Original Four Banger – Schematic & Layout

18 02 2011

I haven’t posted in awhile. I’ve been unbelievably busy with all sorts of stuff. To make up for it, here is the schematic and a layout for the original version of the Four Banger.  The connections for the controls aren’t labeled on the board, but if you use the schematic as a guide, it should be easy enough to figure all the connections out.

Even though the schematic shows an AC128 for the germanium transistor in the Rangemaster section, this circuit can accommodate a wide variety of PNP germanium transistors easily with the (proper) Emitter trimmer to set the bias however you see fit.

Please don’t flood me with how-to questions. I honestly don’t have time to answer them all, and there is more than enough help available to you on the various DIY forums.

The Honey Bee Challenge – Folk Driver DIY Overdrive

19 04 2009

Hi everyone, as some of you may already know, Björn Juhl sent me a Honey Bee pedal to play with. The idea was to listen to the sound and see if it can inspire a nice DIY project. Well, after spending some time with it, I’ve come up with something that sounds good and will certainly remind people familiar with the sound of the Honey Bee.

My goal was to keep the design as simple as possible, but still try to fit in some tricks. This uses both positive and negative feedback to get its sound. R8 is something I learned from the big old red RCA book – it’s positive feedback to boost the gain of the first stage; it was suggested as an alternative to using cathode bypass capacitor in a tube stage, well, it works just as well with a transistor. The combination of R9+C4 is negative feedback to reduce the high frequency gain and give the signature smooth sound. It also promotes stability in the circuit. I settled on the clipping diode combination after trying several different kinds, and the 1N4001+1N4148 combo had the best sound for this thing and reminded me most of the HB.

The Timbre control adjusts both the low-frequencies and the amount of drive. At the 12 o’clock position is the minimum drive amount. At one extreme it’s max gain with lows emphasized, and the other is max gain with the lows cut. It’s sort of like having the HB’s Gain and Nature controls on one knob.

Here is the schematic: Folk Driver
I have a PCB design done up with ExpressPCB so people could order some if they want, and the board is a single-sided design so it is easy to make yourself. I will post the file up after I verify it (probably tomorrow…).
Stay tuned for the full build project.


True Bypass For Boss (without ruining the box!)

15 04 2009

Many people are hot on the “True Bypass” thing. The electronic switching as used by Boss, Ibanez, and many other popular effects is considered passé, as now people want to have their bypassed signal completely un-tainted by superfluous buffers. And in some cases they have a valid point, if you have 6 Boss pedals all strung together, your signal is going through as many as 12 buffers, and in the case of the transistor emitter-follower type as is used in these pedals (which always has slightly less than unity gain), this can result in a substantial signal loss.

So, it has become popular to modify these effects to have mechanical switches that fully bypass the signal when the effect is turned off. There is one big problem; most people seem to think the best choice of switch is the large 3PDT footswitch sold by New Sensor (or Cliff, or Fulltone…) that is popular in many DIY and boutique builds. This is generally a good quality switch, but it is LARGE, and there isn’t adequate space in the Boss Compact series case design to accommodate it. In fact, the Boss case is designed to have a large actuation plate pressing on a very small switch, so there is no space at all for anything but a very small switch. In an attempt to make the large switches fit, there have been countless examples of the attractive and functional appearance of pedal ruined by drilling holes through the actuator plate to fit the switch. You’ve seen them… these ugly things with huge footswitches sticking out of them… terrible.

But there is an elegant solution to this problem, and it’s actually quite simple – just use a small mechanical DPDT pushbutton switch that fits correctly under the actuator. You can see one here:

True Bypass in an old Boss BF-2

True Bypass in an old Boss BF-2

The only trick is to get the height of the switch plunger adjusted so that the actuator presses on it correctly. Foam rubber makes this easy.
I etched a board to hold the switch and simplify connections. It is held in place by a bolt which is mounted through the stud that holds the actuator spring.
Bypass board for Boss Pedals

Bypass board for Boss Pedals

You can see a tutorial which describes using a small switch like this at Small Bear Electonics (and yes, they sell a similar switch). http://www.smallbearelec.com/HowTos/Shell/Shell.html
For switching the LED, I am using R.G. Keen’s brilliant Millenium Bypass circuit. You can read about that here: http://www.geofex.com/Article_Folders/Millenium/millen.htm
That’s it, very simple really – there is absolutely no reason to hack up a Boss pedal to put true bypass in it. And doing it this way retains much of the “soft” feeling that makes Boss’ Compact pedals such a great design.

