Help with a TA722AP

[Bow]

Hello All,

I am working on a radio that uses a TA7222AP Audio Amplifier Chip. The Data Sheet is here:
http://www.datasheetcatalog.org/data.../502310_DS.pdf

The circuit of the Audio section of the radio is Here:

http://riley-music.com/BowsStuff/Cob...AmpSection.gif

My problem is, I am having trouble getting the amplifier to pass lower than 200 Hz.. and I would like to get it down to 80 Hz and up to 6kHz.

The radio was spec'ed for 300Hz - 4.5kHz, but i am looking for a more natural, less pinched sound.

Can you all help me figure out where my bottle neck is?

I realize this isn't Hi-Fi audio, but this is the only forum I know of with this many "Chip Amp" Gurus on it.

Thank you for your time.

[pacificblue]

The first bottleneck is the feedback capacitor. The datasheet specs it to be 100µF, while your radio only has 10 µF there. That seems consistent with your description, because 1/(2*PI*82 Ohm*10µF) = 191,8 Hz.

The second bottleneck will be the 470 µF output capacitor. Depending on the speaker load that may have to be increased as well to achieve a lower roll-off. The datasheet specs a 1000 µF capacitor for a 4 Ohm load. 470 µF would therefore be okay for an 8 Ohm speaker.

[Bow]

Thanks For the reply and the information.

Originally posted by pacificblue
The first bottleneck is the feedback capacitor. The datasheet specs it to be 100µF, while your radio only has 10 µF there. That seems consistent with your description, because 1/(2*PI*82 Ohm*10µF) = 191,8 Hz.

After I posted last night, I saw the graph on page 4 of the datasheet, the first one on the right side. I was going to try the Feedback cap today.

From the graph, it looks like the larger the Feedback Cap, The more pronounced the mid-range is?

Your formula is interesting, Where is that from or what is the formula called? I would find that very useful for some of my projects.

The second bottleneck will be the 470 µF output capacitor. Depending on the speaker load that may have to be increased as well to achieve a lower roll-off. The datasheet specs a 1000 µF capacitor for a 4 Ohm load. 470 µF would therefore be okay for an 8 Ohm speaker.

I didn't mention in my first post that I tried that first, I dropped a 1000uf in the output, it didn't change the response a large amount, but it did help.

Thanks you for your time, I'm going to drop a 100uf in the Feedback and see how that goes.

[pacificblue]

Originally posted by Bow
Your formula is interesting, Where is that from or what is the formula called?

I first learned to calculate the corner frequency of an R-C filter during the physics classes in college. You will find the formula in virtually any textbook that deals with electronics at the beginning of the section that deals with capacitors in AC circuits. 2*PI*f is usually represented by a small omega that looks like a small rounded w.

[Bow]

Great, Thanks for the help

As a side note, I found out that the Amp is doing its thing.. it is the choke/transformer after it that is saturating below 200Hz...

Time for a re-engineer of the system