Hi all,

I would like to dc couple the gain stage and output stage in the schematic below. The textbook that I am using in school does not cover E mosfets very well and I'm having some problem figuring out what Vb is for Q2. Vg for Q1 is 6.94v. In the book that I have it talks about finding "k" for the mosfet. After looking on the spec sheet and using the equation k = Id(on)/(Vgs(on)-Vgs(th) with the variables being Id(on) = 200mA at Vgs = 10v and Vgs(th) = 2.1. I came up with the answer k = .003x 10(-4) mA/V(squared). Please understand that these calculations are a bit beyond where we are in class. Basically I'm looking to bias the output of Q2 at 2/3 Vcc and direct couple it to Q5. Any help would be appreciated. Also I'm looking for opinions on an idea that I have. This is a headphone amp and rather than use a large output capacitor for impedance matching I was thinking of using This transformer:

http://www.sowter.co.uk/specs/8665.htm

I realize that I will have to AC couple the transformer but with a load of 32 ohms using a 12:1 voltage ratio the impedance of the primary comes out to about 4600 which means the coupling cap only need to be: C = 1,000,000/2pi x 10 hertz x 4604 ohms) = 3.45 uF. I think that 5uF will work pretty well. I think that that would beat using a 680uF cap on the output. Opinions?

I would like to dc couple the gain stage and output stage in the schematic below. The textbook that I am using in school does not cover E mosfets very well and I'm having some problem figuring out what Vb is for Q2. Vg for Q1 is 6.94v. In the book that I have it talks about finding "k" for the mosfet. After looking on the spec sheet and using the equation k = Id(on)/(Vgs(on)-Vgs(th) with the variables being Id(on) = 200mA at Vgs = 10v and Vgs(th) = 2.1. I came up with the answer k = .003x 10(-4) mA/V(squared). Please understand that these calculations are a bit beyond where we are in class. Basically I'm looking to bias the output of Q2 at 2/3 Vcc and direct couple it to Q5. Any help would be appreciated. Also I'm looking for opinions on an idea that I have. This is a headphone amp and rather than use a large output capacitor for impedance matching I was thinking of using This transformer:

http://www.sowter.co.uk/specs/8665.htm

I realize that I will have to AC couple the transformer but with a load of 32 ohms using a 12:1 voltage ratio the impedance of the primary comes out to about 4600 which means the coupling cap only need to be: C = 1,000,000/2pi x 10 hertz x 4604 ohms) = 3.45 uF. I think that 5uF will work pretty well. I think that that would beat using a 680uF cap on the output. Opinions?