Dunlop - JDF2 Fuzz Face  [schematic]

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Bside2234
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Post by Bside2234 »

I recently acquired a Dunlop JDF2 Fuzz Face. It needed some repair so I thought I'd do up a schematic for it since as I was going through it a few things seemed kind of odd or at least not the norm from what I know about the Fuzz Face circuit.
Here's what I thought was odd and/or I didn't know what they were for:
C5 - Cap to -9V on the input. What does this do?
C3 - It seems installed backwards to me.
TP2 - It's on the emitter of Q2. I think I usually see this trimmer on the collector?
Fuzz - The way this was hooked up really threw me. I checked it multiple times. Lug 1 goes right to the battery +. Lug 2 is connected to the + of C1 (22uF) and the other side of C1 connects to -9V. This whole thing seemed odd to me and C1 seemed backwards. Lug 3 seemed to be connected to the normal place other than the trimmer TP2 being there.

Any thoughts on any of this? I can check any connections again. I'm pretty sure it's pretty close to accurate though. I've gone through it 3 or 4 times already and it seems to follow this schematic. I took a few pictures while I had it apart too.
JDF2 Schematic.jpg

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Post by Bside2234 »

Oh, I forgot to say that it didn't seem like anything was tampered with before I got in there and did some work on it. Here are some pics:
20190111_143838sm.jpg
20190111_143843sm.jpg
20190111_144033sm.jpg
20190111_144023sm.jpg

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j_flanders
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Post by j_flanders »

Here's the correct schematic:
Image

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Bside2234
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Post by Bside2234 »

j_flanders wrote:Here's the correct schematic:
[ Image ]
Which is what I have but the negative of C3 clearly goes to C5 on the PCB.

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Post by j_flanders »

Bside2234 wrote:
j_flanders wrote:Here's the correct schematic:
Which is what I have but the negative of C3 clearly goes to C5 on the PCB.
Correct, C3 neg to C5. Thanks.
Corrected my schematic:
Image

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Post by Bside2234 »

j_flanders wrote:
Bside2234 wrote:
j_flanders wrote:Here's the correct schematic:
Which is what I have but the negative of C3 clearly goes to C5 on the PCB.
Correct, C3 neg to C5. Thanks.
Corrected my schematic:
[ Image ]
I'm not seeing any difference between your schematic and mine (other than mine has all the header connections). Maybe I'm missing something. What makes it the "correct" one?

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Post by j_flanders »

Bside2234 wrote:
j_flanders wrote:
Bside2234 wrote:
j_flanders wrote:I'm not seeing any difference between your schematic and mine (other than mine has all the header connections). Maybe I'm missing something. What makes it the "correct" one?
You gave the impression having doubts about the one you posted so I posted one from a pedal I traced.
Yours is nice when working on the pedal, with the molex connector and everything. To just get a quick overview what FF circuit they were using it's harder to follow unless you connect the dots and put all the parts in the right place.

Do you remember what transistors were in yours?

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Post by j_flanders »

Oh, and because the thermistor and pot values were missing in your schematic.

(where's the post edit button?)

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Post by Bside2234 »

j_flanders wrote:Oh, and because the thermistor and pot values were missing in your schematic.

(where's the post edit button?)
Oh, I thought maybe there was something not right that I didn't see and wanted to fix it. I have since completed the schematic more. When I posted that I didn't have all the reference done. I hadn't pulled any resistors to see the reference under them yet. I wasn't sure I was going to or not at the time so I just posted what I had.

As far as I know they got rid of the edit button.

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Post by jalmonsalmon »

Interesting FF schemo and I only care about one thing... does it sound good? :hmmm:

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Post by Bside2234 »

jalmonsalmon wrote:Interesting FF schemo and I only care about one thing... does it sound good? :hmmm:
I honestly don't remember. It's been a year since I had it in my hands.

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Post by roseblood11 »

660µF bypass cap? What sense does that make?

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Post by polifemo »

Late to the party...

Just bought a 2:nd hand unit with the plan to build a totally new circuit inside the enclosure, but I find that the Fuzz actually doesn't sound all that bad!

Would like to get rid of C5, or replace it with something considerable smaller, and/or add some series resistance to the input as well as do some fine-tuning of the bias and the feedback loop*.

I realize that I need to remove the rubber pad in order to loosen the switch so my question, to you that have modded this unit, is; Does it come off easy, and is it easy to glue it back on again?


* Does anyone know what the feedback loop is set to as standard?

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Post by polifemo »

Swapped C5/6.8nF for a 220pF cap and the pedal opened up in a nice way (as expected)!

Never removed the switch/circuit board as it was easy to get to the capacitor in question, and as the trimmers for bias and feedback seem to be set to my liking (bias around 4.5v and feedback probably below 100k) I'll leave the pedal as it is (for the moment ;-) ).

A really good Fuzz Face now I would say :-)

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Post by polifemo »

Decided to tweak this one a little bit more:

Lowered the input cap to 0.47uF - which I usually find to be a good compromise between tightness/full low end in a Fuzz Face circuit - and the pedal opened up considerably.

Set the bias a bit higher and tweaked the other trim pot (for the feedback resistor) to my liking.

The fuzz now has more bite, cleans up much better, feels more dynamic and sounds more open overall.

Was planning other mods (increasing the 220r resistor on Q1's emitter in order to lower its gain a bit more, changing the volume pot to 100k and increasing the output cap to 0.047uF) as well, but the fuzz sounds very very good right now :-)

Very easy mods (Swapping C5/6.8nF for a 220pF cap and lowering C3/2.2uF to 0.47uF) indeed!


Ps Might solder a 1.8k resistor in parallel with R2/680r in order to get the output down a bit as I prefer to be able to run the volume pot wide open.
The cleans when rolling down the guitars volume get really sparkly then. Ds
Last edited by polifemo on 09 Dec 2020, 07:36, edited 1 time in total.

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Post by polifemo »

Did the "1.8k in parallel with the 680r resistor-mod" and ended up with a total resistance of 483r which is about the original value (470r) for that resistor.

The output volume is now "better" when running the volume pot wide open, but I think that I prefer the actual sound of 680r.
Might undo the mod and use this FF in musical situations where the fuzz is on all the time.

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Post by soulsonic »

jalmonsalmon wrote: 06 Jan 2020, 05:11 Interesting FF schemo and I only care about one thing... does it sound good? :hmmm:
Mine sounded better after I changed C3 to a 1uF film cap. That's the only mod I've ever done to mine. Cleared up the muddiness a bit.
BTW, those big electrolytic caps are to keep it from oscillating, though I think having separate decoupling for each stage works better.
"Analog electronics in music is dead. Analog effects pedal design is a dead art." - Fran

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Post by polifemo »

Once one gets rid of the muddiness, it's actually a quite nice fuzz.

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