# Deofol OD



## HamishR

Thinking about building a Deofol.  I have a ton of J201s - do I need to bias them/match them/buy them flowers to get the pedal working perfectly?

Thanks!


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## Chuck D. Bones

You do not need to match or select them.  This circuit is very forgiving of JFET DC parameters.  It will have a TON of gain.  You might consider using a larger box and making some or all of the trimmers front panel pots.


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## HamishR

I used to have an Okko Diavolo way back when, so I know what they sound like.  I remember liking the pedal hence my wanting to build one.  I have built some Menatone kinda pedals using J201s before and it was critical to bias them just right so I was hesitant about the Deofol.  So thanks for quelling my fears!  The board has been ordered...


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## HamishR

Well that's a bit disappointing.  Built my Deofol today, took extra care to get it right because it will be a bit of a PITA to take it out again if there is an issue.  And it works but it really doesn't sound very good.  The Presence trimmer does next to nothing but everything else does more or less what it should.  The pedal just sounds a bit flat and I need treble up way high for it to sound at all balanced.  I have the bass trimmer on zero but it still sounds a bit too bassy.  Overall it sounds like badly biased Jfets.  I'll put it to one side and have a look again when I can be bothered.  

FWIW the space for the capacitors is a bit tight.  I had to use cheaper grey 1µF caps because there was no way WIMAs were going to fit.  And even with the grey box caps the caps barely fitted on the board.


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## chongmagic

HamishR said:


> Well that's a bit disappointing.  Built my Deofol today, took extra care to get it right because it will be a bit of a PITA to take it out again if there is an issue.  And it works but it really doesn't sound very good.  The Presence trimmer does next to nothing but everything else does more or less what it should.  The pedal just sounds a bit flat and I need treble up way high for it to sound at all balanced.  I have the bass trimmer on zero but it still sounds a bit too bassy.  Overall it sounds like badly biased Jfets.  I'll put it to one side and have a look again when I can be bothered.
> 
> FWIW the space for the capacitors is a bit tight.  I had to use cheaper grey 1µF caps because there was no way WIMAs were going to fit.  And even with the grey box caps the caps barely fitted on the board.



Did you socket the J201s or did you use SMD?


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## HamishR

I used good old-fashioned through-hole J201s and soldered 'em to the board.  I really don't want to go through and try to bias them now as the board is all soldered and I will only mess it up.


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## blivjc

HamishR said:


> Well that's a bit disappointing.  Built my Deofol today, took extra care to get it right because it will be a bit of a PITA to take it out again if there is an issue.  And it works but it really doesn't sound very good.  The Presence trimmer does next to nothing but everything else does more or less what it should.  The pedal just sounds a bit flat and I need treble up way high for it to sound at all balanced.  I have the bass trimmer on zero but it still sounds a bit too bassy.  Overall it sounds like badly biased Jfets.  I'll put it to one side and have a look again when I can be bothered.
> 
> FWIW the space for the capacitors is a bit tight.  I had to use cheaper grey 1µF caps because there was no way WIMAs were going to fit.  And even with the grey box caps the caps barely fitted on the board.


Hey, I am having a very similar issue. So I'm wondering if you figured what the issue was. If so, please let me know. Thank you!


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## HamishR

Sorry - I have abandoned that one.  Too many other pedals to work on and they usually work.


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## Chuck D. Bones

Hey, Blivjc & Hamish, if you're still having trouble with this pedal, we can check the JFET biasing with a multimeter.  First verify Vcc is around +17V and Vref is around +8.5V (switch in the 18V position).  If those check out, measure each JFET Source (middle pin of the thru-hole device).  Q1, Q5 & Q6 should be around +1V.  Q2, Q4 & Q7 should be around +9.5V.  Q3 should be pretty close to 0V.  There's really nothing to adjust, we're doing this to verify that the JFETs and a few resistors are good.  As for the lack of high-end, there aren't too many things that could kill the treble except the wrong value for C3.


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## Anotherpedalbuild

This was a nightmare build. I bought two boards, and junked the first as it was a version 1 and the current build pdf is a version 2. I think that a couple of the diagrams on the pdf are V1.

I've got a genuine Diablo, and wanted to build a spare.

Here's my thoughts:

Matching the jfets didn't stop the screeching. I matched them, socketed them etc and used genuine units. The whistling and screeching was even present when the effect was bypassed.

The boost on the original Diablo only works when the fx is on. On the Deofol, the boost can be switched on independently. I rerouted the wiring to act like the Diablo.

There's way too much gain, far more than the Diablo.

The R23 & C19 whistling/screeching fix works, but the C19 (10nf) addition blunts the treble badly. The Diablo sounds nice and crisp, the 10nf won't allow this crispness.

I'm not claiming to be a guru, but I wanted to point out my fixes to save some other people from the frustration and lost parts which I had.

