Buddy's Breadboard and Circuit Design Notes

[BuddytheReow]

Chuck's Boneyard post on buffers got me thinking a little bit. Here's a little ditty I came up with. I'll post a breadboard pic shortly and you can see how I cheated. I still have my opamp Muff on the BuddyBoard in case you're wondering.

This circuit is essentially an inverting opamp boost into a dual buffer/splitter that meet back together via a SHAPE (blend) control. Do I need those buffers? The jury's still out on that one. One side is just some hard clipping diodes to ground. The other side is a Devi Ever inspired snippet producing an octave up fuzz. Out of the SHAPE control, this goes into a Marshall tone stack then a recovery stage via another inverting opamp followed by a simple volume control. I call this one the Dev'n Drive. I mentioned that I cheated on my breadboard simply because I have the Marshall stack and recovery stage on a stripboard with a LPB-1 as recovery. The schematic subs out the LPB for another opamp so you can use a TL074 to complete the package.

Another circuit of the day by BuddytheReow

Edit: Schematic updated. I missed a resistor to power the 2 transistors.

 

[BuddytheReow]

It's been a while since I've learned something circuit related. My last post was in January and right before everything hit the fan with my old job and just couldn't take the time to do anything. Now that I've got a new job (finally) I have much more flexibility to mess around with circuits. My latest project isn't a new circuit, per se, but rather I decided to dip into the world of designing a PCB. You can read about my experience here, but I'll try to sum up.

https://forum.pedalpcb.com/threads/solved-diptrace-noob-help-please.16817/

I've seen a bunch of you guys showing off your DipTrace projects. I was hesitant to go down this path for 2 reasons: I had no idea what the cost of this service would be and I was also intimidated by the software. Software more than anything else simply due to the learning curve. Knowing that Diptrace is free, I said what the heck? What have I got to lose other than my time and a couple bucks? So, I took the time with a tried and true circuit, the electra distortion. For those of you that don't know, it's a LPB-1 with hard clippers and I made a breadboarding walkthrough.

What did I learn? Tons of things. First of all, if you aren't sure, just ask this forum. There are a ton of people who will help you out and point you in the right direction. My first hurdle was the component library. OMG there are waaaaaay too many components to choose from. Many of you pointed to the madbean diptrace library which made things much more simple from that perspective.

Secondly, learning happened just by putting the time into the software and watching a few youtube videos. For the record, you must be able to read a schematic in order to do this. Maybe not to the degree of circuit analysis, but to the extent of "this goes here and that goes there".

Third, take your time. Check, recheck, and triple check everything. This is similar to making a stripboard layout, but of a different caliber. With stripboard, you're bound by certain parameters (i.e, the copper strips). With PCB design the only parameters are the size of the board that you want and making sure you don't cross the streams. A nuance of this is with certain high gain circuits where you'll need to separate certain signal paths as much as possible, but I will tackle that with a different project and trial and error.

Fourth, and most importantly, have fun. PCB design is like a puzzle; you just need to figure out how the pieces go together. If problem solving/puzzles aren't your thing this may not be for you. However, it is sooooo satisfying to have it fire up the first time.

TL;DR. Here's my finished product and it works pretty well. I'd like to fool around with this on a breadboard to make it more bass worthy and also put it in a 1590A (a project I've yet to do). I have a few extra if anyone wants one, so just message me if you're interested.

BuddytheReow

 

[BuddytheReow]

The "guts" of a potentiometer.

So, today I tried an experiment with a potentiometer. Many pots that I get recently (tayda mostly) have a sticky residue on them and/or are more difficult to turn. The old engineer's adage is "if it doesn't move and it should, WD40" so I wanted to open up a pot for the first time and get a look at what it's all about. Sure, you can watch a YouTube video, but I'd like to do it myself to actually learn something. Now, before I go any further I should mention that WD-40 is not the best cleaner/lubricant for pots. Nearly any forum search will tell you that, but there are some that swear by it in a pinch. Some will tell you it will make the pot scratchy and others will say it's a waste. My conclusions from my own research are that it will work, but it's not a long term solution. I should also mention I don't have contact cleaner in my arsenal currently. That may change shortly...

Anywhoo, going through my inventory I found this bad boy: 1M linear with solder lugs.


To open up a pot, you'll need to take the dust cover off. Putting a cover on is easy: line everything up and push it all together with your fingers. Doing the opposite is harder (not by much), but you may get lucky if you try it yourself. Take a small screwdriver and push/pry it off.

