Buddy's Breadboard and Circuit Design Notes

[BuddytheReow]

I decided to whip out a TL074 and build something with it. The 074 uses 4 opamps in a single chip. The plus side of this is you only have to power the chip once rather than using 2 separate TL072 or 4558s. This isn't really a new circuit or anything, but rather 2 circuits in one using the same IC. I chose the Mini-Muffin Fuzz and Cold Turkey EQ circuits. The Mini Muffin really needs a tone stack or tone control so I decided to try this one out. For both circuits I took out the volume pots since I'm merely testing the circuits.

My opinion is that this concoction is ok, not great. The fuzz portion is relatively bland and needs a fuzz control on it for both an increase and decrease, but the EQ helps color the sound more to my liking. I did add a 1m pot in lieu of R3 to make it louder, but it did not help much. When I max out the TREBLE pot I get some unwanted hiss, so I'm not sure If that's due to my breadboard, the IC used, or the circuit iself. @Chuck D. Bones helped me with the analysis of the EQ stage since I noticed that changing the MIDS pot kinda took over the other two settings in addition to trying to figure out why the schematic is drawn the way it is. His suggestion was to put the MIDS control in it's own separate opamp stage to make it truly independent of the other controls. Thanks for the tip, Chuck!

Again, not an original design by any means but I will call this one the Turkey Muffin.

 

[Chuck D. Bones]

Stick a resistor in series with C5, that will help with the MID control overriding the other two. Try 4.7K, 6.8K or 10K.

If you really want a 3-band EQ, try copying the EQ section from the Crunch Captain Deluxe. [Or just build the whole thing]

 

[Coda]

Not as detailed as some, but I threw this together this afternoon: Elka Dizzy Tone. I have a GPCB Buzzaround board that I plan on using for a full version. Much more gnarly Buzzaround. Npn Ge…don’t remember what. HFEs are around 50/50/110…

 

[BuddytheReow]

Future Buddy, this is Past Buddy. You've tried breadboarding a simple non-inverting opamp for some time and can't seem to get the circuit to work. You've check over the layout and schematic and see nothing wrong. Your IC voltages seem off even though it's powered correctly. You are telling yourself this is some pretty basic &$#^ that you used to be able to do without any issues when you first started breadboarding.

Future Buddy, pay attention. This is so simple since you used to be able to do this in your sleep. I will refer you to a troubleshooting post you opened up. https://forum.pedalpcb.com/threads/a-breadboarder-needs-help-dist-250.10283/

If you decided not to read it then I will give you a hint of how to tackle this. Refer to a previous project you posted many months ago in this thread. Look at the way the breadboard is laid out, specifically with the feedback loop. Don't switch around the input and output jumpers: the rc filter gets connected to the - input of the opamp, not the output. That's why you're having issues.

You're welcome future Buddy.

 

[Barry]

Stick a resistor in series with C5, that will help with the MID control overriding the other two. Try 4.7K, 6.8K or 10K.

If you really want a 3-band EQ, try copying the EQ section from the Crunch Captain Deluxe. [Or just build the whole thing]

Crunch Captain Deluxe is one of my favorites

 

[BuddytheReow]

I did some experimenting with biasing a transistor and wanted to share my findings here for anyone who's interested. Here's the schematic for my base:

The resistors here don't have values because that was the experiment I tried. Emitter to ground, a shunt feedback resistor from collector to base, and a collector resistor. Everyone, this is a simple fuzz circuit. Now what I did was wire up two 1M potentiometers to act as variable resistors here. As I played through this simple circuit I tweaked the resistors to see what that would do to the sound. Here's what I found. I used a 2n5088 as my starting point.

Rc=1m Rcb=1m, a very heavy overdrive sound with some gating thrown in there. Keep in mind I only have humbuckers in my guitars. As Rcb decreases the sound gets more "pinched" for lack of a better term and volume does decrease, although the signal is still hitting the power rails. I noticed the signal dies at around 15k or so. Turn Rcb back to max and tried the other pot. As the resistance decreases all I noticed was that the gating only gets slightly less until the signal gets choked out. THe signal cutoff I found was around 8k.

