2024-11-01 11:16 AM
Hello everyone.
Regarding an amplifier with two TDA7294 in bridge configuration, looking at the diagram, on IC 1 at pin 3, there is a high pass filter formed by the 0.56uF capacitor C1 and the 22K Ohm resistor. The cutoff frequency is 12,91 Hz.
I would like to get closer to 0 Hz by increasing the capacitance of C1 to 22uF (cutoff frequency is 0,32 Hz).
If you see IC 2, at pin 3 there is another filter formed by C2 (0.56uF) and the 22K resistor.
For symmetry with the first IC, should I also increase the capacitance of C2 to 22uF in your opinion?
Or leave it at 0.56uF?
I thank you very much in advance for your kind reply.
Cheers,
Enrico
2024-11-02 11:04 AM
>> "A switching regulator will have massive problems here because a positive and a negative voltage are required. "
There are switching power supplies on a market that provide both: positive and negative voltages .
With all due respect, all post is just a speculation.
Seems written by AI with very low IQ.
2024-11-09 03:00 AM
2nd copy
Dear Peter, I do not want to waste your time but back to my question from yesterday, with a 5uF capacitor at the input high pass filter, what are the capacitive values for the bootstrap cap and for the two caps of the power supply?
Many thanks for your kind help.
2024-11-09 03:14 AM
@Peter BENSCH wrote:such low frequencies are anything but easy to handle. Not to mention the difficulty of finding a speaker for it.
2024-11-09 04:02 AM
Hi,
- its for audio, right ? (or for test equipment ?)
if audio : What are your speakers ? lower frequ. limit ( - 3 dB ) ? frequ. response ? avg. SPL at 1 W ?
THEN we talk about sense or nonsense to lower the input filter frequ. .
2024-11-09 05:26 AM
The speakers are La Scala II made by Klipsch.
Are you a musician? Do you know what pedal tones are?
THEN we talk about the need to lower the input filter freqs.
2024-11-09 06:11 AM
@Enrico_I wrote:Do you know what pedal tones are?
Yes, but look at the sizes of those pipes!
They are "not feasible" for all but a very few, very specialist situations.
If you want extra-low tones, then you're inherently going to need extra-large components!
2024-11-09 06:19 AM
Hi Andrew, I simply asked the ST technicians the question: if I raise the input filter capacitor from 0.56uF to 4.7uF for the reasons above, what should be the new value of C bootstrap?
I still don't have an answer regarding what formulas should be used etc.
2024-11-09 06:33 AM
That question was answered, and you dismissed the answer saying, "It's just not feasible"
2024-11-09 06:46 AM
The mention of "not feasible" was about the 22uF input capacitor and the related 185000uF and 87000uF capacitors. I then asked if instead of 22uF a 4.7uF was used.
I am still waiting for an answer...
2024-11-09 06:57 AM
There are a few issues with those bootstrap capacitors:
1. Setting big value proportional to (20 Hz / F-new) is likely to damage IC during power up /down, so you can't just increase x20 times w/o designing OCP OVP protection on pin 6.
2. Main purpose bootstrap capacitor is to lower THD, to specified value 0.005% or so. This objective is meaningless for low freq. end, since whatever acoustic system you have it's likely produce 1-5% THD.
Vibrations <20 Hz is also travelling through surfaces, floor / walls, and distortion these "mediums" is also not measurable.