All purpose SS op amp
 

I am still developing my abilities and find myself all too often
struggling with op amp design.

Can anyone here suggest an "all purpose" amplifier built around a
readily available op amp and transistor follower that will operate
within the specifications below? Preferably without changes in
componentry except to upgrade the power transistor depending upon load
requirements.

DC coupled with frequency response DC to 20KHz
Input signal level 1-2V
4 to 12 volts single supply
Low power DIP op amp, suited to battery operation if required
Variable gain, unity to 10 via trimpot (dependent on rail V)
Swing as close to rail as practical without using a rail-to-rail amp
Drive resistive load 20 to 200 ohms (dependent on power transistor
used.)

Other specs are non-critical.

Are any of these, such as the wide supply range, inherently
contradictory to a predominantly fixed value circuit?

Any help would be very much appreciated.

Trev Morton

All purpose SS op amp
 

On Thu, 22 Mar 2007 21:35:33 +1100, Trevor Morton wrote:

I am still developing my abilities and find myself all too often
struggling with op amp design.

Can anyone here suggest an "all purpose" amplifier built around a
readily available op amp and transistor follower that will operate
within the specifications below? Preferably without changes in
componentry except to upgrade the power transistor depending upon load
requirements.

DC coupled with frequency response DC to 20KHz
Input signal level 1-2V
4 to 12 volts single supply
Low power DIP op amp, suited to battery operation if required
Variable gain, unity to 10 via trimpot (dependent on rail V)
Swing as close to rail as practical without using a rail-to-rail amp
Drive resistive load 20 to 200 ohms (dependent on power transistor
used.)

You've just described the National LM386, as if you'd copied that off
the data sheet:
http://www.national.com/ds/LM/LM386.pdf

Have Fun!
Rich

All purpose SS op amp
 

I thought the LM386 was an audio amp (not to DC), but had a try anyway
with a 5Hz squarewave. Distortion was pretty bad. Also, regardless of
frequency, I only get 1V swing out with 6V in. It is supposed to have
a built-in gain of 20. This I don't understand.

Getting back to my original post. Is it possible to have a single op
amp design that will cover the variation in supply voltage and load
described?

Thanks for any advice.

Trevor Morton



On Thu, 22 Mar 2007 23:46:38 GMT, Rich Grise wrote:

On Thu, 22 Mar 2007 21:35:33 +1100, Trevor Morton wrote:

I am still developing my abilities and find myself all too often
struggling with op amp design.

Can anyone here suggest an "all purpose" amplifier built around a
readily available op amp and transistor follower that will operate
within the specifications below? Preferably without changes in
componentry except to upgrade the power transistor depending upon load
requirements.

DC coupled with frequency response DC to 20KHz
Input signal level 1-2V
4 to 12 volts single supply
Low power DIP op amp, suited to battery operation if required
Variable gain, unity to 10 via trimpot (dependent on rail V)
Swing as close to rail as practical without using a rail-to-rail amp
Drive resistive load 20 to 200 ohms (dependent on power transistor
used.)

You've just described the National LM386, as if you'd copied that off
the data sheet:
http://www.national.com/ds/LM/LM386.pdf

Have Fun!
Rich

All purpose SS op amp
 

Trevor Morton wrote:

I am still developing my abilities and find myself all too often
struggling with op amp design.

Can anyone here suggest an "all purpose" amplifier built around a
readily available op amp and transistor follower that will operate
within the specifications below? Preferably without changes in
componentry except to upgrade the power transistor depending upon load
requirements.

DC coupled with frequency response DC to 20KHz
Input signal level 1-2V
4 to 12 volts single supply
Low power DIP op amp, suited to battery operation if required
Variable gain, unity to 10 via trimpot (dependent on rail V)
Swing as close to rail as practical without using a rail-to-rail amp
Drive resistive load 20 to 200 ohms (dependent on power transistor
used.)

What you're desribing is an amplifier. NOT an op-amp.

Graham

All purpose SS op amp
 

On Fri, 23 Mar 2007 14:11:39 +0000, Eeyore
wrote:



Trevor Morton wrote:

I am still developing my abilities and find myself all too often
struggling with op amp design.

Can anyone here suggest an "all purpose" amplifier built around a
readily available op amp and transistor follower that will operate
within the specifications below? Preferably without changes in
componentry except to upgrade the power transistor depending upon load
requirements.

