Casino 12 Amp fixup.
Normally I would just keep this stuff for spares but I realised there is a lot of interest in small amp builds on this forum so with a little effort on my part might help those who wonder which circuit to build.
I'm not claiming it will sound like a bedside Soltarno but I think I've dramatically improved it with little effort.
Hum, So What to do with an unwanted toy amp that shows no sign of life.
This was thrown my way not working so a quick inspection showed the LM2030 power chip was blown. Lucky I keep junk and sure enough I had a LM1875 which was pin compatible so I had it working in no time.
But oh what a horrible piece of trash it was, *insanely bright and harsh* even though it was powering a big 15 inch driver which did not have much treble output.
I pulled it all out, traced the pcb to a schematic, input the data to the simulation and sure enough way to much bandwidth. So after a long head scratch I came up with this, see schematic.
Delete C5 and break the signal,
add 4 components (green circle)
and change the value of 4 resistors.
Bingo success, now it at least sounds like a guitar Amp
The 15 inch driver now shows it's darker tone and you need to wind the treble but most of these amps will be driving much smaller speakers so it would sound close to ideal running a small 6 inch speaker which generally have more high frequency output.
A classic *Too much bandwidth* issue which just kills these things dead as soon as you turn up the bass they just splatter because these little power chips are just not capable of very low freq.
It's wise to wipe it out if you can.
And most distortions sound trashy and cheap with high frequency much above 3kHz so again you need to wipe it.
Stuff in the green circle;
If you want more Treble content, make the 33nF smaller.
If you desire more bottom end, then increase the 10nF.
both values will likely be very dependent on R5 being 10k.
If you need values for the power supply and power chip they can be found on the data sheets.
This rig runs 16-0-16 for power chip, preamp power via 270R drop resistors.
Have fun,, Phil.