My final stripboard for the new "Fetzer Valve" from runoffgroove.com

[Gilles C]

I just finished a layout for the new Fetzer Valse circuit, and it is still untested yet. But I used TinyCAD to enter the schematic, and exported the netlist to a layout editor (VeeCAD) to make the layout, so there should not have any mistake in it.

Today, I bought a batch of new FETs (2N5458) and wanted to begin a series of tests to compare them withh the J201 and 2SK30A I alreay have.

I also wanted to make it easy to test them with signal generator or even with a guitar. So this board can be use to find the perfect FET before soldering it in a circuit.

The method used to find Vp and Idss is a bit different from the one on runoffgroove, but should give the same results. I just find it easier to do that way.

Here is the PDF file that gives everything you need to know to build and use the stripboard, should someone be interested to try it.

http://www.gtechblues.ca/FET_Circuit/FET_Circuit.pdf

If you find any mistake, or see something that could be added or made better, please tell me so. This is the first version of it, and I am working on a new standard for my projects.  So any suggestion is welcome.

You should go to runoffgroove.com for any information related to the circuit. This file is only to show another way to use the info on their site.

Gilles

[stm]

Nice job!  The on-boeard setup procedure is simple and ingenious.

I suppose you mean 2N5458 FET, as the 5448 is a bipolar transistor.

Don't forget that in order to attain reasonable gain boost with a 2N5458 you should use 18V supply.  In my case I settled for a 2N5457 fed from two 9V batteries.

Cheers.

[Gilles C]

Thanks. And you're right, I meant 2N5458... I corrected it. It was too late when I finished it.

I wanted 2N5457s but they only had 2N5458s, so I took the 25 they had.

As for the supply voltage, that's why I identified it as +V instead of +9V on the layout. But I forgot to say "on or two 9V batteries" in the text to go with that. Thanks for mentioning that detail about using 18V with these. I use a power supply in my tests, so I normally change the supply voltage as needed. And that's why I wanted to try the 2N5457 series FET. I wanted a FET with a higher Vp/lower gain and use the circuit with 18V to have a better input level handling for some occasions.

I think I also read in another post about 2N5457-58 being noisier than the MPF102. I wonder about that last detail too.

Gilles

[stm]

I'm not aware of the noise issue.

A 2N5457 has more gain than an MPF102, so in order to make a fair noise comparison you should make sure your are comparing the same gain in the first place.

So far I've used my Fetzer with clean channel and there is a slight background hiss at moderate levels, but again I've also included the presence capacitor that's intended to provide extra gain in the 1k to 10k range.

A 2N5458 and 18V should be just great to handle hot pickups.  In my case I opted for a 2N5457 and a 1Mohm trimpot at the input, so if at some time I detect the FET is being overloaded in a nasty way I can just turn down the gain at the input as needed (just as it is shown in the Fetzer Valve Deluxe).

Cheers.

[Gilles C]

Ok, thanks for the details.

I want to use one of these circuits with my homemade Strat that has Texas Special pickups. That's why I'm interested in having one with a higher signal level handling.

But I also need one for my metal Dobro style guitar that has a noiseless pickup. And it needs some help to sound good...
I'm already using a 1 meg volume in it so as not to load the pickup too much, so the Fetzer Valve Deluxe will be a perfect fit.

And both circuits will be installed inside the guitar.

Gilles

[Gilles C]

Ok, I began populating the stripboard, and I noticed a few things that I will need to change. That's what happens when you work too late...

First, the trimpots are a bit larger than I thought. So the parts on the right of them will have to move 1 hole to the right.

Second, I forgot to mention that for the tests, the Gate of the FET should be connected to the Drain. Use "VR1-2" and "SW1/TP1" for that.

I will add that to the PDF file when I have time later today.

I also noticed that I had problems accessing my website this afternoon.  So I added some files to another website of mine...

A few steps in the making:

http://www.gtechblues.ca/FET_Circuit/FET_Circ_1.jpg

http://www.gtechblues.ca/FET_Circuit/FET_Circ_2.jpg

http://www.gtechblues.ca/FET_Circuit/FET_Circ_3.jpg

I normally don't go through all these steps, but I may prepare a kind of how-to based on these pictures.

Gilles

[Gilles C]

Ok, while building the stripboard with the original layout, I found a few mistakes or corrections to make. And then, I also remembered a trick I was using with my PCBs when a FET was used in a circuit.

So I decided to make a better version of the layout.

Here it is, still unverified again. But I should be able to build it tomorrow, and verify the layout at the same time.

http://www.gtechblues.ca/FET_Circuit/FET_Circuit1.pdf

The trick is to use a 4 pins socket for the FET. That way, both DGS and DSG pin-outs for the FETs can be used on the same circuit. I don't have any transistor socket left so I will use part of a DIP socket instead.

Added: I finished building it, and I couldn't measure a Vp correctly. So I just left it there for a while while my brain thought of something. It was supposed to work...

Added later: Indeed, it works, but only when you connect the Gate correctly. I did a few tests on a breadboard, and realised my mistake...

So, to measure Vp:



I corrected the instructions in the PDF file, and I can now say that the circuit works for the Vp and Idss tests.

All I have left to do now is try it with a signal to verify the audio part of the circuit.

Gilles

[Gilles C]

Ok, this should be the last version of the PDF file for this layout. I added a switch on the drawing to be able to choose between the Normal Operation Mode and the Test Mode. And as long as there is no FET into the socket, there should be no current used from the battery. This stripboard layout is mainly for a testing purpose after all.

http://www.gtechblues.ca/FET_Circuit/FET_Tester.pdf

I used it with a few FETs, and it's working correctly. So unless I find a mistake in the test or in the drawing, I will just keep using it, and will just add what it needs to make it a complete project someday, and add it to my website.

Gilles

[Gilles C]

I changed the format of the PDF file to my new style of Project files for the layouts that I make.

It should now be easier to use and should look more like a complete project that way.

As I mentioned earlier in this thread, I also would like to use that circuit to show how I start a layout from a schematic and make it a complete project. I already posted a few pictures showing a few steps in the making, but as I updated the circuit since then, I will have to wire a new stripboard from that updated file to get a more consistant tutorial.

Nobody's waiting for it, so it could take some time before I finish that tutorial.

Until then, as usual, if somebody ever use that layout, let me know if you find any mistake in it.

Here it is:

http://www.gtechblues.com/My_Layouts/Fetzer_tester.pdf

Gilles