Minima - Audio Module

I have made further Revisions to my Experimental Minima Transceiver Audio Module (see previous post). I still do not exactly enjoy building Audio circuits, but it needs to be done.

I have modified the original circuit to peak my interest. My circuit will incorporate (among other things) some AGC and a little more available Speaker Power. But of course, none of this has been tested and therefore operational results may be different than expected.

My Planned Minima Audio Module

This board will be 2.5x5.0 inches with 84 via's, it is not very dense, because the layout provides a human interface with normal finger spacing, and it is also size to plug onto my other Minima Modules.

I will make the first Prototype board with the Toner Transfer Method (TT) to check operations.

Unfortunately, I will be busy the next few days will not have much time to work on this project.

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Minima - Audio Circuits

With my prototype Minima CPU Module working (see update at bottom of a previous post), I have returned my attention to the Audio sections of the Transceiver. But, I still do NOT enjoy building Audio circuits - the capacitor are just too big :-).

For me, audio circuits are as boring as power supplies.

But, maybe there is room for some adventure and intrigue by implementing an alternate circuit with some very small modern parts. Also, there may be an opportunity to multi-purpose some of the circuit elements. I am just now starting to explore this idea. What ever I build, it will be compatible with the original Minima circuit.

More information will follow.

I will probable eventually build the Minima Audio circuit as originally published.

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Minima - AUDIO Board - Work In Progress

The SMD Caps were received, and therefore layout of my Minima AUDIO and Power Board has resumed.

This initial layout still has a few problems, and it has far too many vias (32) to my liking. I can build vias using the Homebrew Toner Transfer Method, but they are not fun, or at least at the size (40x15 mil) that I want.

This board contains (left to right, top to bottom): On the top row; TxRx Relay and Control, SideTone/CW, Audo PreAmp, Main Power Connector and Regulator (a little lower). On the next row; the KEY Jack, PTT Jack and Mic Amplifier, and the Audio Amplifier and Phone Jack.

My Minima AUDIO and Power Board
Proposed Configuration

If all goes well, the board size will be as shown at 2 x 4 inch. There is still room for additions or modification, but any additions will more than likely mean more vias. :-(

The circuit is a slight modification of the original Farhan Minima Transceiver circuit, I added; the Power Supply with Headers for the other Modules, I included the KEY and PTT circuits on this board because I wanted their Jacks near the Mic and Phone Jacks on the same board. A CPU signal and its Power Header is also included.

I still have to find a suitable Large Cap (500uF - Lower Right), I think the footprint as shown will work.

I just checked, and I need to order more Toner Transfer Paper, I may not have enough to build this board, especially if I make a mistake, Dang !

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UPDATE: Mar 29, 2014 12:16

With a little digging, I found a stash of nice 35V 330uF Caps in my part bins, two of which I will use to replace the single 500uF cap as per the original schematic. The caps that I found are stand-up through-hole mount. I moved the connecting traces to the back side so that they could be soldered without the need for front-side solder (underneath the cap).

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A new Audio Amp for DC Receiver

With my new found abilities of home PCB construction (see previous PCB posts), I have put together the circuit layout for a Audio Amp for my Direct Conversion QRSS Receiver. It has not tested yet, but I am hopeful, . . . (that it does not turn out to be an oscillator?).

 Audio Band Pass Amp using LM324N

Yes, there are four jumpers on the board, plus one under the IC, I did not want to make this a two sided board.

And if you look very close, you can see I forgot one two solder joints on the capacitors to the right of pin 8, and 14.

Forgot Solder Near Pin 8 - This is an Easy Fix!
Note: These are 1210 pads with 1206 parts, also note that there are traces or Ground Plane under many of the parts, it is easy to create solder paste shorts under the parts - as I have found out!

Now for some testing and circuit check out!


UPDATE 1:  Well, . . It is, . . . . an Oscillator! . . . . . I will have to do some more checking on the layout, and maybe some "LTSpice" simulations. Maybe it is just a short, or a miss mounted part - alot more checking is needed.

UPDATE 2:  I think I need to look for another circuit for my "Band Pass" audio amplifier, the circuit that I used was cobbled together without much thought. What I need is about 60-80db of gain with; 200 to 2000Hz Band Pass.

UPDATE 3:   A very old Navy friend of mine, Richard Davis, after seeing the photo, offered this bit of advice on FaceBook: "Don't use Taiwanese electrolytics! ;-)". He must be very observant, as I used the Caps that I had in the junk box. Maybe, I should look at the selection of Caps closer, or maybe the International friends will also have comments.

I found the following Active Band Pass Filter Calculators:

http://www.wa4dsy.net/robot/bandpass-filter-calc

http://www.captain.at/electronics/active-filter/

UPDATE 4:   I found one layout error, the output feedback cap of the third stage op-amp was connected to the bias line and not the the inverting input cap as it should. That would make the op-amp oscillate!

I may change the component values used to implement a 6 pole Chebyshes Filter as the Filter Calculator above suggests, the schematic and layout stays the same (after I fix the layout error found above).

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