marksescon
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Summary
I spent the past few months figuring out the dynamic sag portion of the Smallsound/Bigsound (SSBS) Fuck Overdrive and stuck it into "a Fairfield Circuitry Barbershop + SSBS Mini"-hybrid drive.
The companion effect - an envelope-controlled voltage starve circuit - mimics a dying tube amp and responds to an individual's playing: As described by Brian/SSBS, the dynamic sag circuit is “dynamically modulated (envelope controlled)…turn up the threshold and the harder you play, the more the overdrive crackles, tries to keep up… and fails miserably.” I call it a practice in kintsugi - or discovering and embracing the musicality in the “brokenness” of the pedal.
I have included the schematic of the dynamic sag circuit.
Video Demos
• Diagram of the signal path:
Background
A few months ago, after having built a SSBS Mini clone, I came across a video demo of the Fuck Overdrive. The video detailed a feature within the pedal that was described as an envelope follower that starved a single gain stage. I thought the process would be as simple as a Google search, but whenever I did, I found threads suggesting people just Google the answer which leads to more threads suggesting people just Google the answer which leads to more threads…so on and so forth. In all my hours of Googling and perusing FSB and DIYStompBoxes, I have yet to find anyone who figured out the circuit and produced a functional model.
Eventually I happened across a thread on Reddit in which someone used the phrase “dynamic sag,” which lead me to the Tone God Punisher circuit.
The Tone God Punisher circuit is not so much a pedal as a companion piece for a pedal. Utilizing an envelope filter, a NPN BJT, and a JFET, the circuit starves current and mimics a dying tube amp. The core concept of the circuit (envelope follower and voltage controlled resistors) can be used for a myriad of applications in which an input signal dynamically controls another part of the pedal - be it, gain, volume, delay time (like the Retroflect), clipping, etc. The circuit itself is derived from the Nurse Quacky, which in turn is derived from the Dr. Quack, which in turn EHX Doctor Q.
The dynamic sag feature is a hallmark of the SSBS Fuck Overdrive. More recently The Sheilds Blender sported a similar feature. Fender ostensibly claims the dynamic sag is “the first of its kind,” but clearly it isn’t, lending credence to the fact that Brian/SSBS is (was?) quite ahead of his time.
Research
To say it took me a couple of months to figure out how to get the dynamic sag circuit to work would be an understatement. The original Tone God Punisher schematic was not functional. Through a series of trial, error, soliciting advice, multiple breadboards layouts, meticulously looking at gutshots of the Fuck OD and unpopulated PCBs, and a random late night epiphany, I managed to get the circuit working.
The big changes I had to implement were (1) the biasing of the op amp and (2) the removal of the JFET. The latter was a last minute decision brought about by a post in which a user felt the JFET and BJT interaction would be too unpredictable and warrant careful (laborious) selection of components.
Alas, I got the circuit working and stuck it into a Fairfield Circuitry Barbershop/SSBS Mini hybrid that I joke is the “Frankie Jonas of the two pedals.”
I will also state that based on my analysis of the Fuck Overdrive PCB, my circuit is probably only 80% similar to what's in the Fuck Overdrive - but I do believe it is a fair approximation.
Schematic of the Dynamic Sag
Explanation
The input signal of the circuit gets Y-lined with the input signal of the pedal. The signal goes to an envelope follower which lights up an LED. LED charges up the capacitor, which in turn discharges to the BJT and allows current/power to flow to ground. The current/power that flows to ground is current/power that’s meant for the gain stage, effectively starving the stage in the process. LEDs’ forward voltage must be matched. Vout goes to the power source of the gain stage and R10 is whatever the bias resistor is. A few additional proposals I encountered were to add a feedback resistor on the BJT and/or a resistor from emitter to ground. Admittedly the person who suggested this to me did not elaborate on the purposes of these additions.
(Note. If anything I posted above doesn’t make sense and needs correction, please clarify. I have a rudimentary knowledge of circuits and tried to explain it the best I could.)
The two knobs, Sensitivity and Threshold, control circuit. Sensitivity should be adjusted based on playing style - eg. Picking/strumming strength and Threshold determines how much starve should occur. Mark Hammer proposed that the RC network could be changed in order to increase/decrease the decay or even make the effect less aggressive overall. I postulate that the SSBS Fuck’s compression switch (heavy/low) goes between two different RC networks (R8, C4). Another proposal is to replace R8 with a potentiometer in series with a 50-100 ohm resistor in order to make an Attack control. The two footswitches are Bypass and Dynamic Sag. Bypass activates the drive and Dynamic Sag activates the Dynamic Sag.
Photos 3 and 4 of this album explain how to wire the dynamic sag bypass switch. This will enable you to toggle the dynamic sag on or off. You can also opt for a monetary DPDT switch so that pressing/holding activates the sag and releasing immediately turns it off.
Practical Application
Below is an example of the dynamic sag circuit used in an actual pedal (The Fairfield Circuitry Barbershop). Note that this isn't the same pedal used in the demo videos or the picture. I just wanted to share how the schematic would look once all the pieces are put together.
Further updates will be provided on my blog.
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