Well, I've traced the power amp section of my Badger 30 Watt amp, at least as well a I can.
I've got pretty good photos of the component and track sides, and I've got them nicely lined up, which is "helpful".
Badgering by plybench, on Flickr
(I've got more of the components labelled since I uploaded that image).
It was more difficult than I hoped to trace the circuit, mainly because some aspects of it were quite unexpected. So here's the schematic, at least as accurate as I can get it. Faults are likely.
badger by plybench, on Flickr
It appears to follow the basic ideas shown on this website:
https://www.nutsvolts.com/magazine/article/bipolar_transistor_cookbook_part_7
In particular, figure 9 (quasi-complementary output stage), and figure 19 (PNP long tailed pair differential input stage).
However, the actual circuit has several quirks (by which I mean things I have never seen before and/or don't understand)
Moving from right to left:
1) The diode bias chain has 2 (not 3) diodes. This isn't enough. Did they want cross over distortion?
2) The feedback resistor/divider chain is sandwiched between 2 47µF capacitors, connecting +v power to earth. Is this some kind of frequency filtering?
3) is the diode-180Ω-47µF on the left a power conditioner for the LTP?
4) The filters (capacitor circuits) on the input stage are connected to earth; but the LTP and subsequent driver transistor connect to right down to -Ve power, albeit via a 100Ω resistor.
I've got pretty good photos of the component and track sides, and I've got them nicely lined up, which is "helpful".
Badgering by plybench, on Flickr
(I've got more of the components labelled since I uploaded that image).
It was more difficult than I hoped to trace the circuit, mainly because some aspects of it were quite unexpected. So here's the schematic, at least as accurate as I can get it. Faults are likely.
badger by plybench, on Flickr
It appears to follow the basic ideas shown on this website:
https://www.nutsvolts.com/magazine/article/bipolar_transistor_cookbook_part_7
In particular, figure 9 (quasi-complementary output stage), and figure 19 (PNP long tailed pair differential input stage).
However, the actual circuit has several quirks (by which I mean things I have never seen before and/or don't understand)
Moving from right to left:
1) The diode bias chain has 2 (not 3) diodes. This isn't enough. Did they want cross over distortion?
2) The feedback resistor/divider chain is sandwiched between 2 47µF capacitors, connecting +v power to earth. Is this some kind of frequency filtering?
3) is the diode-180Ω-47µF on the left a power conditioner for the LTP?
4) The filters (capacitor circuits) on the input stage are connected to earth; but the LTP and subsequent driver transistor connect to right down to -Ve power, albeit via a 100Ω resistor.