is this circuit suppose to work as expected? i built it as it is drawn, as a preamp buffer, and im getting wrong voltage readings. everything is slightly higher than drawn, and the output varies from 2v to 0.1v depending on where the volume pot wiper is.
not only that some transistors oscillate, and even explode. so far i got it to work with bc560, bc337 x2, and bc327 on some cases along with 337 but some other times they explode. bc550 overheats with any combination.
rail voltages are 14v +/-, btw.
and the circuit is correctly made, on a pcb.
not only that some transistors oscillate, and even explode. so far i got it to work with bc560, bc337 x2, and bc327 on some cases along with 337 but some other times they explode. bc550 overheats with any combination.
rail voltages are 14v +/-, btw.
and the circuit is correctly made, on a pcb.
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That means you need an input coupling capacitor, a 10uF nonpolarized type.
This is a conceptual circuit, not yet fully designed for reliable operation.
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With heatsinks - nothing super big though.
Increase the value of the 2 ohm resistors, and maybe the 10 ohms as well.
I think 4.7 ohms should get you to the point where BD139s would work w/o a heatsink (though attaching a random piece of metal should be easy enough). Maybe 10-15 ohms for TO-92s.
Don't have any nonpolar capacitors floating about? Make one from two polar caps of 10-22 µF connected back-to-back.
> is this circuit suppose to work as expected?
It is supposed to be (part of) a Headphone Amp ("HPA"). "Hybrid Headphone Amplifier"
Pieter says it idles at 80mA, so can deliver nearly 160mA peak. It will drive 40 Ohms to over 2 Watts.
The 10k at the output is not a load but a cap bleeder.
So probably real over-kill as a line stage. Line inputs need much less than 1mA.
This also explains why you would not DC-couple a volume pot to the front. The input Base current is very large (fraction of a mA). Also why you are getting significant offset.
As Rayma says, "conceptual", "needs development".
As a hasty-hack: increasing all internal resistors 40X (2r to 80r) gets you to 2mA which would be way cool and ought to be plenty for most line stages. A 15X factor (2r to 30r) would let it drive true 600 Ohm loads, and still be just-warm for TO-92 jellybeans. I'd take the caps down by a similar factor. I would not reduce the 47K input R any more than needed, and I would cap-couple it.
It is supposed to be (part of) a Headphone Amp ("HPA"). "Hybrid Headphone Amplifier"
Pieter says it idles at 80mA, so can deliver nearly 160mA peak. It will drive 40 Ohms to over 2 Watts.
The 10k at the output is not a load but a cap bleeder.
So probably real over-kill as a line stage. Line inputs need much less than 1mA.
This also explains why you would not DC-couple a volume pot to the front. The input Base current is very large (fraction of a mA). Also why you are getting significant offset.
As Rayma says, "conceptual", "needs development".
As a hasty-hack: increasing all internal resistors 40X (2r to 80r) gets you to 2mA which would be way cool and ought to be plenty for most line stages. A 15X factor (2r to 30r) would let it drive true 600 Ohm loads, and still be just-warm for TO-92 jellybeans. I'd take the caps down by a similar factor. I would not reduce the 47K input R any more than needed, and I would cap-couple it.
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