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I was contemplating the use of this circuit for a different pedal and I was curious about the role the schottky diode plays, and whether or not it has to be a schottky... I imagine the answer is yes but I thought I'd ask anyway.

I wanted to make a single jfet distortion with 2 red LEDs soft clipping but I highly doubt having 2 negative feedback loops would be a good idea for a single transistor so I wanted to make it a distortion loop that nominally adds some compression. I found a schematic online that shows a compression control potentiometer in the NFB loop of a bluesbreaker circuit but I can't find it now that I actually need it haha.

Thanks for any help in advance and I will continue to try and crack this in the meantime.

After missing out on the last of the fatpants boards two years ago, I get the feeling that one could easily incorporate the comp switch on the flabulance as a variable compression control (a/k/a the exact same as on the aquataur website from which it was derived) and call it the complex. I deleted a later part of this post where I elaborated on the pun ad boredom.

I really, really want a small board that has a low output impedance with a BJT buffer but also a pre-gain bass control off the mp102, which means 3 transistors for like 1 sound... IDK...

So, a caveat: Excuse the missed notes, the poor playing, the bad lighting, the quality of the camera phone microphone, etc. etc. etc. There's a reason this video is unlisted - it's here only to show what the flabulanche can sound like on some different settings.

I mention this in the video, but the guitar is a jazzmaster with seymour duncan p-rails pickups, and the amp is an 18w marshall clone.

Here goes nothing:

So, as some (or even none) of you may remember, I posted recently about modifications to the flabulanche pedal based off of Jon patton's snow day overdrive.

I am pleased to report that I followed his advice and only added the "range" control from the omega circuit.



That's the photo covered with foam, because I wired the range control incorrectly - I accidentally have the 22k in line between the 33k and the 3n3 rather than in series with the 500KA control. Once I fix this I will post a photo showing the correct wiring for the additional range control.

Here's the completed pedal:



I used a 1590B, I think? Thanks to the rullywow breakout board it was enough to fit a battery in there too, should the need arise.

The problem was I originally biased all three transistors off of a battery, which was dying - so when I plugged it up to my 9v supply it hardly distorted at all. I pulled out the multimeter and q1 was biased at 13v, q2 at 13.5v, and q3 at 15.5v! It's possible someone would have liked the soud I'm sure, but it wasn't for me.

Re-biased to where q1 ran at 12v (halfway between 5v and 7v as per the omega circuit), q2 ran at 11.25v (may turn it down some when I get a chance, IDK), and q3 at 13v (as per the original instructions).

I took a demo video, but it was terrible - the volume from my amp overpowered the camera microphone so all you can hear is mic distortion unfortunately :/

I'm out of town until Monday, but here are my impressions from the 30 minutes I got to play it:

- Holy mother of god this is the best sounding boost/light OD pedal I've ever played... at the top of the gain control though it almost sounds like it's hard clipping, but at low/med gain levels it's like playing a combination of the EP booster and the SHO but with edge-of-breakup harmonically rich tones through a pedal
- Cleans up better than any pedal I've ever played... I hope this isn't due to the incorrect wiring of the "range" (bass roll-off) mod... Seriously it goes from AC/DC at 10 to completely clean at 7
- It has that jfet "detail/presence" that makes humbuckers sound like single coils and single coils sound like a piano. Even on completely clean/unity settings it's significantly more present. Again, I hope this isn't an unintended byproduct of the mis-wired "range" control.
- The compression isn't really noticeable from a listener's standpoint, but it's tasty if you're playing. I would like more aggressive compression but then again I used a mpf102 for q1. I notice it, for sure, but it's not even in the same ballpark as my bluesbreaker-derivative pedals or tubescreamer-based pedals. If you think of a boss SD-1 as being a 5/10 on the "compressed" scale, the "hi" position of the flabulanche is like... a 2 or 3. I'm definitely building another but I'm going to revert to something closer to the Aquataur compression circuit (adjustable 500k "sag" control) so I can get really compressed, sustain-y leads when I engage the "solo" footswitch (more on this soon)
- It makes everything really hi-fi... So much so that it makes my 1974x lite iib amp sound like I'm playing through a concrete barrier without it. Similar thing to many boost pedals but this has the additional benefit of sounding spectacular at low volumes.
- I used a mpf102 in q1, so for me, the gain goes from clean to AC/DC levels. I've read quite a few of Jon's posts where he speaks about how much gain the flabulanche makes, so for my purposes (which never foray into metal or anything resembling post-1980s rock n' roll) I figured a lower gain transistor (mpf102 vs. 2n5457) would bring it closer to what I want... boy did it ever.

