Here's a quick demo video of my breadboarded rig. http://www.youtube.com/watch?v=unzQ3NeTnkE

I'm posting this here because I do not know where else to put this.

After a recent discussion with JM Fahey about JFET variations, I started thinking about a test rig idea I came up with a while back. Here is a schematic showing my idea next to a much simpler test rig similar to the one shown on the Fetzer valve page at ROG and, I believe, similar to one JM posted:


With the simple rig on the left with the switch positioned as shown, the absolute value of the JFET's threshold voltage will be shown on the multimeter. In the other position, the 1 Mohm R1 is shunted, and you divide the voltage shown on the Multimeter by the 100 ohm value of R2 to get the IDss.

My rig is shown on the right. U3 (multisim wants to label these as Ux since these parts are not in there master database) enables or disables the test rig according to its gate voltage. U5 is used for shunting R3 to switch between test modes. I added a couple of LEDs to indicate the test mode. The two MOSFETs in each LED setup work as an AND gate. The gate of the top MOSFET in each setup recieves the same enable signal as U3. The bottom MOSFET of the first LED setup recieves the same ON signal as U5. The bottom MOSFET of the second setup recieves an ON signal when the first setup is off.

At first glance, it may seem like I am working on a Rube Goldberg type JFET test rig. After all, this isn't any easier to use than the simpler version, it requires more parts, and the LED indicators are kinda just eye candy. But imagine if you replace the mechanical switches labeled J2 and J3 with the digital outputs of an Arduino board or some other similar board. Then, instead of a multimeter, use an analog input of the Arduino for measurement. Maybe add a button for one of the Arduino digital inputs to tell it when to take the measurements. Then, you simply pop in a jfet, hit a button, and the arduino takes both measurements in an instant. You might not even need the button to tell the Arduino when to take the measurement. You could have an optical switch that is interupted when a JFET is placed in the socket to trigger the measurements. You could write an application to take the Arduino output and automatically populate a spreadsheet or database with your measurements. Then, measuring a bag of JFETs can be done much more quickly.

Take this a step further. Set up a reel feeder to run a reel of JFETs through the tester. Advance the reel one JFET at a time using an optical switch to determine when a JFET is in position. Have a three prong probe or socket move up to engage the pins of the JFET. Then take the measurements. Then advance to the next JFET. Write an application that generates a unique identifier for the reel and print a label with that identifier to put on the reel when you are done measuring. When each measurement is taken, have your application on your PC record the unique identifier, the offset of the JFET from the beginning of the reel, and the JFET's measurements stored in a database. You can then very quickly catalog a whole reel of JFETs.

Tonight, I breadboarded the simple rig and measured several JFETs and recorded them to use for comparison. I then built my rig and demonstrated that it worked. Tomorrow, I'll take measurements of the same JFETs. Then, if I have time, I'll try to get it working with my Arduino. I'll post more stuff later.

I used to have a ruby amp housed inside an electrical outlet box, but that was dismantled.    I do have a couple of other things I can post.

I hope to have something to enter by then. With school and work, I might not can find the time, but I might post pics of a couple of things I've already built.

Anytime.  :tu:

Another idea, you can get a jack with the two normally closed switches, and possibly swap the normally opened contact (the one that curls upward) from the old jack with the normally closed on one the replacement jack. Or, if you are good enough at fabricating stuff, you might can modify the nc contact into a normally open one.

I don't know if you still have the original jack, but you can see the obvious difference between the normally open switch and the normally closed ones. Can't seem to find any like this online. BTW, don't damage the pots. Two of the pots on mine have bent shafts, and I can't find replacements to save my life, though I can find somewhat similar pots. Another thing, I think the stereo jack trick might not work so well with pcb mounted jacks. Soldering a jumper to the pcb to force the connection to be closed might be the best solution. Of course, you damn well better not forget to turn the pedal off when you unplug the cable, or you'll be buying batteries all the time.

Good luck.

If you look closely at the jack here, http://www.smallbearelec.com/Detail.bok?no=770, you can see that this has two normally closed contacts. This is identical to what I see on the output jack on the JH-1. This, of course, is NOT what you want.

This, http://www.pedalpartsplus.com/mm5/merchant.mvc?Screen=PROD&Store_Code=PPP&Product_Code=6010&Category_Code=JAC, is a very similar jack, though I can't tell from this if it does any switching. The manufacturer of this jack is the same for the stock jack on the JH-1.

With the stock switch, part of the switch comes in direct contact with the plug, and the other side does not. With a stereo jack, you can wire the connector for the other signal contact to where the other side of the switch should be connected. When you plug in the mono plug, the ground sleeve will complete the connection between ground and the second signal contact. See here: http://www.generalguitargadgets.com/tech-pages/49-building-information/248-general-instructions for basic info. Of course, you will not be wiring the contact to the - terminal of the battery but rather to where the switch contact should connect to the circuit board.

But if you can find a jack similar to the stock one, this would be much better.

Another thing, the first switch is in contact with the negative part of the plug, so it's obviously being grounded. Maybe the stereo jack trick will work with this.

Or maybe must solder a jumper across on the pcb for a permanently closed "switch". Then, the stomp switch does it all. I noticed that it is the first, normally open, switch that closes when inserting the plug that allows the pedal to turn on. I'm guessing the second switch simply grounds the input.

I noticed on mine that the jack has two switches, a normally open one nearest the opening of the jack, and a normally closed one. On the output jack, they are both normally closed. Of course, inserting the male jack from the cable reverses their open/close status. What kind of switches are on the replacement jack?

I've got one of these. I'll try to remember to take it apart and see what I can figure out. It might be a bit, though, because I'm very busy here lately with work and school. I might end up working this weekend, in fact. But I'll try not to forget to check into it, if no one else solves it before I get a chance.

Hmm. The opposite should be happening.