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[Alexius II]

Hi,

I've drawn this schematic from a pcb of the amp I'm trying to rebuild... but it seems very strange to me.
I've double checked everything, but I can't seem to understand how it works.

Do any of you see a mistake or something?

[J M Fahey]

Mostly accurate but has a couple details.
1) pin 1 shows no DC coupling, it needs 1/2 Vcc (in this case 1/2 33V)
There must be a resistor joining it with a voltage divider generating it.
2) the feedback looks reasonable, (1K5/220uF/22r+10r+0.1r) but the 22K and the 33K look misplaced (they might be what I mention in 1)
3) Only solution: rechecking. Oh well

[Alexius II]

Rechecked.
Good news: there is some kind of voltage divider in the preamp.. joining near the 1uF of pin 1.
Bad news: all things drawn are still there. I just don't get it
(maybe this is why it realy souns like crap?)

There are obvious signs of "modifications" all over the pcb.. and a few components seem to be missing (a resistor, diode and a capacitor, all near the power section).

I give up. I will use the datasheet tda2030 layout/pcb, since I doubt the cheap internal speaker could even tell the difference.

[joecool85]

Using the datasheet probably is your best bet, but if you want to get the circuit traced we might be able to help if you get us some photos of both sides of the board.

[Enzo]

Or just tell us what the amp is you are trying to trace out, and we can probably look up the schematic.

[Alexius II]

Thanx for the offer, I realy appreciate it, but I don't think it's worth the effort

@Enzo: it's Epiphone EP10.

[Manfred]

Hi,

there is an so-called current feedback amplifier. The speaker current is included in the feedback loop now.
The current feedback increases the output impedance of this power stage, thus the stage works in matters of damping like a tube power amp. Have a look to the Marschall Valvestate or Peavy schematics, there is the current feedback applied.