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The poor little thing would get too hot at full output with a 16V supply and a speaker less than 32 ohms.philba said:Im not sure aboutwhy they spec'd the -4 at 32 ohm
From the DIY perspective, Class-D is rather unfortunate. Because of the extremely high switching speeds, a compact layout is essential, and SMD (surface mount devices) are a requirement to get the performance needed. The stray capacitance and inductance of conventional through-hole components is such that it is almost impossible to make a PWM amplifier using these parts. Indeed, the vast majority of all ICs used for this application are available only in surface mount, and a look at any PWM amplifier reveals that conventional components are barely used anywhere on the board. Since SMD parts are so hard to assemble by hand and the PCB design is so critical to final performance, DIY versions of PWM amps are very rare indeed (I don't know of any).
audioguru said:Texas Instruments have many class-D audio amp ICs. They are all surface-mount with very small lead spacing and their power is up to 240 Whats (about 150 Watts). Some require the bottom to be soldered to the ground plane of a pcb while it is surrounded with pins going elsewhere. Try doing that by hand.
The TDA7480 class-D amp specs don't mention high frequency distortion, which is the worst thing about a poor class-D design.
That is why it is in an old through-hole DIL case. New ones are all surface-mount.i_build_stuff said:Maybe it's an old design or something?
This thread is 6 years old.
The 1k resistors are simply wasting battery power. Since the input current of an opamp is extremely low the resistors can be 100k or more. Then the filter capacitor between them will work better.Isn't a 1k voltage divider unsuitable for the non inverting insput? shouldn't it be 47k at least? That's only 2k between Vcc and GND
Not to mention the gain of 1000, which would require an op amp with at least 20MHz GBW to realize 20kHz audio bandwidth.The 1k resistors are simply wasting battery power. Since the input current of an opamp is extremely low the resistors can be 100k or more. Then the filter capacitor between them will work better.
It is a stupid design because the very low input impedance of the inverting opamp shorts away a lot of the mic level. The opamp should be in a non-inverting design with an input impedance of at least 22k ohms, not only 1k ohms (R1).