DC coupled with frequency response DC to 20KHz
Input signal level 1-2V
4 to 12 volts single supply
Low power DIP op amp, suited to battery operation if required
Variable gain, unity to 10 via trimpot (dependent on rail V)
Swing as close to rail as practical without using a rail-to-rail amp
Drive resistive load 20 to 200 ohms (dependent on power transistor
used.)

What you're desribing is an amplifier. NOT an op-amp.

---
Funny, it seems that's what he was asking for in his second
sentence.


--
JF

All purpose SS op amp
 

John Fields wrote:

Eeyore wrote:
Trevor Morton wrote:

I am still developing my abilities and find myself all too often
struggling with op amp design.

Can anyone here suggest an "all purpose" amplifier built around a
readily available op amp and transistor follower that will operate
within the specifications below? Preferably without changes in
componentry except to upgrade the power transistor depending upon load
requirements.

DC coupled with frequency response DC to 20KHz
Input signal level 1-2V
4 to 12 volts single supply
Low power DIP op amp, suited to battery operation if required
Variable gain, unity to 10 via trimpot (dependent on rail V)
Swing as close to rail as practical without using a rail-to-rail amp
Drive resistive load 20 to 200 ohms (dependent on power transistor
used.)

What you're desribing is an amplifier. NOT an op-amp.

---
Funny, it seems that's what he was asking for in his second
sentence.

So why "op amp" in the thread title and above "Low power DIP op amp....." ? I
suspect here may be some confusion in the OP's mind.


Graham

All purpose SS op amp
 

On Fri, 23 Mar 2007 15:17:15 +0000, Eeyore
wrote:



John Fields wrote:

Eeyore wrote:
Trevor Morton wrote:

I am still developing my abilities and find myself all too often
struggling with op amp design.

Can anyone here suggest an "all purpose" amplifier built around a
readily available op amp and transistor follower that will operate
within the specifications below? Preferably without changes in
componentry except to upgrade the power transistor depending upon load
requirements.

DC coupled with frequency response DC to 20KHz
Input signal level 1-2V
4 to 12 volts single supply
Low power DIP op amp, suited to battery operation if required
Variable gain, unity to 10 via trimpot (dependent on rail V)
Swing as close to rail as practical without using a rail-to-rail amp
Drive resistive load 20 to 200 ohms (dependent on power transistor
used.)

What you're desribing is an amplifier. NOT an op-amp.

---
Funny, it seems that's what he was asking for in his second
sentence.

So why "op amp" in the thread title and above "Low power DIP op amp....." ? I
suspect here may be some confusion in the OP's mind.

---
I see no confusion; he seems to know exactly what he wants.

The "Low power DIP op amp" is what he'll use to drive the output
transistor, the combination being the "all purpose" amplifier he
wants, while "All purpose SS op amp" is less clumsy than "All
purpose SS op amp amp."


--
JF

All purpose SS op amp
 

John Fields wrote:

Eeyore wrote:
John Fields wrote:
Eeyore wrote:
Trevor Morton wrote:

I am still developing my abilities and find myself all too often
struggling with op amp design.

Can anyone here suggest an "all purpose" amplifier built around a
readily available op amp and transistor follower that will operate
within the specifications below? Preferably without changes in
componentry except to upgrade the power transistor depending upon load
requirements.

DC coupled with frequency response DC to 20KHz
Input signal level 1-2V
4 to 12 volts single supply
Low power DIP op amp, suited to battery operation if required
Variable gain, unity to 10 via trimpot (dependent on rail V)
Swing as close to rail as practical without using a rail-to-rail amp
Drive resistive load 20 to 200 ohms (dependent on power transistor
used.)

What you're desribing is an amplifier. NOT an op-amp.

---
Funny, it seems that's what he was asking for in his second
sentence.

So why "op amp" in the thread title and above "Low power DIP op amp....." ? I
suspect here may be some confusion in the OP's mind.

---
I see no confusion; he seems to know exactly what he wants.

The "Low power DIP op amp" is what he'll use to drive the output
transistor, the combination being the "all purpose" amplifier he
wants, while "All purpose SS op amp" is less clumsy than "All
purpose SS op amp amp."

You reckon he only needs *one* output transistor ?

Graham

All purpose SS op amp
 

Trevor Morton wrote:

I am still developing my abilities and find myself all too often
struggling with op amp design.

