Yet another N-Channel Amplifier

[richie00boy]

Originally posted by keypunch
So lower the Ciss the better not just from quality of high's reproduced perspective, but also from a greater opportunity of cross conduction?

Yes.

Originally posted by keypunch
I hear alot of reference to the "miller" charge time. Is this bascailly the charge time you reger to or the collective charge times that can be listed, i.e. Qg, Qgs and Qgd, the latter of which is "miller" charge time. I have noticed how these values are listed against the Id, Vds, Vgs parameters of test. They are in nC units which I have no clue what that is, but no need to explain that for now, I can dig on internet to find out. The question is, and I have been thinking about it for few weeks, there any way to distill these by way of some sort of ratio so I can compare apples to apples of different devices of same company, let alone of different companies? I tried to apply what math I know, but not being a EE or of thatknowledge I have not figured out how to distill this to common ration I can use to compare different devices on this charge time issue.

Miller is Qgd. nC Refers to the unit of charge which is C for columb, n refers to nano.

Device selection is a combination of various parameters, ranked according to the particular design and application you are trying to achieve. The parameters are all tradeoffs so you will never get a device with all ideal parameters.

Originally posted by keypunch
Do any such topologies exist that have symetrical source/sink current ability in the driver stage that can work with N-Channel output stage or are these design oppsites challenges?

Almost. Designs with active current source loaded VAS tend to have this feature. However, once you decide that you must use quasi output then you spoil the symmetry somewhat as the upper half is working as a source/emitter follower and the lower half as CFP. This causes differences in the way that you can suck out charge from the devices, and their transfer characteristic especially around the transition. Using equal values for both emitter and collector resistor in the driver transistor for the lower device (R17 and R13 in Pelle's schematic) can help in this respect, as can the addition of a diode (for BJTs) or capacitor (for MOSFETs) across the emitter resistor.

Originally posted by keypunch
How would one modify the Holton N-Channel or is Pelle's design able to currently or with some modification handle up to 4 output device pairs? I have need for 4 pairs at 100-120W leve, then hope I can do a 80W at 2 pair level, a 40 and 20 at one pair level. So the only issue is current Holton desigh is for 3 pairs of output devices. I assume there are changes needed to accomodate a 4 pair design/modification. I am not sure 3 pairs will meet my higher power needs.

From what I recall of this design, Holton claims that it will drive a large number of output devices without modification. Usually all that is required is to run the VAS and drivers at higher current.

As for Pelle's amp, darkfenriz's comment is exactly what I would say. I do not like to drive MOSFETs directly from the VAS because their capacitive input makes for a heavier load at HF, increasing distortion right when feedback is rolling away. He is running the VAS at 7mA which is OK to drive a single (non-high capacitance) pair of devices.

Originally posted by keypunch
Any comment on pros or cons of N-Channel sound quality vs say the LYNX bi-polar design assuming reasonable excustion of circuit. I am aware there can be sloppy and exceptional designs that will skew the generally expected results.

True complementary designs have more linear output due to greater chance of symmetry around the transition point from upper to lower half conducting. That said, you can make a great quasi amp if you just pay attention to the right details.