TDA7293 homebrew first try

[booj]

Hi all,
  My first post. My first try with the TDA7293. Its a mess. It's based on the circuit in a Marshall AVT100. It's basically that minus the FDD circuit. If the attachment doesn't come up I'll repost. (I don't see it in the body of this message but I've attached it...I think)

[booj]

Cool! it came up kinda big. I'll fix that later. any input welcome!

[J M Fahey]

Hi booj
1) Where is the signal input?
2) That's no power supply for *any* power amplifier driving a speaker.
Very poor and barely acceptable to power a preamp.
3) If the original schematic calls for 390r and 0r1, it's not right to replace them with 3k9 and 1r *unless* you also use an 80 ohms speaker to keep things in proper scale (and you're happy with 1/10 the power)

[teemuk]

1) It's an inverting circuit so probably at the inverting input. Nevertheless, no idea what input resistor is used to define gain, if any.

Having one is essential!

2) Truth. And the operating voltages are +-12V. Why even use a TDA7293 chip for that when the full output power can't even be extracted in the first place. There are much better chip choices for lower voltage and lower power circuits.

3) Exactly. This circuit is very sensitive for a proper amount of current feedback. If it's omitted or in a wrong scale the circuit will behave very erratically. For example, omission of CFB would through the gain through roof and even an input resistor in a Megaohm range would not be enough to tame it.

Sorry to say this as rudely booj but it's a botched design. It's your first try with the chip so may I suggest you start with the proven datasheet circuit and proceed into variations once you know how they operate.