Fjord Fuzz Berserk

fjordfuzz.no

BERSERK

fjordfuzz.no fjordfuzz.no

Wow, I'm actually pretty impressed with the amount of information the maker is sharing about the design and encourages experimentation:

The input and output impedances of this circuit are flipped as compared to modern practices. This creates a few problems, but it also causes that amazing clean tone you can get when rolling back your guitar's volume knob. However try placing it after a buffer or a wah. No thank you.

Fjord Fuzz to the rescue! Many have used the very cool AMZ pickup simulator trick to solve this and while this does kind of work, it also adds a bunch of noise and definitely impacts the volume knob cleanup. The rightmost push button on BERSERK engages a simple, weirdly biased, single transistor gain stage preamp in front of the original circuit.

Gone are the wah and buffer issues, but does it still clean up? Does it still allow you to get that super sticky, thick, asymmetric clipping? YES! It's almost indistinguishable from the original preampless circuit, with none of the problems. Doesn't this turn it into more of a MK2 style fuzz though? Yes and no. Topologically speaking it definitely does, and by dialling back the thickness knob you can get into the MK2 territory, but the intention here was to retain all the tonal characteristics of the smiley pedal and I did.

There's a trimmer on the inside to help you match this feature with you specific use case. If you don’t intend to stick this pedal after a wah or a buffer or whatever, you can also use the trimmer to increase gain and chase down that MK2 route even further if that's more your speed!

[...]

BERSERK is biased to 6.66V which is how most of my pedals are biased, but you can change that if you want. Go for 3V for that Johnson farty boy tone or 4.5-5V for a more vintage correct fuzz tone, if there is such a thing. The PCB is clearly marked with instructions on how to do this!
Click to expand...
 
Here's the Roland Space Echo Preamp, right outta the service manual. It runs at 15V, would need some resistor value tweaks to bias correctly with +9V. Q3 & Q4 can be any of the usual suspects, we just tweak R13 or R14 to get Q4-E around 1/2 Vcc. Gain is approx 15dB.

Roland Space Echo preamp.png
 
From the description on the website, the Fjord Fuzz Berserker is a Si Fuzz Face with a preamp & Thickness control in the front and a booster at the end. This is familiar territory. The Skreddy Lunar Module is a Si Fuzz Face with a preamp & Tightness control in the front. The output is easily boosted by altering the resistors ratios in the output stage's collector load. The Basic Audio Scarab is a Si Fuzz Face with a preamp & Fat control in the front and an emitter follower at the end. The Suhr Rufus Fuzz is a Si Fuzz Face with a source-follower preamp & Fat switch in the front and a JFET booster at the end. The Hermida Dover Drive is a Si Fuzz Face with one Hell of a booster at the end.

All are variations on the same theme. Sure, using two Space Echo preamps as the output booster is a clever idea. I wouldn't mind seeing a trace of the whole thing so I can breadboard it.
 
Chuck D. Bones said:
Here's the Roland Space Echo Preamp, right outta the service manual. It runs at 15V, would need some resistor value tweaks to bias correctly with +9V. Q3 & Q4 can be any of the usual suspects, we just tweak R13 or R14 to get Q4-E around 1/2 Vcc. Gain is approx 15dB.

View attachment 16688
Click to expand...
What about ditching R14 and R13, using a 27K for R17 and a 5K trimmer for R18 with the wiper going to R15 for biasing?
 
Hmmmmm. Just ran a sim. For that to work, the JFET must have a very low Vp, like a J201. For that matter, the original circuit also requires a very low Vp. In my sim, the trimpot has to be turned all the way to where the wiper is at ground. I think a better solution is to remove R13 and jumper R14. Make R18 a 10K trimpot and put a cap in parallel with the trimpot. Then the gain will be way high, so we add a resistor in series with the cap to bring the gain back to normal.

1633385510958.png

There's nothing magic about the Space Echo Preamp. It's just a JFET gain stage and an emitter follower. That config crops up frequently in my designs! I didn't even realize I was copying a classic, LOL.
 
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Chuck D. Bones said:
Here's the Roland Space Echo Preamp, right outta the service manual. It runs at 15V, would need some resistor value tweaks to bias correctly with +9V. Q3 & Q4 can be any of the usual suspects, we just tweak R13 or R14 to get Q4-E around 1/2 Vcc. Gain is approx 15dB.

View attachment 16688
Click to expand...
I was just looking for this amongst the plethora of PCBs on PedalPCB — it needs to be added to the wish list (the CDB's modded version of course!)

AKA — a modded Nocturne Brain Seltzer, or whatever Tavi is calling it now.


PS: Would it be good to add an output cap to your modded circuit, say 100n?
 
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Feral Feline said:
I was just looking for this amongst the plethora of PCBs on PedalPCB — it needs to be added to the wish list (the CDB's modded version of course!)