My fixes were:

Using a board mounted gain pot rather than the right angled pcb mounted type. I used wire for lugs 1 and 2. I used a 1meg resistor between the pcb and lug 3. This scrubs gain, and alleviates the whistling.

Use a 1n8 cap for C19. This was the lowest value to minimise the whistling.

I used a jump wire on R23.

I wired the on/off foot switch as a master switch using the boost foot switch as a subsidiary loop of the master on/off foot switch.

To kill the ghost whistling audible when the fx was in bypass, I put a 470pf cap between the master foot switch 'fx in' tag and the ground tag of the switch.

This circuit design seems to be extremely unstable (the Okko design) and it was a nightmare build.

After two boards, I have a usable unit but the Okko is definitely better. For a cheap backup, the Deofol is great. I recommend using the Triangulum boost or Isosceles boost in front of it.


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## Anotherpedalbuild

Wiring reroute


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## phbrick

Hi, sorry to bump an old tread, but I have an issue with too little gain in my build. I have to bump FEED to max and BODY to min
to get any breakup. The boost part seems to work OK, though I haven't tested it much. I'm using MMBFJ201, soldered to the board (a major PITA!).

My measurements:
Vcc: 16.9 V
Vref: 8.45 V
Q1 source 1.33 V
Q2 source 7.42 V
Q3 source 0.14 V
Q4 source 7.92 V
Q5 source 3.78 V
Q6 source 0.38 V
Q7 source 9.49 V

Maybe someone could offer advice on what to check from the board? Is the biasing wrong?


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## Chuck D. Bones

phbrick said:


> Hi, sorry to bump an old tread, but I have an issue with too little gain in my build. I have to bump FEED to max and BODY to min
> to get any breakup. The boost part seems to work OK, though I haven't tested it much. I'm using MMBFJ201, soldered to the board (a major PITA!).
> 
> My measurements:
> Vcc: 16.9 V
> Vref: 8.45 V
> Q1 source 1.33 V looks good
> Q2 source 7.42 V too low, should be higher than Vref
> Q3 source 0.14 V looks good
> Q4 source 7.92 V too low, should be higher than Vref
> Q5 source 3.78 V might be ok, where were BASS & TONE pots set when this measurement was taken?
> Q6 source 0.38 V looks good
> Q7 source 9.49 V looks good
> 
> Maybe someone could offer advice on what to check from the board? Is the biasing wrong?



According to your measurements, the gate voltage is higher than the source voltage on Q2 & Q4.  For NJFETs, the gate voltage should never be higher than the source voltage.

Things that might be wrong on the board: 
Q2 & Q4 drains not connected to Vcc.
Q2 & Q4 are damaged or _fugazi_.
R6 & R10 wrong value.


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## phbrick

Many thanks!

I re-soldered Q2, Q4 and Q5, now I'm getting plenty of gain both in 9V and 18V modes.
Measurements:
Vcc: 17.08 V
Vref: 8.54 V
Q1: 0.19 V
Q2: 9.14 V
Q3: 0.03 V
Q4: 8.66 V
Q5: 2.48 V
Q6: 0.37 V
Q7: 8.89 V


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## phbrick

So, next day there was again very weak sound.
Probably a bad solder joint.

I bought more mmjf201s, soldered them on adapter boards,
measured with Run Off Groove's jfet tester 2.0, and messed with
my solder joints until I got a set of 7 jfets with similar, stable 
Idss and Vp. BTW, it is better to use leftover leads from resistors
etc. instead of pin headers for the adapter boards because those
do not fit in the sockets of the jfet tester.

Now the pedal works very well, nice breakup and cleans up nicely with
guitar volume. For reference, the Idss range of my fets is .63 - .68 mA and
the Vp range is .82 - .86 V.


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## synchu

Another bump of an old one, same problems though. This pedal drives me crazy - after fixing a bad trace between R6 and Q1 drain which took some hours. Don't know whether this is due to this specific board gone bad, but whatever.
I got the poor thing working and sounding just plain bad with no attack and mid-high, high frequencies at all. Did some head scratching exercise, and some googling 'till managed to find the issue, e.g. the supposed "fix" of 39k/10n that's setting what is rather extreme Low pass filter. 
I took the effort to model the thing in Micro Cap and passed couple of analysis stepping the low pass cap value from 1pF to 10nF (through some common values - 220pf, 470pf, 1nf, etc.) and below are the results - green - captured at R12 and blue at the output). As one might see and definitely hear - there's quite a bit of difference - and it sounds nowhere near as good as when this 10nf cap is removed or at least decreased to a more sensible value.




