Tube Screamer Tone Mod

If you have a Ibanez Tube Screamer or clone you know that the pedal has a very pronounced mid range boost which personally I don't like too much. I know this gives the pedal its characteristic tone, but it is pretty easy to change the pedal's tone either by swapping out the capacitor that precedes the clipping stage of the pedal or by adding a switch and additional caps to enable changing the value of the capacitor on the fly. Note that this mod has nothing to do with the tone pot control, which functions as an active tone control. The capacitor in question is the 0.047uF cap at the center left of the schematic below which functions as a high-pass filter and thus rolls off low frequencies.

There are a couple of approaches to changing the value of the this cap. You can solder in a cap of a different value or, as with the B.Y.O.C. "overdrive 2" clone of the Tube Screamer available here the approach is to use a SPDT switch (on-off-on) with three different capacitors which allows you to change the effective cap values on the fly to suit your needs while playing. The schematic below shows the B.Y.O.C. approach where the single 0.047uF cap is replaced with a switch and three caps, the original 0.047uF cap, a second 0.047uF cap, and a third 0.150uF cap. The center (off) position selects the right 0.047uF cap alone. The first on position selects the right 0.047uF cap and the left 0.150uF cap together in parallel. The second on position selects the right 0.047uF cap and the center 0.047uF cap together in parallel. The total value of capacitors wired in parallel is the sum of the individual capacitor's values. So the total values here would be 0.047uF, 0.197uF, and 0.094uF, respectively.

According to this page on modding the Tube Screamer, the following cap values correspond to the following corner frequencies of the high-pass filter:

Capacitor Value--Frequency
0.047uF--720 Hz
0.1uF--339 Hz
0.22uF--154 Hz
0.47uF--72 Hz
1.0uF--34 Hz

The fundamental (open) frequency of the guitar's six strings are as follows:

E--329.6 Hz
B--246.92 Hz
G--196 Hz
D--146.8 Hz
A--110 Hz
E--82.4 Hz

So the stock capacitor value of a Tube Screamer attenuates notes below the 12th fret on the high E string. Higher capacitor values will thus lower the corner frequency of the high-pass filter and increase bass response. Thus the the B.Y.O.C. overdrive 2 approach allows you to chose higher cap values that will give you corner frequencies corresponding approximately to 339 Hz (open high E string) and 154 Hz (open D string). These switching options increase the bass response significantly.

I still wanted more bass however, and as the Fat Bass for Tube Screamers page suggests, an even higher cap value will lower the corner frequency of the high-pass filter even further. My goal was to set this value below the lowest frequency of the guitar, 82 Hz for the low E string. I desoldered the middle 0.047uF cap in the B.Y.O.C. overdrive 2 schematic above and replaced it with a 1.05uF cap which, when combined in parallel with the original 0.047uF cap, gives a corner frequency below that of the low E string on a bass and no attenuation of bass frequencies. When I switch in this cap in the pedal there is certainly a lot of bass, and as the original designers of the Tube Screamer were trying to avoid, probably too much bass at high drive levels. At lower drive levels it sounds good, however, and gives you additional tonal options with this classic pedal.

DIY Fuzz Pedal

More kit love. This one is the B.Y.O.C. extra special vintage fuzz kit which is based on a Fuzz Ace and is available here. This is the second B.Y.O.C. kit I have put together and it was an easy build. The board layout is great and the instructions are easy to follow. One caveat with this kit, however, which is that you need to carefully adjust the bias trimpot to get the pedal to work properly. If you do not you will get a thin sound out of the pedal which may lead you to believe that you have done something wrong in the build, which with me is always the mostly likely cause. In this case I started troubleshooting the pedal before I adjusted the trimpot, which the instructions clearly state that you should do first. In my haste, I thought that I had inserted the germanium transistors incorrectly and in attempting to reseat them (I won't tell you how many times I did this), I broke off one of the leads. Fortunately the kit comes supplied with two SS-9013 transistors for testing and troubleshooting and I am currently running these in the pedal until I buy replacement germanium transistors. You can get these through B.Y.O.C.'s parts store here. The pedal sounds awesome as is and I expect it to sound more awesomer when I get the germanium transistors. I'll update the post when I get around to buying them.