AKA — a modded Nocturne Brain Seltzer, or whatever Tavi is calling it now.


PS: Would it be good to add an output cap to your modded circuit, say 100n?
Click to expand...
Definitely needs an output cap and a Level control. If the Level control is 50K or larger, then 100nF would be good. Rnew could be a C5K pot to vary the gain.
 
Chuck D. Bones said:
Here's the Roland Space Echo Preamp, right outta the service manual. It runs at 15V, would need some resistor value tweaks to bias correctly with +9V. Q3 & Q4 can be any of the usual suspects, we just tweak R13 or R14 to get Q4-E around 1/2 Vcc. Gain is approx 15dB.
Click to expand...

I've seen this configuration pop up in all sorts of devices before and after the Space Echo. Some use JFETs in Q1 (Q3), but many others use BJTs in that position instead.

What is the purpose of the emitter follower? I've seen that a lot too, like in the Super Fuzz or the Bosstone. In the Super Fuzz I think it plays a part in the feedback of that stage; but in some of the countless other Japanese octave fuzzes in that family they just have a single JFET or BJT input booster.
 
The whole input and output stage around a Fuzz Face reminds me of a rabbit hole I went down a year or two ago. I breadboarded a bunch of different ideas, trying to make something different (I know, something different with the Fuzz Face *eye roll*)

One thing I remember was an op-amp buffer in front and I tried different active tone controls after, including a Baxandall and a Klon treble control, which was actually pretty sweet as I recall. Some series resistance (10k - 100k) between the buffer and the Fuzz Face helped get rid of some of the harshness and noise. I don't remember how the clean-up was, as I never cared much for that feature in the first place.

The hardest part was biasing, so I would often go for external bias controls and I liked the textural changes this allowed for. I ultimately abandoning the Fuzz Face entirely in favor of finding something less sensitive to bias and other external factors like impedance and temperature. I also felt dissatisfied about presenting YAFF to the world if I wanted to publish or commercialize my hobby.

I never boxed any of these up, but I drew up everything I found even remotely interesting. Maybe a schematic dump is in order when I get my work area back together...
 
wintercept said:
The whole input and output stage around a Fuzz Face reminds me of a rabbit hole I went down a year or two ago. I breadboarded a bunch of different ideas, trying to make something different (I know, something different with the Fuzz Face *eye roll*)

One thing I remember was an op-amp buffer in front and I tried different active tone controls after, including a Baxandall and a Klon treble control, which was actually pretty sweet as I recall. Some series resistance (10k - 100k) between the buffer and the Fuzz Face helped get rid of some of the harshness and noise. I don't remember how the clean-up was, as I never cared much for that feature in the first place.

The hardest part was biasing, so I would often go for external bias controls and I liked the textural changes this allowed for. I ultimately abandoning the Fuzz Face entirely in favor of finding something less sensitive to bias and other external factors like impedance and temperature. I also felt dissatisfied about presenting YAFF to the world if I wanted to publish or commercialize my hobby.

I never boxed any of these up, but I drew up everything I found even remotely interesting. Maybe a schematic dump is in order when I get my work area back together...
Click to expand...
I like the fuzz face quite a bit, and I can see room for improvement or tweaking for personal preference with particular rigs
 
The key to the FF (for me at least) is understanding that it has a low input impedance and is therefore current-driven. Guitars with passive pickups have a high output impedance and that works well with the FF's low impedance input. Dialing back the guitar's volume control not only reduces the guitar signal, it also changes the guitar's output impedance. That makes the guitar's volume control a very effective gain control for the FF. Put a pedal between the guitar and a Fuzz Face and all bets are off. I like to put a pot in series with the FF's input so I can vary the FF's input impedance. That pot can be used as a Gain or Voice control and will make the FF play nicely with any pedal that comes before it in the chain.

To answer wintercept's question about emitter followers, their purpose is to convert a high impedance circuit to a low impedance circuit without coloring the signal or adding any gain. Looking at the Space Echo Preamp circuit above, the output impedance of the first stage, taken at Q3-D, is pretty much the resistance of R17, 22K. Any load we put on that point can alter the gain, the tone and the headroom. Emitter-follower Q4 presents a high impedance load to Q3 and a low impedance output to drive Volume control VR3 and whatever comes after VR3.
 
Thank you for the info @Chuck D. Bones, that makes perfect sense.

I love the Fuzz Face sound too, but hate working with the circuit. And having spent so much time on it, it doesn’t surprise or challenge me anymore, it just annoys me.

That said, I am getting my first germanium stuff soon, so I kind of have to build a Fuzz Face or something else in that family and I am very excited.

Back to the Fjord, I too would like to see a schematic because I’m curious about that preamp circuit.
 
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