I have a question. I ordered a few of STA540 op amps (not the kit) and built the circuit according to the data sheet (and then verified it against the kit for it that is sold here, with slightly different cap values). I can’t seem to get any audio out of it at all. I have a 2A 12V supply and have verified the voltage (And really at this stage, it doesn’t matter since I’m just trying to get it to function). The main difference between the kit and my setup is I am not using the LM358 Op Amp to push it. Does this amp need to be driven by the LM358 first or should I be able to pump in a signal from my computer and output to standard headphones with the STA540 alone?
Let me know if a schematic of my wiring is needed.
Looking at the kit schematic it appears that there’s a pot to attenuate the incoming signal followed by the LM358 which provides a voltage gain of 2 and some bandpass filtering. Therefore I’d say you should be OK, level-wise, feeding signals into the 540 from any line level source. One thing to be sure about is keeping the DC blocking caps, C11 and C12, in the path … after your source and before the 540 IC.
There are a few “540 not working” threads here, you might want to read them to see if any help your case.
From what I can tell, these guys are quite sensitive to routing issues, so be careful, especially with ground impedance and isolation between input and output.
A few things jump out at me:
You have two of the four amps just floating. I’d at least tie the inputs to ground.
Pin 7 is standby, and needs to be pulled to Vcc through a 10k series resistor to enable the part
The 100uF bulk cap may be a bit small; the data sheet recommends 1000uF and it should have 100n in parallel, right at the IC pins, to take care of high frequency noise