UPDATE (1/2014): I have finally gotten around to sorting out the problems with this pedal. I purchased a second set of AC127 germanium transistors (which were used in the original version [rev 2.0] of the pedal) and later a set of  AC128 germanium transistors (which are used in the new version [rev 3.0 of the pedal), neither of which worked. Meanwhile, B.Y.O.C. came out with a new version of the pedal (rev 3.0), which among other significant differences, has replaced the 0.1uf film capacitor (the yellow capacitor in the photos above) with a 0.01uf film capacitor. I thought swapping out the cap for one with the new value would work, and it did the trick. I ordered a .01uf film cap from Mouser, soldered it in, and the circuit worked as originally intended. The internal bias pot now has plenty of range. I still have not gotten the AC128 transistors to work, but the original AC127 transistors work well. I would recommend making this change if you have rev. 2.0 of the pedal and have had problems getting the germanium transistors to work.

Crybaby GCB-95 True Bypass

If you have an old Crybaby you know that it is a major tone suck when the wah is switched off. It's pretty easy to swap out the original SPST switch with a modern 3PDT switch to mod the pedal to true bypass. Really you only need a 2PDT switch but you can use a 3PDT switch, which seems to be easier to find, and leave one of the rows empty. I bought a couple 3PDT switches from B.Y.O.C.'s parts store here. Instructions and photos for rewiring the pedal are available from Castledine Electronics here. Note that their instructions are for a 2PDT switch. You will have to adapt their instructions for a 3PDT switch (or follow what I did in the photo above). Castledine also has instructions and photos for a couple different revisions of the pedal. In my usual manner of screwing things up as I go along, I originally wired the 3PDT switch the wrong way. As in the photo above the three tabs that make one pole of the switch are aligned vertically ( | | | ) rather than horizontally (- - -). Of course I could have checked this with a multimeter before I wired it up. Oh well. The switch is not at right angles in the photo above because the support for the pot is in the way. You will probably need to swap out washers and nuts until the feel of the switch is right. Combine this with a new pot and your old Crybaby will sound pretty darned good.

DIY Overdrive/Boost Pedal

More kit love. This one is the overdrive 2 kit from Build Your Own Clone available here. This is the first kit that I have put together from Build Your Own Clone and it was a great experience. The kit came complete with all parts including chassis and extra parts for the most common mods. The board was laid out clearly including labels for cap and resistor values. The web site has easy to follow directions, including the most common mods. There is an optional MOSFET conversion kit which can be ordered for an additional few dollars. Here are a couple photos of the kit going together. The magnifying loop in the first photo is only there because of my poor eyesight. I have trouble seeing color stripes on resistors and the loop helps.


The folks at Build Your Own Clone clearly put a lot of effort into the design of this pedal. It it based on the Ibanez Tube Screamer with a host of mods as well as an additional boost channel which can be used separately from or in conjunction with the overdrive channel. There are also two toggle switches, one which lets you select additional silicon or led clipping and a second 3-way EQ switch which adds highs and lows or lows to the tone stack. The kit comes with two op amps which you can choose from, a JRC4558D op amp which was in the original Tube Screamer and the Burr Brown OPA2134 op amp. The chip is socketed so you can swap them out as easily as changing the battery. In addition there are three trimpots on the board for minimum and maximum distortion as well as level in the overdrive channel. You can build the kit according to the original Tube Screamer specs or tweak it however you want. What is truly amazing is that all of this is crammed into a standard 125b chassis.


Building the kit took about three hours, included sorting out the resistors and caps. I am still getting a handle on all of options for the pedal. My wife ran hiding when I first plugged in the pedal and had the pots all opened up. My son nodded knowingly when I got the level turned down with the overdrive all the way up. I recently got a Fender Champion 600 amp and wanted to have a classic overdrive pedal to drive the front end of the amp. This is an awesome kit and is highly recommended.

