Dunlop - JD-F2 Fuzz Face, revision D

nek314 · Post by **nek314** » 19 Apr 2008, 23:56

I have a Dunlop Fuzz Face ("Dallas-Arbiter", as it was marketed, but the Dunlop reissue,) the JD-F2 model, revision D. The circuit has a couple more parts than the standard fuzz face, including two gain adjusting trimpots, a few extra caps, two oddly large (330 uF) electrolytics, and what I believe is a thermistor (designated as RT1, perhaps to deal with the known temperature instability of the germanium transistors; this pedal supposedly has NKT275s) ; I wonder if anyone has a schematic of it handy or has had any experience with this particular version. I've looked all over the net, but the only available schema are of the classic, bare-bones fuzz face. I'm trying to do a combination of the Roger Mayer and Fuller mods shown at http://www.geofex.com/article_folders/f ... fftech.htm, but this slightly more complex circuit has thrown me for a loop. I'm consider just "devolving" it and cutting it down to the original circuit.
Anyway, sorry for the overlong post, my first, as it happens.

analogguru · Post by **analogguru** » 20 Apr 2008, 06:15

with some photos of thre track (solder) side and the comp side you could be helped.

analogguru

Solidhex · Post by **Solidhex** » 20 Apr 2008, 10:17

Yo

Yeah I have the same version. I know they get a bad rep but I honestly think a lot of the Dunlop fuzz face reissues sound pretty damn good. As far as that circuit goes I've been able to figure some stuff out that might help. In no particular order the -9v feed seems to be the top layer of the board, bottom layer is ground. Collector of Q2 is routed through the 100k trimpot labeled "TP2" then through another resistor to Q1's base. That would be your normal fuzz face 100k feedback resistor. No need to mess with that for the Hendrix mods. The collector of Q1 is routed through the other 100k resistor so that's doing the job of the 33k. Leave that alone too. We need to find the 470 ohm and the 8.2k resistors. I believe the .1 cap (small red with 104 on the side) would be the output cap so if you trace that back you'll find the resistor located to the far upper left ( when looking at the board with the footswitch on the bottom and the big electro caps on the top right) is connected between it and the collector of Q2 making it the "8.2k". Sort of weird there's no trimpot there? You would replace that with the hendrix mod 18k value. The other resistor connected to the output cap seems to be the one on the bottom right of the circuit board. You would unsolder a leg of that, connect it to lugs 2 and 3 of a 1kb pot and connect lug 1 to the pad you had unsoldered the leg from.
In the Hendrix mods you would replace that 470ohm with a 1k. I'm not sure how differently the Fuller contour control would work with these new biases going on. Someone with more experience would have to let us know. You could leave the 470 in there and see how it works with the 1k pot. If its weird replace the 470 with a 1k. Last but not least you need to either replace your Fuzz pot with a 2kb or insert a 1k resistor between the Fuzz pot and ground ( lug one far right when looking at the back of the pot)
Having said all this I would actually just recommend building your circuit from scratch and replacing the board completely. GGG has one that would work well. There's a bunch of extra stuff on there and who knows if it will all jibe with the mods, I dunno. Its such a simple circuit. If you do be sure to save the brass colored potentiometer nuts. I remember them having a special role in keeping the pots in place on that enclosure. Hope that helps

--Brad

nek314 · Post by **nek314** » 20 Apr 2008, 13:11

Wow, Solidhex, that was much more info than I could have possibly hoped for. Thanks a lot! I'll be sure to let you know how it works out.

nek314 · Post by **nek314** » 20 Apr 2008, 14:45

For Analogguru, pics of the top and bottom of the board.

