Hi Sean,

Sounds like you are doing spice modeling. I'm not a big fan of that method,
being a former teacher I feel it is much more important to get a feel for
the real parts before simulating them.

John Payson read me correctly when he said I meant to design the amplifier
so it depended little on the characteristics of the transistors. Whether
you are designing an amp with negative feedback, or one with a dc servo, or
with degenerative feedback, anything with multiple stages cannot be
predicted accurately enough to rely on transistor specs. This is probably
even more true with single transistor amplifiers. For instance, if you
build a one-stage common-emitter amp, you have the choice of running with
as much gain as the transistor has, or reducing the gain to a calculable
number by using a resistor in the emitter(degenerative feedback). Your
choice, but the performance with regenerative feedback will be predictable,
and it's a better amplifier, too(as far as linearity, distortion and
bandwidth).

I've strayed from PICs a little, so you might reference
http://www.bobblick.com/bob/stamp/tonedec.html because it's a project that
has a PIC-based Basic Stamp in it(see, I got PICs into this email!), and a
single transistor mic preamp of the crappy type, getting as much gain out
of a single transistor as possible, but it works well enough for DTMF tones.

Cheerful regards,

Bob


At 01:26 PM 7/8/97 -0400, you wrote:
>At 09:21 PM 8/16/97 -0700, you wrote:
>>At 11:38 PM 8/16/97 -0400, you wrote:
>>
>>>What am I supposed to do if I want to accurately design an amplifier
without
>>>guesswork?
>>
>>Parameters vary widely due to operating conditions and manufacturing. An
>>amplifier should not rely on transistor specs to define its operation. Most
>>transistor spec sheets reflect this - they will list the limits that the
>>transistor can withstand, and the design is up to you.
>>
>>Manufacturers will also quite often target a series of parts for a specific
>>use - you should familiarize yourself with them.
>>
>>Cheerful regards,
>>
>>Bob
>
>Thanks for the reply, Bob.
>I guess you are saying that it is up to the actual user of the components to
>measure their characteristics. For me, there is only one problem with this,
>I am at this point only an electronics hobbist. I am studying to become an
>electrical engineer. I don't have the money to buy the test equipment needed
>to measure all the characteristics I need to know.
>I do need to know the H parameters of a transistor for an amplifier because
>the input/output impedances depend upon this. I don't see how an amplifier
>can avoid relying on transistor specs.
>Also, I realize that most parts have a specific target use. However, even if
>I know that, say, a 2N2222 is a general purpose amp, this just guides me in
>choosing this component for my application. I still need to know its
>characteristics.
>
>Thanks,
>Sean
>
>

http://www.bobblick.com/