TDA7439 tone control IC any good?

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#4
I've made an amplifier based on this chip (see this post). I found the tone control (especially mid range) quite aggressive, but it could be due to the values I've choosen for external components (or maybe 2dB steps are too large). Leaving the controls flat, the sound is very good and the inputs switch and volume control work very well.

One thing that I don't understand from the datasheet is the internal structure of the mid and bass tone controls; datasheet shows in and out pins where to connect external components, but I can't figure out how the active part works. I found ST datasheets are always too poor of information.Can someone explain me? Thanks.
 
#5
pierluigiugolotti said:
I've made an amplifier based on this chip (see this post). I found the tone control (especially mid range) quite aggressive, but it could be due to the values I've choosen for external components (or maybe 2dB steps are too large). Leaving the controls flat, the sound is very good and the inputs switch and volume control work very well.

One thing that I don't understand from the datasheet is the internal structure of the mid and bass tone controls; datasheet shows in and out pins where to connect external components, but I can't figure out how the active part works. I found ST datasheets are always too poor of information.Can someone explain me? Thanks.
Click to expand...


I don't think you need to know how the active part works, you just need to use the equations on p. 9 to get the behavior that you want. Just choose the gain (Av) and Q that you want and then solve each equation on p. 9 starting at the top. Ri is fixed, so you don't even need to choose a value to start. For the midrange Ri = Rm = 25k

I would also lower the Q in addition to the gain. With high Q, the high gain settings are useless. From the equation for Q on p. 8 it looks like they chose a Q of 1.5, I would choose something lower like 1 or maybe even less?

Btw, what did you think about the noise of the TDA7439 with the gain cranked up? This is my main complaint against the LM1036.
 
#6
pulexirritans said:
I don't think you need to know how the active part works, you just need to use the equations on p. 9 to get the behavior that you want. Just choose the gain (Av) and Q that you want and then solve each equation on p. 9 starting at the top. Ri is fixed, so you don't even need to choose a value to start. For the midrange Ri = Rm = 25k
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Yes, this is clear. I was just inquiring on how the stage work.

Regarding the noise, with the input gain stage and volume at 0dB, the amp is totally silent. With my hear just in front of the tweeter the noise is almost inaudible.

My power stage needs 1V for 60W output, so, with a -10dBV signal I have to set the input gain at +10dB. Even so, there's no audible noise, but sourcing input will destroy my hears, so... an exellent SNR in my opinion.

Regards.
 
#7
pierluigiugolotti said:
Yes, this is clear. I was just inquiring on how the stage work.
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Sorry, I really misinterpreted that. I think the last two paragraphs in the data sheet description are about as far as you're going to get without talking to someone at st-micro...

pierluigiugolotti said:
Regarding the noise, with the input gain stage and volume at 0dB, the amp is totally silent. With my hear just in front of the tweeter the noise is almost inaudible.

My power stage needs 1V for 60W output, so, with a -10dBV signal I have to set the input gain at +10dB. Even so, there's no audible noise, but sourcing input will destroy my hears, so... an exellent SNR in my opinion.

Regards.
Click to expand...

Awesome, this is exactly what I want to hear. Thank you!
 
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