DIEFET: A French Diezel VH4 Jfet Simulation

[kupervaser]

I finished it finally. It works.

Here is the sample for those who are interested.
Recorded on a Matamp GTO 120 and a SG tuned to B:
http://www.soundclick.com/bands/default.cfm?bandID=435410

[kupervaser]

Here are some pictures.
After I paint the enclosure I will post some pic's from the inside:

[fluoreszenz]

I finished it finally. It works.

Here is the sample for those who are interested.
Recorded on a Matamp GTO 120 and a SG tuned to B:
http://www.soundclick.com/bands/default.cfm?bandID=435410

Nice Diefet you got there. Which version of the Diefet did you build?
I'm still waiting for parts to come for building one (for Version1.2).

Any hints on how you solved some challenges you mentioned before?

[kupervaser]

Hello, i built the first one: Version 1. from diefet v1.pdf

The one problem that I had was the oscillation in the feedback circuit of the opamp.

There are 2 capasitors on the schematic, one is 0,1uF (C27 on the layout). If you look in the partslist in the pdf files the C27 is 1n. So i followed the schematic and put 0,1uF in it.

The other capasitor in the feedback loop of the opamp (C31) has no number. I don't know why. I just experimented there, i think I have 3,3,nF there at the moment. As soon as I fixed that, the pedal starting working again.

I couldn't have fixed this pedal without help from the people on this forum, freestompboxes.org and a dutch forum www.newtone-online.nl

Good luck and post your questions here.

[kupervaser]

I still have a problem with my DIEFET.

In bypass I hear oscillation when the gain is past 3 ocklock. It is kind of a peep, like the one you hear in your ears after expoxing them to loud music. It is not loud, but very disturbing. When I turn the gain past 3 ocklock till the max level, i hear changes in the peep, it gets higher. What can be the problem?
This problem doesn's accure when the effect is on. When on, is working perfectly!!


I used this offboard connection:


Some people on other forums told me this could be the problem in the offboard wiring and advised me to use this one:


Could this be the solution?

[Ripthorn]

That might just work.  The reason why is because it grounds the circuit input when it is in bypass.  In theory, if you don't put anything into the circuit, then there is nothing for it to amplify and oscillate.  Of course, there will be a little that leaks in if your enclosure isn't well insulated.  What pcb layout did you use?

[kupervaser]

I used version 1 on the beginning of this topic. I will connect it the way the second picture shows.

[Ripthorn]

I built using a different layout, so I can't speak to that, but try the grounded input wiring.

[kupervaser]

I also built it with a voltage doubler based on ICL7660S IC.

[Ripthorn]

You might be getting some leakage from the switching of your voltage doubler into your signal path somehow (maybe through the ground?).  Why don't you try it on 9V by disconnecting the voltage doubler and see if you still get the noise.

[fluoreszenz]

Here's my try with version 1.21

Parts came this morning, time for pcb printing, etching and tinning...



Drilling took forever, *note on to-do-list: Buy small drill-press, that portable battery drill is just  *

[caspercody]

Question, what (if anything) connects to the "J1-J7" points on the pcb board? I am using the pcb that DSV has the link to. Mostly wondering about J2-J5.

Thanks

[Ripthorn]

J is for jumper.  Check for jumper locations on the layout.

[caspercody]

The jumpers are shown on the layout, but these look to be different. On the schematic they are called AJ-2 thru AJ-4 (and also J2 thru J5). They connect to one side of the trim pots. It does not look like I need to connect them on the pcb to get this to work, but wondering what they are meant to do.

[Ripthorn]

Those are probably etched jumpers to connect pins 2 and 3 (or 1 and 2) of the trim pots so that they act as variable resistors for biasing the jfets to one half supply voltage.

[caspercody]

I got it to work, but the volume is not there. I have to have the volume turned to 100% to get the same level as when I bypass. I used a audio probe, and it is loud after Q5 source output (point A on schematic). But after C21 or R17 it gets quieter. I know the tone stack is passive and drops it down, but should this boost the level with the volume barely turned? I tried replacing the some of the tone stack pots, and the volume also replaced the IC but none of this did anything. I did not put a jumper in the J2 thru J5 points on the pcb. It looks like these would ground the drain side of the J201's if I did this. Looks like they might be for adding a output jack after each gain stage (according to the block diagrams on the schematic)?

Please help, should the volume on this cause a huge boost to the signal? Does anyone have any voltage readings? (maybe more after Q5?)

Thanks

[Ripthorn]

There is no huge boost, but you can get a decent volume increase by replacing the final 220k series resistor with a jumper.  That's just the way it is.

[kupervaser]

I had to put volume on around 15:00 to have the effect on the same volume as bypass. I buitl version 1.1 though. Maybe you should put that jumper there.

[caspercody]

Thanks! I will try the jumper in R25.

I built version 1.21.

On the pdf sheets for this project I see (4) switches on the panel front, I wonder if these are for the J2-J5 jumpers??

[caspercody]

Took out R25, no big difference. I bypassed the tone stack, and that made a big difference. It was much louder, and still had the deep control. So, either I have a bad component in my tone stach, or this thing just does not get loud. Which sucks, because to get this at the same level as when bypassed I have to turn the volume on the pedal to max. And this hurts the clipping tone.

Added the jumpers to the J2-J5 spots, no sound at all. Clipped off one at a time, and no sound till all were cut. Not sure what they do, but it does not work with them in.

I think I will put this aside, and start a new pedal. I hope I have something wrong on mine, bad component, or..... Because not to impressed with this pedal. The Krank Distortus Maximus gives about the same gain, and a lot easier to make.