Unusual Bias Method

Why did you post the 1 KHz version? It doesn't work.

The thetaJA is much less, and there is 116mV of margin you seem to be missing.

Nope. You're wrong there. Plastic transistors of that era were failing leaky.

If R14 varies 5%, the voltage across R1 varies 5%, likewise if R10 varies 5%, the voltage across R5 varies 5%, the 30:1 has no meaning.

To ensure Q3 turns off on the down-stroke.

You're missing the Vbe deltas and how it works in general. Run the LTspice list... there's 116mV to play with before you can lose the Q3 current.

Yes. But it's you who are missing how that mirror bias works. After I do another chandelier ;-) I'll post the HAND math. ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

Run my DC bias sim. It's easy, no subcircuits or Spice hacks.

Nominal Q3 current is 59 uA.

Move R14 low by 5%, it drops to 29 uA.

Then push R1 up 5%, and you get 13 uA.

Now skew R10/R5 too. You can pretty much turn off Q3.

You seem to be counting on 5% resistors to be within about 1%. Is that Good Engineering Practise?

OK, return to ideal values, and increase the temperature of Q2 by 30C, which is conservative. The Q3 current drops by about a factor of 4.

Not good, especially in combinations!

OK, let's take a break. You hang lights and we'll do a half-day at Squaw Valley. We've only had about a foot of snow this season, but it's cold at night and the big ski areas are making snow. We talked to the operations guy at Northstar, and he said that they spend $75,000 a night to make snow.

Just to show concept. You apparently thought it was to start a fight.

Electrician's box protrudes from ceiling :-( Grrrrr! ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

I don't have mine anymore, but I had 150 watts in there ?

Greg

What it looked like 3 years ago. I bought it new.

Greg

I always wire things hot. It's more interesting.

Time to let this one go Jim.

I certainly don't (try to). I've gotten bitten from a neutral more than once. I don't like such surprises when I'm on a ladder.

The place we rented in Cambridge, when I was an MIT student, had wiring on ceramic stand-offs. And a smaller fuse on common than on hot... as I found out... my standard student wiring procedure was... blow the fuse and do your wiring before someone replaces it... but I got bit this time :-( ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

That's a keeper.

Cheers, James Arthur

Don't believe her. That's what they tell you, then they give you cooties.

As Sherlock said, that's elementary, dear Watson.

(My sister shamed me to no end, chasing boys and spreading the contagion. Several besieged targets parlayed with me, hoping I'd intercede.

"And get cootilized (i.e., infected) myself? No thank you!")

Cheers, James Arthur

The main ingredients including models...

To simulate my circuit in LTspice, open a text editor and type the following...

• Jim Thompson's 1977 Z Amplifier

* ** Analysis setup ** .tran 0 10m 0 100n .OPTIONS ITL1=1500 .OPTIONS ITL2=2000 .OPTIONS ITL4=1000 .OPTIONS STEPGMIN .OP X1 IN OUT VCC 0 My_1977_Z_Amp VCC VCC 0 13.3V VIN IN 0 SIN 0 4 1K 0 0 0 .INC "C:\InsertYourPathToCopyOf\My_1977_Z_Amp.sub"

• .END

Since those posts, I've fixed the bias droop that occurs under long continuous amplitude tones. (You remember, that fault that Larkin so gratuitously stuffed up my nose ;-)

I'll post the modification along with a number of extra simulations, and a functional description, once I get done with honey-do projects ;-) ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

Oooops! Forgot to copy this part...

Save as whatever name rings your chime, say...

"JimThompson'sMarvelousAmplifier.cir" >:-}

Then open LTspice. On the Tools/Control Panel/Save Defaults section check both Save Subcircuits... check-boxes.

Then Open "JimThompson'sMarvelousAmplifier.cir"

Then Run

View whatever node voltage or device current you like.

...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

The "new and improved" version is much better... even survives selective resistor ratios designed to kill it. And the mods are quite trivial. I'll post as soon as I can get to writing up a functional description. (Including a LTspice run-able listing.) ...Jim Thompson

--
| James E.Thompson                                 |    mens     | 
| Analog Innovations                               |     et      | 
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    | 
| San Tan Valley, AZ 85142   Skype: Contacts Only  |             | 
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  | 
| E-mail Icon at http://www.analog-innovations.com |    1962     | 
              
I love to cook with wine.     Sometimes I even put it in the food.

scheme.

in

Plus,

Maybe i will stuff it into LTspice, and look at it that way. Would i need good device models for that? If so, would please post them? I suspect that i could just use appropriate common parts in the LTspice standard libraries, but which ones?

?-)

In other words, it survives 5% resistors being 5% resistors?

And the mods are quite

So the Master Circuit Designer, the "biasing expert", screws up now and then.

Don't forget about Q2 self-heating.

Is it going to servo with a continuous 1 KHz input?

That is just dirty pool Jim. That is so sneaky that i would proud it if i had done it.

?-)

I calculated (well, simulated) 22 mA. That's about the current through R14, and it is a mirror after all. The drop across Q2 is maybe 6 volts or so. So, around 130 milliwatts. Assuming 200 K/W for a TO92, Q2 self-heats maybe 26C. Multiply that by 2.5 mV/degC and its Vbe is 66 mV less than that of its nearby friends. The circuit runs with 13 mV nominal across R3!

Hint: this is Expert biasing!

It's bad enough that Jim is redesigning it. Should be fun.