I used twisted cat5 for signal wiring and did not have any interferences. When I added second channel for input I had to use shielded cable as the cables running along induced crosstalk to each other. I have zero humm or interferences. In my opinion shielded cable is not needed if not routed near power wires or other input source.
An externally hosted image should be here but it was not working when we last tested it.
LT1122(buffer)+LM3886 (inverted)
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Sorry, I'm probably just dim, but where is the buffer on that PCB? Nice looking boards though. If you have a thread with other info, can you just link that so I dont pollute the photo gallery?
Cheers!
I'm guessing it's on the underside, maybe an soic 8. It'd be nice to see a pic from the other side as well as underneath, to see the speaker output connections and signal input connections. All I see is what appears to be power input on the left - everything else is covered up by arrays of big electrolytics!
bottom side PCB
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I could see no buffer also??? but after a re-look at the underside and wondering why so many electros on the top side... ... yes some sort of chip buffer for a chip amp??? Does a chip amp need a buffer??
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It's probably too subjective to say yes or no, but my LM1785 sounded much better when I built a economical B1 Buffer (B1 buffer --> volume pot --> LM1785) driving a pair of BR Mark Audio CHR70s. A B1 buffer clone is so cheap, you might as well build one and see
This is the one I built, which includes toner transfer images. PM me if you want more info (or start a new thread).I think another part of the secret is the (inverted) part here:
The input and feedback resistors mush be fairly low to keep noise down, so the inverting mode has a much lower impedance than noninverting mode. Thus a buffer is needed to drive the circuit from most audio sources, which expect a higher input impedance.
This makes the whole amplifier inverting, but that can be fixed by swapping the speaker wires.
Using a chip amp (or op amp) in inverted mode (the positive input goes to ground, and the signal is put at the resistor going to the negative input that would otherwise go to ground (through an electrolytic cap). There's been discussion that this runs with lower distortion than non-inverting mode. It certainly seems reasonable, as the LTP input transistors don't have a varying voltage on them in inverting mode (or it's orders of magnitude less), and thus don't add any distortion that might be added from them moving up and down with the input signal in the noninverting mode.
The input and feedback resistors mush be fairly low to keep noise down, so the inverting mode has a much lower impedance than noninverting mode. Thus a buffer is needed to drive the circuit from most audio sources, which expect a higher input impedance.
This makes the whole amplifier inverting, but that can be fixed by swapping the speaker wires.
Just a little stereo amp using 4 tda2030a chips. Powered by an old 2.5 amp radio shack 12v power supply. Sounds pretty good.
An externally hosted image should be here but it was not working when we last tested it.