Now, when it is removed the reason for it becomes obvious - the pedal sounds absolutely phenomenal, until you raise the gain/level - it oscillates like crazy - and after some time spent with matching all different varieties of J201 (SMDs and a bunch of NOS Fairchilds), changing few cheap ceramics that came with the kit purchased, I tend to think there's something with the PCB layout going on here. 
I am not keen on purchasing a different kit with a different PCB (as at this point I well may have purchased a 2nd hand Diablo). I definitely can play with the biasing (and intend to do so - starting with Q3 source resistor), but this doesn't seem to be used in the original.
As it seems the current revision of the PCB needs a bit of tackling. 
Will report back should I get somewhere further.

With respect,
Niki


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## Smrtokvitek

I have the same oscillation problem. I have omitted the high cut filter in rev 2 because it is not needed in the original one. It squeals in the top third part of the gain knob.
*This is probably a PCB problem and should be fixed.* I will try to select transistors with lower gain but I don't think it will be that easy to fix it.


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## Smrtokvitek

OK so I think I've found the problem. There is an error in the schematic that raises gain circa 2 times in every gain stage.

This is revision 2





This is the schematic that can be found on the internet with the different connections of C4, C9 and Bass+ trimmer.




This is the quick simulation in LTSpice to see the effect








I will try to fix it on the PCB tomorrow probably.


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## Robert

When you did you purchase your PCB?

That RC filter on the Gain pot was removed some time ago and the capacitors on the muamp stages were relocated.

I'll have to go back and look at the Boost circuit, I don't recall about that one.

The build doc is outdated and needs to be updated, but I'll have to build one of these now just to reconfirm that everything is as it should be.


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## Smrtokvitek

That is a pity I thought this was the problem :-/ I have rev2 PCB which I have bought from musikding as a kit in December.


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## Robert

Musikding _might_ have an outdated PCB...  I don't have the layouts in front of me on this PC so I can't say if Rev 2 is the absolute newest revision. 

Let me look into this and try to make sense out of it.

There has been a lot of debate on multiple forums about the orientation of that capacitor and it seems that oscillation has been an issue on other PCBs and vero layouts as well.....   I might have no choice but to just buy one and trace it myself.


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## music6000

Robert said:


> Musikding _might_ have an outdated PCB...  I don't have the layouts in front of me on this PC so I can't say if Rev 2 is the absolute newest revision.
> 
> Let me look into this and try to make sense out of it.
> 
> There has been a lot of debate on multiple forums about the orientation of that capacitor and it seems that oscillation has been an issue on other PCBs and vero layouts as well.....   I might have no choice but to just buy one and trace it myself.


There have been some Duds drawn up of this circuit.
When it was first available, it had Epoxy all over it.
Later versions don't have Epoxy,


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## Robert

I can't find a single picture of an _original_ unit with the Gain, Tone, and Level trim pots.....


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## Chuck D. Bones

Smrtokvitek said:


> OK so I think I've found the problem. There is an error in the schematic that raises gain circa 2 times in every gain stage.
> 
> This is revision 2
> 
> 
> 
> This is the schematic that can be found on the internet with the different connections of C4, C9 and Bass+ trimmer.
> 
> 
> This is the quick simulation in LTSpice to see the effect
> 
> 
> 
> 
> I will try to fix it on the PCB tomorrow probably.


I don't trust Internet schematics.  Seen too many wrong ones.
It's true that moving the bootstrap caps above the source resistors lowers the gain.  It also raises the output impedance and makes the circuit more sensitive to loading.  Plenty of pedal circuits have the bootstrap caps from source to gate, but I have yet to see one that has a source resistor below the cap.

High-gain circuits are very sensitive to layout and grounding.  Not just on the board; the off-board wiring and grounding has to be carefully laid out too.


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## Robert

Chuck D. Bones said:


> I don't trust Internet schematics.  Seen too many wrong ones.



Absolutely.   If it's not a classic circuit with plenty of confidence backing it (Fuzz Face, Muff, TS, etc) then I'm going to have to trace it myself these days.

Not saying there weren't good intentions, or that I don't make mistakes myself, but I've been bitten too many times.

I'm working on getting one of these now so we can find out once and for all, then I'll rework the entire PCB layout to try and address any oscillation problems.


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## cooder

I am defintely keen to find out about the correct schematic of this! I have the Deofol as per earlier pcb built but I find that have to have the tone control always dimed otherwise it sounds flat and dull.


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## Barry

From those gut shots it looks like a lot fewer parts than the one I built, which I never bonded with and sent to a buddy


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## Smrtokvitek

Barry said:


> From those gut shots it looks like a lot fewer parts than the one I built, which I never bonded with and sent to a buddy


It looks like it but there are different versions of this type of Diablo. There is a *Gain+*(pedalpcb) that has a switchable gain stage with trim pot adjustments and there is something like *Boost+ *(the photo from music6000 probably) which has only a different pot (setting of gain) that is changed by the switch.

