~100+ watts mono board without on/off thump?

Hey folks, do you know what full-range (40hz-18k at least) board I should buy?
I'm looking for mono 100-120 watts Class D.
Cannot have any on/off thump like my 60W mono board has.
Or a stereo board that can be bridged to 100+ watts.

Or bonus points if you can find me a Bluetooth board with built in amp that can be bridged mono. :)

Will be using a 21 volt LiPo battery pack.

I'm okay buying from China but would prefer a supplier stateside.


2011-04-29 8:37 pm
Oh dangit. Thank you.
Do you know of an online calculator for me to figure this out?
I'm not too good with the math behind it.

Vsupply / 2.818 = Vrmsmax (maximum rms voltage output, single ended amp )

Vrmsmax x Vrmsmax / Rspeaker = POWERmax (single ended amp)

Multiply POWERmax by 4, if the amplifier has bridged outputs (since the output voltage is doubled)

Also there's the question of how long the battery can last powering the amplifier.
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Vsupply / 2.818 = Vrmsmax

Vrmsmax x Vrmsmax / Rspeaker = POWERmax

Multiply POWERmax by 4, if the amplifier has bridged outputs

Okay, I think most stereo boards out there are already bridged internally to provide the stereo output?
So am I correct in interpreting your calculations?

Vsupply = 21V LiPo battery pack
Rspeaker = 4 ohm speaker


21 / 2.818 = 7.45

7.45 x 7.45 / 4 = 13.88

13.88 x 4 = 55 watts

Is that correct?
If so, thank you.
It's very helpful!

I'm looking for a board but thanks. I can Google the TDA7498 chip to find one that doesn't have on/off thump.
Thank you so much!

The battery only needs to last a couple hours at medium-high volume.
It's five 18650 LiPo batteries.

Assuming those batteries are somewhat standard in capacity, they will be approx 2250mAh. ( 2.25 Ah )

They should therefore be capable of supplying 750 mA ( .75 Amps) for three hours.

My concern is that 3.6 volts * 5 = 18 volts.

18 volts * .75 A = 13.5 watts

If the average current drawn by your 100 watt capable amplifier is under 13.5 watts, the battery should last the duration of your event.
(assuming it is 3 hours or less)

However, if, you are actually drawing 20 watts of power that equates to 1100 mA being drawn from the battery pack. (18 volts * 1.1 Amp = 20 watts)

At 20 watts, the battery might last 2 hours. (Tough to tell exactly, it will depend on lots of factors, but to me, you are cutting it too close for comfort.)

If you are really drawing 100 watts from the battery pack you propose, it will draw 5.5 Amps from the battery and run for 20-30 minutes at best.

I know you are looking for a 100 watt amplifier. If playing most music, and if Class-D, the average current draw will most likely be 10 watts or less, but who knows...

You might want to perform some tests with your current amplifier and the proposed battery pack, and your specific program material to see how long it will play. It might give you some comfort the alternative amplifier board you eventually find (with no "on/off thump) might work for the duration of your event with the battery capacity you've supplied.

Joe L.