Can anyone here suggest an "all purpose" amplifier built around a
readily available op amp and transistor follower that will operate
within the specifications below? Preferably without changes in
componentry except to upgrade the power transistor depending upon load
requirements.

Is there any particular reson you want to use discretes for the output stage ?
You'll increase complexity lots.


DC coupled with frequency response DC to 20KHz

Do you mean audio ?


Input signal level 1-2V
4 to 12 volts single supply

If it's a single supply you'll have to AC couple the signal ! Unless you want a
bridge tied load of course (more complicated).


Low power DIP op amp, suited to battery operation if required

Well, power dissipation is likely to be predominantly determined by any quiesent
current in the output stage (to avoid cross-over distortion) actually.


Variable gain, unity to 10 via trimpot (dependent on rail V)
Swing as close to rail as practical without using a rail-to-rail amp
Drive resistive load 20 to 200 ohms (dependent on power transistor
used.)

Other specs are non-critical.

Are any of these, such as the wide supply range, inherently
contradictory to a predominantly fixed value circuit?

Any help would be very much appreciated.

The simplest best bet might be to look at some car audio amplifier chips.

Graham

All purpose SS op amp
 

Trevor Morton wrote:

I thought the LM386 was an audio amp (not to DC), but had a try anyway
with a 5Hz squarewave. Distortion was pretty bad. Also, regardless of
frequency, I only get 1V swing out with 6V in. It is supposed to have
a built-in gain of 20. This I don't understand.

You have to tie a cap from ground to one of the gain set pins to get that.

Graham

All purpose SS op amp
 

On Fri, 23 Mar 2007 16:37:48 +0000, Eeyore
wrote:



John Fields wrote:

Eeyore wrote:
John Fields wrote:
Eeyore wrote:
Trevor Morton wrote:

I am still developing my abilities and find myself all too often
struggling with op amp design.

Can anyone here suggest an "all purpose" amplifier built around a
readily available op amp and transistor follower that will operate
within the specifications below? Preferably without changes in
componentry except to upgrade the power transistor depending upon load
requirements.

DC coupled with frequency response DC to 20KHz
Input signal level 1-2V
4 to 12 volts single supply
Low power DIP op amp, suited to battery operation if required
Variable gain, unity to 10 via trimpot (dependent on rail V)
Swing as close to rail as practical without using a rail-to-rail amp
Drive resistive load 20 to 200 ohms (dependent on power transistor
used.)

What you're desribing is an amplifier. NOT an op-amp.

---
Funny, it seems that's what he was asking for in his second
sentence.

So why "op amp" in the thread title and above "Low power DIP op amp....." ? I
suspect here may be some confusion in the OP's mind.

---
I see no confusion; he seems to know exactly what he wants.

The "Low power DIP op amp" is what he'll use to drive the output
transistor, the combination being the "all purpose" amplifier he
wants, while "All purpose SS op amp" is less clumsy than "All
purpose SS op amp amp."

You reckon he only needs *one* output transistor ?

---
That's what he wants. Can't you do it?


--
JF

All purpose SS op amp
 

On Fri, 23 Mar 2007 13:55:19 -0500, John Fields wrote:
On Fri, 23 Mar 2007 16:37:48 +0000, Eeyore
John Fields wrote:
Eeyore wrote:
John Fields wrote:
Eeyore wrote:
Trevor Morton wrote:

I am still developing my abilities and find myself all too often
struggling with op amp design.

Can anyone here suggest an "all purpose" amplifier built around a
readily available op amp and transistor follower that will operate
within the specifications below? Preferably without changes in
componentry except to upgrade the power transistor depending upon load
requirements.

DC coupled with frequency response DC to 20KHz
Input signal level 1-2V
4 to 12 volts single supply
Low power DIP op amp, suited to battery operation if required
Variable gain, unity to 10 via trimpot (dependent on rail V)
Swing as close to rail as practical without using a rail-to-rail amp
Drive resistive load 20 to 200 ohms (dependent on power transistor
used.)

What you're desribing is an amplifier. NOT an op-amp.

Funny, it seems that's what he was asking for in his second
sentence.

So why "op amp" in the thread title and above "Low power DIP op amp....." ? I
suspect here may be some confusion in the OP's mind.

I see no confusion; he seems to know exactly what he wants.

