Multiple replies here...
Bob Scott wrote:
1.) That is about all the output voltage swing you can expect...
2.) I was wondering how much power you were hoping for...
3.) ...heat sinking...
4.) ...I would change the output transistors to a higher power type with a metal case...
5.) ...bridged output version...
6.) You might try adding a one more 1N4001 bias diodes in the diode series...kind of circuit where you want to make sure that no excess (current) flows.
7.) Make sure you have resistors from Base to Emitter on the 3055s. They will help the 3055's turn off. 250 ohms or so should work. The high (+) drive already had two transistors in darlington configuration? Now it has three, and the transistor current gains are multiplicative.
8.) I think we're finished...
1.) I figured that the max swing I could expect should be at least supply - (~2 x output junctions), so 12 - (~2 x (0.6 x 2)),
12 - (~2.4) or ~ 9.6 volts +-, between 9.5 to 10 V. Just my empirical guess because you have to take into account the
output junctions and some loss due to other parts (resistors, capacitors and speaker inductance - the ~2 x's).
2.) Once the formula for power was shown to me, I did a quick calc to show at most 1.6 W, but that would really be pushing it.
3.) Yeah, I saw the current running through them in the sims and knew that they would need to be cooled somehow. I have
some sheet aluminum I could use if I wanted. RS has the "grease".
4.) I thought that later maybe some 2N2222A's - the TO-18 cased one's would be better.
5.) That would be easier to do with OPAMPs for the inputs. A dual for mono, or a quad for stereo. I know the LM324 is a quad,
is the LM1458 a dual? Gotta look that up. I'd love to see your take on that.
6.) When I wrote my last post with stats, I tried doing that to see what would happen. While the output was slightly
increased, I didn't like the increase in current through the Q3 - Q8 stages. AND, I set the input to 0 V (no input) and saw that
the current running through those transistors was doing nothing but heating them up. Looks like 3 diodes work very well in this
design, keeping everything working efficiently and cool.
7.) When placed in the schematic, it looks like the resistors are helpful when the speaker impedance drops to 4 ohms or less.
The sine wave becomes slightly jagged without them. At 8 ohms, the wave looks just beautiful. As for the multiplication, I'm
being lazy right now and letting the software do the work. I am learning though.
8.) Well, almost. You had mentioned a current mirror, and I have seen some amps that use what look like differential inputs.
From what I can see, a current mirror takes place of the diode string and that could give you the ability to adjust the
quiescent current. Am I correct? What advantage would a differential input give you? Stability?
From a post further above - "Jameco Catalog", I have one of those as well as MCM, All Electronics and another one I can't
find right now. I have been able to find most things in the on-line stores, but paper is so much more convenient to look
through. Would you believe that MCM actually has the best stock of Ge transistors? It does! And at a better price!
PS, anyone else interested in this topic may jump right on in. I welcome the participation.