Moment of truth - I'd already replaced C2 and C3 before I posted this topic, not having a quite full understanding of the circuit. C2 I think was the same as C5 and was replaced with a .47 Mallory. C3 was some kind of tantalum, replaced with a 4.7uF electrolytic, thinking it was the input cap. So now it's pretty messed up, I only barely get any output, even at max. So obviously, something is wrong. Anyway, I'll be working on these today, so hopefully I'll get it up and running soon. Thanks for the quick replies, guys.

nek314 · Post by **nek314** » 20 Apr 2008, 16:25

So upon further inspection, I'm now pretty certain that I was correct; C3 is the input coupling cap, originally 2.2 uF electrolytic (in the classic fuzz, I'm not sure what it is in this model,) now 4.7 uF electro. C2 is the output coupling cap, originaly .1 uF, now .47 uF. This, of course, brings to mind the questions, "What does C5 do, if anything (one leg doesn't look like it's connected to anything,) and what are those huge electros on the corner for? Also, why doesn't it work? We'll see how that works out.

Solidhex · Post by **Solidhex** » 20 Apr 2008, 20:13

The big electros appear to be connected between the -9 supply and ground. C5 appears to be connected from the pre 2.2uf input signal and ground. I think RT1 is connected from the Q1 collector/Q2 base junction to ground. Possibly to eliminate Radio intereference? Your output cap looks more like a .047 than a .47 to me. Should work fine. The 2.2uf looks like its oriented correctly but the fact that it was non polarized to begin with might mean that is what's meant to be used there in the circuit? Might be the reason for your output problem. Not sure.
Like I said before it would take less time to wire a board up from scratch than to fiddle with this board. Also the transistors that are in this board might not bias up correctly once you've changed their biasing resistors with the hendrix mods. Since they aren't socketed you're stuck with them. If it doesn't work you'll have to reverse your mods. Mucho time wasted.

--Brad

nek314 · Post by **nek314** » 21 Apr 2008, 12:19

Thanks for the advice, Solidhex, but I'm not worried about the time or effort involved. This is one of my first forays into modding pedals and I'm just trying to learn the ins and outs of it, so I'm trying to just work with what I have.
Anyway, I got it working again; it seems that the schematics on the site I linked are incorrect with respect to PNP transistor models - the input cap's positive side is supposed to be connected to the base of Q1, not the negative. I took it out, suspecting this, and sure enough, there was a positive DC voltage on that side. Luckily, I ordered extra, being that the first one I put in there is probably hosed. It works! It's sounds pretty crazy, but I'm glad to get that far. I'll be replacing the voltage divider resistors on the collector of Q2 with 1k and 18k, it seems to have the standard 8.2k and, crazily, a 6.8k (unless I'm reading the color code wrong, which I doubt, that resistor is the one just above the right side of the switch in the photo above, if you care to give a second opinion.) I'll be working up the schematic for this model, if you care to see it.

Solidhex · Post by **Solidhex** » 21 Apr 2008, 21:54

Yo

That is very strange. The schem in the RG article is correct for PNP fuzz faces. The negative end of the cap should be connected to Q1's base in a pnp fuzz face. If yours is working the other way it must be a negative ground version? Well if it works screw it, go ahead with the resistor changes.....
All right just when and took a look. It is a NPN circuit. They must stamp NKT-275 on the tranny's for mojo-ness. The "6.8k" appears to be 680 ohm to me. Just throw the 1k there.

--Brad

nek314 · Post by **nek314** » 21 Apr 2008, 22:24

Those bastards! That's awful shady. Well, I'm about to dig in and try and get all these mods done. Quick question, though. Why the big electros? It's not like they're needed to filter AC or anything. I'm not sure what they're up to there.

Solidhex · Post by **Solidhex** » 22 Apr 2008, 05:12

Yo

In a regular FF circuit the Q1 emitter goes straight to ground. Here you'll the trace from the emmitter hits a 330 ohm resistor to ground then the 2 330uf electro's to ground. Something to smooth power supply would just go between the power rail and ground. Lots of weird stuff ( to me ) in this circuit.
I would imagine all these changes would be to make the circuit work with their transistors and also eliminate certain problems that aren't acceptable in modern pedals ( radio interference, germanium bias drift). My knowledge is pretty limited so I'm not quite sure what is doing which here.

