Hi Group,

Got a 706 which has a 500 or 600 ohm mic input impedance. I have a D104 which
best I can tell has a high output impedance.

If I use a 60Hz step down transformer, say, 120V in gives 10v out, the turn
ratio is 120/10 or 12:1. Given that I attach the mic output to the primary and
the rig on the secondary, this should step down the impedance by a factor of
12^2 or 144 so that a D104 with 50K on the output is now seen as about 400 ohm.

Here are a few questions,

1: Will a 60Hz transformer work well keeping the base sound and pass upto
3KHz?

2: Is the calculation of the impedance correct?

3: Would the audio as seen on the secondary be reduced by a factor of 12 such
that the audio would be weak?

4: Other?

Tnx de KJ4UO

I'm no transformer expert, but the transformer you mention may be kind of
lossy for an audio application. I would look for a suitable audio
transformer at
www.mouser.com . I believe power transformers are wound using larger wire
and forms, and are designed to be efficient at their operating frequency of
60Hz....

Mark W4UDX


"PDRUNEN" wrote in message
...
Hi Group,

Got a 706 which has a 500 or 600 ohm mic input impedance. I have a D104
which
best I can tell has a high output impedance.

If I use a 60Hz step down transformer, say, 120V in gives 10v out, the
turn
ratio is 120/10 or 12:1. Given that I attach the mic output to the
primary and
the rig on the secondary, this should step down the impedance by a factor
of
12^2 or 144 so that a D104 with 50K on the output is now seen as about 400
ohm.

Here are a few questions,

1: Will a 60Hz transformer work well keeping the base sound and pass upto
3KHz?

2: Is the calculation of the impedance correct?

3: Would the audio as seen on the secondary be reduced by a factor of 12
such
that the audio would be weak?

4: Other?

Tnx de KJ4UO

PDRUNEN wrote:
Hi Group,

Got a 706 which has a 500 or 600 ohm mic input impedance. I have a D104 which
best I can tell has a high output impedance.

If I use a 60Hz step down transformer, say, 120V in gives 10v out, the turn
ratio is 120/10 or 12:1. Given that I attach the mic output to the primary and
the rig on the secondary, this should step down the impedance by a factor of
12^2 or 144 so that a D104 with 50K on the output is now seen as about 400 ohm.

Here are a few questions,

1: Will a 60Hz transformer work well keeping the base sound and pass upto
3KHz?

2: Is the calculation of the impedance correct?

3: Would the audio as seen on the secondary be reduced by a factor of 12 such
that the audio would be weak?

4: Other?

Tnx de KJ4UO

You could use a simple op-amp buffer circuit, with a resistive
attenuator to knock the voltage down if necessary. Even with the 9V
battery to power the thing it'd be no larger than your transformer, and
would certainly give better audio than a power transformer.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Got a 706 which has a 500 or 600 ohm mic input impedance. I have a D104
which
best I can tell has a high output impedance.
=====================
Don't know the D104 mic ( Shure ?) However many socalled High impedence
microphones are dynamic low imp. mics. with a small transformer fitted
inside the mic. housing. Examples : Mics supplied with Yaesu valve
transceivers from the 1960 -70s.
By disconnecting the transformer it is just a 500 - 600 Ohms microphone.

Frank GM0CSZ / KN6WH

"PDRUNEN" wrote in message
...
Hi Group,

Got a 706 which has a 500 or 600 ohm mic input impedance. I have a D104
which
best I can tell has a high output impedance.

If I use a 60Hz step down transformer, say, 120V in gives 10v out, the
turn
ratio is 120/10 or 12:1. Given that I attach the mic output to the
primary and
the rig on the secondary, this should step down the impedance by a factor
of
12^2 or 144 so that a D104 with 50K on the output is now seen as about 400
ohm.

Here are a few questions,

1: Will a 60Hz transformer work well keeping the base sound and pass upto
3KHz?

2: Is the calculation of the impedance correct?

3: Would the audio as seen on the secondary be reduced by a factor of 12
such
that the audio would be weak?

4: Other?

Tnx de KJ4UO

Paul -

First, The D104 microphone was manufactured by Astatic, a division of
Omnitronics.
Omnitronics LLC
341 Harbor Street
Conneaut, OH 44030
http://www.astatic.com/

There are several models of the D104 microphone (e.g., stand combinations,
transistorized preamp, etc.) - detailed on their web site.
All D104 microphone that I am aware of ... use a high impendence
ceramic/crystal microphone element.
Wiring diagrams for the 8-pin Icom (not the RJ-45 jack version) is on their
web site.

Some operator have switched the D104 to Heil dynamic elements (HM-4 or
HM-5).
Astatic no longer has the crystal elements, but Mouser has a good Far East
substitute.
http://www.mouser.com/

This make a big difference in your approach -- since some of these bases
have a low-Z / high-z switch in the amplifier OR
actually have an audio transformer in the base for this purpose.
The Heil XT-1 is a suitable transformer, Mouser has several candidates in
their catalog.
Radio Shack use to some suitable audio transformers for $ 2 or so.