The "Low power DIP op amp" is what he'll use to drive the output
transistor, the combination being the "all purpose" amplifier he
wants, while "All purpose SS op amp" is less clumsy than "All
purpose SS op amp amp."

You reckon he only needs *one* output transistor ?

That's what he wants. Can't you do it?

Nat Semi has a pretty cool app note:
http://www.eetkorea.com/ARTICLES/200...6_AMD_AN03.PDF

Cheers!
Rich

All purpose SS op amp
 

I am sorry if my original post caused confusion. Yes, I am looking for
an op amp because of the DC requirement. The LM386 I tried to no
avail.

Phrasing it another way, why is there no predefined op amp/Darlington
configuration, or off-the-shelf power op amp, that can do the all same
things as the LM386 does with audio, but down to DC?

Single supply
Wide supplyvoltage range
DC coupling
Easily variable gain
Low power
Etc.

At first, I thought such specs might be mutually exclusive. However,
if there are such design limitations, they seem to be receeding fast.

For example, there is the "new" OPA569, rated at 2A. It meets all my
requirements except it only operates up to 5.5V. I need a range of 4
to 12V.

http://focus.ti.com/docs/prod/folders/print/opa569.html

Can someone explain, why can't something like this be done with a
CA3130 and a couple of transistors.

Trevor Morton





On Fri, 23 Mar 2007 17:23:09 +0000, Eeyore
wrote:



Trevor Morton wrote:

I am still developing my abilities and find myself all too often
struggling with op amp design.

Can anyone here suggest an "all purpose" amplifier built around a
readily available op amp and transistor follower that will operate
within the specifications below? Preferably without changes in
componentry except to upgrade the power transistor depending upon load
requirements.

Is there any particular reson you want to use discretes for the output stage ?
You'll increase complexity lots.


DC coupled with frequency response DC to 20KHz

Do you mean audio ?


Input signal level 1-2V
4 to 12 volts single supply

If it's a single supply you'll have to AC couple the signal ! Unless you want a
bridge tied load of course (more complicated).


Low power DIP op amp, suited to battery operation if required

Well, power dissipation is likely to be predominantly determined by any quiesent
current in the output stage (to avoid cross-over distortion) actually.


Variable gain, unity to 10 via trimpot (dependent on rail V)
Swing as close to rail as practical without using a rail-to-rail amp
Drive resistive load 20 to 200 ohms (dependent on power transistor
used.)

Other specs are non-critical.

Are any of these, such as the wide supply range, inherently
contradictory to a predominantly fixed value circuit?

Any help would be very much appreciated.

The simplest best bet might be to look at some car audio amplifier chips.

Graham

All purpose SS op amp
 

On Sat, 24 Mar 2007 07:48:15 +1100, Trevor Morton
wrote:

I am sorry if my original post caused confusion. Yes, I am looking for
an op amp because of the DC requirement. The LM386 I tried to no
avail.

Phrasing it another way, why is there no predefined op amp/Darlington
configuration, or off-the-shelf power op amp, that can do the all same
things as the LM386 does with audio, but down to DC?

Single supply
Wide supplyvoltage range
DC coupling
Easily variable gain
Low power
Etc.

At first, I thought such specs might be mutually exclusive. However,
if there are such design limitations, they seem to be receeding fast.

For example, there is the "new" OPA569, rated at 2A. It meets all my
requirements except it only operates up to 5.5V. I need a range of 4
to 12V.

http://focus.ti.com/docs/prod/folders/print/opa569.html

Can someone explain, why can't something like this be done with a
CA3130 and a couple of transistors.

---
Please bottom post.

The main reason you can't get what you want is because you're
specifying a single supply and DC coupling and expecting an output
which can swing negative.

For example, this circuit:


