Low Power Amp output voltages, for capacitor sizing

travm

Member
2019-12-05 12:17 am
I'm building a low power powered speaker, amp is a TDA7496. The data sheet has dc blocking capacitors at 1000uf, but doesn't give any indication of the expected voltage. My gut says go with 50v, but I cant find much on this, or maybe dont know what i'm looking for.
Powering the amp with 12v, and connecting to 4ohm 3w speakers.

I might even just be searching for the wrong terms, and guidance appreciated.
 
I'm building a low power powered speaker, amp is a TDA7496. The data sheet has dc blocking capacitors at 1000uf, but doesn't give any indication of the expected voltage. My gut says go with 50v, but I cant find much on this, or maybe dont know what i'm looking for.
Powering the amp with 12v, and connecting to 4ohm 3w speakers.

I might even just be searching for the wrong terms, and guidance appreciated.


A DC blocking capacitor used like this typically has half the supply voltage across it. The voltage across the DC blocking capacitor can never be more than the supply voltage. The maximum supply voltage is 32V. Use 35V rating for your 1000uF capacitors.

NB: Douglas is right, as long as you use a 12V supply 16V capacitor rating is fine.
 
Last edited:
perfect.
The only confusing bit of this is, how do higher power amps get more power into 4ohm speakers at the same input voltage? I was thinking the only way this made sense was the amplifier somehow pumped up the voltage.

No, a supply voltage of 24-32V, which the TDA7496 can also handle, is sufficient for more output power. The TDA7496 is intentionally limited in output power by a peak current limiter of typically 1.3A and worst-case 1.0A.
 

travm

Member
2019-12-05 12:17 am
No, a supply voltage of 24-32V, which the TDA7496 can also handle, is sufficient for more output power. The TDA7496 is intentionally limited in output power by a peak current limiter of typically 1.3A and worst-case 1.0A.

I meant other amplifiers. some that can do 5 or more W into 4ohm @ 12v supply. I dont understand the relationship between supply voltage and output power. It appears to defy ohms law.
Or class D amps that can do 10-20W at 5v supply.
 

travm

Member
2019-12-05 12:17 am
No, a supply voltage of 24-32V, which the TDA7496 can also handle, is sufficient for more output power. The TDA7496 is intentionally limited in output power by a peak current limiter of typically 1.3A and worst-case 1.0A.

I meant other amps. Some can output more watts into 4ohms @ 12v, or even something like 3w into 4ohms at 5v. It appears to defy ohms law.
 
Ohms law is always valid. Ohms law is not always taken into account.

More than 5W in 4 ohm from a 12V supply is possible with BTL coupling.
10-20W from a 5V supply is largely empty promises from sellers who do not know Ohms law.
In principle, you can boost 5V to any voltage you like but I am not aware of a single chip that both includes a power amplifier and a voltage booster.
 
Back to capacitors,
I'm assuming I should use specific "audio grade" capacitors for the DC blocking? They are considerably more expensive than std electolytics. X7R's for the ceramics?
I have my digikey cart full, its a little more than I was hoping for.

Don't get ridiculous with this ... a 12v powered amp isn't going to be reproducing sound at concert volumes and I certainly would not spend a ton of money on capacitors for a general purpose chip amp. The supply bypass and output caps should be low ESR types which should cost you a couple of bucks each. The rest can be ordinary film or ceramic types which should be just a few cents each.

"Audio Grade" generally translates to ... "Okay, it's an audiophile, the price just doubled". Most of the time there's no advantage to it at all. Just use reasonable quality new parts and you should be fine.
 
perfect.
The only confusing bit of this is, how do higher power amps get more power into 4ohm speakers at the same input voltage? I was thinking the only way this made sense was the amplifier somehow pumped up the voltage.


Hi travm


ohm law is always valid.
more supply voltage - here at the pic - +Vcc and -Vcc give the amp the "chance" to go up/ down to the supply voltage. --> more power into the load - e.g. 4R

your amp is a single supply amp so the - Vcc is GND - 0V.



As FF wrote - the Voltage is the first part of the "power part" --- the chip must handle the current - this is the limiting factor now.


chris
 

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