So, my plans for a future pedal include two things - a separate footswitch to put a 100k pot in parallel with r23 (I think, it's one of the two that for the voltage divider on the output section of the circuit) and a 500k pot in place of the existing 220k "hi" control. The idea is that they'll work like a 'solo' switch, where I can increase the volume and compression for lead lines and still keep the pedal on all the time. Rather than have a set volume increase, a 100k pot wired correctly will allow someone to change the ratio of the divider network (100k in parallel with 10k = 9k ohm, so it would have a slight volume boost even at zero, but then again it's a solo switch so... yeah.) whereas the additional compression potentiometer can be added to the existing compression scheme, so you can have an additional boost/compression circuit without extensive modification.

Honestly, my biggest complaint is that this pedal isn't more popular... I took a chance seeing as it was a jfet-based OD with new and exciting compression circuit, but I would take that chance again 10 out of 10 times... It's really like having another amp attached to your amp lol.

FWIW, my modifications were:
- Q1: MPF102
- RS(Q1): 340 ohms (calculated value for mpf102 as per ROG)
- C2: 4.7uf (vs. 470nf)
- RS(Q2&3): 390 ohms
- Exclude R1
- 1M -> 3n3 -> 22k + 500ka potentiometer part of ROG's "omega" circuit wired to the input

So, I had some questions regarding the flabulanche and some modifications I wanted to make. I noticed that ROG made a "high gain fetzer valve" (the omega circuit) which I was interested in not so much for additional gain but rather for the variable input loading - additionally I wanted to move the gain control from between q1 and q2 to the source of q2 - the idea is to essentially convert the flabulanche to a cascaded boost festival.

I want to add input loading to the flabulanche to make the volume knob cleanup as righteous as possible. I know it's great already from the videos but I want to experiment because I'm weird like that. In no particular order:

1. If I use a mpf102 in q1 and feed the circuit 24v, can I substitute a fixed value resistor to ground for the gain pot, and add a potentiometer to q2 to adjust the gain via q2 bias (like the fatpants does)? Or would that be too much gain? I want light clipping at noon on the "gain" (slash fat) control.
2. If I add the omega input impedance control, will I need to change the rest of the cascaded fetzer part of the circuit to a higher resistance? (For example, using 50k trim pots on the drains). I ask because the omega article seems to imply that it's specifically sensitive to changes in input impedance - so I was curious is the high circuit impedance (pre-buffer) is necessary to get the most out of the "range" control.
3. if I wanted to implement a 'body' switch, should I just wire another cap in parallel with C2 (and a 10m resistor between the two) and use a spst switch? (again, like in the fatpants) Or should I add this to Q2?
4. If I use higher resistance drain trim pots, will I have to change the source resistors? Or will 470 work fine?

Thanks in advance for any help, I'm going to try and answer these questions myself through research in the meantime.

Can you adjust frequency response (for example a bass rolloff circuit) by varying the resistors/capacitors on the source prong of a Jfet?

I ask because I'd like to add a potentiometer in conjunction with the "Fat" control, instead of a body switch, to adjust the frequency response of a JFET boost. I've been looking at the ROG Omega and I became curious if you could add a 'fat' control (q1 gain like in the fatpants) and something like a 'body' control but lower frequency so that it acts like a bass cut (I don't know if you'd be able to boost bass or what have you, I'm just spitballing really because I just watched a youtube video on how to calculate the gain of a transistor and I was completely lost.).

Obviously this wouldn't be a true treble/mid/bass tonestack, just a way to implement a similar functionality by adjusting the input impedance ('range' on the ROG), gain ('fat' on the fatpants), and whatever affects bass response. The overall goal for the pedal would be an always-on low parts count tone shaper/conditioner/enhancer with an output buffer. Maybe as part of an OD/Dist/Fuzz pedal eventually, I don't know. I'm mostly curious as to whether this is possible.

As always, thanks for any and all replies.

