current from the step-up.
Now for the rest, let's assume:
efficiency DCDC 3.7V (Battery) -> 5V (USB out): 75%
efficiency 5V (USB out) -> 12V (Power put): 85%
Combined : (75% * 85%) -> 0.75 * 0.85 = 64%
Current drawn from power bank output: 100mA/0.85 = 117mA avg.
Current drawn from battery: 100mA/0.64 = 156mA
Runtime approx: 10Ah/0.156A= 64h
(Assuming a constant efficiency for the power banks internal DCDC stepup)
Feel free to insert your own numbers.
Hmm, lets see.
Is BTL? Yes!
12V*0.7=8,4Vrms
8,4Vrms*8,4Vrms/8Ohms=8.8Wrms per Channel.. ideally but consider Rdson of the amps output stage = 2*0.2Ohms so:
8,4Vrms*8,4Vrms/(8Ohms+2*0.2Ohms)=8.4Wrms more or less.
So having 8.4Wrms per channel or 16.8Wrms in total, does ~34Wpk worst case.
34Wpk != 15Wpk of your power bank.
Quiescent current of the amp is ~25mA + some mA for the rest of the board, let's say 40mA in total. Considering the musics crest fractor of of 5:1, the average output power seen by the power input is 1/5 of 34Wpk = 6.8W at high volume. Lets say, you wont run at full volume, but on half volume, this results in 1/10th in power -> 680mWpk or 57mA. Together with your 40mA quiescent current you're at 100mA average current from the step-up.
Now for the rest, let's assume:
efficiency DCDC 3.7V (Battery) -> 5V (USB out): 75%
efficiency 5V (USB out) -> 12V (Power put): 85%
Combined : (75% * 85%) -> 0.75 * 0.85 = 64%
Current drawn from power bank output: 100mA/0.85 = 117mA avg.
Current drawn from battery: 100mA/0.64 = 156mA
Runtime approx: 10Ah/0.156A= 64h
(Assuming a constant efficiency for the power banks internal DCDC stepup)
Feel free to insert your own numbers.
Thanks for the detailed answer 🙂
If I understood correct, I could power with my powerbank 2 speaker at a total power of 6.8 w for 64h?
Actually, each speaker has 20W :/
So i am going to use 4 li-ion cells instead of the powerbank...
Again, thanks for the answers!
If i am allowed, I'd like to ask a off-topic question...
Do you think a 2.5l housing will be enough for 2 3.3" Broadband speakers? (With PR, if that matters).. Thanks in advance 🙂
If I understood correct, I could power with my powerbank 2 speaker at a total power of 6.8 w for 64h?
Actually, each speaker has 20W :/
So i am going to use 4 li-ion cells instead of the powerbank...
Again, thanks for the answers!
If i am allowed, I'd like to ask a off-topic question...
Do you think a 2.5l housing will be enough for 2 3.3" Broadband speakers? (With PR, if that matters).. Thanks in advance 🙂
Without TSP for the speaker chassis parameters noone can tell what it will be/sound like. You may consider using an additional passive radiator to get more ompf.
Regarding Watts n Ompf:
Two times volume/loudness needs ten times the power.
I.e. 20W is twice as loud as 2W, or with your numbers 20W would be barely +6dB louder than 6W, it's not that much at all. I'd consider using 4Ohm speakers, as double current would give you +3dB more loudness. If your supply voltage is low, your speakers resistance needs to be low as well.
If you want to use 4 Li+ in series, get yourself a protection pcb with integrated balancer and a small DCDC buck/boost converter with CC/CV. Then you can charge your batteries from nearly every supply.
Like:
4*4.2V charge cutoff voltage = 16.8V
Charge current i.e. 0.5C = 1.3A (for 2600mAh cells)
So your DCDC converter gets set at 16.8V with 1.3A current limit. Then you charge from supplies low as 5V to up to 30V with something like this:
LM2577 Automatic Boost Buck Converter 4-35V to 1.25-25V CC CV Voltage Regulator | eBay
Not the most efficient ones, but the cheapest known to work okay. They still might need a diode at output for connecting them to your pack to prevent draining the cells without having a charger connected.
Protection + Balancer:
4S 30A 14.8V Li-ion Lithium 18650 Battery BMS Packs PCB Protection Board Balance | eBay
Dirt-cheap but working good, even if 30A is a bit high here.
Regarding Watts n Ompf:
Two times volume/loudness needs ten times the power.
I.e. 20W is twice as loud as 2W, or with your numbers 20W would be barely +6dB louder than 6W, it's not that much at all. I'd consider using 4Ohm speakers, as double current would give you +3dB more loudness. If your supply voltage is low, your speakers resistance needs to be low as well.
If you want to use 4 Li+ in series, get yourself a protection pcb with integrated balancer and a small DCDC buck/boost converter with CC/CV. Then you can charge your batteries from nearly every supply.
