Interesting thread, would someone care to summarize what the most important mods are for this amp board? So many posts are confusing to follow. it seems that the initial recommendations are to swap out the Op Amps, replace the 4 Wima Caps, and possibly replace the Power supply? but it gets confusing after that.
Yes, you have correctly generalized the easiest and most obvious modifications of this amplifier:
1. replace operational amplifiers with better ones (to your taste).
2. replace the 4 original Wima Caps 1µF or 2,2µF with 10µF to reduce phase distortion of the input signal.
Next are non-obvious modifications that can cause controversial opinions about their expediency:
3. if you have large speakers with 10 or 12-inch drivers, then you need to replace four 470µF/50V capacitors with two (three/four) LowESR 2200µF/63V electrolytic capacitors (this will be enough to provide dynamics at low frequencies). To test the dynamics at low frequencies, you can use
these two audio-tracks. When listening through a good quality amplifier, the sound of a bass drum from first track resonates in your chest and makes it difficult to breathe.
4. replace the 30 kOhm resistor with 10 kOhm, which raised the frequency of the modulator from 450 kHz to 600 kHz. This will cause increased heating of the TPA3255 chip, so it is necessary to make ventilation holes in the upper cover of the case.
5. shunting a 220uF/63V electrolytic capacitor to power the chip TPA3255 with a 1nF/100V film capacitor to remove some of the high-frequency ripples.
6. we improve the quality of the power supply of operational amplifiers and the modulator in TPA3255 by replacing the parts around the converter voltage from 36-50V to 12V LM2575HV.
I made all six of these modifications on my amplifier and am pleased with their result!
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