| Author |
Message |
    
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1192
Registered: 9-2004
| | Posted on Wednesday, February 15, 2006 - 12:45 am: | 
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i have been reading on a few ham sites that the D104 with a preamp in it is not matched well for modern transceivers like our beloved CB's.
first, is this true?
second, they say that to properly match the input impedance of a modern set; you should put an approx. 1meg ohm resistor in series with the audio line coming from the mic element.
they say that this will bring back the lost bass freqs.
so what is the consensus here on the forum?
has anyone done this?
what did you think?
any and all are encouraged to reply,
matt |
Road_warrior
Senior Member
Username: Road_warrior
Post Number: 1240
Registered: 7-2004
| | Posted on Wednesday, February 15, 2006 - 7:45 am: |
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Yes, from what i've seen that is true. That's
why they sound tinty. There is a modification
to help with that. Not sure of the exact
modification, but, my friend did it and it
worked and sounded alot better.
My friend tried it on my 600 ohm Silver Salute, but, it didn't work. I ended up changing the
Mic element from 600 ohm to 500 ohm. That got me
the sound i wanted. Took element out of a Superstar stock mic. But, the Mod did work on
his Silver Eagle (D104). I will ask him what Mod he used. |
Semi
Junior Member
Username: Semi
Post Number: 16
Registered: 7-2005
| | Posted on Wednesday, February 15, 2006 - 9:50 am: |
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Kid
Try putting a .01 uf wafer from audio line to ground. It's easy and seems to tame the highs a little. Works great if you talk any sideband.
Semi |
Hollowpoint445
Senior Member
Username: Hollowpoint445
Post Number: 1087
Registered: 6-2004
| | Posted on Wednesday, February 15, 2006 - 5:14 pm: |
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Impedance matching in not important with an amplified microphone. The amplifier acts as a buffer between the radio and the element so impedance is not an issue. Then you can adjust the output to the proper level for the radio.
The impedance mismatch in amplified D104s is between the element and the amplifier that Astatic used. There are lots of modifications, but unless the amplifier is altered or replaced with one that better matches the 50k impedance of the crystal element, it's the same old story. Simple modifications with resistors or capacitors don't address the issue fully.
Search for D104 and mpf102 to find lots of D104 modifications on the internet.
There's also a good post by about microphone basics here on the forum that you'll want to read:
http://www.copperelectronics.com/cgi-bin/discus4/board-auth.cgi?file=/34/77285.html |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1197
Registered: 9-2004
| | Posted on Thursday, February 16, 2006 - 10:47 pm: |
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the mods i have read are all on the ham sites.
not too much about this on the CB sites.
they say to put the resistor in series with the audio line going INTO the amplifier.
i realize that this isnt a magic fix, but if it increases the bass response of my D104, im going to try it.
matt |
Capt205
Junior Member
Username: Capt205
Post Number: 49
Registered: 5-2005
| | Posted on Friday, February 17, 2006 - 10:06 am: |
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Let us know how it works. I've been told that I sound tinny with thw D-104 on the S9 base. Might try that fix myself. |
Hollowpoint445
Senior Member
Username: Hollowpoint445
Post Number: 1092
Registered: 6-2004
| | Posted on Friday, February 17, 2006 - 8:37 pm: |
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Just a resistor won't do much of anything. An audio transformer would work well if you don't want to wire up the mpf102 circuit as a buffer between the element and the astatic amplifier.
Radio Shack used to carry audio transformers. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1198
Registered: 9-2004
| | Posted on Friday, February 17, 2006 - 9:28 pm: |
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i like that circuit hollowpoint, i might just build it, but i'll probably read about it for eight years first! LOL
matt |
Tech291
Moderator
Username: Tech291
Post Number: 372
Registered: 11-2004
| | Posted on Friday, February 17, 2006 - 10:03 pm: |
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Matt,
check out this link;
upgrade d-104
TECH291
CEF#291
KC8ZPJ |
Wally38
Member
Username: Wally38
Post Number: 79
Registered: 3-2005
| | Posted on Saturday, February 18, 2006 - 11:26 am: |
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Our local radio tech did a mod to his D104 and it sounded 100% better. I wonder if it was this mod. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1202
Registered: 9-2004
| | Posted on Saturday, February 18, 2006 - 9:12 pm: |
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thanks for the link dennis!
so as i understand it; the need for the impedance matching is only for the old style unamplified D104's. the preamp circuit built into the silver eagle and others accomplishes the same task.
however, in the link that hollowpoint provided, a very similar circuit to the one in this link is shown installed on the existing preamp board.
so does this mean that the stock preamp leaves a bit to be desired, and can be improved upon?
also, on one site, someone disagreed with using the MPF102 and recommended another transistor. i cant remember exactly what it was but i think the numbers were 5454.
just trying to extract some info here, thanks for the help guys,
matt |
Hollowpoint445
Senior Member
Username: Hollowpoint445
Post Number: 1095
Registered: 6-2004
| | Posted on Sunday, February 19, 2006 - 2:07 pm: |
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Astatic designed the amplifer so their high impedance microphones could be used with low impedance radios. Apparently they didn't do a good job. I've read a lot about the issue on the internet and in amateur radio magazines, and universally they say that the amplifier that Astatic used is not designed to properly load the element. That's why all of the modifications are out there.
There are simple and complicated circuits out there, but they all pretty much revolve around the mpf102 because of it's low cost and the high input impedance. It can be used with an unamplified D104 strictly to match impedance, but it can also be used as a buffer between the Astatic amplifier and the element.
Someday when I'm really bored I might build a Doug DeMaw design from CQ magazine for a Silver Eagle that I have sitting around. I got it in a box lot and the element is fine, but the amplifier is missing. A switch to bypass the amplifier when using it with a high impedance radio will also be part of the circuit. I might even include a compression circuit just for grins - there's a lot of room in the base of those microphones. |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1215
Registered: 9-2004
| | Posted on Sunday, February 19, 2006 - 11:46 pm: |
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wouldnt it be neat to find a compression amplifier that used FET's?
it could be interesting!
matt |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1216
Registered: 9-2004
| | Posted on Sunday, February 19, 2006 - 11:49 pm: |
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here's a neat link!
http://www.qsl.net/hcara/D-104.htm
matt |