And as for the rest of this old BF-2? I did a handful of simple mods to help to improve it. Firstly, I removed elements of the old switching circuit to accommodate the new mechanical bypass circuit. Then, I replaced the old worn-out electrolytic caps and upgraded them with better types. I also replaced the signal opamps with better low-noise types. The stock 4558s are fine for an old Tube Screamer, but they’re pretty lousy if you want a nice hi-fi sound. Some the two 1uF electrolytics in the signal path were replaced with Nichicon MUSE audiophile grade bipolar types, and a pair of 220nF caps that were previously electrolytic have been replaced with film types for a definite improvement in fidelity. That’s about all this on needed to get some good improvements and lower the noise a bit.
Here’s a pic:

Modded Boss BF-2

Modded Boss BF-2

I hope this little article gives you some ideas for your own mods to the Boss Compact Series. They’re really fun to work on, and little changes can sometimes go a long way.


Octavia Experiments/Improvements

5 03 2009

I finally got around to trying the Octavia circuit. I’ve been fooling with it on breadboard in my spare time the past couple days, and I’ve figured out some interesting things.
Just to make sure we’re on the same page, I’m using the Tycobrahe Octavia schematic on Analogguru’s site.
There are a couple minor differences in my test circuit; firstly, I’ve oriented the MPSA18 the correct direction with the collector towards earth. I did try it the original backwards way, and it does work, but it sounds so bad it’s not worth messing with to try and be “vintage correct” with Tycobrahe original. For the other two transistors, I’m using 2N2907… not for any special reason, that’s just what suitable PNP silicon transistors I had handy. They do the job fine. The transformer is the Mouser 42TM022 that Small Bear sells for DIY Octavia. I’m using 1N34A for the diodes. Most of the resistor values are the same as the schematic with a couple little subs where I didn’t have the exact value, but nothing that would make a difference.

So, I build up the basic “stock” circuit. It works, but it sounds rather… ugh… not so great. It gets octave, but it’s only really happening when you play high up on the neck. I know that’s a well-known characteristic of it, but that doesn’t mean it has to be that way. It also gets incredibly splattery/mushy when you turn the fuzz up. I guess this is normal too. The problem is that the distortion of the fundamental totally hides the octave when the fuzz is up… you can hear it better with lower fuzz settings, but it’s still very dependent on dynamics and working the strings to get the note to come out. I suppose this is a testament to Hendrix’s mastery of the effect.

I listen to these things, and to me, they sound like problems that can be solved. So, I play and listen… and what do my ears tell me? They tell me there is too much low frequencies saturating the primary of the transformer and that the overall response is too slow to dynamics. I try a much smaller capacitor coupling from the third transistor to the transformer – C6 in AG’s schematic – this is normally 33uF… I try 330nF…..
Now there is octave all the way up and down the neck; on the low strings, too! Then, I replace C7 (220uF) with 47uF; dynamics are now much improved; less slow compression at high fuzz settings.

I don’t like the diodes going straight to the volume control and then the output; it looks like you would get inconsistent results with different amps/effects after it, and that might affect how well it does the octave thing. I put a buffer after the diodes with another PNP transistor. Works great. Put the volume control at the very end after the buffer. The signal coming from the diodes is low enough that the buffer stays clean even with the full output going to it.

Now, I want to be able to have both the “traditional” Octavia splat sound as well as my new improved octave, so I did a compromise and tried a 10uF coupling cap with a 100k pot to fade it in on top of my new lower value C6. Works very well at dialing in two very different responses; though you may want to experiment with tapers/values for the pot. I keep my new value of 47uF for C7 in any case because it sounds better than 220uF regardless.

One more thing I tried: put a resistor in series with the transformer’s primary connection to ground. The idea here is to reduce the loading of the primary on the stage that’s driving it. This is another attempt at reducing the amount of squishy-ness in the sound. I just tried a 1K resistor. It worked to a degree. As expected, the output volume dropped a bit because the driving signal is now being divided between the primary and the resistor, but there was still enough output to be usable. This gave a very dramatic change to the timbre of the octave effect… very hard to describe; it was still a fuzzy octave sound, but just sounded different than it did before. To me, it sounded like the octave wasn’t as pronounced in a subtle way, so I dropped the resistor, but it has given me reason to experiment with a transformer that has a higher-impedance primary in the future.

My conclusion is that the transformer and how it interacts with the drive circuit is absolutely the determining factor in the character of sound you get from this. The changes I made to try and improve it were all centered around changing how the circuit responds with the transformer, so I’m certainly going to get different transformers to play with.

I’m going to build one up based on what I have on the breadboard now – it sounds really neat and I was able to get some super-cool sounds with different pickup selections and different playing techniques. I totally got this cool “Robot Blues” thing happening.

I’ll draw up a schematic and share the final design as a full DIY project once I get it put together. But, before that, I have a bunch of Four Bangers that need built!


Free Schematic and PCB Software!

