CryBaby Wah Mods.

I didn't mind the fact that my original Dunlop Crybaby Wah pedal sounded a little weak, but what I didn't like was it had a switching problem and when I would play in bypass, my guitar didn't sound as great as it did with the wah out of my signal path. With that said and a little inspiration from Mr. Emerson, I decided to modify my wah pedal. There are actually quite a few mods that can be done to this pedal and many websites to research. Here are a list of websites I checked out:
www.wah-wah.co.uk
www.diyguitarist.com/DIYStompboxes/WahMod.htm

I broke the modifications into two main categories to make it really simple. One I wanted true bypass so that my guitar tone didn't sounds bad when the wah pedal isn't engaged and I also wanted Led on/bypass indication as well. Two I wanted to change the way the wah sounded.

The true bypass is done using a DPDT foot switch or a 3PDT foot switch. The advantage of a 3PDT switch is I can have simple led indication. True bypass literary means when the effect is disengaged the signal path is just a wire.

As you can see in the figure above all three switch components are switched at the same time and there are two states. Most effects have one led for when the effect is engaged, but I wanted two leds. Call it overkill, but I like having the indicators this way. 3PDT foot switches can be found on ebay or if you can find a parts supplier.
http://cgi.ebay.com/3PDT-guitar-effects-pedal-footswitch-true-bypass-mod_W0QQitemZ150372119024QQcmdZViewItemQQptZGuitar_Accessories?hash=item2302e071f0

For my wah pedal two components need to be desoldered and a trace needs to be cut.






Second, I wanted to mod the sound of the pedal. When the pedal sweeps from the bass to treble, its not that smooth and the mid-range is not at all how I want it. There are a few mods and even one that doesn't require soldering. The mods I did are from this website: http://www.wah-wah.co.uk/. I'm still in the process of tayloring the sound, but the mods I have done are the Vocal Mod with the 68K resistor, Gain & Bass response with a 330ohm resistor, and the Volume mod with a 56K resistor.

I also moved the sweeping pot back a bit to have more of the bass range. This mod can be done just with a phillips screw driver. All you do is unscrew the brace that is against the sweeping bar that has ridges on it to moves the sweeping pot. Then you turn the pot a bit to have either more bass or treble in your foot motion.

Both the websites have some simple and great information on Crybaby Wah mods and should be checked out.

"All life is an experiment. The more experiments you make the better."
- Ralph Waldo Emerson

Krank Distortion "Distortus Maximus" Pedal Repair. Why isn't there a zener diode in this thing?

I got this pedal from a client. I had no clue what was wrong with it from my first inspection. I plugged in and powered it up. No sound when engaged. When disengaged I got a clean tone, but this is due to the true bypass switching! I haven't seen true bypass on a commercial pedal. True bypass has been done by guitar players and tone freaks to have an unaffected guitar tone when the pedal is disengaged. Once I opened it up I noticed that the main IC, a LM386 audio amp, was crooked in the DIP socket. A DIP socket!!! What?!? The major guitar pedal manufactures don't put DIP sockets in there electronics! Well this company goes all out in design. After removing the IC I see that the socket is completely damaged. It looked like it was melted. I assume that the IC got really hot, blew, and melted the DIP socket plastic. If you look close it's actually pin 6 of the DIP socket that is melted. Pin 6 on the LM386 is the supply voltage pin.







What caused this? Really I would think that larger current from the wrong power supply did the trick. From what I saw the pedal doesn't have a zener regulator to protect it. This would actually be an improvement on Krank's part if they added it. Maybe I should send then an e-mail and share this idea with them. After switching out the DIP socket and a new LM386 the pedal sounds awesome. This repair job is a great example why adding a zener diode on the power supply input of the pedal can save money and the life of your guitar pedals.

Guitar Pedal Repair Short Guide

Here are some tips when diagnosing a guitar pedal. Remember that some pedals have warranties on them and you should send them in and have it repaired. This is more a guide for pedals without warranties and any steps followed from this site is at you own risk. It's always good to get a bit of electronics basics before diving into a pedal if you aren't already familiar.

1) Get all the information about the pedal first.
a)When did it stop working and what happened?
b)What is the pedals track record? Did it see the rigors of the road or stayed on the shelf at home in a temperature controlled studio?
c)Research the problem online. The Internet is a powerful tool and more often than not there are people out there with the same pedal problems and have conveniently posted a solution.

2)What does the pedal do when its powered up? If you have the correct battery or power supply voltage, the cables you are using are good, your guitar is good, and you amplifier is good, then it's time to get into the pedal.

3) Always have something to put all the hardware and parts in. Make sure you keep note of what screws go where. I've made a few mistakes when I put the entire pedal together and I forgot to put a couple washers on to the potentiometers.

4) Check for any visible signs of problems. Broken wires, broken leads on components, burn marks or discoloration, and broken solder joints. Most of the time a broken solder joint just needs to be reheated with a soldering iron and it's good to go. In the case of burn marks or discoloration, it could be a sign that something is getting way to hot or the component has burned out and is now damaged. So the component can just be replaced. One thing to watch for, is what caused the component to fail? If the component itself wasn't the problem but something else is, the component will continue to blow and the really problem needs to be found.

