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d104 mic element

camaro1 said:
radioshack $2.99 just add a resistor to the base to power up the element,, these work great have several of them being used now with these elements. do a search, there is a couple other posts about these radioshack elements around here
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RS left Canada many years ago and won't ship here (what did we do wrong?) so I had to do a little extra searching and found something similar in spec and a much better deal when it comes to $$; $2.49 for 10!

10pcs Omnidirectional Back Electret Condenser Microphone 9 7mm 56nu llP 08N | eBay



BTW: we don't miss ya RS!

 
Some of the people selling these elements have overlooked more than a few things. SSB users like the electret element sold for this application because SSB has limited bandwidth. When used on AM they will sound "muddy" in most applications. You need to add an extra coupling cap between the element and preamp to roll off the low end earlier. Because the preamp has a 1 meg input impedance the coupling cap will be small. Between 470 pf and 1000 pf depending on your voice and radio.

The reduction in gain noticed with this mod also has to do with the preamp input impedance and the wrong 1000 ohm resistor picked to feed voltage to the element. That 1000 ohm resistor is also controlling the output impedance of the element and it's very far away from matching the preamp. The result is a loss in gain. Use a 3300 ohm resistor and the gain will come up. Going higher will create a better match but will not pass enough current to drive the element.

If you have a D-104 with a good crystal element, the last thing you want to do is be duped into this mod for Hi-Fi purposes. Few people realize how wide the bandwidth is on that huge crystal element thanks to Astatic messing up the design when they added all preamps in the base. The stock element reaches down below 30 cycles before hitting the 3 db rolloff point. Nearly twice as low as the electret.

The problem goes right back to the preamp input impedance not matching the stock element. The preamp runs at 1 meg and the element can only provide good bass response when it's loading is not below 4.7 meg. It is not possible to build a preamp with an input impedance this high using bipolar transistors like the stock preamp uses. You will have to change the first stage to an FET. Doing that in conjunction with a good crystal element and radio has proven second best only to a full rack of audio gear and a studio mic.
 
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Shockwave said:
If you have a D-104 with a good crystal element, the last thing you want to do is be duped into this mod for Hi-Fi purposes. Few people realize how wide the bandwidth is on that huge crystal element thanks to Astatic messing up the design when they added all preamps in the base. The stock element reaches down below 30 cycles before hitting the 3 db rolloff point. Nearly twice as low as the electret.
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I think the main reason for this thread is because the crystal element is bad. That's my reason and the OP's anyways. "camaro1" seems to be satisfied with the real world results. Looking at the spec's for this Electret the frequency range is 20 to 16000 Hz. That seems like a pretty good start in the chain for hi-fi audio one would think. How does that make the audio "muddy" on SSB?

Otherwise, I'm going to order the 10/$2.49 and use a 3300 resistor. Appreciate the additional details.

 
several other guys here now use the d104 with the radioshack element after they heard mine and my buddy's. I started with a 1K resistor to power up the element, it works fine but better results / more volume with a 4.6K resistor

great sound on am and ssb

this element also works great and is a drop in replacement(very minor clearance work on some) for my optima mk3 mic , magnum 257 mic, and superstar pistol grip mics. the optima mk3 in my mobile gets audio compliments all the time!!
 
It doesn't sound muddy on SSB because SSB transmitters do not have good bass response. Go to AM and the electrets can easily sound muddy if you don't use an appropriate value coupling cap. If your original element is bad, take Loosecannon's advice in post 27 and remelt the wax to bond the diaphragm back to the crystal. That works at least 50% of the time.
 
According to the video pasted earlier,the guy who built his bass and treble adjustable D-104 preamp said that Astatic started installing preamps for their D-104's to fix the impedance mismatch problems that the pre preamp models had.

D-104 Microphone amplifier / Equalizer for Ham Radio - YouTube

Plus,if you look at the schematic he shows,you can pretty much build your own preamp board just in case if your's is on the way out.
 
Lil'Yeshua said:
According to the video pasted earlier,the guy who built his bass and treble adjustable D-104 preamp said that Astatic started installing preamps for their D-104's to fix the impedance mismatch problems that the pre preamp models had.

D-104 Microphone amplifier / Equalizer for Ham Radio - YouTube

Plus,if you look at the schematic he shows,you can pretty much build your own preamp board just in case if your's is on the way out.
Click to expand...

That is true because the output impedance of the element being 4.7 meg would not match any newer transistor radios. The Astatic preamp does match the impedance of today's radios but unfortunately it does not match the impedance of the crystal element. To be fair on Astatic, they didn't have much choice when the preamp was designed. FET transistor were not around and the best they could do with bipolar transistors was the 1 meg input.

The link you posted shows a schematic using an op-amp as the preamp. It's fed balanced and has a pair of 2.2 meg resistors to ground. That forms a 4.4 meg impedance to the element assuming a high impedance FET op-amp is used. I haven't tested this circuit but it appears to be able to provide good frequency response. I prefer a single FET transistor as the first stage because it can be less problematic dealing with and bypassing RFI.
 
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marrowbone boy said:
Dont go back to stock. Contact me here and I can hook you up! I have several HEIL usits here that will do you justice Much better than stock! You will be pleased!
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Don't underestimate the stock element. Guys with old boat anchors like a DX-100 that use the old G-stand with no preamp can tell you these elements are hard to beat. That's because the preamp installed after the 1960's ruined the frequency response. Not the element. This is well documented online and easy to fix by changing the first transistor to an FET with a gate resistor of 4.7 meg.
 
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Shockwave said:
Don't underestimate the stock element. Guys with old boat anchors like a DX-100 that use the old G-stand with no preamp can tell you these elements are hard to beat. That's because the preamp installed after the 1960's ruined the frequency response. Not the element. This is well documented online and easy to fix by changing the first transistor to an FET with a gate resistor of 4.7 meg.
Click to expand...

I hear ya! I'll keep that in mind
 
Well, I used a 4700 resistor and the W2ENY Electret element (I bought before I knew any better) on a silver eagle stand and got excellent audio reports on SSB. Looks like no need to go through a FET transplant. I guess I can now move on to wide-banding the RX/TX sections on the radio it is being used on, a Cobra 2000.
 
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Klondike Mike said:
Well, I used a 4700 resistor and the W2ENY Electret element (I bought before I knew any better) on a silver eagle stand and got excellent audio reports on SSB. Looks like no need to go through a FET transplant. I guess I can now move on to wide-banding the RX/TX sections on the radio it is being used on, a Cobra 2000.
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FYI: I've tested the frequency response on this Electret D104 setup and measured 500-18500hz from the AUX jack of the Cobra 2000 after wide-banding the microphone input section. I received my 10/$2.50 lot from China but have not tested yet.
 
here is another d104 amp modification I found for running the radioshack style electret element, basically it just by-passes one of the transistors on the board, tried on another d104 and works great:

just remember when putting the electret element in the head the + from the element goes to the white wire and the - from the element goes to the red wire
 

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take a voltage reading across your mic element when you key the mic, if you have voltage there 1-9v it might work,, take note of what wire is + and - . if you do have voltage across your stock element, id just disconnect your element and wire in the r/s element and give it a try, don't even have to mount the element or put the mic together, just wire the new element in and key it up and see what you get.
 

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