Jim Weir: help to add car radio to aviation audio panel music input

Didn't spend too much time in engineering school, didja?

Oh here we go. Somebody dares to question the great Jim Weir and is going
to catch a rash of it. His next post will tell us again how many years he's
been doing electronics and how anybody not wanting to use their real name on
usenet is a coward.

Asking you for help on usenet is like calling into a radio talk show
psychologist. While the psychologist is usually right, the caller soon
becomes very sorry he asked.

Scott wrote:

Didn't spend too much time in engineering school, didja?

Oh here we go. Somebody dares to question the great Jim Weir and is going
to catch a rash of it. His next post will tell us again how many years he's
been doing electronics and how anybody not wanting to use their real name on
usenet is a coward.

Asking you for help on usenet is like calling into a radio talk show
psychologist. While the psychologist is usually right, the caller soon
becomes very sorry he asked.

Yeah, I really hated it in school when the teachers made you think...

Shame they didn't do it more often...

I answered the person asking for help straight up with several answers that
solved his problem. What is your beef with that?

If you are talking about the guy that answered without doing the homework,
what is your beef with that?


Jim


Asking you for help on usenet is like calling into a radio talk show
psychologist. While the psychologist is usually right, the caller soon
becomes very sorry he asked.

Without all the name calling here's what I took about a minute to do:

Stereo preamp out: 4V, into 10K impedance
Audio panel input : 500mV, into 510ohm impedance.

Using formula :P=V^2/R I get

Stereo preamp outputs 1.6mW=2dBm
Audio panel plays full volume at .5mW= -3dBm

So we're in the ball park. You've got a little more power (about 5dB)
coming out of the preamp, but that's a a nice place to be because its
easy to lose power, hard to add it (you need to do crazy stuff like put
in amplifiers ;^) ).

Regarding formal engineering education, unless you're Dr. Weir, I win
that contest which really shouldn't be a requirement to participate in
a forum like this anyway.

Stereo preamp out is almost always given as volts peak-to-peak. The person
giving us the question stated that the audio panel input voltage was rms.
You will note that I converted into like units in my original post. If
Alpine DID give their output in RMS, then you will note that they are trying
to swing within less than a volt to the 12 volt rail and ground -- and I
can't conceive of any quality audio manufacturer trying to do that.

We can go either way, but the easy way is to convert the p-p to rms. 4V pp
= 1.4 volts RMS. 1.4^2 / 10E3 = 200 uW.

Audio panel plays full volume with 0.5^2 / 510 = 500 uW (in round numbers).

Seems to me we are just a bit short here. No transformer is 100% efficient,
so the problem gets worse as we go along. We start off life being down (10
log (500 uW/200uW)) (about -4 dB) and any passive solution simply adds to
the problem.

Let's give you the benefit of the doubt. Let's say that Alpine has their
act together and gave the output voltage as RMS. The equation then tells us
(as you noted) that we have 1.6 mW output and need 500 uW input, or an
excess of 5 dB. Let's see if we can practically do the solution you
propose.

You have to design for people who don't have access to their own transformer
factory as well as those in East Undershirt who only have access via mail
order, so let's examine the usual suspects.

Rat Shack has nothing of the kind.

Mouser has a few, the 42TU011 being the best of the bunch. However, if you
examine the curves of the transformer, you find that the frequency response
down in the bass is particularly terrible. The 3 dB points are given as 300
Hz and 3.4 kHz. respectively, so this great little Alpine tuner has turned
itself into a tin horn. I find that solution unacceptable.

Digi-Key is no joy, as is LKG/Philmore, Jameco, and half a dozen other
lesser lights.

One possible jury-rig solution may be to use a filament transformer as an
audio transformer to get the low frequency end, but if you have ever tried
this, you find that the high end falls off WELL before a couple of
kilohertz...lots of bass, but dearly lacking in treble. Not a solution.
Not only is it not a solution, but with a hunk of iron that will get down
into the tens of hertz range, you start picking up a fair amount of weight.
Remember, this is an AVIATION as well as an ELECTRONIC problem.

As to power, the fellow already needs to pick off power for both the tuner
and the audio panel. Stuffing a tiny single stage transistor impedance
converter inside either of these boxes and tying into the existing power
coming into the box isn't a great problem. NPN transistors can be had by
the bucketful at your local Hobby Shack store, as can a couple of resistors
and a couple of capacitors. Weight? A couple of ounces with enough left
over to stuff a flea's navel.

As to the Dr. Weir, no, I dropped out of the doctoral program when I
realized that what was being taught was roughly five to seven years behind
the stuff that I had already done. That wasn't what I wanted to waste my
time on ... and my own company wasn't going to pay me one cent more for a
doctorate. I'm the "dumb" one of the family; both my brothers have their
PhD.

I find your solution, while theoretically possible, to be difficult to
impossible to do practically.

Jim







wrote in message
oups.com...
Without all the name calling here's what I took about a minute to do:

Stereo preamp out: 4V, into 10K impedance
Audio panel input : 500mV, into 510ohm impedance.

Using formula :P=V^2/R I get

Stereo preamp outputs 1.6mW=2dBm
Audio panel plays full volume at .5mW= -3dBm

So we're in the ball park. You've got a little more power (about 5dB)
coming out of the preamp, but that's a a nice place to be because its
easy to lose power, hard to add it (you need to do crazy stuff like put
in amplifiers ;^) ).

Regarding formal engineering education, unless you're Dr. Weir, I win
that contest which really shouldn't be a requirement to participate in
a forum like this anyway.