Now, the actual pot needs to come apart. This part isn't difficult if you've got a small screwdriver (like the one in a kit eyeglasses or the one you use for tightening knobs). There are 4 small tabs that "grip" the shaft to the metal cavity and those can be pried open with the same screwdriver.


Once those are lifted the shaft comes right out and the metal casing is just that.


Here is where we can sorta see the "guts" of a pot, but not really. I tried unscrewing that middle piece, but it wouldn't take the driver. I've read that this is a one way street if you do take it off, meaning you can't put it back on. So, I left it as is. At a different angle, you can see what looks like black paint that goes around the wafer from lug 1 to 3 and vice versa. This is the carbon resistive coating that makes up the total resistance of the potentiometer and is highlighted here.


What changes the resistance between lugs 1 and 2 or 2 and 3? Why, it's this little "fork" right here. This piece has continuity with lug 2 and the signal (DC or AC) wants to travel through the path of least resistance which is why turning the knob and the position of the "fork" allows us to control certain aspects of a signal (i.e the resistance).


With the metal casing off, I noticed that I can spin the knob forever without it stopping/reaching the "end". That's what these 2 pieces do. Stupid simple.


Anyways, I bit the bullet and gave the inside a super quick spray with WD-40 and spun it around a bunch of time. A huge improvement! I'll need to test this on a breadboard for the scratchiness, but this looks promising so far.

 

[BuddytheReow]

Continuing from the post above, I soldered some scrap wire to my pot to try it out. NO SCRATCHING! Clean as a whistle and spins really nicely. I first tried it as a volume control (simply dumping the signal to ground) and it worked perfectly. I then wanted to try it a different way, so I used my breadboard to make a simple low pass filter with a 1n cap. Works like a charm! As I mentioned above, I won't use WD-40 every time, but in a pinch it should work out when I've got sticky knobs that need to be taken care of.

 

[BuddytheReow]

First of all, I've been keeping my own "thread", well, really more of a blog than anything else given the amount of traction compared to the other threads for just over 2 years now. Sheesh. Maybe I need to take up a hobby .

Anyways, since I've been playing bass primarily over the past few months I wanted to design something more geared for all you Bass heads out there. I've built a handful of bass dirt circuits (fuzz mostly and a OD) and was not 100% impressed with the results. Perhaps I just don't like the sound of distorted bass since I keep going back to just a clean sound with some compression. Of course I like to screw around with an envelope filter or octave pedal thrown in there for kicks.

So, what I was looking for was a fuzz circuit that I can blend some clean signal into. Fuzz attenuates a lot of low end unless you know how to tune a circuit (someday I'll learn how to do that). Anyways, this was a good excuse to whip out my breadboard and experiment. The inspiration behind this circuit was the Mini Muffin Fuzz from PPCB, which is similar to the EHX Muff Fuzz. It's a stupid simple dirt circuit and was a good starting point to build around. That circuit is basically 2 building blocks: a boost and a clipping stage. Each uses it's own opamp. The boost section by itself already produced opamp clipping so I needed a control to adjust it. For my bass, I start getting opamp clipping around 9-10 oclock. Fully ccw and you're at unity gain.

I needed to throw a blendable clean signal so I threw in an inverting gain stage to keep the signal phases in line. The clean signal needed a little bump to not be drowned out by the dirt. The diodes I chose were 1n4148 and BAT46, but of course you can experiment to see what you like. I think asymmetrical clipping sounds more interesting. With BOOST around the 9-10 o'clock position, you can blend between 100% clean and 100% dirt. Up the boost control and you've got 2 different types of dirt to blend.

In the early stages of this I simply threw on a volume pot and was pretty happy with the result. Blendable fuzz with opamps and is a first for BtR. In lieu of making this a one trick pony I wanted to throw a EQ section in there. In my research on bass schematics it really boils down to 2 categories: BMP or Baxandall/James style controls. I chose the latter and is pretty simple on a breadboard until you start putting pot jumpers on there. This is then followed by a simple volume control.

So, how does it sound? While I don't have good recording equipment other than a smartphone, I can still tell you about it. This works equally well IMO on both guitar and bass. A truly versatile circuit. The Mini Muffin Fuzz is a one trick pony, but the trick isn't that impressive. My take on this one allows so much more TOANS. The EQ controls more pronounced on guitar, but still work well enough for bass. Turn the BLEND fully ccw and you've simply got a (potential) boost pedal with some EQ...a Preamp!!! Fully clockwise and you're in Muff territory.

I'll see if I can knock out a stripboard layout for this one shortly, but I'm going away on vacation for a week. My breadboard uses 2 TL072s, but I'll try to save some space/traces but utilizing a TL074. Either way you'll need 4 opamps total. It's easier to breadboard 2 dual opamps than a quad. I basically went with the first name that came to mind and haven't been able to find something better. I present to you, the DUST BUSTER.