Let's try the pots at their lowest settings possible. For my setup, Rc~2.8k and Rcb~14.8k. The sound produced here was actually pretty clean and the treble comes though very well. It is not a clean booster but a more treble-y booster of sorts. As I increased Rc, more "gain" like in a guitar pedal setting comes through more and the bass also comes back into play. Now we're back into heavy OD/fuzz territory! OK, reset back to the lowest settings for each. As I increased Rcb, "gain" comes back, but there is a quick volume drop and slowly comes back as it's increased further. The gating starts coming back right after noon.

Having both pots at noon gives a lot of harmonics come through more.

When I change to different transistors I noticed that if the hFE is lower for the transistor, there is a lot more gating happening at the settings mentioned above. The opposite is true for higher hFE transistors and seems to be more forgiving.

Some other comments/notes:
-Running the circuit at 18v gives a lot more headroom and allows the signal to not hit the power rails as hard although the clipping is unaffected. This is a great way for me to understand headroom and running circuits and different voltages.
-The most "tweakability" range for me was when the resistors had relatively low values (<100k). Perhaps I should try this experiment again but use 100k pots.
-The lower the values of the resistors the closer to an overdrive it sounded.


Future Buddy, try this experiment again using 100k pots. Also try other topologies to see what you can come up with.

 

[Chuck D. Bones]

When you turn those pots, you're changing the signal path and the transistor's bias at the same time. There are a LOT of settings where the transistor is either saturated or cut-off when no signal is present. When you hit the circuit with some guitar signal, then the transistor gets pulled out of saturation or cut-off until the note decays to the point that it can't overcome the transistor's extreme bias. Voilà! Gating. When you find a setting you like, take note of the collector voltage. This biasing scheme is VERY HFE dependent. Two transistors with the same part number may well sound different.

 

[BuddytheReow]

Also check out ESP for "Designing With Opamps" Parts 1 & 2 by Rod Elliott.

Dude, I completely missed this when you posted it. There's a lot of good reading material. I'll take a look through it tonight and throw it into the resources thread in the Test Kitchen

 

[BuddytheReow]

More experiments this afternoon and here are my findings for those that are interested in circuit design. I decided to put together a different configuration of getting a transistor to conduct. This is pretty much a common emitter amplifier with tweakable resistors. You can find this configuration on an LPB-1 minus the pulldown resistor. It's considered more stable and you'll see why in a minute. You can also call this a voltage divider bias (I'm looking at Electronics-Tutorials site for the names). Here's the schematic I put on my breadboard. I'm labelling the base resistor B, the collector resistor C, and the emitter resistor E (duh)...I used a 2n3904 here and at the last minute switched to a 2n5089.

Why a 9.1k resistor to ground? Well, using a simple voltage divider calculator, I found out that having B at 100k and Rb at 9.1k will give me nearly the lowest voltage to turn on the transistor. Basically, I would play and turn the knobs until I got sound and saw how much the sound changed.

Here's the short version of what I found and doing next to no math (sorry, Chuck):

-This configuration is more stable than using the collector resistor feedback method I did previously. When I say "stable" I mean that the sound that comes out the other end is between clean and a light to medium overdrive. That's it. This configuration is really meant for amplification rather than clipping and it makes sense that the LPB1 is laid out this way. It's a simple amplifier.

-B pretty much needs to stay maxed out (100k) in order for anything to work. As E is increased you get slightly more wiggle room but not much. The signal sound gets "starved" really quickly.

-As E increases, the value of C needs to increase in order for signal to pass through. You also get more wiggle room in terms of min and max resistance for sound to pass through

-There's clearly a difference in the amount of clipping/amplification when going between single coil and humbucker pickups. Humbuckers drive this harder obviously.