5 02 2009

Greetings friends,

Please visit this page for some nice simple Freeware Schematic and PCB drawing software.

Many thanks to forum member Celadine for the link!



Crackle NOT Okay!

8 01 2009

Recently, the Four Banger became a bit of a small hit at The Gear Page. I’ve gotten a good number of orders and I shall be quite busy for the next few weeks. Thanks!
But…. some people seemed to take issue with my inclusion of the circuit inspired by the ZVex Super Hard-On (the section labeled “S” in the Four Banger). Despite the work I put into designing the Four Banger from scratch, including that simple cheap little thing makes me an unoriginal thief in the eyes of certain people.

Since I’m not interested in having to defend myself against being called a “cloner”, I decided to throw out the SHO entirely and design something new to put in there. It took me about three days of experimenting, but finally I came up with what I desired: a circuit that captures the same sound and response as the SHO without that awful crackling noisy gain control!

Here it is, the thing so many DIYers have tried to do, but none have ever accomplished, the Crackle-Free SHO!

Now, I admit, it’s not exactly like the SHO, but your ears will have a very hard time telling the difference! When you look at the gain control, you see that the input impedance of the circuit goes down as gain goes up. This is a key ingredient to the SHO-style high gain sound. The input impedance of the original SHO changes like this too, because of the relationship of the feedback resistance vs. gain. Freestompboxes member “estragon” was kind enough to give an excellent explanation about the change in impedance which I shall quote here:

…the input impedance of the SHO is not 5 Mohm as the popular belief dictates. No, it varies big time with the bias pot. At min gain, the end of the upper 10Meg resistor is tied to an inverted copy of the input voltage, not ground, so overall input impedance actually becomes 3.3Mohm when you do the proper math to find out the equivalent thevenin resistor (this has been verified in the sim as well). As the bias pot is reduced and gain increases, something very convenient happens: the input impedance starts going down, down to 140 kohms at max gain. This certainly helps taming the high frequency resonance of any guitar pickup (around 2-5kHz), thus taming highs and helping to the musicality of the clipping. Again, this is because the upper 10Meg resistor is effectively tied to a voltage source that is an amplified version of the input voltage, and not a simple ground point.

So, I have managed to be able to control both the gain and the input impedance in a way which is analogous to the action of the SHO, but with a new method that doesn’t make noise!

What causes the noise in an original Super Hard-On’s gain control, you may ask? It’s not actually the control itself that’s making the noise – attempts at using top quality low-noise controls have been fruitless – it’s the transistor that makes the noise. What happens is that as the gain control is adjusted, the transistor’s bias changes; and because of this change, it switches on and off momentarily while it stabilizes. The two resistors which connect to the Gate (10M in the SHO, 2M2 in my version) allow the circuit to automatically bias to the center of the voltage swing “window” which it has available. But it doesn’t do this automatically, it takes a moment for it to happen; and in the meantime, the transistor is cutting out and crackling. It’s very interesting to hear if you turn the gain control of an SHO very quickly from minimum to maximum gain; the sound will cut out completely for a second and slowly fade back in… very odd behavior, and hardly something I would consider desirable!

So, now we don’t have to put up with that noise any more, because since my version has the Source at a constant level, there is no crackling, popping, fading, etc… because the bias is constant. Instead of using the ratio of Drain to Source resistance to control gain, my circuit uses the ratio of Gate series resistance to Drain/Gate feedback resistance to control gain – just like how you see in an Inverting Op Amp circuit. It’s just as simple and elegant as Vex’s design… except it’s how he should have done it in the first place so he wouldn’t have had to waste so much time and effort convincing people that a noisy junky-sounding gain control is “Okay”!

Where can you go with this? There are many possibilities for this kind of circuit. Just look at Vex’s product line; a substantial number of his things are just various numbers of SHOs all together. With my circuit, I urge that you try something creative; even if you’re keeping it simple, you can do fun things like add an ultra-high impedance input buffer which would allow you to scale down the values of the gain stage’s Gate resistors and Gain control, so you don’t need to use the high values to get a high input impedance. You’ll see how useful that is if you ever try to find 5M controls to use for a super hi-Z version…. High values of resistance contribute noise as well, so there are many advantages to using a buffer with it.

When I find the time, I will put up a DIY project with a printed circuit board layout you can use for your own experiments. And I reiterate, this is now the boost which is used in my Four Banger in the spot previously inhabited by the SHO.


Jetter Gain Stage Red

26 04 2008

Recently, this appeared at my doorstep.Jetter Gain Stage Red

So, being the always-inquisitive individual that I am, I opened it up to inspect.Jetter Gain Stage Red Inside

Well, you can imagine how offended I was to see all this ugly stupid goop inside there, so I rolled up my sleeves and went to work removing the disgusting offal.Disgusting Offal

Goop is a cancer, and as dutiful Practitioners, it is our obligation to remove this cancer whenever it is encountered.

