Wednesday, 17 September 2014

EHX Germanium Overdrive

Thanks to Miro for the excellent trace job he did on this.

Hope you're stocked up on 470nF caps.  They were all polarised but I have shown poly for the caps with a 5mm pitch because I expect that is what most people will use.  I have shown electrolytics for the two with only a 2.5mm pitch just so people know the polarity if anyone would like to build it with electrolytics, but again I expect most would use poly or maybe 2.5mm multilayer ceramics for them.  Any PNP germanium can obviously be used an an alternative to the NKT275, and I suspect more people will have 2N3906's in stock than 2N5087's, so try those for Q2 and Q3.

Info about the original:
Classic '60s Germanium transistor overdrive and more. In addition to a Gain control, the Electro-Harmonix Germanium OD allows the user to control Bias for attack and the circuit Volts for that sweet spot found when a battery's voltage dips. Dial up that slightly torn speaker sound OR dial in total Germanium "Satisfaction."

Germanium is an element like carbon or gold. Germanium transistors were used extensively back in the 1950s and ‘60s. Eventually they were replaced by components that were considered “better.”  The EHX Germanium OD and Germanium 4 Big Muff Pi use these old school transistors. They have a distinctive sound, some say smoother or “spongier.” You be the judge, hear the Germanium OD here.








and the schematic




Thanks to ξεναγός νεκρόπολης for verifying and providing the following working voltages.

Q1
e 5,41
b 4,17
c 3,76

Q2
e 4.37
b 3,75
c 0

Q3
e 3,02
b 2,43
c 0

Monday, 15 September 2014

Ibanez BB9 Bottom Booster

Here we go with one of my personal favourites. To me, the sound is simply amazing. As Dirk's notes on the schematic suggest, you won't be saving any money by building this. New ones sell for pretty cheap and one should be able to score a used one for a very decent price. I still wanted to see how compact i could possibly get this and yes, i'm rather happy with the results. I did cut a few corners though. I omitted the six 100n power decoupling caps from each opamp as adding those would have made this way bigger (let's just hope this doesn't add to noise floor). The input resistor is 12k on this layout, but to make it verbatim, you should take 5k1 and 6k1 resistors in series in its place - or a value of 11k2. I also dropped the 100k resistor and 47p cap from the output. If you want to add those, just solder them between lugs 1 & 2 of the Level pot. I also made a couple of small changes to the power supply section input. I burned the LT1044 on my original unit, and that was way easy to do. So i added series protection and a zener+100R resistor after that. Should be pretty fool proof like this. Charge pump produces +9V/-9V swing, so you're safe with your 16V rated electrolythic caps. Should be a nice fit for 1590B.

Snippet for the marketing text:
Sometimes it's best to keep it simple. Which is why, in a world of dizzying often over-complex technology, the durable, dependable, and simple stomp box continues to be the most widely used and effective means to expand, color, distort, mutate, sustain, and twist tone. The Ibanez BB9 is a booster that provides a fat bottom end with a powerful sound, perfect for the player who wants to push their amp into overdrive without losing any of their low-end. This pedal is designed to help clean tones reverberate even more and bring more intensity to a player's sound. Combine it with a distortion pedal to create of a wide variety of tone colors.



Thursday, 11 September 2014

ROG Britannia

Here's a challenge for those who want theirs in  1590B. Should fit, but it'll be a challenge.

From ROG:
The English Channel was our first attempt to adapt the Vox AC-30 Top Boost amplifier for use as a guitar pedal. Released in 2004, the English Channel was a straightforward JFET implementation that was heavily based on the amp's schematic using the so-called "FET by numbers" approach. While this approach did certainly capture the amp character to certain degree, the overall sound of the resulting circuit was not as refined as its valve counterpart.

Through the years since the English Channel was released, we've been polishing the manner in which the different valve stages used in guitar amps are adapted to JFET-based circuits. This involves taking several aspects into account, such as the effective frequency response of the stage after considering parasitic capacitances, input and output impedances, gain and dynamic range, and clipping characteristics. Furthermore, in some cases we have taken the artistic license to replace certain portions the circuit with something that provides the intended function without necessarily looking like the original circuit.