Version 4
SHEET 1 880 680
WIRE -192 64 -416 64
WIRE -80 64 -112 64
WIRE 64 64 -80 64
WIRE 336 64 144 64
WIRE -80 192 -80 64
WIRE -48 192 -80 192
WIRE 64 208 16 208
WIRE 176 208 144 208
WIRE -240 224 -272 224
WIRE -192 224 -240 224
WIRE -80 224 -112 224
WIRE -48 224 -80 224
WIRE 240 272 240 256
WIRE 336 272 336 64
WIRE 336 272 240 272
WIRE -416 288 -416 64
WIRE -240 288 -240 224
WIRE -80 288 -80 224
WIRE 240 304 240 272
WIRE -416 416 -416 368
WIRE -240 416 -240 368
WIRE -240 416 -416 416
WIRE -80 416 -80 368
WIRE -80 416 -240 416
WIRE -16 416 -16 240
WIRE -16 416 -80 416
WIRE 240 416 240 384
WIRE 240 416 -16 416
WIRE -416 480 -416 416
FLAG -416 480 0
FLAG -272 224 +12V
FLAG 240 160 +12V
FLAG -16 176 +12V
SYMBOL Opamps\\LT1055 -16 144 R0
WINDOW 0 30 88 Left 0
WINDOW 3 27 117 Left 0
SYMATTR InstName U1
SYMBOL npn 176 160 R0
SYMATTR InstName Q1
SYMATTR Value 2N3904
SYMBOL res 224 288 R0
SYMATTR InstName R2
SYMATTR Value 20
SYMBOL res -96 272 R0
SYMATTR InstName R3
SYMATTR Value 10K
SYMBOL res -96 208 R90
WINDOW 0 94 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL voltage -240 272 R0
WINDOW 0 -50 100 Left 0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 12
SYMBOL voltage -416 272 R0
WINDOW 0 -50 100 Left 0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value SINE(6 .1 10)
SYMBOL res -96 48 R90
WINDOW 0 -36 49 VBottom 0
WINDOW 3 -35 52 VTop 0
SYMATTR InstName R5
SYMATTR Value 1K
SYMBOL res 160 192 R90
WINDOW 0 -41 58 VBottom 0
WINDOW 3 -37 56 VTop 0
SYMATTR InstName R6
SYMATTR Value 1K
SYMBOL res 160 48 R90
WINDOW 0 -39 56 VBottom 0
WINDOW 3 -34 57 VTop 0
SYMATTR InstName R1
SYMATTR Value 10K
TEXT -396 450 Left 0 !.tran 1 uic


will do what you want, but because of the single supply and no
capacitor rule, the input signal must be offset and the output
signal will swing about a DC value, which will waste power in the
load as well as in the single (which is what you asked for) output
transistor.

The circuit list, above, is for LTSPICE, and if you don't have a
copy you can download one, free, at:

http://www.linear.com/designtools/software/

One caveat: the output transistor I used can't dissipate the power
needed to feed the 20 ohm load shown, but I didn't want to spend a
lot of time looking for the right one this early in the game.


--
JF

All purpose SS op amp
 

"Eeysore

Trevor Morton wrote:

I thought the LM386 was an audio amp (not to DC), but had a try anyway
with a 5Hz squarewave. Distortion was pretty bad. Also, regardless of
frequency, I only get 1V swing out with 6V in. It is supposed to have
a built-in gain of 20. This I don't understand.

You have to tie a cap from ground to one of the gain set pins to get that.



** No you don't - fool.

See the very first schem under Typical Applications.




....... Phil

All purpose SS op amp
 

"Trevor Morton"

I thought the LM386 was an audio amp (not to DC), but had a try anyway
with a 5Hz squarewave. Distortion was pretty bad. Also, regardless of
frequency, I only get 1V swing out with 6V in. It is supposed to have
a built-in gain of 20. This I don't understand.


** Try again - you got it fouled up somehow.

With a 4 volt supply, square wave drive and 33 ohm load ( no coupling cap),
the output is a clean. 2.6 volt p-p square wave at *any* frequency up to
20kHz.

With a 12 volt supply, same set up as above, the output swing is 10 volt
p-p.

Same p-p swings apply to a sine wave input as well.


BTW

Make sure your input signal does not have a DC offset.



........ Phil

All purpose SS op amp
 

On Fri, 23 Mar 2007 18:13:20 -0500, John Fields
wrote:

On Sat, 24 Mar 2007 07:48:15 +1100, Trevor Morton
wrote:

I am sorry if my original post caused confusion. Yes, I am looking for
an op amp because of the DC requirement. The LM386 I tried to no
avail.

Phrasing it another way, why is there no predefined op amp/Darlington
configuration, or off-the-shelf power op amp, that can do the all same
things as the LM386 does with audio, but down to DC?

Single supply
Wide supplyvoltage range
DC coupling
Easily variable gain
Low power
Etc.

At first, I thought such specs might be mutually exclusive. However,
if there are such design limitations, they seem to be receeding fast.