I've just tried to "beep" my PCB and it looks like it is routed according to a schematic from the rev2 document I have posted. So I could try to relocate the capacitors connections to see if it helps.


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## Robert

Smrtokvitek said:


> There is a *Gain+*(pedalpcb) that has a switchable gain stage with trim pot adjustments



See that's what I was thinking too, but this guy does a review of the Gain+ and only mentions two internal trim pots. (Bass and Presence)








						Okko Diablo Gain + Review
					

Now, this is a pedal I’ve been curious about for years — there are a number of clips on YouTube but the astonishing thing is, they all sound wildly different from each other!  As if the…




					thoughtfulguitarist.com
				




I'm really concerned that we've fallen victim to another case of "This is _probably_ what's in there" or "This would be better if it were like _this_"...

As far as I can tell there are zero photos of the unit that was traced for the schematic that has been passed around the net.


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## Robert

Alright, I have the newer 125B (or maybe 1590B?) version incoming.   It's a start.


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## synchu

Great - waiting for the schematic here as well. 
I kinda made it work for me, by keeping it on the verge of oscillation (removed the low pass filter that made it sound dull, did a few more trimmers for biasing the trannies) and with careful gain staging and operating it sounds good. 
But this feeling that - "I am missing something"  ...


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## Smrtokvitek

I moved those 2 caps yesterday and it helped but it did not solve the oscillation problem totaly. The gain is definitely lower and the oscillation is still there but only at the very end of the gain pot. I will try to select transistors with higher Vp. Right now I have all of them in the range from 0.7V to 0.8V.


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## synchu

I checked my notes and I put a 100R trimmer in place of R9/R8 (at Q3 source) and played a bit with the bias - it also works in the right direction. Now, I am coming mostly from tube/valve technology - but the caps in discussion will be a typical bypass cap arrangement in one case (i.e. cap across the resistor) providing more gain and wider frequency response. While on the "Internet" schematic, it would be similar to providing for negative feedback and stability purposes, i.e. taming the high frequencies (albeit with tubes these are typically in the pF range and combine with the inherent Miller capacitance of the tube, etc, etc).
In short, this might make sense - nevertheless - an affirmation would be great.
And I might also pull the PCB out of the box and try that change


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## Robert




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## Robert

Who needs goop when you have a soldering iron...


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## Robert

Tis but a scratch!


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## Robert

I still have to pull and measure all the caps, but here's what I can tell you so far... 

The capacitor in question is directly across the Gate/Source.   The _original _schematic was correct in that regard before folks did their "magic".

However...   the Body control is completely different.   Granted this version uses a toggle switch instead of a pot, and it's entirely possible that the functionality was changed at some point, but it's not the same.

There are also one or two component differences.


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## fig

Wow, they didn't sandblast the resistors?


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## Chuck D. Bones

Robert said:


> Who needs goop when you have a soldering iron...


what a joke.


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## carlinb17

The best would be If they have the value of the capacitor screen printed on the PCB!

Secondly how much does the person scoring the capacitors make...


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## benny_profane

Sooo, melting caps is a marketable skill?


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## synchu

So that makes somewhat sense that the capacitor is for stability (and taming high frequency response purposes). Excellent progress, I’ll pull mine out and get the iron hot (watching not to score the caps  ).


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## Robert

benny_profane said:


> Sooo, melting caps is a marketable skill?



It's a foolproof way to prevent a trace by anyone who doesn't own a soldering iron and DMM.....  




synchu said:


> (watching not to score the caps  ).



It's not like the original if you don't ...


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## cooder

I guess the scorched caps gives it the hot soundz.


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## synchu

Got the caps across the q2 and q4 source and gate. Much better and sounds much better (didn’t try the scorching - “may it improves sound, though” )


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## music6000

Robert said:


> It's a foolproof way to prevent a trace by anyone who doesn't own a soldering iron and DMM.....
> 
> 
> 
> 
> It's not like the original if you don't ...



Let me know if you damage the Traces, I'll send some matching coloured circles! 


This seems to be repetitive:


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## Smrtokvitek

Robert said:


> I still have to pull and measure all the caps, but here's what I can tell you so far...
> 
> The capacitor in question is directly across the Gate/Source.   The _original _schematic was correct in that regard before folks did their "magic".
> 
> However...   the Body control is completely different.   Granted this version uses a toggle switch instead of a pot, and it's entirely possible that the functionality was changed at some point, but it's not the same.
> 
> There are also one or two component differences.


That is good to know. So this means the current oscillation problem is probably caused by the bad layout I guess.

Can you also measure Vpp and Igss of the jfets? I am curious if they are off the shelf component or if they are pre-selected for having specific parameters.


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## Robert

Yes, very likely.    I have a much improved layout for the new schematic worked up, I'll have a prototype built in about two weeks.

I'll run the JFETs on the DCA75 as soon as I get a chance.


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