--Brad

nek314 · Post by **nek314** » 22 Apr 2008, 17:54

I finished working on this pedal yesterday, all is well. Sounds pretty good, too. I wound up dropping the 6800 pF cap from the input; I like to let all the highs through and deal with them at the amp. I also added a 220 pF cap across the trimpot and 10k resistor off the collector of Q1, for supposed smoother distortion. No complaints here. Thanks, Solidhex, for your help. I also modded my TS-9 last night (successfully!), which I'll post on in another topic.

Solidhex · Post by **Solidhex** » 22 Apr 2008, 18:05

Right onnnnnnnnn

--Brad

nek314 · Post by **nek314** » 23 Apr 2008, 12:02

By the way, to any board admin who happens to see this, upon further thought, this topic probably belongs in the "Workbench" forum. My bad.

nek314 · Post by **nek314** » 05 Jun 2008, 15:23

Hey all, as promised several months ago (I've been busy,) my take on the schematic of the Dunlop Fuzz Face reissue, circuit JD-F2, revision D. Hopefully someone around here can explain what all that extra crap in the circuit is; it's certainly a bit more cluttered than your standard fuzz face. Although the trimmers are nice. One further note- in the schematic I have the input cap's negative leg on the base of Q1, but in my Fuzz Face, I replaced that cap and it's only works with the positive end on Q1, as mentioned earlier. I'm not sure why, it is most definitely a positive ground circuit, thusly PNP transistors, but beyond that, I'm stumped. But hey, it sounds good, so I won't complain.

Solidhex · Post by **Solidhex** » 14 Jun 2008, 18:39

Yo

Yeah. I went back and did a continuity test between the grounded side of the resistor connected to q1's emitter and the positive battery terminal. Got a beep. I Wonder why I ever thought it was a NPN circuit?

--Brad

soulsonic · Post by **soulsonic** » 14 Jun 2008, 23:10

I have one of these too. It's a decent Fuzz Face to my ears. Only difference I see between yours and mine is that mine had a Tantalum cap for C3. I replaced it with a 1uF film cap and it made it sound nicer and more "boutique-y". 1uF still lets enough low end through for it to get the usual Fuzz Face kinda sound. It actually makes the 2.2uF seem excessive to my ears.

nek314 · Post by **nek314** » 15 Jun 2008, 14:34

Mine had a tantalum cap on the input as well, I replaced it with the electrolytic in the photo, though I can't remember what value I used.

nbabmf · Post by **nbabmf** » 02 Mar 2010, 03:29

I've got one of these and thought it was way too woofy. I got rid of C5 and it helped considerably. I also noticed the trimmers weren't really set for a very nice sound from the start, so I tweaked them a bit, too. It's not a bad fuzz, but I think it needs work before it should be sold in the red Frisbee!

nek314 · Post by **nek314** » 02 Mar 2010, 10:50

I've used it with and without C5 (as referenced in the above schematic,) which is there to prevent the fuzz face from being a radio, and settled on some value less than 1 nF which I think does the job without attenuating any audible frequencies. The trimmers adjust the collector voltage of Q1 and the negative feedback from the emitter of Q2 to the base of Q1, but both have an effect on the voltage on the collector of Q2, to which I've added another trimmer to fine tune. I try to have minimum feedback while still getting close to half the supply voltage on both transistors (both socketed and replaced with NOS PNP germanium.) Another nifty thing to do if you have a spare power supply laying around, such as one for a broken external hard drive, is to splice on a battery snap and say goodbye to batteries forever. Of course, you have to be careful about polarity and make sure that the PSU has an isolated ground, but the results are quite nice. I used a 12 volt supply as I like my fuzz to be somewhat crisp and cleaner than usual, but I also installed a pot to drop the supply voltage if I felt like it. Sounds quite nice to my ears. I can post pics if anyone is interested.

Dunlop - JD-F2 Fuzz Face, revision D [schematic]