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Topics - Aleph Null

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General Questions / OTAs, How do they work?!
« on: February 07, 2024, 10:29:12 AM »

I'm trying to understand the LM17300, but haven't been able to find much information beyond the data sheet. Explainer articles or videos all insist on using a split power rail and don't do much in the way of practical examples. Does anyone have a source that shows how to use an OTA as an amplifier (as opposed to a resistor, or in a filter)? I'm especially interested in examples of using an OTA without a split power rail.

Thanks, all. I know someone here must have some experience.

General Questions / Grounding to the Enclosure
« on: December 20, 2023, 11:38:44 AM »
This isn't really an issue with PCB builds, but with vero I find it difficult sometimes to get grounding wires to everything. I've been thinking about just using the enclosure as a ground plane—tying lugs to the back of the potentiometer, etc. Aside from possibly corrosion breaking the ground connection, is there any other reason not to do this? Does any one else do it this way?

Build Reports / Peacock Parallel Fuzz
« on: December 11, 2023, 02:56:13 PM »
This project started when I was toggling between two different dirt boxes with very different characters and thought to myself, "These would sound great in a mix together if I double tracked guitar with them!" My next thought was, "Why double track when I can just split the signal and run the effects in parallel?!" The result is the Peacock Parallel Fuzz: two distinctly voiced fuzzes that can be run independently or in parallel.

I had originally planned a two-tone finish on the enclosure with water slide decal graphics and labels, but a defect in the powder coat precluded this. I went for hyrdodip instead.

Boxing was as thrilling as a 1590A build despite being a 125B. This was a cram!

An input buffer feeds two fuzz circuits which are then mixed by an active mixer at the output. The "bybpass" switches really just cut off the clean input when the fuzz is engaged and ground the LED, or ground the fuzz output when the fuzz is off.

The yellow channel is a Harmonic Percolator that has been voiced to be as mid-range focused and percussive as possible. This stock circuit does not like being placed after a buffer. I tested a few different ways to address this including series resistance at the input and a pickup emulator and found that a mosfet in Q2 behaves much more nicely than a BJT and doesn't require any of these other, more involved solutions.

The green channel is a Fuzz Face doing its best Big Muff impression. The feedback resistor has been greatly increased to increase the available saturation. The mosfet in Q2 helps with this as well (and makes the circuit play nice with the input buffer). The tilt eq is voiced to be especially scooped. This leaves room for the yellow channel to poke through when the two fuzzes are used together.

Here' s a demo:

Here's the vero layout in case any one wants to build their own.

And here's the bypass layout since it might not be obvious from the schematic.

Build Reports / Effects Layouts Krokie Kenobi (Benson Preamp)
« on: September 20, 2023, 10:39:00 AM »
I decided to try my hand at surface mount and this was one of the few projects I could find. It's a faithful recreation of the Benson Preamp. The circuit is pretty ugly proof, but it also doesn't have that much personality—at least not in my rig. I understand it's based on the preamp section of a Benson amp and I could see how the circuit would work well as a fairly neutral pedal platform amp. As an overdrive, it just doesn't have much personality. I word of caution; with this wide layout, the jacks are too close together to accommodate pancake jacks. 

All in all it was fun to experiment with SMD. This is a nice circuit, it just isn't what I'm looking for in an overdrive right now.

Build Reports / Bananafanafophasor (Glasshole with mods)
« on: August 29, 2023, 10:33:21 AM »
This turned out to be an expensive pedal as I had difficulty sourcing all the parts. 1/8w resistors have become difficult to find! Still, it's a fun build and a great sounding phaser.

The small LED is the rate indicator. I jumped the pins of the rotary switch so that the LED works no matter how many stages are selected. I accidentally made more work for myself by placing both LED's under the PCB. There is essentially no clearance, but a little electrical tape keeps things from shorting out. I tested a few different colors and found that LEDs with higher forward voltages don't work consistently as rate indicators: red and yellow are fine, blue and green are not.

This is a very chewy phaser, which can be a lot of fun, but, like most phasers, it's incapable of subtlety and can mask the sound of the guitar. I added an "Intensity" switch to combat this. In the down position R8 is the stock 10k. In the up position, R8 is 20k. This reduces the phased signal getting mixed into the output, which effectively halves the depth of the phase cancellations. It still sounds like a phaser—just less intense.

I also found that I could stop the LFO and get a "parked" sound by connecting leg 3 of the Depth control to the 9v rail. The brightness of the internal LED could then be controlled with the Depth knob, allowing me to tune the phase effect. This only gave me access to about half the range of the phaser and only the first half of the Depth's rotation really did anything, so I decided not to implement it. Maybe someone more clever than me can find a better implementation of this.

All in all, a very good circuit. It does classic phaser sounds. Eight stage phasing allows you to get flanger-like sounds. Two-stage phasing with low depth and intensity sounds somewhat Leslie-like. There are lots of good sounds to be found.