So, earlier today I completed my fatpants build (just have to install the indicator LED) - I fired it up to see if everything was working and much to my chagrin it was. I had the buffer working since forever but only recently got the boost section functioning.

I know there's no good reason to use carbon comp resistors but I did anyway. When my 12v adapter comes in (already got an appropriate charge pump and internals to run at 23v btw) I will have this running at the full mccoy. If not for the zener diode it would work up to 15v (or 30v internally) but I'm going for as close to the echoplex as I can.

Instead of a TIS58 I used a MPF102 for Q1 - I've read that this is very close to the TIS58 and significantly cheaper so I went with it. Q2 is a standard J201 which I like very much.

It was kind of a pain to get everything working properly because I included a true bypass/buffer dpdt switch so I could hear the effect of the buffer a little better (and potentially use it in conjunction with my buffered pedals like my modded SD-1), but after studying the sunking build guide I was able to get everything working properly. The trickiest part was the "sw" part of the board (I copied the layout of the PCB onto perfboard because I'm not creative enough to design my own) but once I figured that out it was smooth sailing.

I still have to clean a few things up (the fat control isn't insulated very well so if I jostle it around I get jumps in volume and intermittent scratchiness) but overall I'm pretty much there in terms of the build.

I also used exclusively red wire so it was insane trying to get everything wired up. For my next few builds I will definitely do exactly the same thing because all I have is red wire and I don't want to spend money on more. But in a perfect world I would use different colored wire.

Hmmm

I don't have a demo video yet (and am hesitant to say when I will post one if I do at all) but you've all seen the youtube video of the fatpants in the 1590A enclosure. It sounds like that. I built mine in one of the tiwanese BB seconds enclosures that Small Bear sells. I'll post some pictures later so you all can see just how hideous and awful the inside of it looks - if you're squeamish or OCD I would just skip coming back to this thread once I post photos lol.

Really, really like this pedal though. Gorgeous clean sounds out of it and later on if I get some alone time I will report on how it sounds into a cranked 1974x baby will (18w marshall clone).

Would I connect the start of the circuit to the source of Q1 and then to ground? I imagine I'll need a capacitor in series with the clipping diodes to roll off some bass?

Also, (and this is a separate question) if I wanted to get Q2 to clip, would I increase the value of R9? I was reading about the jfet Vulcan and he uses diodes to prevent hard clipping of the transistors, would this be necessary/a good idea in this application?

To be clear I'm just curious. Thank you in advance for any and all help.

Edit: when I say curious I mean I'm definitely going to add this feature to the fatpants... I'm just not super well versed in circuit design so I'm uncertain as to how to proceed.

So, I posted another thread in the general discussion, but as it turns out all of my problems were either misinterpretations of the schematic/layout or bad solder joints, so I fixed those.

My charge pump however is still not working right - It's the 3PRR which is a charge pump/true bypass thingy.

I'm seeing (with a 9.6v input) ~10.3v right now at the +18 pad. I'm seeing ~9.2-9.3v at the + pad of c3, and ~10.2v (sometimes 10.3v) at the + pad of C4

I used 5818 diodes (I think those are the ones - their part number/designation is one higher than the ones recommended in the build document), and the charge pump by itself worked fine. Thing is they do take out about .3v - and with R2 the I/C (LTR 1054) is seeing ~8.2v or so.

Pin 1 on the LTR shows 1.15v, Pin 2 shows 1.5v, pin 3 shows 0v, and pin 4 shows -.95v
Pin 5 shows -1.5v, pin 6 shows 2.6v, pin 7 shows 1.45v, and pin 8 (which I think is getting 8v from the supply)

Also it seems like a ~1v drop for a 10r resistor is a bit much so I'm going to check r2.

So, my suspicion is that my charge pump is torched, because if I'm looking at this correctly (and I may not be because I'm a huge newb) I should be seeing a combined 9v from the outputs of pin 2 and pin 4 from IC1. Is that right? Do I need to get a new IC?

Thanks in advance for the help and I may socket the IP next time I make one of these haha

So, I tried to do my best to copy the fatpants layout seeing as right now they're unavailable.

