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Xenfasa

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  1. Hi HarryA, Thanks for the suggestion. It looks good but in the first paragraph of the datasheet makes me wonder sense is says... "The LM3886 is a high-performance audio power amplifier capable of delivering 68W of continuous average power to a 4X load and 38W into 8X with 0.1% (THD a N) from 20 Hz –20 kHz." 20Hz? I wonder if they just say that to appease savvy audio people or can the chip actually amplify DC & sub 20Hz frequencies. I would think no caps on the input side would be important so the diagram you mention in there without caps make sense for sub 20Hz but I wonder if chips like this have some internal filter for filtering out super low frequencies. Like you mention, it says "Pure DC" amp which would be 0Hz signal which would be great but not of this is clear. Everywhere I look you'd have to make at least some assumptions. I'm not 100% sure what terminology I should be searching for to be led to what I need. Maybe DC Amplifier?.... but I still need some frequency response. If my project was just amplifying square waves it would be easy. I have some triggered input mosfets that pulse on/off for that. The problem is really amplifying the sawtooth. I've tried varying the duty cycle of the mosfet trigger pulses that with the right Capacitor should smooth them into a sawtooth but that has not been accurate. At least it does not appear correct on the oscilloscope. Maybe need bigger caps. Any other suggestions on how to amplify DC to 20 Hz signals that are made up of higher frequency harmonics themselves. Maybe the pre-build ebay item could work... but I'd need to remove any capacitors on the input side? Thanks again
  2. Hello, I'm working on project to produced Pulsed ElectroMagnetic Fields (PEMF) at LOW frequencies (0-100Hz) using various wave functions. (sine, square, triangle, sawtooth) The whole design is very similar to what an audio amplifier and speaker setup would be since speakers are essentially coils with low resistance/impedance. The input signal would ideally come from a 3.5mm headphone jack or even better Bluetooth as I see some small pre built class D amplifiers include such. I've considered using OpAmps, transistors, Mosfets but seems pre-built class D amps gets me near 95% there so why build from scratch. Any off the shelf class D amp would work except for one problem. The low cut of frequency of all pre-build amplifiers is often between 14Hz and 20Hz and understandably so since they are made for audible sounds. Ideally, I need to account for super low frequencies, 1Hz or even lower, 0.5Hz, 0.1Hz etc. Power between 10 watts and 50 watts. Though I can solder and have build projects before, Ideally, the less building the better. So, my question is this. Is there any off the shelf audio amplifiers that would also amplify signals even as low as 0-20Hz ? Probably what would be considered a bad quality/cheap amp? If not, are there any that could be easily modified by changing any input filers (RL) that would allow lower frequency signals to pass into the amplifier? Something like this would be great if could amplify 0-20Hz: https://www.amazon.com/Bluetooth-Receiver-Amplifier-Audio-Fosi/dp/B087FTV362/ Looking at the specs of the chip (TPA3116D2) it contains ... https://www.ti.com/product/TPA3116D2#tech-docs ...it is not clear to me if a lower input frequency can be permitted by removing or changing external components Would not be easy on this pre-built device since it does not use normal regular size capacitors and resistors that would be much easier to work with. I'm open to suggestions. I may be going in a completely wrong direction. It seems there should be a simple answer but my project is not so common. Requirements again: Amplify low power signal from 3.5mm jack or phones bluetooth. input signal 0-20Hz made up of various common waveforms Total Power 10-50watts Drive copper coils/speakers 4-8ohms Adjustable output power/volume knob pre-built or minimum modifications to a pre-built amp. Worse case will build it Fast and Easy is more important than cost at this point. Thanks again for any suggestions or feedback. I'm open to anything that may take me in an unforeseen direction. Ben
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