Build Reports / Otolith — A High-Gain Turducken
« on: June 27, 2023, 09:37:54 AM »
I saw a few YouTube demos of people getting super sludgy, doomy sounds by running a Rat in front of an Acapulco Gold. This design began with asking, "What would happen if you just shoved the LM386 gain stage right inside the Rat where the clipping diodes usually go?" A high-gain turducken! There ended up being more to it than that, but that's where it started.

Bare metal felt like the right look.

This layout should fit in a 1590B. If you were really ambitious, you might be able to cram it in a 1590A.

A short demo:

The "Focus" control grew out of the Ruetz mod for the Rat. The values were changed so that turning the Focus up cuts bass frequencies, but also increases the gain significantly. The clipping diodes help to limit how hard this first gain stage hits the input of the LM386—it can only take so much input signal before it turns to mush—and the asymmetrical arrangement emphasizes 2nd order harmonics, making the guitar sound more nasal and mid-range focused. This feeds the LM386 which is set up the same way we've seen it in the Acapulco Gold, the Smash Drive, the Clari(not) and other designs. Last is an active tone control that creates a high shelf at 720Hz. It's capable of -13dB to +7dB. This design isn't the most versatile, but I think it does very convincingly get into that Sleep/Sunn O))) territory.

..and the layout for anyone that might be interested in building one.

Special Sauce is for when your tone needs a little something extra. It's a PT2399 based delay with envelope controlled pitch modulation that does chorus, vibrato, doubling, or slap-back delay.

The board is mounted to a wooden standoff with hot glue. It sounds precarious, but it's the best way I've found to mount vero builds.

This circuit is tuned for short, bright delays ranging from 30–150ms or so. The short delay time meant I could use the first CMOS stage of the PT2399 as an input buffer instead of for filtering. A Mosfet at the output supplies 0—35dB of gain. The real trick here is using the voltage on pin 8 as an envelope follower (as discovered by DeadAstronaut). Instead of applying the pin 8 voltage directly to pin 6, I used it to control a 2N5089 set up as a voltage sink. This makes the pitch bending much more pronounced, especially at shorter delay times.

Here's  a short demo:

Here's my layout, if anyone else wants to build it.

Build Reports / Electra Supreme
« on: May 09, 2023, 01:51:47 PM »
I've had this one boxed up for a while and have been hesitant to make another Electra post, but I do think there are some interesting features in this iteration. I started with a list of all the features I wanted in an overdrive pedal and ended up with this: pre-gain bass control, post-gain treble control, a "texture" control (which I'll explain more later), and enough output to boost other pedals downstream.

The texture control was inspired by Jack Orman's articles on "warp" controls, where a potentiometer is used to vary the clipping threshold of different arrays of diodes. I didn't see the arrangement I ended up using, but it definitely inspired me to explore. When the texture control is fully counter-clockwise, you get symmetrical clipping. This is the familiar squishy and harmonically rich sound you'd expect. As the control is turned clockwise, the clipping becomes increasingly asymmetrical. This emphasizes the even-order harmonics, creating a reedy, nasal, and in extreme settings, almost octave-up kind of sound. The advantage of the particular arrangement I've used is that the volume is very consistent across the range, unlike a lot of other diode-switching schemes.

The values above reflect the circuit as I built it. If anyone else is interested in building this circuit, let me know; some of the values could probably be streamlined with little effect on the sound. 

General Questions / Rotary Switch for Glasshole
« on: May 04, 2023, 10:39:29 AM »
I'm looking for a rotary switch for an upcoming Glasshole build. They are currently out of stock at Small Bear and it's not very clear what the manufacturer/spec should be. Does anyone know of another supplier, or at least the make/model that's appropriate for the Glasshole?

Thanks for the help!

Build Reports / Tape Delay
« on: December 05, 2022, 01:08:50 PM »
This is an original design that draw's a lot of inspiration from Jon Patton's Hamlet Delay. I've implemented a version of Jon's "Noise" control. I've also included DeadAstronaut's envelope modulation. I experimented with resistor and capacitor values in the modulation section and found I like the range I can get. It sounds pretty lush and is capable of pitch bending at higher "Warble" and "Delay" settings. It's not actually intended to sound like tape, but I couldn't resist the pun. Buffered bypass allows for tails.

I used a block of wood as a standoff for the circuit board. The block is hot glued to the enclosure and the board is glued to the other side. It's unconventional, but it's stable and effective. The 4.7k resistor in the feedback loop has been replaced in my build with a 25k trim pot. Most people would probably want a resistance of 10–22k there.

The schematic and layout for anyone that's interested. Where I to build this circuit again, I'd probably update the layout to include more power filtering for the 5V supply and also maybe add capacitors in the buffer feedback loops. As it is, it works well, but because the output of the PT2399 is always connected, it might be a good idea to test multiple chips. I had a noisy one that made motorboat noises when the "Delay" was above noon. A different chip fixed that. Additional filtering might help too.

