Unexpected Interesting Reward!

[Dmans]

Shadetree,
Thanks for the confirmation. I'm going to make a note and IF/WHEN I get back to this, it should be easy. (If I can find my note!)

73
David

 

[Dmans]

Finally finished up the Adafruit microphone module in the “Drake” Astatic microphone. Hooked it up to the TR-296 aka “The Turd” and got some good audio reports.
Now to get back on finishing the TR-296 and see if it can make a little output power!

What I really like about this modification is that from all appearances, this microphone looks stock. (Except for my straight mike cord replacement).


73
David

 

[Shadetree Mechanic]

Quick update about the audio capacitor and the audio range, namely the bass response. The big cap does great on a stock radio that is already narrow in the audio department. Like the Cobra 29 or my Galaxy 99. However, there was too much bass for my Cobra 29 that I did the Goldfinger mod to and my Stryker 440 was sounding muddy as well. The solution was to put the caps on a switch and flip it back and forth depending what radio I am on.

I used a 3 position switch to run the smallest cap in the center off position. Flip it one way to put another slightly bigger cap in parallel, flip it the other way for the big capacitor in parallel.

The values I used are 186.6nf for the high center position, 330pf for the mid cap and 2.3uf for the big cap. Your results may vary.

 

[Dmans]

I used a .1uF cap in this one. (No internal audio mods done to the radio) I was a bit more selective in the "dropping" resistor in the audio line. After several tries and scope measurements, I ended up with an 82K in the audio line. Best audio reports on SSB are with the Mic Gain control about 3/4 full.

73
David

 

[Mudfoot]

I just got an old Dukane mic. I am going to see if I can fit two AA batteries in the base.
View attachment 30451

Never heard that name. Mic looks nice. I'm partial to that style mic.

 

[Shadetree Mechanic]

Bump for the guys working on their D104s. The adafruit board with a 3v lithium works great.

 

[nomadradio]

DuKane. Made industrial intercom and PA systems, like you'd find in a high school decades ago. Bought their mikes from the usual suspects and added a "DuKane" badge.

73

 

[Shadetree Mechanic]

Bump for recent D104 inquiry. I also like to read through good threads from time to time. Anyone who has worked on a MIC should try this Adafruit MIC.

 

[Tokin]

Bump for recent D104 inquiry. I also like to read through good threads from time to time. Anyone who has worked on a MIC should try this Adafruit MIC.

Just bought 2 from mouser to try out on my tug8.

 

[Dmans]

Tokin,
These modules have a TON of gain. Be prepared to experiment with a resistor in the audio output line to prevent squealing, feedback and overdrive. Frequency response is great once the output gain is nailed down.
Have fun and save a classic!

73
David

 

[Tokin]

Tokin,
These modules have a TON of gain. Be prepared to experiment with a resistor in the audio output line to prevent squealing, feedback and overdrive. Frequency response is great once the output gain is nailed down.
Have fun and save a classic!

73
David

Thats what i keep reading. Im sure i can get it right. Will i need to bypass the original amp?

 

[Dmans]

I believe I would bypass the original amp. You definitely won’t need it.

73
David

 

[Shadetree Mechanic]

Quick update, trying to find a way to get a little punch in the audio. An equalizer could dial it in, but I wanted to have it all inside the mic. I came across an online calculator for a passive notch filter. By reducing the audio signal at 500hz, it takes out some of the mud. The way this filter is designed, it also attenuates the lower frequencies some which isn't a bad thing with a full range element like this. I mocked it up on a bread board and tested it with a breakout cord that I used to put my headphone amp inline at one time. Listening to it on another radio with headphones confirmed that it was definitely worth doing.

Edit: just wanted to note that I experimented with the mic that already has a capacitor on the audio line. The value of this capacitor will determine how much bass your audio has too. This filter reduces the power of the signal, so I might remove the jumper on the mic board to increase the gain some.

Here is the calculator, I used 500hz but other points might help too.

http://www.learningaboutelectronics.com/Articles/Notch-filter-calculator.php#answer1

 

[Handy Andy]

So you know @Shadetree Mechanic ....

Grab an old schematic of a typical component Stereo - with PHONO inputs...

Note how your filter and the schematic are similar.
​

RIAA used a method of Emphasis, De-emphasis scheme to handle Records - they emphasized Treble "compression" and Bass "Attenuation" during the Recording (Transfer) process - then your stereo used a filter thru the op amp to re-establish (expand and equalize) the RIAA offset (emphasis) using the filter for De-emphasis - restoring the original sound.

Stereos were rated for their ability to track and recover such recorded information as a statement of being qualified as Fidelity equipment. 20Hz - 20,000Hz (20kHz) +/- 3dB sort of thing...(Sales pitch)

So looking at the above graphic, compared to the diagram you provided - in this this posts' diagram, the circuit loop will restore Bass and cut Treble (Lo-Pass) - your variant cuts' Bass (Hi Pass) all because of how the caps and their route to ground (Shunt) works.

I gave you an example above to help you in case you wanted to restore the Mics' audio gain level to drive the radio.

​

 

[Shadetree Mechanic]

Bump for microphone rebuild goodness.