-Using a higher hFE transistor (I used a 2n5089) I get much more wiggle room for turning the collector knob. Other than that, not much different sonically.

BTW I did write down resistance values when signal pass through or not, but the above pretty much sums it up here. Again, this is a super simple, basic topology where I'm trying to answer the question "Why is this circuit built like this? What does it do?" Now I know.

BuddytheReow

Edit: If you look at some common emitter amplifiers out there you'll notice a cap also going from emitter to ground. This will increase the amplification and some of the gain. I noticed diminishing returns after about 10uf or 22uf. This seems to be the sweet spot in my given circuit.

 

[BuddytheReow]

Whipped up a Baxandall Tone stack on stripboard today for circuit design. Another one to add to the collection. Found it on http://guitar-fx-layouts.238.s1.nabble.com/Bax-in-a-box-active-baxandall-tonestack-td7264.html

Not the neatest layout, but for it's purpose it works just fine. This can be a standalone "effect" and put in an enclosure if you choose. This layout works.

Now it's time to create something!

 

[BuddytheReow]

I took a little bit of time over the weekend to explore the famed pt2399 chip. This chip is used in many delay pedals, and maybe a chorus or reverb pedal if tweaked correctly. Before understanding the chip itself I was looking for the most simple circuit to breadboard and found this. Keep reading below.

So, first of all, this circuit works, but not the way I wanted it to work. It acts more as a reverb than a delay. Because this circuit worked when I breadboarded it I wanted to see how this unusual chip actually works and perhaps start designing my own. Here are some great resources I found that helped me understand it.

I hate to put this up here since I really can't read datasheets to the fullest extent I am putting it up here. Why? Well, in the handful of google searches I found useful they reference the datasheet since it also has 2 pretty good applications of this circuit that can almost be directly applied to guitar effects. These are the 2 topologies that are the backbone of many delay circuits.

https://diyaudiocircuits.com/wp-content/uploads/2012/09/2399.pdf

Of course, one of the first search results that popped up under "pt2399 analysis" is the one done by electrosmash. I think it's pretty good, but some of the things talked about kinda went over my head since I'm not an EE but I do have a good base understanding of electronics. This helped clear up some of the things about the chip itself (what does pin 6 do?, etc)

ElectroSmash - PT2399 Analysis

Circuit analysis of the PT2399, a CMOS echo/delay/reverb processor by Princeton Technology.

www.electrosmash.com

Here's another good high level analysis of the chip and it's applications. Mods are discussed with some other links in here about what others have done with this chip.

PT2399 Digital Delay IC - DIY Audio Circuits

The PT2399 is one of the most rewarding chips a DIYer can experiment with. A stock circuit from the datasheet can nearly complete a guitar pedal project, and there are …

diyaudiocircuits.com

To really help solidify my basic understanding of the chip is to see it in action in a working circuit. This video really helped me understand a basic delay circuit with the common controls (level, repeats, time) that can be found in others. There is no LFO here (I still can't seem to breadboard a working one yet ) which helps to simplify things. This guy goes through the schematic nearly piece by piece and says "hey, this resistor is placed here because it does..." which is really helpful for a regular dude like me.

Anyways, looking at the most common mod (pin 6 controls the delay time) I decided to put a 100k pot (most circuits have 50k) to fool around and see what sounds I could make with it. The longer the delay time the more distorted the signal gets and the more noise comes through. I still kept the original circuit on my breadboard with just that one mod. It works with the mod, but needs tweaking since the two pots don't interact very well. It can squeal like a piggy...

I think the next step would be to whip up a PPCB circuit and start fooling around with it, but I think the 90 minutes I spent breadboarding the "basic" circuit and going through analyses were fruitful.

 

[BuddytheReow]

I found this the other day while browsing around the net. This is a collection of Devi Ever circuits, their various topologies, and stripboard layouts for them. There are 7 topologies in here with variations of them to arrive at the various pedals done over the years. The circuits themselves seem pretty basic and are definitely worth breadboarding at least to tweak them to you taste. Since I do not own any Devi pedals I cannot trace them to confirm whether or not they are accurate in the file.