Jetter GSR, Offensive Goop Removed

After the goop has been removed through our Art, we then must trace the circuit the share with the world and spread the Shining Light of Knowledge.

Jetter Gain Stage Red Schematic

What’s this? Does this schematic look familiar to anyone? Those who visit Freestompboxes will no doubt recognize this circuit as the same one which can be found in the Hermida Audio Zendrive! Any differences between the two are negligible and paltry. This is a great shame when a company which makes claims to having original designs has to hide behind goop to disguise the fact that it is not only unoriginal, but a blatant copy of another popular design.

But another, and arguably even greater, shame is poor workmanship! The Jetter was full of cold solder joints caused by poor soldering technique at incorrect temperatures. You can see here:

Jetter bad soldering 1Jetter bad soldering2Jetter bad soldering3

These kinds of joints are unacceptable in any electronic construction.

Another strange point of worry was the small toggle switch. Apparently, because it doesn’t fit properly, the solder lugs have been chopped off of it and the wires were just tack-soldered into place.

Jetter switch - lugs chopped

All the solder lug connections within the Jetter unit are tack-soldered in this manner. This means that the wires are just barely touching the lugs and the solder is used like a glue to hold it in place. This makes a poor connection both electrically and mechanically, and coupled with the cold solder joints is a failure waiting to happen. Completely unacceptable.

And what’s up with this?Jetter Battery Snap Why would a boutique guitar effect in the $200+ price range use the cheapest low-grade battery snaps? We’ve all seen these before and we all know that it won’t hardly last a year before falling apart. Again, this is unacceptable.

There are numerous other amateur-level mistakes to be found in the construction of this device: from the hot-melt glue used to hold the board in place, to the very poorly drawn artwork on the PCB itself. The word I kept saying to myself while dissecting this thing was, “Why?”. Why do they think they can get away with this? Why do so many guitarists think this poor level of construction quality is acceptable? Why has it become normal for people to charge $200 to $300 for something that’s lower quality than the average Boss pedal? Why are consumers continuing to put up with companies who don’t respect them either as customers or as intelligent thinking humans? It’s really a sad state that we’ve come to.

I know I’m beginning to rant, but this is something I believe is important; I have become completely fed up with the unprofessional and disrespectful attitude that I see from the “boutique” community. This isn’t just Jetter; what I’m talking about appears to be common to the majority of them. I’m only singling out Jetter because they are the subject of this article, and therefore, are the subject of this particular critique. I am tired of seeing people on message boards get all excited about every piece of shit these “boutique” shysters sling at them. It seems like all one has to do is repackage a stolen circuit in a fancy box and people will gladly pay out the nose for the goop-shrouded mystery that promises sonic nirvana.

And how does it sound? Bland, boring, common… I was able to cop its signature “chewy” midrange tone with any number of common overdrive boxes. It sure doesn’t sound anything like a Dumble or any other tube amp, and I find it especially dishonest that they would compare it in such a way. To be fair, it sounds nice at low gain settings when used to drive an already-hot tube amp; but as the gain is turned up, it becomes progressively more and more generic sounding. Honestly, if a one desires the sort of sound this box creates, I would recommend supporting the original designer and purchasing an Hermida Audio Zendrive.

Seriously, who thought this thing sounds like a Dumble? I could see how it could possibly give certain dirty tube amps a tone which could be more akin to a Dumble, but the unit by itself does not sound anything like a Dumble (or any tube amp!)… not even close. The only thing it sounds like when fully overdriven is that standard opamp/diode clipper distortion that has become the normal thing to expect from Boss/Maxon-inspired pedals.

To learn more about this, or to join in further discussion, please visit Freestompboxes.org

Of course, the statements in this article are my personal opinions… but I believe my opinions to be well-informed based on my first-hand personal experiences. The rather harsh critique I have given of the build quality has been seconded by an experienced Electronics QA Engineer who inspected the unit personally and gave a much harsher opinion than I.


Ed. Note:
I have disabled comments on this article. People need to to keep their misinformed shit-talk to themselves. If you don’t like what I have to say here, then try being an adult and ignore it. Yeah, I know lots of people like the GSR. If you own one and love it, then good for you… it doesn’t make any difference to me.  I don’t have any personal beef with Jetter and this article isn’t intended to defame anyone. It’s an honest and unbiased review given by a me – a person who has years of professional experience building and repairing electronics. If I say I think a certain stompbox is poorly built, I’m speaking sincerely and with the same standards of judgment I use for any piece of electronics I review. If it doesn’t live up to my personal standards for how something should be built, then don’t get all bent out of shape if I say I think it’s junk.