TDAxxxx wattage?!

[Renegadrian]

I built some TDAs amps, 2822, 2005, ecc...
I see in the datasheet that they behave different and have different output just changing something, like voltage (and type, say single or double), speaker impedance, ecc...

Is there a way to know how many watts a particular combination will give out!? THX

[boppy100]

Hope the following helps.  I have been "lurking" for a while and while I have not built any pedals, I have learned a tremendous amount about low voltage circuits from all here.  I do not play guitar, got here while trying to learn how during a down period and trying to build low wattage practice amps.
Any how, I use the TDA2822m in cigar box amps, ipod/phone speaker docks, bluetooth speakers etc.  It is a hobby and orders have been word of mouth and gifts.
I usually use these at 5volts (usb power) or 6 volt and they work great

There are two good circuits here on the forum.  One is yours, Adriano and the other is in the Punch amp thread on page 5, by Mr. B Tremblay.  I have used similar combined with NPN boosters in the amp circuit as well as combined with the Valvecaster

TDA2822M - usually use a 5 or 10K pot

    Load          dc volt          output watts
                                       bridged     stereo/channel[/b]

      4R                5               1            0.32
                          6              ---           0.65
       8R               5               0.7            ---
                          6               1.35        0.38
                          9               ----           1
       16R              6               0.8          0.3
                          9                2             ---
        32R           4.5              ---            0.06=60mw
                           6              0.4           0.12
                           9               1             0.3

Tayda also sells a TDA2822L made by UTC which is rated slightly differently than the 2822M, but I have had no problems in the same circuits.

[teemuk]

Is there a way to know how many watts a particular combination will give out!? THX

Yes.

Download the datasheet of the IC in question. It should have a graph that plots output power vs. power supply voltage. The output power is often plotted at different load impedances.

[Renegadrian]

Yeah I know, sometimes it's not easy to decipher those DSs and several circuits using the same tda declare different wattages...Also some state BEFORE CLIPPING, so not on full throttle right!? Before distortion comes...

[FiveseveN]

BEFORE CLIPPING, so not on full throttle right!? Before distortion comes...

It's not really binary: you get some power @ 1% THD, more at 10% and so on. Depends on what you're willing to tolerate.

[tca]

> Also some state BEFORE CLIPPING...

Most of those chips will clip easily, roughly a Si diode drop voltage (sometimes less than that) at input and have IMO too much gain, this makes the task of designing good input stages hard.

[PRR]

> different output just changing something, like voltage (and type, say single or double), speaker impedance, ecc...

Ohms Law. (And power formula.)

Say you have a 10 Volt supply. Apply it to a 10 Ohm resistor. 1 Ampere flows. 10V*1A is 10 Watts power.

Change to 5 Ohms. Now 2 Amps flows, 20 Watts power.

Go back to 10 Ohms but apply 20 Volts. Now you get 2 Amps, at 20 Volts, is 40 Watts.

Short formula: Volts Squared divided by Resistance.

There is a BIG correction for Audio power. I'll get there later.

The *chip* does not make power. It modulates between your supply and your load. If the chip isn't crap, it will deliver "most" of the supply voltage to the load.

So you pick a load, figure the Voltage needed to make your Power goal, then round-up and find a chip that won't die in those conditions.

I said supply voltage and load resistance. But in Audio we work with both-ways signal and a rounded "Sine" wave as our power reference. So a 10V supply will only make 3.5V of "Sine" output. Obviously this in 3.5 Ohms would be 3.5 Watts; in 10 Ohms, only 1.2 Watts.

I said "most". Nothing is perfect. Amplifiers have losses. You can bet you won't get 90% of what you put in. Sometimes 80% is doing good.

There are three main ways to rig an Output Stage. You need two (at least) big transistors, strung across your available voltage supply. The center-point idles in the center, then pulls-up then pulls-down to cause the back and forth motion in your speaker.



Simplest is a single supply. Say 50V DC. We make the audio output idle at 25V DC, go both ways from there. We get (taking 10% loss) 22.5V peak swing or 45V p-p swing, so 16V Sine RMS. But this sits on a 25V DC level which will burn our speaker. As in many audio amps, we can cap-couple to lose the DC and get just the audio. However a good cap for music in 8 Ohms is 1,000 uFd, at over 25V, a BIG cap. Still the supply is simple and the cap protects against some common failures.

Next is the Split supply. We have +25V and -25V (still 50V total). Now the speaker can go to zero V, no coupling cap. But the power supply has twice as many parts (including another big cap). Turns out that for Stereo, split-supply is 2-bits cheaper (2 big caps instead of 3). For mono, it's a wash; but stereo systems dominate so even for a mono system we often use the split-supply.

And then there is Bridge. *2* power output stages on a single supply. This comes into play when your supply choice is "forced". Such as in a car, where +12V is super-easy and anything else is extra-hard. Turns out that by bridging into a 4 Ohm load you can get about 20 Watts from a single 12V supply, and 20 Watts is ample in a factory radio (especially if you do left-right front-back 4 speakers, 80 Watts). The added power stages would be a hassle to build, but demand is so high that multiple makers print the whole two four or eight stages on single chips. A minor downside is that both speaker leads carry a strong DC voltage. Does not hurt the speaker but can make trouble when you stuff metal boxes against trunk speakers. Or use the metal speaker jack we like for guitar speakers.

[Brymus]

Paul ,that explanation really helped me visualize whats going on.
Best simple explanation I have seen,thank you.