First cut at modular front-end PCB

[Carl-NC]

Here is a first stab at the PCB for the front-end PI circuit. I don't think I made any changes to the schematic I posted a short while back, so it should match the PCB.

I tried to keep it fairly small, but wanted to stick with a through-hole single-sided design to keep it easy to make. Where I could, I threw in some extra holes for improvising.

Feedback, comments, tauntings are welcomed...

- Carl

[bbsailor]

Re: First cut at modular front-end PCB

Carl,

What is the pysical size of the boards?

It looks like board will allow some serious experimenting. The two preamp stages will allow for some expanded bandwidth and increased gain.

It is interesting that you chose to make it capable of driving two active coils, I assume in a DD configuration?

Great Job!

bbsailor

[Carl-NC]

Re: First cut at modular front-end PCB

Size is 2.9 x 2.5 inches.

I put in two full TX stages, for driving a DD coil, such as is done in the Twin Loop project, and Gary's PI. You can also use a DD with one drive stage for the TX coil, and connect the RX coil through the other stage, but strictly as a receiver (not driven).

- Carl

[Eric Foster]

Re: First cut at modular front-end PCB

Hi Carl,

What is the thinking behind using a split input resistor and two pairs of back to back diodes on the opamp input? Is it to reduce the effect of diode capacitance? I noticed that the amplifier recovered slightly quicker when I tried it.

Eric.

[Carl-NC]

Re: First cut at modular front-end PCB

Yup, just a couple of things I wanted to play with. Lower capacitance makes sense, I've used that trick in IC design with ESD diodes.

Anything else worth throwing on the board?

- Carl

[Brian King]

Re: First cut at modular front-end PCB

Hi Carl,
Looks good. What about provision for a Polyfuse in line with Power inputs? They are always handy on experimenter boards with power devices.

Brian K

[Ray(NM)]

Re: First cut at modular front-end PCB

Carl one thing I added in line in the power supply was a high current diode to prevent my hooking up power backwards which I did do on the prototypes I built of your circuit. Just my thoughts. I would add one regardless even if there was not a spot for one.
Ray(NM)

[Eric Foster]

Schematic correction?

Hi Carl,

Just a query about the two stage preamp. IC1 gives a flat response to 180kHz (-3db). IC2 is 3db down at 1.6kHz with the values shown. If you make C2 560pf and put 47pf across the 10k feedback (couldn't read the number), then you get a similar bandwidth for the second stage. These may need to be trimmed for best pulse response, but you would be in the right ball park.

Eric.

[Carl-NC]

Re: Schematic correction?

The component values were meaningless, really... just placeholders. Some values are remnants from the old copy-paste.

- Carl