A few things I noticed:

-The circuits themselves are pretty simple as mentioned above.
-Some of the circuits I have no idea why they are laid out like that. The LP and Electric Brown for example
-Devi likes to use very similar value components in the various builds. 100nf caps, 2.2m and 3.3m resistors, and MPSA18 transistors. It would be worth stocking up on these to try em out. You can get everything on Tayda since they are all pretty basic components

devi-ever-diy-info-manual-aw-heck-yes.pdf

drive.google.com

 

[fig]

I also enjoy building datasheet examples. The 2399 was actually one of the first I ever did, or tried. I can't remember if it worked or not...no matter, I learned through it...and I'm still learning. Your write-ups are great! Thank you for taking the time to put them together. They really are appreciated.

 

[BuddytheReow]

It's been a while since I've posted something here. 4 months, really? Huh. I guess i've been too busy with work and house projects to get some experiments done.

Anyways, I recently posted a breadboard tutorial how to build a RAT. You can find it here if you're interested.

TUTORIAL - Muroidea - Proco Rat

Ah, the Proco Rat. Built in the 1970's and popularized in the 1980's, it can be considered a "standard" in the distortion community. This little baby can do it all: pseudo-overdrive or light distortion, distortion, and borderline fuzz territory. Due to its simplistic circuitry and versatility it...

forum.pedalpcb.com

I'm about to embark on modding this fantabulous circuit and I realized that I have a good comparison of all the different RAT pedals out there. In case anyone is interested here it is. I don't remember who sent this to me so if you're that person, thank you!

I gotta come clean. I also wanted a reason to bump this thread for any new members who are curious about circuits and how they work. Once again, the RAT saves the day!

 

[BuddytheReow]

I had some time today (time? What’s that?) to myself and I wanted to see what the Mach 1 Overdrive was all about since I’ve seen a handful of them in the Build Reports recently. People here claim it’s a pretty “transparent” overdrive so I cleaned up my rat and put it on there. This is more of a preview of the next breadboard tutorial. I see the appeal of overdrive circuits, but it’s not really my style of playing (although I tend to play a sweet blues riff with some overdrives). I will, however, stack it before another dirt pedal to get a different sound that I tend to like when I do use overdrives. Anyways, here’s my Mach 1. Coming soon to a “New Posts” near you!

 

[BuddytheReow]

Chuck and I are working up something for budding circuit designers, so I thought I would document what I did here. We're working on an output booster circuit block. So, I made a quick dirt pedal with Chuck's help. The GAIN control goes from little to no gain all the way to a searing fuzz/distortion. 2M may be a bit high for the value since they are not super common, but 1M would work just fine. The output booster is really loud and in hindsight I think maybe a volume pot is not necessary? Anyways, here is how it's laid out:

FUZZ>Hard Clippers>BMP Tone Stack>Output Booster>Volume knob

I call it the "Wish Not Buzz Not"

 

[Chuck D. Bones]

Try putting the VOL pot between the tone stack and the output booster. A100K. Replace the BOOST pot with 100Ω.

I'll breadboard this puppy and see if there are any other potential mods.

 

[fig]

Those MOSFETs are powerful critters.

 

[BuddytheReow]

Try putting the VOL pot between the tone stack and the output booster. A100K. Replace the BOOST pot with 100Ω.

I'll breadboard this puppy and see if there are any other potential mods.

What's the reason for changing the VOL pot to 100k if moved? How does it interact with the rest of the circuit?

 

[Chuck D. Bones]

The BMP tone stack was originally designed to drive a load around 80K. Play with the value of R4 in TSC and see what it does. We can design a BMP tone stack to drive just about any load, and it need to be tuned to the load to get the best sweep. I find good results when the TONE pot and load are the same value.

While we're talking about loading, what kind of load does the MOSFET booster present to the tone stack in the above schematic?

Any guesses?