For example, there is the "new" OPA569, rated at 2A. It meets all my
requirements except it only operates up to 5.5V. I need a range of 4
to 12V.

http://focus.ti.com/docs/prod/folders/print/opa569.html

Can someone explain, why can't something like this be done with a
CA3130 and a couple of transistors.

---
Please bottom post.

The main reason you can't get what you want is because you're
specifying a single supply and DC coupling and expecting an output
which can swing negative.

For example, this circuit:


Version 4
SHEET 1 880 680
WIRE -192 64 -416 64
WIRE -80 64 -112 64
WIRE 64 64 -80 64
WIRE 336 64 144 64
WIRE -80 192 -80 64
WIRE -48 192 -80 192
WIRE 64 208 16 208
WIRE 176 208 144 208
WIRE -240 224 -272 224
WIRE -192 224 -240 224
WIRE -80 224 -112 224
WIRE -48 224 -80 224
WIRE 240 272 240 256
WIRE 336 272 336 64
WIRE 336 272 240 272
WIRE -416 288 -416 64
WIRE -240 288 -240 224
WIRE -80 288 -80 224
WIRE 240 304 240 272
WIRE -416 416 -416 368
WIRE -240 416 -240 368
WIRE -240 416 -416 416
WIRE -80 416 -80 368
WIRE -80 416 -240 416
WIRE -16 416 -16 240
WIRE -16 416 -80 416
WIRE 240 416 240 384
WIRE 240 416 -16 416
WIRE -416 480 -416 416
FLAG -416 480 0
FLAG -272 224 +12V
FLAG 240 160 +12V
FLAG -16 176 +12V
SYMBOL Opamps\\LT1055 -16 144 R0
WINDOW 0 30 88 Left 0
WINDOW 3 27 117 Left 0
SYMATTR InstName U1
SYMBOL npn 176 160 R0
SYMATTR InstName Q1
SYMATTR Value 2N3904
SYMBOL res 224 288 R0
SYMATTR InstName R2
SYMATTR Value 20
SYMBOL res -96 272 R0
SYMATTR InstName R3
SYMATTR Value 10K
SYMBOL res -96 208 R90
WINDOW 0 94 56 VBottom 0
WINDOW 3 32 56 VTop 0
SYMATTR InstName R4
SYMATTR Value 10K
SYMBOL voltage -240 272 R0
WINDOW 0 -50 100 Left 0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 12
SYMBOL voltage -416 272 R0
WINDOW 0 -50 100 Left 0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value SINE(6 .1 10)
SYMBOL res -96 48 R90
WINDOW 0 -36 49 VBottom 0
WINDOW 3 -35 52 VTop 0
SYMATTR InstName R5
SYMATTR Value 1K
SYMBOL res 160 192 R90
WINDOW 0 -41 58 VBottom 0
WINDOW 3 -37 56 VTop 0
SYMATTR InstName R6
SYMATTR Value 1K
SYMBOL res 160 48 R90
WINDOW 0 -39 56 VBottom 0
WINDOW 3 -34 57 VTop 0
SYMATTR InstName R1
SYMATTR Value 10K
TEXT -396 450 Left 0 !.tran 1 uic


will do what you want, but because of the single supply and no
capacitor rule, the input signal must be offset and the output
signal will swing about a DC value, which will waste power in the
load as well as in the single (which is what you asked for) output
transistor.

The circuit list, above, is for LTSPICE, and if you don't have a
copy you can download one, free, at:

http://www.linear.com/designtools/software/

One caveat: the output transistor I used can't dissipate the power
needed to feed the 20 ohm load shown, but I didn't want to spend a
lot of time looking for the right one this early in the game.

---
This is better:


Version 4
SHEET 1 880 680
WIRE -16 -32 -336 -32
WIRE 240 -32 -16 -32
WIRE -448 0 -480 0
WIRE -272 0 -368 0
WIRE -336 32 -336 -32
WIRE -608 48 -640 48
WIRE -480 48 -480 0
WIRE -480 48 -528 48
WIRE -368 48 -480 48
WIRE -272 64 -272 0
WIRE -272 64 -304 64
WIRE -208 64 -272 64
WIRE -80 64 -128 64
WIRE 64 64 -80 64
WIRE 272 64 144 64
WIRE -368 80 -480 80
WIRE -240 160 -432 160
WIRE -16 160 -16 -32
WIRE -16 160 -240 160
WIRE 240 160 240 -32
WIRE -432 192 -432 160
WIRE -16 208 -16 160
WIRE -80 224 -80 64
WIRE -48 224 -80 224
WIRE 64 240 16 240
WIRE 192 240 144 240
WIRE -240 256 -240 160
WIRE -192 256 -240 256
WIRE -80 256 -112 256
WIRE -48 256 -80 256
WIRE 240 272 240 256
WIRE 272 272 272 64
WIRE 272 272 240 272
WIRE -480 304 -480 80
WIRE -432 304 -432 272
WIRE -432 304 -480 304
WIRE -640 320 -640 48
WIRE -432 320 -432 304
WIRE -240 320 -240 256
WIRE -80 320 -80 256
WIRE 240 320 240 272
WIRE -640 448 -640 400
WIRE -432 448 -432 400
WIRE -432 448 -640 448
WIRE -336 448 -336 96
WIRE -336 448 -432 448
WIRE -240 448 -240 400
WIRE -240 448 -336 448
WIRE -80 448 -80 400
WIRE -80 448 -240 448
WIRE -16 448 -16 272
WIRE -16 448 -80 448
WIRE 240 448 240 400
WIRE 240 448 -16 448
WIRE -640 512 -640 448
FLAG -640 512 0
SYMBOL res -96 304 R0
WINDOW 0 -40 46 Left 0
WINDOW 3 -47 77 Left 0
SYMATTR InstName R3
SYMATTR Value 10K
SYMBOL res -96 240 R90
WINDOW 0 -33 58 VBottom 0
WINDOW 3 -33 59 VTop 0
SYMATTR InstName R4
SYMATTR Value 10k
SYMBOL voltage -240 304 R0
WINDOW 0 -50 100 Left 0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V1
SYMATTR Value 12
SYMBOL voltage -640 304 R0
WINDOW 0 -50 100 Left 0
WINDOW 3 24 104 Invisible 0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
SYMATTR InstName V2
SYMATTR Value SINE(0 .4 10)
SYMBOL res -112 48 R90
WINDOW 0 -36 49 VBottom 0
WINDOW 3 -35 52 VTop 0
SYMATTR InstName R5
SYMATTR Value 1K
SYMBOL res 160 224 R90
WINDOW 0 -27 57 VBottom 0
WINDOW 3 -26 56 VTop 0
SYMATTR InstName R6
SYMATTR Value 1K
SYMBOL res 160 48 R90
WINDOW 0 -39 56 VBottom 0
WINDOW 3 -34 57 VTop 0
SYMATTR InstName R1
SYMATTR Value 10K
SYMBOL res -352 -16 R90
WINDOW 0 -36 54 VBottom 0
WINDOW 3 -29 58 VTop 0
SYMATTR InstName R7
SYMATTR Value 10k
SYMBOL res -512 32 R90
WINDOW 0 -37 54 VBottom 0
WINDOW 3 -34 56 VTop 0
SYMATTR InstName R8
SYMATTR Value 10k
SYMBOL res -416 288 R180
WINDOW 0 -59 74 Left 0
WINDOW 3 -51 44 Left 0
SYMATTR InstName R10
SYMATTR Value 9k
SYMBOL res -448 304 R0
SYMATTR InstName R9
SYMATTR Value 3k
SYMBOL nmos 192 160 R0
WINDOW 0 -34 47 Left 0
WINDOW 3 -76 -9 Left 0
SYMATTR InstName M1
SYMATTR Value IRF6635
SYMBOL Opamps\\LT1218 -336 0 R0
WINDOW 0 -76 100 Left 0
WINDOW 3 -100 126 Left 0
SYMATTR InstName U3
SYMBOL Opamps\\LT1218 -16 176 R0
WINDOW 0 32 86 Left 0
WINDOW 3 9 115 Left 0
SYMATTR InstName U1
SYMBOL res 224 304 R0
WINDOW 0 -40 46 Left 0
WINDOW 3 -36 74 Left 0
SYMATTR InstName R2
SYMATTR Value 20
TEXT -624 480 Left 0 !.tran 1 uic


The source is DC coupled and ground-referred, and since you're using
a single positive DC supply, the output is operating
emitter-follower class A and varies about a quiescent Vcc/2.



--
JF