My Tube Distortion Pedal

in the current state of near-completion. You can see the Step Up Transformer ( converts 12V AC to 120V AC, 169V Peak, 200+ V rectified ) The 12V Rectifier is actually out of a wall wart, with an additional capacitor added. The plate selector switch selects either 12V or 200V for the second plate to operate at. ( This will affect output. I may add a dropping resistor to the switch as well later ) The future location of a footswitch, and the EMG Presence control I had laying around.

More details and samples when completed. Please forgive the spelling errors in the pics, I fat-fingered a couple while editing the photos.

Jim

An idea for 3 pickup Gibsons

An online buddy needed some help modifying a Gibson SG Custom Re-issue. Here's what I came up with for him, using a normal 2 pickup toggle switch. Click HERE for Bigness

My Simple FET Booster

Here's my extremely simple FET booster circuit. It's so incredibly simple, anyone can build it, and it's cheap, while offering great results.




















I've used the 2N5485 and the 2N5457 interchangeably ( I hope I got those numbers right, I'm typing this from memory ) I use an axial electrolytic cap for the bypass on the 100 ohm resistor, and tantalum for the other two, because they're small, no other reason I could think of. Confession: 3k came out to be a great load resistor, but I didn't have a 3k, so I put a 1k and a 2k in series). I really think I could hide this in my Les Paul control cavity if I wanted to, and definately could put it in my strat, if I were to forego a couple of trem springs for battery placement. Hmmmmm . . . but that won't happen. This is going to be the first gain stage in my TUBE HOTTIE real tube distortion pedal. You can see waveforms of this preamp in the post below, the first pic being this preamp running on a 9V supply.


















I used half of one of those Radio Shack experimenter's circuit boards, the one designed for a 16 pin DIP IC, I simply cut it in half on a band saw at work. The 9V battery is shown simply for size comparison. I could probably put in on an unclad breadboard the size of a dime if I had to. The wires are color coded so I don't have to think about them a second time. Red and Black are obvious, the blue is input, and the yellow is output. Think about this: Which signal will be hotter, and which color is hotter? This makes things a little more fool-proof when final assembly comes. I started this habit when I was the electronics designer at Conklin Guitars back in the 1990s. Any of you that have ever heard the Conklin On-board Parametric EQ are proof that this simple philosophy works. I label all my pedals this way too, simply because I can hook them up in near darkness.

I measured an input and output signal with a true RMS Fluke multi-meter, and after doing the math, it looks like I'm getting nearly 16 dB gain at 5kHz. Holler at me if you have any questions.

Jim

Distortion on the O-scope

Here are a couple of circuits on the Oscilloscope I've been messing around with. The circuits are going into my Tube Hottie Stompbox in the next few days. While testing each individual gain stage, I snapped some photos. First, let's look at the FET ( Field Effect Transistor ) This type of transistor is super-easy to bias, hard to screw up, and offers a HUGH input impedance, for acoustic instruments, or electric. Additionally, alot of folks think they can build a FET circuit to sound just like a tube, but here I'll show you the difference.

















Above is my simple single stage FET preamp, with a .5V peak-to-peak signal in, and about 2.3V p-p out, showing a gain factor of about 4.6. The supply voltage for the preamp was 9 volts, a common value in the stomp-box world.
















Same Preamp, same applied input voltage, but with a 12V power source. Note the increased gain created by a slightly higher bias current. The additional headroom doesn't hurt either.
















Here's the preamp back at 9V power, with 1V p-p on the input. Notice the bottom of the wave form is not exactly the same shape as the top. This is the beginning of distortion. Chances are you'd never hear this, but it's there all the same.

















Here's a 5V p-p input, and the output is clearly distorted. The flat spots on top show the transistor is cut-off, meaning the input signal can not drive the current any lower than it can during a negative voltage input swing. The flat spots on the bottom show the transistor current is saturated, meaning it can't carry any more current: more positive voltage input will not result in an increased signal output level.
















Here I'm just applying a 15v p-p signal, which is just plain stupid. Note that it does not increase the output voltage, but our square waves are about as square as we can make them. This is how early function generators made square waves for test equipment.

















Here's a tube circuit: a 12AX7 running on about 150V. The input signal here is about .2V p-p, the output signal is around 8V p-p, a gain factor of 40.

