General Questions / PT2399 Tape Stop Effect
« on: September 21, 2022, 02:43:12 PM »
I recall reading somewhere that it was possible to get a PT2399 delay to do a "tape stop" effect where the delayed signal slows to a stop. For the life of me, I can't find the forum post anymore. I think it involved grounding a pin through a resistor, but I don't remember which pin or recommended resistances. Has anyone else hear of this? Can you point me to a forum post somewhere?

Build Reports / Rock Dove (A Rat-Inspired Overdrive)
« on: July 26, 2022, 09:05:37 AM »
This doesn't sound like the Rat distortion; while it's capable of a fair amount of gain, it's generally less aggressive—and in my opinion more versatile. That said, if you squint at the schematic, it looks a lot like a Rat. What is a pigeon but a rat with wings?

Wiring vero builds is always an undertaking. I tried to keep wires neat while leaving enough length for troubleshooting if needed.

Like the Rat that inspired it, a non-inverting opamp feeds clipping diodes to ground. The high pass filter is less aggressive, starting at 148Hz. There's also a 6dB high shelf at 1.4kHz to add a little sparkle when it starts to saturate. Clipping options include, opamp, LED, and germanium diode. The tilt EQ has a broad mid bump between 480Hz and 1kHz. The "Flat" control bypasses the EQ and increases the output a little. The transistor buffer keeps the volume control from effecting the tone. I used a BJT instead of a JFET because they're easier to source and work just as well in this application.

It goes from clean in some settings to proper distortion in others. It's strength is overdrive. The EQ and voicing is mid focused, but not as extreme as the Rat (or even a Tube Screamer). Were I to build a version 2, I'd probably use a dual opamp chip and use the second stage to buffer output instead of a BJT. I don't expect there would be an audible difference, but the layout might be a little more compact.

Build Reports / Aion FX Calliope (Karma Suture)
« on: July 20, 2022, 10:25:07 AM »
This is a stock silicon version of the Calliope, which is the Catalinbread Karma Suture, which is based on the Interfax Harmonic Percolator.

Aion layouts always make for clean builds. I used a 2N3906 for Q1 and a 2N5089 for Q2. I bread boarded the circuit and played with some components, but the original is so well voiced I found I couldn't add anything to it. Increasing R2 made it more splatty and grating. A BS170 for Q2 made for softer saturation and more germanium-esque sounds. The Harmonic Percolator circuit seems to be pretty insensitive to value changes on the whole.

Purple and pale pink hydro dip finish over red powder coat.  I'm finding I like to put down two sparse layers of hydro dip color because it gives the finished product more depth.

This effect is hard to describe. If's an overdrive with the heart of a fuzz.

Build Reports / Elevating the Humble Electra Distortion
« on: June 06, 2022, 11:35:27 AM »
I've built quite a few dirt boxes, but I keep coming back to the Electra Distortion circuit. Recently, I discovered a roll of magical 1N34A germanium diodes at my local electronics shops, so I decided to build one more Electra, this time with some extra mojo.

I wanted to keep the circuit simple and avoid adding unnecessary features, but I wanted to tune it and refine it a little bit. I kept it to one knob: a gain/bias control

The board is mounted to the potentiometer. This leaves enough height for full-size electrolytics.

The gain range is limited to a modest 5–26dB—the sweet spot for this circuit. Much more that 30dB gain tends to get farty anyway. Magical 1N34A diodes provide just the right amount of clipping with a forward voltage around 450mV. The 220nF capacitor in parallel with the 510 ohm resistor creates a 2dB shelf at 1.4kHz. This adds just a little bit more clarity and articulation without making it sound bright. The 68nF output capacitor trims off just enough bass to keep things tight, especially when using the Electra to push another overdrive. The 1nF capacitor rolls off the "fizz" above 16kHz. This is much more subtle than a typical tone control. It's unnoticeable at lower gain settings, but tames the harsh harmonics at higher settings.

These are all small changes, but I think it takes the circuit from simple to elegant. This almost certainly isn't the last overdrive I'll build, but it's probably the one that will stay on my board.

Build Reports / Pig Butt 2019
« on: May 23, 2022, 09:59:49 AM »
This is a fairly stock Pig Butt. I had to get a little creative as I didn't have some of the specified resistor values on hand. The decal gave me a lot of trouble, but after about half a dozen attempts, I think patience paid off.

The jack connections at the top of the board made it very easy to keep the insides tidy.

I socketed all the capacitors in the tone stack. This was definitely a good idea as the stock tone stack was too scooped for my tastes. After a lot of experimentation, I settled on the values below. The result is a low pass around 460Hz and a high pass around 1.6kHz. This is actually pretty close to Ram's Head spec.

It definitely sounds like a Muff, but it's a little more ragged and mean than it's discreet counterparts.

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