DIY Envelope Filter Pedal

More kit love. This one is a General Guitar Gadgets DOD 440 Envelope Filter replica kit. I can't say enough about these kits. Super easy to put together. This pedal is subtle, and I still haven't worked out the best sounds for it. It is an autowah and you have to fine tune the knobs to come up with something useful. There isn't much on the web about the DOD original, although I found a pdf of an original manual here. The manual really doesn't give much information. The left knob is level, the right range. If the range knob is turned up too high there is a fair bit of distortion. A lower setting, up to maybe 2:00 or so seems to work better. I actually prefer using the pedal with a bass rather than with a guitar. Think Bootsy Collins. I had the notion of replacing one of the resistors with a pot to get more variation, something along the lines of the Q control on an Electro-Harmonix Q-Tron, following some vague instructions I found on the web. I desoldered the resistor, resoldered it to the bottom of the board and soldered the pot in parallel on the topside. This didn't seem to do much so I removed it. You can see the space where the 430K resistor would be in the close up (it still soldered to the bottom of the board). If anyone has any ideas about modding this circuit send me an email and I'll try it. I also had half a notion to try to install the guts of one of these kits directly in my Jaguar. Jaguars have plenty of extra space in the various control cavities to do this, including space for a 9v battery in the trem cavity. This would involve rewiring the entire guitar and using the rhythm circuit controls on the upper bout to control the effect. In theory you could do this with any effect that had only two controls and a small enough board. I went so far as to order some pots and switches to try this, but once I started tweaking the kit itself, I never got around to it. I really didn't want to get to the point where I started chiseling out wood to get everything to fit. I may try this in the future.

Crybaby GCB-95 Repair

The Dunlop Crybaby wah pedals are very repairable. I have a GCB-95 I bought in 1988 or so (my first fx pedal inspired by listening to Hendrix all the time) which was in pretty bad shape. Mostly this was due to a crackling pot. Dunlop sells replacement 100k pots for these here. These pots come with the gear included and installed, so you can drop it in with minimal soldering. Pretty simple fix, really. Blow the dust out of the pedal, pop in a new battery, and it's good to go. The only adjustment to make is the range of the pot. Just unscrew the stop holding in the rack gear, separate the gears and adjust the pot to your liking. I like mine with as much treble as possible. These things are damn near indestructible.

DIY Tremolo Pedal

I finally got around to adding tremolo to my guitar setup this past weekend thanks to the EA tremolo kit offered by General Guitar Gadgets. The kit included the resistors, caps, transistors, LED, PCB, jacks, pots, knobs, footswitch, wire, and case--everything to put together a complete stomp pedal. The instructions are downloaded from their site. The build took about 4 hours from start to finish with a couple breaks and was a lot easier than it first appeared when I opened the box. The most time-consuming part was figuring out the resistor values. I have red-green colorblindness and it took a magnifying glass. The pedal sounds great. It has a volume control which allows you to match the volume when the pedal is bypassed. The speed control has a wide range, as does the depth control. The led flashes at the speed rate when on. I have an 80s-era Fender solid-state amp that has a great clean channel and spring reverb but no tremolo. The amp has an effects loop located before the power amp so I patched the tremolo pedal in. At first I thought that something was wrong in the build, as the pedal only worked when in bypass, but I realized that I had reversed the cables into and out of the pedal. So I quickly fixed that problem. Make sure you use a new battery--I used an old one and didn't realize how great the pedal is until I switched it out. Highly recommended. I am not a great solderer, but this actually wasn't too hard. I used small diameter solder for the first time which works great. It also helped to clip off the extra length of the components as I went along to make more room to get at the next point. Once you start cramming everything into the case the soldering gets a little harder, so measure all the wires carefully to make as much room as possible. I might swap out the red LED for a blue or green one just for fun. I don't have any interest in finishing it--nothing wrong with raw aluminum and masking tape.