Now we present Britannia, a fully redesigned adaptation of the AC-30 for use as a guitar pedal which has been optimized for playing into a clean solid-state amp. We hope that you will find this project a nice approach to the sound that was made famous by many artists, including The Beatles, Tom Petty, The Edge, and Brian May, to name a few, without having to invest in or carry around the real thing.

Here is the usual circuit walkthrough for those interested in the savory details: First, Q1 is our standard high impedance input stage, very "booster friendly" thanks to the two red LEDs at the Gate. Next, you will readily recognize a scaled version of the Gain control section, which together with Q2 form a treble booster. You will also notice that all JFET stages but Q2 are prevented from clipping hard by virtue of the back-to-back diodes present at each Gate. This helps retaining the sweetness and dynamics of the sound. However the original amp has some degree of grittiness in it when pushed hard, and this is achieved specifically by Q2, which is a high gain stage borrowed from the Omega booster. Apart from its higher gain, this stage is generous in 2nd order harmonics. Then comes Q3 as a voltage follower driving a slightly modified version of the original tonestack. Some additional gain is provided by Q4, then a cousin of the original Cut control, which in our case was wired backwards with respect to the original, and therefore labeled Brilliance. Next, the op-amp U1a provides the final touch of soft overdrive, followed by U1b that implements the ultimate toneshaping: a 200 Hz resonance characteristic of a 2x12" cabinet and some high frequency rounding.

Jon Patton's official demo:



Saturday, 6 September 2014

Nick Greer Green Giant

Request.  Sorry Zach (rocket88), I was in the mood to do a quicky and this fit the bill nicely :o)
This is very close to the Ghetto Stomp and probably could be thought of as a cut down version with saturation control on the diodes.  Oh another pedal that used it before Fuller's ridiculous patent!
Anyway, a nice quick one for anyone with half an hour to kill.

Info about the original:
One of Nick Greer's personal favorites. Formerly built by Greer Amplification for endorsers only. A basic distortion unit with a limiter between the output of the signal and the clipping section of the diodes. The knob is labeled clean mix and allows the user to limit the amount of signal being distorted, resulting in a sound much that of the clean signal being mixed in on top of the distorted signal. Great for country players and rock and blues players who want good sounding distortion with the ability to dial the amount of hair. 





Friday, 5 September 2014

Test box 2.0

We always recommend trying the boards out before soldering everything in to the enclosure. Main reason being that if you have an error on your build, it's about a hundred times harder to find it inside the otherwise finished build. Like Madbean says - Build it, Rock it, Box it. There is a reason for that order. One could, of course, simply use a breadboard and/or simple screw terminals to achieve the same goal, but if you are building more than one circuit every now and then.. Well. Then i'd suggest you'd build yourself a test box. I've had a few different methods of trying the boards out before boxing, but my latest, equipped with a little more sophisticated screw terminal block was closing in on the end of the road. It was simply falling apart due all the use it had seen. So. I wanted to build myself a new one with slightly more features than the previous one. And while i was at it, i snapped a few (poor) shots of the process. A slight warning: This "photo essay" may not be detailed enough for someone who's doing anything like this for the first time. But if you know what you're doing, you're more than welcome to try something similar out. Here's my "Test box 2.0", which includes a switchable audio probe input. Let's start out with what you'll need.


Most things needed are your standard pedal parts.
  • Enclosure (i used a plastic box that can be found through Tayda)
  • 4-way speaker terminal and bolts/nuts for it (again, Tayda)
  • 2 mono jacks
  • Binding post for "banana" connector (mine isn't exactly like this, but once again - Tayda)
  • 3PDT On-On toggle switch
  • DPDT On-On toggle switch
  • 1µ polyester box capacitor (higher the voltage rating, the better)
  • Small piece of stripboard
  • 2 LEDs (i used diffused red and orange)
  • 2 1K2 resistors for the LEDs
  • Holders for the LEDs
  • A few meters of wire of your choice
  • Heat shrink tube etc. etc.
I drilled the enclosure first and started with mounting all the ingredients. Due to location of everything on my bench, i went with jacks on the left, speaker terminals on the right, DC jack on top and probe binding post at the bottom. I Placed the switches on the upper half, because it just looked like that would be a good place for them. The LED holders are below the switches. You should probably think the geometry of all the parts so that it'll suit your needs and bench.


