On Thu, 03 Mar 2011 22:17:46 -0600, John - KD5YI
wrote:
On 3/3/2011 12:04 AM, John Larkin wrote:
On Wed, 02 Mar 2011 22:45:48 -0600, John -
wrote:
On 3/2/2011 10:24 PM, John Larkin wrote:
On Wed, 02 Mar 2011 22:06:41 -0600, John -
wrote:
On 3/2/2011 8:52 PM, John Larkin wrote:
On Wed, 02 Mar 2011 20:40:27 -0600, John -
wrote:
On 3/2/2011 8:32 PM, John Larkin wrote:
On Wed, 2 Mar 2011 17:59:58 -0800 (PST), Bill Sloman
wrote:
On Mar 3, 2:11 am, John Larkin
wrote:
On Wed, 02 Mar 2011 18:36:25 -0600, John Fields
wrote:
On Wed, 02 Mar 2011 08:40:42 -0800, John Larkin
wrote:
I've always sort of liked the classic "GE" tape head/mic preamp
circuit:
ftp://jjlarkin.lmi.net/GEcircuit.jpg
but it occurred to me that it might also make a nice headphone amp...
ftp://jjlarkin.lmi.net/GE_headphone_amp.JPG
Audio tends to be nonsense, but at least the audio guys have fun
playing with circuits, whether they make a lot of sense or not.
John
---
Even though you scorn and ridicule audio, there's nothing wrong with
anyone seeking perfection there, just as there's nothing wrong with
your search for perfection in the genre which pleases _you_ to pursue.
So, speaking of fun, why don't you do a complete design and assign
values to the circuit components and identify the semiconductors?
You're not playing the game. You are sitting in the henhouse, clucking
about the people who do.
He's not playing your game, which involves telling John Larkin how
cute his circuits are.
He's not designing circuits, which is what this newsgroup is about.
You aren't either. Both of you start to cluck and peck when people do
design circuits. No surprise.
Or is that legwork _we're_ supposed to do in order to flesh out your
divine revelation?
Chickenleg work!
It's half the story - a few component values make it a lot easier to
work out what a circuit is doing.
You can't look at a circuit this simple and see what it's doing? OK,
no surprise.
John
Well, I thought designing a circuit included supplying component values.
No?
I posted topologies. Values can be scaled to the application, but you
need a topology first. If I were actually going to build this, for
money, of course I'd have to define specs and then compute values.
That's just grunt work.
John
Not really. I have a few circuits I could throw out and claim that they
are topologies and you would not be able to use them without values.
Granted, mine are more complex than the one being discussed, but I'm
hoping to make a point.
John (not Larkin)
I think circuit topologies are fun to play with. Lots of textbooks
show, and discuss, circuits without explicit values. Once you have a
topology, then you can proceed to specs and component values.
If you think all circuits should be posted with values, post some.
John
You are correct, John. Now you have a topology. Please post the
component values.
Thanks,
John
Given i/o specs, the DC analysis is simple. But there are two AC
aspects that are sort of interesting: the lf response, and loop
stability. I'm sort of disappointed that nobody has commented on
either.
As I'm disappointed in how many people want to whine and cluck about
personalities, and avoid actually discussing electronics.
John
Okay, I put some values to it. It looks like a nice circuit, I admit.
Good gain, low distortion, reasonable input impedance. Mind you, I
didn't try to optimize it. I did notice that the feedback took higher
than expected resistance and I was a bit surprised that the emitter
capacitor of the output stage made the response do a camel hump at the
beginning if too high.
Yeah, C3 gives the overall amp response a low frequency bump, and C1
and C2 each contribute a low frequency rolloff. They all have to be
balanced to make it flat. Probably eliminating C3 is a good idea, if
the DC biasing still works. When I used this as a tape head preamp,
the LF boost was an asset, part of the tape head response
equalization.
R2 could be a lot lower. The open-loop voltage gain of Q1 is just
R5/R2, which is only 5, which is pretty low... even lower when it's
loaded by Q2. Or, another way to look at it, R2 kills the
transconductance of Q1, and adds noise.
If you do my power amp version, with a mosfet for Q2 and an inductor
for R4, there's another LF rolloff and the loop stability situation is
horrifying.
John