On Thu, 7 Jun 2012 21:54:21 +0100, "Ian Field"
wrote:
"Jim Thompson" wrote in
message ...
On Thu, 7 Jun 2012 15:32:20 -0500, "Dave" wrote:
"Jim Thompson" wrote
in
message ...
On Tue, 5 Jun 2012 22:12:30 -0400, "Tom Del Rosso"
wrote:
Jim Thompson wrote:
On Tue, 5 Jun 2012 18:28:22 -0400, "Tom Del Rosso"
wrote:
Jim Thompson wrote:
On Wed, 23 May 2012 15:40:17 -0500, "Dave"
wrote:
Posted a while back about a project I am trying to concoct- an
intercom for my front door- and have made some progress.
Unfortunately I hit a speed bump when I added transistor Q4.
Now it only gives me noise at the output, and lots and lots of
that. Capacitors are all 100uF 35V, which I am thinking may be
the problem (maybe the last couple need to be 50 or 75V?)
Originally thought I might be overdriving Q4, so I replaced it
with a 2N5296 from my junkbox, but that just doubled the volume
of the noisy output. If anyone sees something I should but
don't, please post. The only thing I can think of is upping the
voltage on C8 and C9.
Any help is *greatly* appreciated...
Dave
Back up and do a little math. Calculate the bias current in that
last stage. (In fact, calculate all your stage biases.)
In my head, it's 14ma. That can't be right. The calc concurs. Is
that a little bit too much?
Aren't the emitter caps about 10 times as big as needed?
Ian did notice that he was just throwing gain at the problem though.
Yep, I was stunned... Ian said something cogent. But his buddy, Dave,
is beyond all hope... rude little POS.
I don't have AoE in reach, but I don't think they mention bias current
in
their approach to design. They approach it with the rule of thumb that
the
input impedance should be 10x the output impedance of the previous
stage.
Similar. (The input impedance of the OP's stages are only slightly
higher
than the previous output impedance.)
I'd like to know if you use any rules of thumb for this sort of thing.
Or
is everything just optimized by multi-variable calculus? 
I don't know if there are "rules of thumb"... maybe just calculate
rather than doing a NOLA white-trash guess ?:-)
...Jim Thompson
Does it really make you feel good to talk that way about other people,
calling someone you don't know a POS, and white-trash? Personally, I
think
it says a lot more about you than it does about me.
And no, I don't know anything about the calculations involved in anything
as
simple as an audio amp. Like I said, I'm making this up as I go along. I
don't know anything. I'm just trying to learn.
Dave
I tried to help, suggesting you calculate the bias currents. Rather
than asking what I meant, if you're "just trying to learn", you
smart-mouthed.
And I don't respond well to smart-mouthed brats... it's enough of a
problem to deal with Larkin ;-)
You declared war on JL by being a spitefull old fart.
Take care now - you're way past fighting on 2 fronts.
Look at his posts. Nothing but boasting about how smart he is, how
many things he's done, how many great ideas he has. But no content, no
help, nothing but the occasional Spice graphs from who-knows-what
secret circuits. He apparently expects all deference due to a
self-declared "Master Circuit Designer" and gets all hen-squawkey when
he doesn't get it. He doesn't seem to be interested in electronics at
all.
He doesn't "try to help", he just tries to inflate his ego. It's not
working. Sad excuse for "war."
--
John Larkin Highland Technology, Inc
jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro acquisition and simulation