Don't forget to Solder all Ground Connections to Back of Guitar Pot

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To clarify the capacitors. I have an electrolytic cylindrical one for C1 10 uf.I have a green polyester one for the C2 0.1 uf And the C3 100pf is a brown ceramic one. The guy at the store asked about voltages. But how the heck would I know. I believe there is a formula out there somewhere that you can work out capacitor voltages you need. Im as thick as two bricks when it comes to this stuff. But I want to give it a shot with some tips.
Hmm. The more I look at the pic of wot goes where it is becoming clearer to me what to do. I need advice on those capacitors I mentioned though.
Hi Jonno,
My own thoughts would be use what you have and see if you like the result.

I have done a bit of searching on the www because I was interested in knowing for sure.

From what I can find it will work.

This site
Suggests above 1 to 2 microfarads electrolytic caps are better because they add less noise to the signal.

The original Tillman description
Says C1 is a coupling capacitor to remove DC current from the output signal.

From this website
Point 2.1 to 2.2
It suggests polyester caps will work fine and for a preamp electrolytic caps will not make a noticeable difference.

The only way to know for sure would be to compare both types for yourself. If you like the result with what you have I would stick to that.

One point to make is that unlike resistors capacitors can be easily damaged by the heat from the soldering iron conducting up the wire leg of the cap to the body causing permanent heat damage. Unless you are very quick at soldering you can help protect the capacitor by clipping a alligator/crocodile clip on the leg of the capacitor you are soldering to act as a heat sink.

cheers David. Started putting this together. Check this site for answers. Talk about one stop shop
Hmm. Pretty frustrating stuff..i decided to do this up point to point to see I had the fundamentsls right. The main thing I paid special attention to was making sure I connected to the correct pins of the fet and to the positive leg of the sole electrolytic capacitor. I connected one side of R1 to the gate pin of the Fet. The dc positive thru R2 and to drain pin of fet. C1 I determined the longer leg to be the positive and connected to source pin of fet via R3. I connected everything else up.. Triple checking connections and paths correct..msde sure bsttery worked by trying it in my six string which hss a pre smp.. Plug into comp..sudio interfsce and guitar effects softwsre sll ok..Now attach battery to thr fet circuit. Plug in leas and try. Hmm. Clesrly some kind of signsl..tspping piezo and sound comes out comp speskers..But pretty fsint..full volumes. Still fsint.
I'm thinkin msybe C2 capacitor is culprit..Its rsted 50 thst too high? Mind you. I still understand next to nothing bout this %&it.
Are you able to take and post some photos?
Lol David. I got a reputation to uphold he he. No way I'm uploadin a pic of the %&it fest I put together he he.

There are two things I want to nail down. First is what are the voltage ratings for the capacitors in the pic. Is the circuit exposed to a max of 9 volts ? So I need capacitors that can handle 9 volts. Correct? Secondly. The 'ground' on far right of board pic goes where?. The top right indicates to ground lug on pot.
Hi Jonno,
LOL - I suspect everyone is a bit shy about showing the soldering on their early projects.

This article explains about voltage ratings for capacitors.
(Aim for a rating at least twice the voltage of the circuit, going higher is fine, go lower and the capacitor might explode).

Ground on the far right-
Any powered audio circuit needs going in input+ input-
and battery+ battery- then going out output+ output-

All the grounds need to connect for the circuit to work (this is why on guitar circuit diagrams often the positive wires are shown and the grounds shown as a triangle pointing down to show they all go to the common ground point)

So working through these
Input + = piezo in blue line
Input - = black piezo wire to the back of the guitar pot.
Battery + = 9v+ red line
Battery - = bottom lug of stereo Jack (so using the Jack plug as a on/off switch. On your output Jack socket check the positive goes to the tip connector and common ground goes to one lug connecting to the plug shaft and the battery - connects to the other lug connecting with the plug shaft. If you just insert a guitar lead and you will be able to see which lug is connecting to which bit of the plug).
Output + = blue line to preamp volume (then positive signal goes green wire middle lug preamp vol to guitar pot, then middle lug yellow wire to jack socket output positive lug.
Output - = black wire from back of guitar pot.

Finally you need to check all grounds go to a common ground point and to do this the the top right ground (the black GND wire going nowhere) needs to connect to the common ground point (back of the pot labeled guitar which has the piezo ground soldered to it) will complete the circuit.

The ground wire going to the bottom lug of the preamp volume pot is there to complete the circuit this pot needs to work like a volume pot. Personally I would have wired this like a normal volume pot, so instead of having the ground wire to the circuit board I would wire this ground to the back of the same pot (preamp volume) and then send another ground wire from the back of this same pot to the common ground point on the back of the guitar pot.
Like this.

Just because I prefer to ground all pots and you have one wire less coming off the circuit board that can come loose. As you have already wired it up for this one just add the GND wire from the top right to the back of the guitar pot.
Hi David. Thanx so much mate for taking time to give me some pointers. It seems veey quiet in this corner of Cigarbox Nation. The additional grounding info you gave and the pic are great. I am gonna start from scratch again. I think some of components i have are mismatched maybe. I have half watt and quarter watt resistors. Maybe that dont.matter. as for cap voltages i think i got enuff voltage ratings for them. Cheers. Jonno
Thanx a bunch David and to the original poster of this thread. I have now a working pre amp and can start playing my cbg thru the computer and record using Reaper and a multitude of vst plugs. I found this challenging to make as I dont have soldering skills and due to a lot of tremoring I find fine hands work hard. Anywsy I used Wire Glue which I have used for other diy stuff like pickups. I use blobs of blue tac on a board to hold all components such as pots and jscks and the perf board for pre smp. I used the legs of each pre amp components to join together thus reducing glue points. Also when glueing have to be careful drops of glue dont drip onto another contact point and create a short. This is easy to do with the blue tac being able to hold a component at any angle to avoid errant drips. This website rocks.

All up cost about 25 bucks for components and Wire Glue.


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