The Steel Guitar Forum

If you do a search for Tilman Preamp or Fetzer Valve (runoffgroove.com) - a number of layouts will show up & could easily be modified for this FET based circuit.

There's also a freeware program called DIY Layout Creator (Windows/Linux/MacOS). It allows you to do layouts (pcb, perfboard, veroboard,...) It's simple to use & how-to videos on youtube.

OK, I edited the schematic, it's in the original post I did.

Hi again folks,
With regard to this circuit can ask a question .
How will the circuit run using 2 X 2.7 M ohm resistors instead of the 2.2 M ohm ones as per schematic values.I am finding it hard to get 2.2 M values and I have a couple of 2.7M ones.
Thanks for looking .
Regards Dave

Dave, 2.7 meg should be fine for that bias voltage divider in this circuit.

Thanks Chris.

Hi Folks ,
Yet another question!
The 500 k pot ...is it a variable resistor in this schematic or just a normal potentiometer ?
Where does the 47 K resistor go relative to the pot lugs? I realise one end goes to ground which makes me think it is not a variable resistor .Can you explain please.I have built the rest of the circuit and now need to wire the pot up.
Thanks for looking Dave

Yes, it is a variable resistor. You'll likely want fully clockwise to be 500k and counter-clockwise to be zero. Then the fixed resistor in series sets the minimum z.

You can put the fixed resistor on either side of the pot (variable resistor). Doesn't matter.

B

That 47k resistor is a limiter resistor so the 500kA pot doesn't go lower then 47k ccw.

Hi Brad and Mark,
Thanks for the help .So I take it that the 47k goes like this.....
1) one end to ground
2) the other end to one of the 2 lugs used as an in and out of the pot.
Regards Dave.

The resistor can go between ground and the CCW lug on the pot.

Then the center (wiper) lug goes to the input signal.

It's also a good idea to also tie the CW lug to the center lug. It's a variable resistor and even if the pot gets dirty, there will always be the 500k load present no matter what.


B

Perhaps something like this.

Thanks Brad thanks Mark .Can now finish off the project !
Regards Dave

bOb, SGF seems faster since the change-over. Thanks for all that you do

Hello Guys,
I really like the drawing Scott included on this Steel Buffer project. The reverse current battery protection is a plus, especially if no mechanical safeguard is built in place to prevent battery or polarity reversal. I always hate changing out batteries and using a standard diode really shortens the battery life. There are a couple of options that are quite useful: you could use a Schottky diode with a much lower forward voltage drop or even better would be to place a P-channel MOSFET parallel with the original diode and reference its gate back to the ground (neg) side. This would have a minimum voltage drop on the circuit and clamps shut with a reversal. MOSFET's have a very low resistance from Drain to Source. See: TI Application Report SLVA139, 2003

One of my Covid hobbies is learning about electronics. I bought a breadboard and the parts to try this circuit. Thanks for all of your efforts and input on this. I worked from the schematic and experienced a big volume loss across the range of the pot. I added the jumper across the lugs as in the napkin diagram and it works better but I don't understand why. Can somebody enlighten me? Thanks.