This circuit isn't that hard to build. I hope someone tries this on their own and provides other feedback. I guess I'm a little biased with my own circuits.

BuddytheReow

 

[zgrav]

Nice job describing the process and sounds.! I like having clean blend options on compressors and fuzzes.

 

[BuddytheReow]

Here's my attempt at a demo. Forgive the shoddy playing. I just finished some yardwork before this. This was just done on a smartphone, so not the best quality. Especially the bass video. Believe me: the low end is there!!

 

[BuddytheReow]

And here's my stripboard layout. The diodes and 1 resistor are standing. 2 other resistors only have a total width of 3 holes, but you can fold the lead over to make it work. This layout is verified. The stripboard pic is upside down.

 

[BuddytheReow]

Recently @MBFX was having some trouble getting a booster to work on his breadboard. The booster was just a 1 transistor circuit and looking at the schematic I kept wondering what else I could do to make it more tweakable. Then I wanted to go back to basics and build a 1 transistor circuit from scratch using a LPB-1 as the main semicondutor. Took me an afternoon and a bit of tweaking the next day, but I think I found something that's workable.

1 BJT circuits in my experience can be pretty boring sonically. With these...you've got options!

First, a blendable input cap and into a standard LPB-1. I wanted to keep this part stock simply because you can't go wrong with a textbook amplifier. The next stage is where I had 2 different versions and more happy with the second one. The first version can blend between asymmetrical diodes to ground or the raw signal. The second iteration has a variable resistor to those diodes only rather than a blend control. The latter makes this more of a dirty boost. After that is a stock Rat filter block acting as a treble cut and then the volume pot. I didn't realize for a long time that the volume pot value affect impedance for the next pedal.

These circuits are more meant for guitar, but you can get a ton of low end when a bass is hooked up to it.

What should I call these two circuits? Hmm, let's see. Halloween is coming up so maybe I should use that as a theme.

Behold! The Boo-ster and the Spooky Dookie!!



Here's the Boo-ster on the breadboard.


and the Spooky Dookie!

 

[Chuck D. Bones]

Nice!
A few observations...
1. What? No Ref Des?
2. The Bass Blend up front will have a better feel if it's C-taper (assuming min resistance is full CW). You might even want to go higher, like 500K. See the input stage of the Sabbra Cadabra for an example. Since this pot is right at the input, it will interact with the guitar's pickups and knobs.
3. The clipping is always asymmetric (even with symmetric diodes) because Q1 and the collector resistor drive the diodes asymmetrically. Pick a diode pair that sounds good, or install a toggle switch. See the BJFe Folk Fuzz for an example.
4. Did you forget the 3.3nF tone cap in the 2nd circuit?
5. For better bias stability, increase the 390Ω to 1K. You will need to increase the 47K a bit.
6. For more gain, put a 10uF cap in parallel with the 390Ω (or 1K) resistor. See the Chrysalis for an example. Come to think of it, the Chrysalis Drive would be another fun breadboard project.
7. The advanced breadboarder might try a JFET or MOSFET in place of Q1. Biasing will have to be changed accordingly.
8. Duracell batteries are and will leak electrolyte all over your nice circuits. If you must use a battery, the eco-friendly way to do it is to use rechargeables. I recommend Panasonic Eneloop.

 

[BuddytheReow]

Nice!
A few observations...
1. What? No Ref Des?
2. The Bass Blend up front will have a better feel if it's C-taper (assuming min resistance is full CW). You might even want to go higher, like 500K. See the input stage of the Sabbra Cadabra for an example. Since this pot is right at the input, it will interact with the guitar's pickups and knobs.
3. The clipping is always asymmetric (even with symmetric diodes) because Q1 and the collector resistor drive the diodes asymmetrically. Pick a diode pair that sounds good, or install a toggle switch. See the BJFe Folk Fuzz for an example.
4. Did you forget the 3.3nF tone cap in the 2nd circuit?
5. For better bias stability, increase the 390Ω to 1K.
6. For more gain, put a 10uF cap in parallel with the 390Ω (or 1K) resistor. See the Chrysalis for an example. Come to think of it, the Chrysalis Drive would be another fun breadboard project.
7. The advanced breadboarder might try a JFET or MOSFET in place of Q1. Biasing will have to be changed accordingly.
8. Duracell batteries are and will leak electrolyte all over your nice circuits. If you must use a battery, the eco-friendly way to do it is to use rechargeables. I recommend Panasonic Eneloop.