Xicon has some candidates (e.g. Mouser # 42TM017; 42TM019; 42TM024) .. with
differing input impedances (25K and 10K) and power capability (not a major
issue for your application)

Greg, w9gb

there was an article in QST (circa 1992 IIRC?) on adapting the astatic
d104 microphone using a single dual op amp, setup for 300 to 3,000 hz pass
band, for impedance conversion to 600 ohms output impedance. Some d104
mikes had an adapter built-in using a 9 volt battery, one recently sold on
Ebay ($21-ish) with the mike ;-)

hth bobm
--
************************************************** *********************
* Robert Monaghan POB 752182 Southern Methodist Univ. Dallas Tx 75275 *
********************Standard Disclaimers Apply*************************

"PDRUNEN" wrote in message
...
Hi Group,
Got a 706 which has a 500 or 600 ohm mic input impedance. I have a D104
which
best I can tell has a high output impedance.
If I use a 60Hz step down transformer, say, 120V in gives 10v out, the
turn
ratio is 120/10 or 12:1. Given that I attach the mic output to the
primary and
the rig on the secondary, this should step down the impedance by a factor
of
12^2 or 144 so that a D104 with 50K on the output is now seen as about 400
ohm.
Here are a few questions,

The other, more practical questions are answered by others, but:



2: Is the calculation of the impedance correct?

YES. Power remains the same on both sides of the transformer. If "V"
drops by a factor of X, the "I" increases by the same factor. R (or Z) = V
/ I

Z Pri = Vin / Iin
Z Sec = Vout / Iout
Vout = Vin / X
Iout = Iin * X
Zsec = (Vin/X) / (Iin*X)

= Vin/Iin / X / X
= Z Pri / X^2


3: Would the audio as seen on the secondary be reduced by a factor of 12

Yes.

such that the audio would be weak?


The low Z mics have less output voltage than Hi Z mics and since you can
simply use a mic transformer to go between the two, you shouldn't have a
level problem.

--
Steve N, K,9;d, c. i My email has no u's.

"PDRUNEN" wrote in message
...
Hi Group,

Got a 706 which has a 500 or 600 ohm mic input impedance. I have a D104
which
best I can tell has a high output impedance.

If I use a 60Hz step down transformer, say, 120V in gives 10v out, the
turn
ratio is 120/10 or 12:1. Given that I attach the mic output to the
primary and
the rig on the secondary, this should step down the impedance by a factor
of
12^2 or 144 so that a D104 with 50K on the output is now seen as about 400
ohm.

Here are a few questions,

1: Will a 60Hz transformer work well keeping the base sound and pass upto
3KHz?

2: Is the calculation of the impedance correct?

3: Would the audio as seen on the secondary be reduced by a factor of 12
such
that the audio would be weak?

4: Other?

Tnx de KJ4UO

Paul -

Here are additional links on Astatic D104 restorations and "how to's" for
using with modern & Icom radios
... TIME FOR READING and PRINTING ...

W8CWE has a web page -- just what you are asking about (Google.com is great)
http://www.qsl.net/w8cwe/d104/d104.html

This is a D104 index you should "bookmark" in your browser
http://www.qsl.net/wa2mzf/d104.html

Doug DeMaw, W1FB (sk) FET circuit for D104 - CQ February 1994
(mentioned in web pages below)
http://www.qsl.net/wa2mzf/d1045.jpg

http://members.cox.net/n4jk/d104.htm

http://www.n9vv.com/K8LKC/k8lkc-d104.html

D104 and Icom equipment
http://www.qsl.net/wa2mzf/d104icom.jpg

IF you are looking for an 8 conductor coiled cord .. BUX COMM has a great
bargain 8FTCURLY at $ 1.99 !!!!
Would look nice on the D104
http://www.packetradio.com/xsinventory.htm

W9GB

"PDRUNEN" wrote in message
...
Hi Group,

Got a 706 which has a 500 or 600 ohm mic input impedance. I have a D104
which
best I can tell has a high output impedance.

If I use a 60Hz step down transformer, say, 120V in gives 10v out, the
turn
ratio is 120/10 or 12:1. Given that I attach the mic output to the
primary and
the rig on the secondary, this should step down the impedance by a factor
of
12^2 or 144 so that a D104 with 50K on the output is now seen as about 400
ohm.

Here are a few questions,

1: Will a 60Hz transformer work well keeping the base sound and pass upto
3KHz?

2: Is the calculation of the impedance correct?

3: Would the audio as seen on the secondary be reduced by a factor of 12
such
that the audio would be weak?

4: Other?

Tnx de KJ4UO

One more

D104 mods
http://www.d104mods.com/