Next up, we'll wire the grounds. The DC jack pictured here has its longer leg as sleeve and shorter as tip, so we'll take a wire from the short one to lug 2 of the DPDT switch - and from that pin to the second speaker terminal lug - and from that to input jack's sleeve - and from that to output jack's sleeve - and from that to lugs 1, 4 and 5 of the 3PDT switch. Here's picture of all the grounds connected:


Now, the small piece of vero. We're using that as a tiny daughter board for our LED resistors, just to keep everything neat. 4x5 board is enough. We'll wire two red wires to one row with two resistors and one wire for each row that has the other end of the resistor. Those wires are for the LED anodes. Like so:


Now we can wire up all the "hot" leads inside the box. To attach the tiny board to the enclosure, i used Tesa PowerBond Outdoor branded two sided adhesive tape. 3M's similar product doesn't insulate the connections, so do not use that. With slightly bigger board one could use a plastic, or even metal PCB standoffs, but i've found the Tesa tape to be sufficient solution. LEDs go their respective holders (i'm using red for bypass/3PDT and orange for probe/DPDT) and cathodes need to be soldered to lug 3 of the DPDT and lug 6 of the 3PDT. The longer free red wire goes to DC jack's sleeve and the shorter to the first speaker terminal lug.


Now we have all the grounds and supply wires hooked up. Next we'll need to solder up the signal wires. Connections are pretty much per the standard outboard wiring, but please do read this twice to make sure you got it:
  • Green wire - from 3PDT lug 2 to speaker terminal lug 4
  • Blue wire - from speaker terminal lug 3 to 3PDT lug 9
  • Yellow wire - from input jack's tip to 3PDT lugs 3 & 7
  • Orange wire - from 3PDT lug 8 to DPDT lug 4
  • Brown wire - from DPDT lug 5 to output jack's tip
All that wiring is depicted here:


We're pretty much all set, but the probe section is still missing. The box does work as it is now, but there's no use for the binding post and the DPDT switch does nothing - but light up the LED when set to probe mode. Now we'll need to solder two wires to the 1µ capacitor. Like this:


Other end of that wire is then fastened to the screw at the bottom of the binding post. The other end needs to be soldered to DPDT lug 6. I used a small piece of the two sided adhesive tape to keep the capacitor nicely in one place. Like so:


That's it. Simple and straight forward. The 3PDT bypass switch acts as a true bypass in the same manner as in any pedal. The speaker terminal connections are the ones where you'll snap in your just finished new effect board. One for supply voltage, one for ground, one for circuit input and one for circuit output. Here's a shot of the thing in action:


Some of you may think "why add the binding post for the probe?" Here's the reason - let's assume i've built a board, hooked it up to this box and it doesn't work. There's no signal passing through. We already have the ground wire for the circuit connected, so why should we rip out all the cables (excluding the supply/ground) and clamp an alligator clip to a ground point on circuit, plug the probe to the amp and start probing? For no reason. With this setup, we can simply connect a multimeter's test lead to the binding post, flick the probe switch and start probing. Even when debugging a broken factory pedal, this solution eliminates the need for a separate probe. Just connect that pedal's grounds to the ground slot of the speaker terminal and start probing.

How am i going to remember which of the speaker terminal slots is which and which jack is which? I'm probably not going to, so. I added some Dymo tape to mine...


I = Input, O = Output, G = Grounds and V = voltage in. Don't bother pointing out that the speaker terminal is upside down. It isn't. This way i can snap the wires in without having to lift the box off the table.

The idea for this box is rather simple and you should be able to add the features you want/need. Like for example - a negative charge pump and separate 2-way speaker terminal for the -9V and ground. That feature would enable you to try out positive ground circuits with the same test box. Why i'm not doing that? Because i have a lab supply on my bench and i want to be able to try the circuits out with higher voltages than just 9V. So ICL7660S with maximum input of 12V doesn't really suit my purpose.

One last thing. If you don't have a lab power supply with quick fuse, please do not test your circuits with a wall wart power supply. Even the slightest short will burn your supply or its regulator in a heartbeat. For testing purposes - solder a standard DC plug to a battery snap and go with that. You'll be able to drain a battery in ten seconds with a short, but it'll be a lot cheaper than burning wall socket adapters.