You know, I was JUST about to pack up this project when I decided to check on here real quick. Let me try out your tweaks!

 

[Chuck D. Bones]

And put some knobs on those pots while you're at it .

 

[BuddytheReow]

Nice!
A few observations...
1. What? No Ref Des?
2. The Bass Blend up front will have a better feel if it's C-taper (assuming min resistance is full CW). You might even want to go higher, like 500K. See the input stage of the Sabbra Cadabra for an example. Since this pot is right at the input, it will interact with the guitar's pickups and knobs.
3. The clipping is always asymmetric (even with symmetric diodes) because Q1 and the collector resistor drive the diodes asymmetrically. Pick a diode pair that sounds good, or install a toggle switch. See the BJFe Folk Fuzz for an example.
4. Did you forget the 3.3nF tone cap in the 2nd circuit?
5. For better bias stability, increase the 390Ω to 1K. You will need to increase the 47K a bit.
6. For more gain, put a 10uF cap in parallel with the 390Ω (or 1K) resistor. See the Chrysalis for an example. Come to think of it, the Chrysalis Drive would be another fun breadboard project.
7. The advanced breadboarder might try a JFET or MOSFET in place of Q1. Biasing will have to be changed accordingly.
8. Duracell batteries are and will leak electrolyte all over your nice circuits. If you must use a battery, the eco-friendly way to do it is to use rechargeables. I recommend Panasonic Eneloop.

Alright Chuck. Here are my comments:

1. Ref Des once I write a schematic on my computer.
2. C-taper changed. I kept it at 100k since I forgot the 1M pulldown resistor.
3. I chose BAT41 simply because I had the bag already out.
4. 3.3n cap added on my drawing
5. I just swapped the 390 to 1k
6. I completely forgot about the bypass cap! 10u added
7. I may do just that with a JFET, but need some guidance how to change the bias.
8. Yea, that Duracell. That's there as a last resort if I can't plug into my power brick on my pedalboard. I haven't changed that battery in over a year and it's not plugged in on my pics. That's the main power supply.

Here's the second iteration of the Spooky Dookie



Happy with the knobs, Chuck? lol. TBH, this isn't a very loud circuit simply due to too many passive parts (clipping and Hi Cut filter). Unity gain is almost fully cranked.

Knobs from left to right: BOOM, BITE, CUT, and VOLUME

 

[Chuck D. Bones]

1. Right, because your pencil broke.
2. Do you get enough bass cut with 100K? If not, try C500K.
3. Schottky diodes have low Vf, hence low output. One solution is to stack them. Another is to add a gain recovery stage at the end, à la Chrysalis.
7. When you go JFET, delete the 470K and put in a 10K trimpot for the source resistor. Tweak the trimpot for somewhere around 3-4V on the drain and tune by ear after that. Because the diodes limit the drain voltage swing, there is no advantage in centering the drain voltage at 1/2 Vcc. Try different JFETs. JFETs won't have as much gain as a BJT, but it may be enough, especially with BAT41 clippers. You can also try Germanium diodes, just not Russian ones (too leaky).

The knobs are nice. Isn't it helpful to know the pot position?

You might want A or C-taper for your BITE pot, depending on whether min resistance is at 7:00 (A-taper) or 5:00 (C-taper).

Another way to implement the BITE pot is to connect pin 1 to GND, pin 3 to the 220nF cap and connect the diodes between pins 1 & 2. That way, you can dial the diodes completely out of the circuit. Try B50K for the pot. See the Karma Suture for an example.

 

[BuddytheReow]

Another way to implement the BITE pot is to connect pin 1 to GND, pin 3 to the 220nF cap and connect the diodes between pins 1 & 2. That way, you can dial the diodes completely out of the circuit. Try B50K for the pot. See the Karma Suture for an example.

This is exactly what I was trying to do. Take the diodes completely out with a pot! I'll have to try this one.

 

[BuddytheReow]

For you @Chuck D. Bones . Here's version 2.

 

[Chuck D. Bones]

Looking good. You might want to try 68K for R3.

I'd use a higher value for the VOL pot, otherwise the volume will drop when you turn CUT down.

 

[BuddytheReow]

I'd use a higher value for the VOL pot, otherwise the volume will drop when you turn CUT down.

Why? How do these 2 interact?

 

[Chuck D. Bones]

They make a voltage divider, don't they?

Another option is the Stupid Simple Tone Control. Volume won't change when the TONE knob is rotated because the resistance between C4 and the VOL pot will be constant.

 

[BuddytheReow]

They make a voltage divider, don't they?

Duh, Buddy!