I used the 3PRR and ran the tip of the input to a dpdt switch - the first side goes into the footswitch/charge pump (for true bypass) and the other side is connected to the "in" (which is in turn connected to the "in" part of the circuit)

Also, I've connected the "sw" portion (that activates the buffer) to the two unused prongs in the 3PRR (middle and bottom all the way left if you're looking at the PDF) so that when I'm on the buffer setting and the footswitch is "off" it should still be buffered. I've since disconnected these so that the buffered setting no longer works, right now. As it turns out, for some reason that I still can't figure out, while all of the other parts of the 3pdt switch work right, those two prongs always share an electrical connection (and because of this I would always be running the buffer and never the effect)

Now, I have a few problems:

- The charge pump which originally worked great now only reads 10.6v (from the +18v out) when plugged into a 9.6v power source. Interestingly enough if I move the black end of my multimeter to the -9v output it reads 12v, which is still way short of 18v
- The "on" setting for the effect only engages the buffer - the "soft" and "body" switches as well as the "fat" control have no noticeable effect. The level control only turns the effect off when turned fully counterclockwise but otherwise has no discernible effect on volume.

I've checked my wiring and it all looks okay (aside from being a complete rat's nest) - I have photos of the board that I'll attach when the email sends (cell phone photos but you can see everything). I don't know if it will help but I sure hope so.

So, in summation,
- Only getting the buffered output even when the effect is engaged (which makes me think the "sw" part is connected somehow but I've double and triple checked and I can't see where the connection would be)
- I'm like 8v shy of where I need to be so even the buffered output is slightly lower volume than bypassed.

I would love any help you guys have to offer but I will continue to work on this and post again if I do ever figure out what I've messed up.

Edit: I'm using the LTR1054 or w/e the one with the 14v input is, and an mpf102/j201 for q1 and q2. I've omitted the portion of the charge pump to the "left" of R11 and "below" R9 if you're looking at the fatpants 2013 PDF.

Double edit: Q1 is seeing voltage but Q2 is not

Triple Edit: (I'll keep updating the first post with my progress so the thread doesn't get bumped to the top) - Cold solder joint on R11, fixed, now Q2 is seeing voltage - at full bias it's ~10v at the (drain? that's what it looks like from the diagrams), and .45v at the source, and 0v at the gate. Again I'm about as green as they get so this is just me working backwards from the diagrams using the internet. There may be some more cold solder joints so I'm going to troubleshoot those.

Still trying to figure out the charge pump and the whole buffered/true bypass switching.

I just wanted to make sure I was correct on this - for the 3PRR - the road rage with the 3pdt switch incorporated - there's a hole next to the bypass pad (which is a square). Can you wire up a spdt switch to that and leave one prong empty to switch between buffered and true bypass? Or am I completely off on this?

The project is a perfboard fatpants minus the charge pump (which is what I'm using the road rage portion for)

Thanks again for any help. If I get it up and running before a reply I'll just post here with my results.

Hello, I was interested in doing a fat pants build but it seems as though all the boards are sold out.

Does anybody know about how long takes for the shop to get them back in stock?

I had planned on doing the build for a while but haven't really had enough free time until this upcoming week to actually sit down and build the thing.

I saw Haberdasher has PCBs available for discontinued builds, but AFAIK the fat pants isn't discontinued, just out of stock.

Thanks for any help.

I apologize if this is the wrong forum, but I didn't know where else to post this.

I'm interested in running a fatpants pedal on a 12v power supply, on the theory that the result will be closer to a true echoplex (transistors running at ~23v), and additionally I've heard (but can't confirm) that the dirt cheap MPF102 transistor is actually pretty close to the highly sought after TIS58.

My question is this - for sourcing parts, I need to make sure everything is rated for over 23v, correct? I know that C11 needs to be rated for at least 25v on the standard 18v build, so I imagine I need to look for one in the 30v range? Also, and this could be my noobishness showing, but does the 25v requirement mean that either of the transistors are already seeing voltages like that?

I also saw that there's a 9.1v zener diode which I imagine is part of the charge pump, should I substitute a 12v zener diode for this application?

I'm sorry for all the questions - I have only a very basic competency when it comes to pedals. The demos I've heard of the fatpants all sound fantastic anyway, maybe I'm overthinking things with the contemplated 12v conversion. If that's the case, don't be afraid to say so - again I'm very new to this. All help is greatly appreciated.