Here's the tube with an input signal of .5 volts, we could also call it 500 millivolts, hotter than any guitar signal by itself. Notice the distortion waveform. We've never really reached saturation for the tube ( I hope the lower plate current will make it last longer ) but we do get a good solid cut-off at the top of the wave. Look at the left side of the square sections. The gentle rounding of the square section ( like a bar of soap ) is why Tubes sound better, less harsh than a transistorized distortion. Yes I know this is asymmetrical distortion, but I want to try it.
















Here's the two wave forms side by side, so you can see the difference between FET distortion and tube distortion. The one on the right will be more pleasant, and more musical.

I will use both sections in my stomp box pedal. The FET section will be an easy way to get some increased voltage signal ( while staying clean ) to make sure I get into the overdrive section of the tube, which is why I'm building the pedal in the first place. - Jim Cox

My DS1 Mod

I was introduced to the DS1 Keeley mod by a local friend/work acquaintance that sold parts to the company I worked for. He offered to loan it to me, and I was very intrugued.

When I got the pedal, it was pretty obvious that the clamping diodes had been replaced by a higher-breakover voltage LED. All diodes exhibit a forward voltage drop, where they will simply hold a drop of .3V ( germanium ), .6V ( Silicon, as in the stock DS1) and higher, with 1.6V being 'textbook typical' of most LEDs. Again, I say typical, but not written in stone. I've seen higher. I did experiments on things like this back in high school Vo-tech electronics class, we called them clamping circuits. Clipping was a description best left to actual amplifiers.

The Keeley shop had also added several 'sonic' components to increase clarity. I cannot confirm nor deny that these upgrades sound better. I believe in the theory of their component selection, but I personally do not hear it. However, I continue to salute and respect them for creating an industry within and industry, and am proud to follow in their footsteps, along a slightly different path.

One thing that was missing in the Keeley DS1 was the 'big Marshall tone' that I kept reading about on the 'net. There wasn't enough bottom end for that kind of sound, so that's where I went to work. After I had changed out the clamping diodes with LEDs, I placed the LEDs on a switch, so you could run the op-amp output either with the clamp circuit, or wide open when the diodes were effectively removed by the switch. Then came time for the big change. I started experimenting with the tone section of the DS1. This is very similar to the tone of some of the EH/Muff devices of the 1970s. When I had the bottom end sound I was looking for, I knew I had my mod.

Here's a video showing the screen capture of my multi-track software playing and recording the intro to 'Working Man' thru my old POD, and three variations of the DS1. Stock; My mod clamped; and my mod un-clamped. Note: I selected 'Working Man' simply because it uses alot of different techniques; Open strings, power chords, and single notes, ( and it's easy )

the set up for the audio file was as follows:

Recording Setup for WORKING MAN INTRO

all DS1 knobs 1/8th turn to the right of 12.00

POD: Amp- Modern Class A; Drive- 9 oclock; Bass, Mid, Treb- 12 oclock
Channel volume- 3 oclock
Effect- Delay; Effect tweak- a hair above 9 oclock; Reverb ZERO
all straight into my highly refined $20 cheapo soundcard.

Additionally, I labeled the DS switch for clamp/boost on the side of the unit. I've sold a few dozen here and there, and had one customer ask me to put in a switch for the bottom end boost as well. I use this in my regular church gig as a lead guitar player. I'll turn it on for solos, because the extra distortion will give me just a little more 'cut through the room' in the same manner the BBE enhancers add distortion to the higher frequencies to increase brightness without adding noise. Not only does it add brightness, it adds a nice full bottom end. You can judge for yourself.

If you think you need one, you can contact me by email coxster@yahoo.com

Jim

My First Mod Ever

My FIRST Mod ever, started when I was a teenager. Money was never plentiful in my home growing up, and 9V batteries might as well have been made of gold. they seemed so expensive to a kid that earned $4/wk mowing lawns, so I modded the first pedal I ever owned: a MXR Distortion+. It had a hole in it where someone had tried to put in a dc jack ( 1/8" phone ) so I simply added a power jack to it, in parallel with the 9V connector leads. I saved a wall wart from something ( I still save wall warts to this day, but now I sort them ) and used wall current to power it. I got this used somewhere around 1980. I never noticed before, but look at the recessed MXR Script logo on the back cover.