5) If there aren't any visible signs, do the tapping technique. Grab a pencil or some non-conductive object and lightly tap the PCB while the pedal is on and you are playing guitar. If you can hear your guitar come through when you tap, find the spot where the tapping helps the most. There could be a bad solder joint or there could be a break in the PCB trace. To fix the bad joint just reheat it with an iron and/or add a bit of solder. In the case of a broken trace, you need to find which trace it is. Use a multimeter and check continuity between the solder joints at the ends of a trace. If you get one without continuity that is the culprit. To fix this make a jumper wire between the two solder joints at the ends of the broken trace and solder it in. This will solve the broken trace problem. I repaired a Digitech Whammy pedal with this method.

6) Check to make sure that nothing is grounding out either where it shouldn't be. Use a multimeter and check continuity between the signal path and ground. From there find the near by culprit. I've had a guitar's potentiometer solder lugs making contact with the shielded cavity.

7) Semi-conductors are usually the first thing to go in a pedal if its a component. Sometimes the easiest thing to do is start swapping things out and see if it works. It's possible that a resistor is bad, but very unlikely. To check a resistor use a multimeter and check its resistance. It should be close to it's value. Capacitors can be checked by measuring resistance. With a capacitor the resistance should be well above 15K ohms and it should just rise up as you measure. Inductors can be checked for continuity and the DC resistance like a resistor.

8) If you've done these steps but are still having problems it is time to hand it over to a professional or if you have the equipment, do a signal trace. This is a long process, but it can be helpful when wondering where the signal is actually going and where it ends. The equipment needed is a function generator and an oscilloscope. Apply a 20mV 1KHz sine wave on the input of the pedal and check where the signal is going or what is happening to it with the oscilloscope. It also helps to get a hold of the schematic. Sometimes companies don't mind sending schematics, but if not check search engines. You may stumble across someone who has went through the same problems and posted a schematic that they have spent hours making.

I hope this guide helps. I've used these steps to repair pedals, amplifiers, guitars, and anything else that is electronic audio equipment. Don't be afraid to get your hands dirty, but remember know what you are doing first. Get some basic knowledge of electronics. A great website to go to is www.allaboutelectronics.com. The author even has a downloadable pdf format of the entire online book for free. This comes in handy if you don't have immediate Internet access. Even after reading you don't feel comfortable leave the repair work to a professional because they need to get paid. Good luck everyone!

Don't put a beer on top of your Amplifier!

Here is a recent repair job I did on a B-52 AT-100 guitar amp head. The client had low volume output, two power tubes glowing really hot, and a story about spilling something on the amp. After opening it up I noticed that one of the screen resistors were blown. The screen resistor is used to control the amount of current from the bias supply to the screen of the power tubes.






Each power tube will have a screen resistor. After more inspection the underside tube socket had carbon build up all around it. This is a sure sign that something is wrong. I de-soldered the tube socket and to my surprise there was a hole burnt through the board and a substance in the hole. Apparently what got spilled was still there and it created a pseudo resistor. The resistance of this substance was much lower than 470 ohms which is the screen resistors value, and with the pseudo resistor and the actual screen resistor in parallel, the resistance would be decided by the pseudo resistor. A smaller resistance means more current.
Once I cleaned out the gunk and soldered everything back together the amp worked great! Something to take from this is don't set your beer on top of your amp when your playing a show.

Multiple Output Headphone Amp

Haven't posted in awhile with my current work load with school and all, but I came up with an amazing idea! How about I solve my headphone problems and get in an electronics design project at the same time!

Just to inform, I've been working on getting a small recording studio setup in the basement, but we don't have all the equipment we need. Sure we've got a computer, DAW, mixer, power amps, effects, headphones, and microphones, but where is the capability to power multiple headphones at once? Wouldn't everyone like to hear the track on headphones while mixing? Wouldn't everyone like to hear the music while recording group vocals or record two musicians at once?

My idea is to create a headphone amplifier that will do this! I figured I need a 4-6 headphone output that will accept a range of different headphone impedances and have a separate volume control for each output. Sure I can go purchase one off of musicians friend for like fifty bucks, but this is a perfect project! My first step is to research my options and try to design the cheapest and most effective system I can build. I'll have some schematics and design ideas in a future post.

After some research I stumbled across a distribution headphone amplifier kit from www.paia.com.





The kit can drive six pairs of headphones using two op-amps for each set. The gain of each op-amp is set to a fixed gain of ten, and each output has a separate volume control which consists of a dual ganged potentiometer. The dual ganged potentiometer is needed to control the left and right channels at the same potential so that one side is not louder than the other. This design is very simple. Seeing as I don't need six channels I'm planning on building a four output headphone distribution amp. The Paia design also uses the NE5532 op-amp which is a dual package. I have three of these currently making it easy for me to build a three output amplifier at a minimum. I also have LM386's which is another option in my design. The problem with this component choice would be that the left and right channels would need to be mixed together as the LM386 is a single package and I do not have enough LM386's to have two per headphone pair. This can be done with a single op-amp on the input to mix the left and right channels. Then the output of this amp is feed to the inputs of the LM386's. This would actually help isolate the amps from the signal source so not to load it down. This isolation can also be used to improve the Paia design by adding a buffer for both the left and right channels on the input.

I'll have more design Ideas and some schematics in the near future as I continue my research and design.