Like:
4*4.2V charge cutoff voltage = 16.8V
Charge current i.e. 0.5C = 1.3A (for 2600mAh cells)
So your DCDC converter gets set at 16.8V with 1.3A current limit. Then you charge from supplies low as 5V to up to 30V with something like this:
LM2577 Automatic Boost Buck Converter 4-35V to 1.25-25V CC CV Voltage Regulator | eBay
Not the most efficient ones, but the cheapest known to work okay. They still might need a diode at output for connecting them to your pack to prevent draining the cells without having a charger connected.
Protection + Balancer:
4S 30A 14.8V Li-ion Lithium 18650 Battery BMS Packs PCB Protection Board Balance | eBay
Dirt-cheap but working good, even if 30A is a bit high here.
I recommend testing the TDA7492 board on the bench with 1kHZ sinewave, proper load and oscilloscope before going ahead with the project. I bought 3 different class D pwr amp boards from Parts Express here in the U.S., and 2 of them had major oscillation problems when pushed up near clipping. All 3 were made in China, and came with no documentation at all.
Hey, thanks for the answers!
Actually i wanted to use visaton f8sc speakers, but now i will look for some 4 Ω. Is there any major difference by lower resistance?
For example frequency spectrum? Or does it only depend on the size of the speaker?
Is this true:
If i charge the batterys with 5V 2A by a boost up converter, it will " arrive" as 16.8 and approx. 0.6 A?
Then charging via 12V jack would be better than usb, right?
@Bob Richards
Unfortunately I dont own a oscilloscope... Also the amp takes 30 days to be delifered from china :/
Btw, this is just going to be a fun-diy-project, and as i am new to hifi-diy i dont expect a very good sound of my speakers 😉
Tobi
Actually i wanted to use visaton f8sc speakers, but now i will look for some 4 Ω. Is there any major difference by lower resistance?
For example frequency spectrum? Or does it only depend on the size of the speaker?
Is this true:
If i charge the batterys with 5V 2A by a boost up converter, it will " arrive" as 16.8 and approx. 0.6 A?
Then charging via 12V jack would be better than usb, right?
@Bob Richards
Unfortunately I dont own a oscilloscope... Also the amp takes 30 days to be delifered from china :/
Btw, this is just going to be a fun-diy-project, and as i am new to hifi-diy i dont expect a very good sound of my speakers 😉
Tobi
Only difference in voice coil impedance. The FS8C is available in 4ohms as well but not available new from Visaton. As these chassis are magnetical shielded they weight more than unshielded ones and eat up more inner box volume.Actually i wanted to use visaton f8sc speakers, but now i will look for some 4 Ω. Is there any major difference by lower resistance?
For example frequency spectrum? Or does it only depend on the size of the speaker?
You may want to look at "Tangband": http://www.tb-speaker.com/
They're availbe from i.e. OmnesAudio:
https://www.oaudio.de/Lautsprecher-Selbstbau/Lautsprecher-Chassis/Tang-Band/
or SpectrumAudio:
http://www.spectrumaudio.de/breit/tabelle.htm
Kind off, if power transfer is 100% efficient. (Which is not, more like 0.8-0.9)Is this true:
If i charge the batterys with 5V 2A by a boost up converter, it will " arrive" as 16.8 and approx. 0.6 A?
Then charging via 12V jack would be better than usb, right?
When using an combined buck/boost you can charge with "everything" like 5V USB, 12V jack, 19V laptop supply etc.
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Hey!
The Tangband speaker would fit into my project, but unfortunateley they are on about 25+ €... and on oaudio.com shipping costs to austria 50€ ?!
This is why i'd rather buy a visaton - i can get them in austrian stores and they are cheaper, too... (I know, also not that good as tangband 😉 )
So... maybe a Visaton FRS 8 /4ohm?
FRS 8 - 4 Ohm
The Tangband speaker would fit into my project, but unfortunateley they are on about 25+ €... and on oaudio.com shipping costs to austria 50€ ?!
This is why i'd rather buy a visaton - i can get them in austrian stores and they are cheaper, too... (I know, also not that good as tangband 😉 )
So... maybe a Visaton FRS 8 /4ohm?
FRS 8 - 4 Ohm
Or this one:
FR 8 - 4 Ohm
Gives about 6dB more at 200Hz, but isn't that robust due to foam ring (not rubber).
FR 8 - 4 Ohm
Gives about 6dB more at 200Hz, but isn't that robust due to foam ring (not rubber).
Hey, I decided to buy the FRS8 (Deeper frequency response).
Now I have another question... :
If I use an old laptop charger (19V, Max 4.7A) and transform it to 16.8V, will the current be too high for the batterys? Or do they only "take" what they can handle?
I dont think my cheap BMS board has an overcurrent protection :/
Tobi
Now I have another question... :
If I use an old laptop charger (19V, Max 4.7A) and transform it to 16.8V, will the current be too high for the batterys? Or do they only "take" what they can handle?
I dont think my cheap BMS board has an overcurrent protection :/
Tobi
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