Following this discussion, I dug out one of my early prototype based on N types for the output (and most of the rest).
It is a very crude amplifier, and has not be refined or optimized in any way, but it does have some noteworthy peculiarities:
-Full N output (without the quasi trick)
-No emitter resistors, yet thermally stable
-DC-coupled and compatible with symmetrical supplies despite a natively single supply topology.
I had to reverse-engineer it, as I couldn't find a schematic, but the task was not too difficult, given its simplicity.
The sim works, but it is not too faithful: it has difficulties driving a 8 ohm load, when the real amplifier easily copes with 4 ohm.
Probably caused by the 2N3055 models, weaker than the real ones.
It wouldn't be difficult to fix though.
Why did I apparently reject it at the time? Probably because of the performances: something incapable of going below 0.1% THD is not worth pursuing, and the average THD of this amp is around 0.3%, depending on the conditions.
The real amplifier does better than its sim though: it has roughly half the simulated distortion.
There is certainly a lot of room for improvement, and since there is a growing interest for simplistic, old-style amplifiers, such a toy should please many fellow DIYers (and it's a tweaker's heaven!).
It would be very easy to convert it back to a single-supply, capacitor-coupled configuration.
The topology is fundamentally a totem-pole, but with some deviations: normally, R1 and R6 should be connected between E and B of the OP, with a CCS instead of Q2/Q3, and emitter resistors for thermal stability.
With the connection of Q2/Q3, the output transistor is current-driven for quiescent conditions, and Q2/Q3 compensate thermally this current drive (they are coupled to the heatsink).
The scheme works well enough: the heatsink is a smallish and flimsy piece of 1mm thick aluminum, the OP's are isolated with ungreased mica's, and the thermal contact of Q3 is not very good, yet it shows no sign of thermal runaway.
This is the 2N3055 model I used, it is the closest to reality I could find, but it is not perfect:
.model Q2N3055 NPN(Is=974.4f Xti=3 Eg=1.11 Vaf=50 Bf=99.49 Ne=1.941 Ise=902.5p Ikf=4.029 Xtb=1.5 Br=2.949 Nc=2 Isc=0 Ikr=0 Rc=.1 Cjc=276p Vjc=.75 Mjc=.3333 Fc=.5 Cje=569.1p Vje=.75 Mje=.3333 Tr=971.7n Tf=39.11n Itf=20 Vtf=10 Xtf=2 Rb=.1 Vceo=60 Icrating=15 mfg=Texas)
Have fun!!!
It is a very crude amplifier, and has not be refined or optimized in any way, but it does have some noteworthy peculiarities:
-Full N output (without the quasi trick)
-No emitter resistors, yet thermally stable
-DC-coupled and compatible with symmetrical supplies despite a natively single supply topology.
I had to reverse-engineer it, as I couldn't find a schematic, but the task was not too difficult, given its simplicity.
The sim works, but it is not too faithful: it has difficulties driving a 8 ohm load, when the real amplifier easily copes with 4 ohm.
Probably caused by the 2N3055 models, weaker than the real ones.
It wouldn't be difficult to fix though.
Why did I apparently reject it at the time? Probably because of the performances: something incapable of going below 0.1% THD is not worth pursuing, and the average THD of this amp is around 0.3%, depending on the conditions.
The real amplifier does better than its sim though: it has roughly half the simulated distortion.
There is certainly a lot of room for improvement, and since there is a growing interest for simplistic, old-style amplifiers, such a toy should please many fellow DIYers (and it's a tweaker's heaven!).
It would be very easy to convert it back to a single-supply, capacitor-coupled configuration.
The topology is fundamentally a totem-pole, but with some deviations: normally, R1 and R6 should be connected between E and B of the OP, with a CCS instead of Q2/Q3, and emitter resistors for thermal stability.
With the connection of Q2/Q3, the output transistor is current-driven for quiescent conditions, and Q2/Q3 compensate thermally this current drive (they are coupled to the heatsink).
The scheme works well enough: the heatsink is a smallish and flimsy piece of 1mm thick aluminum, the OP's are isolated with ungreased mica's, and the thermal contact of Q3 is not very good, yet it shows no sign of thermal runaway.
This is the 2N3055 model I used, it is the closest to reality I could find, but it is not perfect:
.model Q2N3055 NPN(Is=974.4f Xti=3 Eg=1.11 Vaf=50 Bf=99.49 Ne=1.941 Ise=902.5p Ikf=4.029 Xtb=1.5 Br=2.949 Nc=2 Isc=0 Ikr=0 Rc=.1 Cjc=276p Vjc=.75 Mjc=.3333 Fc=.5 Cje=569.1p Vje=.75 Mje=.3333 Tr=971.7n Tf=39.11n Itf=20 Vtf=10 Xtf=2 Rb=.1 Vceo=60 Icrating=15 mfg=Texas)
Have fun!!!