RST Engineering wrote:

As to the Dr. Weir, no, I dropped out of the doctoral program when I
realized that what was being taught was roughly five to seven years behind
the stuff that I had already done. That wasn't what I wanted to waste my
time on ... and my own company wasn't going to pay me one cent more for a
doctorate. I'm the "dumb" one of the family; both my brothers have their
PhD.

Dumb isn't lacking a Ph.D., it is having your own company. :-)

Matt

"Matt Whiting" wrote in message
...
RST Engineering wrote:

As to the Dr. Weir, no, I dropped out of the doctoral program when I
realized that what was being taught was roughly five to seven years
behind
the stuff that I had already done. That wasn't what I wanted to waste
my
time on ... and my own company wasn't going to pay me one cent more for
a
doctorate. I'm the "dumb" one of the family; both my brothers have
their
PhD.

Dumb isn't lacking a Ph.D., it is having your own company. :-)

Matt

Amen.... (having been there).....

On the one hand:

B.S. = Bull ****
M.S. = More ****
PHD = Piled Higher and Deeper

But the truth is:

(Sung to the tune of the Mickey Mouse theme song)

M..I..T
P..H..D..
M..O..N..E..Y..!!!

8-)........................

Netgeek wrote:
"Matt Whiting" wrote in message
...

RST Engineering wrote:


As to the Dr. Weir, no, I dropped out of the doctoral program when I
realized that what was being taught was roughly five to seven years

behind

the stuff that I had already done. That wasn't what I wanted to waste

my

time on ... and my own company wasn't going to pay me one cent more for

a

doctorate. I'm the "dumb" one of the family; both my brothers have

their

PhD.

Dumb isn't lacking a Ph.D., it is having your own company. :-)

Matt


Amen.... (having been there).....

On the one hand:

B.S. = Bull ****
M.S. = More ****
PHD = Piled Higher and Deeper

But the truth is:

(Sung to the tune of the Mickey Mouse theme song)

M..I..T
P..H..D..
M..O..N..E..Y..!!!


Yes, but the sad part is that an MBA will get you even more money for
less upfront time investment.


Matt

RST Engineering wrote:

jury-rig solution

Okay, this is way off topic but I have to know the history of this
expression. It is my understanding that the correct term is
"Jerry-rigged" or "Jerryrigged" which is based on the pejorative term
"Jerry" for Japanese, used during WWII. The way it was told to me is
that near the end of WWII Jerry (the Japanese) were badly beaten and
much of their equipment was non-operational. However the Japanese
were very resourceful at doing whatever it took to get things working.
So people started talking about "Jerry-rigging" things.

Obviously the term "Jerry" is racially insensitive which probably led
to the alteration of the term. However, isn't "Jerryrigged" a
complimentary term when you consider it implies resourcefulness?
Lemmonaide from lemmons?

So, when I read Jim's post I did a quick Google search and found a
different explanation:

Most sources claim that the origin of the word jerryrig is unknown,
but William and Mary Morris, in Dictionary of Word and Phrase Origins
(see my bibliography), indicate that the term is likely a corrupted
form of juryrig, which referred to temporary rigging on a ship. Jury
as used in juryrig (which arose in the 17th century) likely comes from
Old French ajurie `help, relief.' The 'temporarily repair' sense
remained with the word juryrig, while its nautical roots faded away.
The vulgar expression to which you refer is likely patterned after
juryrig and jerryrig.

To say that something is "jerryrigged" is to mix idioms a bit,
because the proper term is "jerrybuilt." A "jerrybuilder," a term
dating to 19th-century England, was originally a house builder who
constructed flimsy homes from inferior materials. The "jerry" in the
term may have been a real person known for the practice, or may be a
mangled form of "jury," as in "jury-rigged." I tend to think that
"jerrybuilt" arose separately from "jury-rig" simply because their
senses are slightly different. Something that is "jury-rigged" is
concocted on the spur of the moment to meet an emergency, but
something "jerrybuilt" is deliberately constructed of inferior
materials to turn a quick buck.


So, what do folks out there think?

Carl.

PS- Isn't it strange what catches your interest sometimes?

In article ofC9e.56373$lz2.17509@fed1read07,
Carl / KG6YKL wrote:
RST Engineering wrote:

jury-rig solution

Okay, this is way off topic but I have to know the history of this
expression. It is my understanding that the correct term is
"Jerry-rigged" or "Jerryrigged" which is based on the pejorative term
"Jerry" for Japanese, used during WWII. The way it was told to me is
that near the end of WWII Jerry (the Japanese) were badly beaten and
much of their equipment was non-operational. However the Japanese
were very resourceful at doing whatever it took to get things working.
So people started talking about "Jerry-rigging" things.

All well and good, except for one fact. "Jerry" referred to the _Germans_,
not the Japanese.

Oh, yeah, a second "inconvenient" fact -- the term _was_ in use *before*
WWII.

Obviously the term "Jerry" is racially insensitive which probably led
to the alteration of the term.

Obviously "nonsense". grin

However, isn't "Jerryrigged" a
complimentary term when you consider it implies resourcefulness?

It's usually used in a mildly disparaging way -- implying an "ad hoc"
solution of a _temporary_ nature, and, thus, a lack of durability,
Something where it will be necessary to "come back later, and do it right".

In an _emergency_ situation, such methodologies are justified.
In a non-emergency, it's because somebody wasn't willing to expend
the effort to 'do it right' the _first_ time; with the expectation that
"somebody else" will be responsible for 'making it right' later.

Thus, the pejorative meaning -- because it is _usually_ applied to
"non-emergency" constructs.