This one has been on many peoples list for years...
Traced by Deadend Fx and the schematic is avaiable HERE.
A "Sag Depth" pot is the only mod but if you want to build it as the original, just replace the pot with a 1,5k resistor.
Verified by Tom.
This one has been on many peoples list for years...
Traced by Deadend Fx and the schematic is avaiable HERE.
A "Sag Depth" pot is the only mod but if you want to build it as the original, just replace the pot with a 1,5k resistor.
Verified by Tom.
HALLELUJAH! I've been waiting for this. Now off to order some parts...
ReplyDeleteHeck yah! Long time coming.
ReplyDeleteI'm getting gobs of fuzzy dirt, plenty of volume and the treble control is working but nothing else is functioning yet. I tried pf5102's and J201's.
ReplyDelete10k in row 9 should connect to IC 6 not 5. I'll have to search more another day with fresh eyes.
DeleteI watched a demo. I think that it is working. The gating isn't as extreme as I would have expected. I'll have to tinker but I think you can tag it. Thanks as always for the elegant layout.
DeleteOh yeah, the Sag control seems a bit useless. I'll probably ditch it.
DeleteThanks for diving right into it, Tom! Did you follow the build notes re: the trimpot? If not, I imagine it would open up the utility of the sag control.
DeleteI used a "stringed instrument" and everything. It does interact with the gating sensitivity. But honestly you have so many controls related to the gate, which is relatively subtle in the end (light/heavy being especially subtle). I'd probably decide on a general value and add a fixed value instead. Maybe you or one of the other folks will have different results, or find something that I missed. Don't forget to share your impressions, I'd be interested.
DeleteAh, yes, a "stringed instrument" [twirls moustache, chuckles with French accent].
DeleteThere are a hell of a lot of controls for that one function, you're right. I was thinking of ditching the momentary switch and just making the on/off switch into a stomp. And good to know the light/heavy switch is subtle, I might mess with the cap values on that. Won't be able to get around to it until at least next week, but I'll definitely report back to share results!
I think auditioning JFETs is needed with this circuit. Trimmers on the drains are probably necessary honestly. I double checked my work and checked the layout against the schematic this evening and didn't see any anomalies. But when I checked voltages I saw that they didn't match the listed voltages on the schematic. The layout works, and the drive sounds rad. It gates when the drive is backed off and the LED responds as it should but I think the FETs need to be optimally charged for the desired effect. (Unless you have a bucket of J201's.) I don't.
ReplyDeleteThe extra sag control is a necessary evil, otherwise as our experience with an original unit proved, sag dimishes as drive is increased. Once I got passed noon on the drive, the "snap, crackle, pop"effect faded greatly. Even the owner of the original unit stated the same, so are experimentation was to correct this. It basically adjusts the bias of the BJT base to ground, and as we pointed out in the DEFX build doc, has a limited range, generally between 9 and 3 o'clock. If you want to try a 2k2 pot, instead of a 5k, go for it. I figured covering a larger range would make up for potential variations of BJT and JFET combos in the sag section. We posted a short clip of it in action on our IG page;
ReplyDeletehttps://www.instagram.com/reel/CyEDYriOIkl/?igshid=MzRlODBiNWFlZA==
As for the J201's, yes, audition you must. As well as the 5457's, and the 5089. I initially breadboarded this with NOS thru hole parts from my stash, and then settled for SMD 201's. There are build pics here;
https://ilovefuzz.com/viewtopic.php?f=151&t=3277&start=6075#p1437693
With the plethora of bogus parts floating around now (especially jfet's!), would not surprise me if non-working builds are due to that.
BTW, in our build doc, the PF5102 is only recommended as a replacement for the 5457, not for all the jfet's. Since they are acting as VCR's, there's more flexibility with these. I tried many different fet's to replace the 201 as well, but they just didn't have the same mojo as the 201's, so I stuck with them.
DeleteDino! A million thanks for your work at resurrecting these lost treasures.
DeleteHey, thanks for that info. Very appreciated.
DeleteThis comment has been removed by the author.
DeleteYou're all very welcome. As for the extra depth pot, consider setting up this way; start by setting the sag depth pot to the mid position, then set the amount of drive desired. Once drive is set, set the threshold via observing the envelope threshold LED. When you engage the sag, finalize the sag depth pot to get the desired burning amp effect on the decay.
DeleteNow the cat is out the bag...
Deletehttps://4.bp.blogspot.com/_9QRLddwrs68/TP3TdRxrZ0I/AAAAAAAAAjc/dElFxd9jjCM/s1600/Picture%2B3.jpg
My 2013 Fuck has the 2 tiered board layout ( the base drive and crackle circuits are separated) but has a similar component selection to this older board. 330nfs, a 1N914 diode and a 22uf instead of one of the 10ufs - haven't traced it to see which one but just thought I'd add this in.
1N914 instead of the 1N4148.
DeleteAlso, even though the board is marked for the same JFET configuration, one of my J201s is actually another 2n5457
Interesting, thanks for the inside scoop, Ross. The diode swap is basically 1-to-1, since they have the same forward voltage and similar capacitance. I'm assuming the 330nF cap is a substitution for one of the 220nF caps, eh? And that's curious about the 22uF cap - might be cool if it were on the heavy/light switch. All in all, worth experimenting perhaps?
DeleteThe 22uf is on the drive board as opposed to the crackle board. It's coming off either Q2 or Q3 but I haven't traced it to check.
DeleteBoth of the 220nfs are 330 in my version (also printed on the board like the old version I linked). Looks like the design has been updated over time.
Q1 or Q3 but I believe it may be 3
DeleteMonths later and after much tweaking, it seems like the one component that has the single greatest impact on the crackle circuit overall is (in this layout) D1, the LED from pin 5 to ground. I think (correct me if I'm wrong) that it biases the crackle circuit, so the forward current of the LED (as indicated by its colour) will completely change the response & range of the controls. I settled on a diffused green LED: much broader results than yellow, but all still very usable. Red offered almost no range, while blue was way over the top.
ReplyDelete