Thursday, July 30, 2015

Fixing the pots on a Maxon OD808

I was recently gifted the pedal pictured above. If you don’t know what a Maxon OD808 is, then you should have a look here:

From the above link: “Originally released in 1979, the Maxon OD808 pedal was one of the first tube-amp overdrive simulators to hit the market. Its smooth, creamy crunch tone caught on quickly, and helped to launch a long line of imitators. Today, the OD808 design is without a doubt the most used, most imitated and most lauded overdrive circuit of all time. The reason for this is simple--tone. Simply put, the OD808 provides the natural, mild overdrive of a tube amp without sacrificing your guitar's original tone. In addition, it can be used as a clean booster to provide increased gain without compromising the sound of your amplifier.

In short, it’s basically the original overdrive pedal that eventually got rebranded as the Ibanez Tubescreamer.

Unfortunately this particular one had a few issues. At first it looked like it was just missing a knob, but it turned out that all three pots were able to rotate freely (through 360 degrees) without affecting the sound at all. The pot shafts could also move in and out by about 6 mm, which really shouldn’t be the case.

So I took the back cover off to access the circuit board.

Removing the two screws at the bottom end of the board revealed a second board that houses the pots and status LED.

Removing that revealed exactly what I was expecting, which was that all three pots had fallen apart (evidently someone has tried to hold one together at some time in the past with a cable tie).

In fact you can see the top parts of the pots still attached to the enclosure:

Sadly this pedal has made a bit of a (bad) name for itself because of this exact issue. Not only are the pots prone to mechanical failure in this way, but it is also quite hard to find exact replacements, which in case anyone ever needs this information are as follows:
  • Overdrive: A500K (ALPS brand, part number RK09L1140-F12-C0-A504)
  • Tone: A20K (ALPS brand, part number RK09L1140-F12-C0-A203)
  • Balance: B100K (ALPS brand, part number RK09L1140-F12-C0-B104)
And here's the specs document for these ALPS pots for those that may want it:

Having had little initial luck locating replacements, I decided to see if I could just put the pots back together. This was surprisingly easy to do and the fix feels pretty strong.

This worked for the Overdrive and Balance pots, but unfortunately the Tone one was still very spotty, even with a squirt of contact cleaner.

So this time I decided to completely remove and disassemble that pot. It breaks down into several parts, but on the plus side, it's surprisingly serviceable.

From top to bottom you can see the securing nut, the shaft collar, the shaft, the carbon strip/legs, the wiper, the back cover and the securing clip (which both holds the enclosure together and also secures it to the board).

So first I gave the carbon strip a good clean with contact cleaner and a cloth:

Then checked the wiper to make sure it was in shape and clean.

Then started putting the whole thing back together.

First the wiper is placed against the carbon strip, making sure that it is in a suitable position (i.e. not outside if its usual rotation range—I put it in what would be its middle position):

Then the back cover is replaced:

Now the shaft is located so that it sits correctly in the wiper part (the shaft has a little key so that it will only sit correctly in one position).

The collar is slid over the shaft and pushed solidly against the rest of the pot.

Before putting the clip back on, I slowly and carefully bent the ends so that they were close to straight:

And then bent the whole legs so that they were a little tighter than parallel.

This was so that they wouldn’t have a tendency to open after putting the pot all back together.

Finally, the ends were pressed back into a 90 degree angle:

The pot was tested and passed with flying colours:

And re-soldered to the board:

Finally the whole thing was put back together and correct replacement knobs were put on too.

I tried it out (it works fine) and have to say this pedal sounds great and is definitely a keeper.

Sunday, May 10, 2015

How to set up a Fender Telecaster-style guitar

Today I’m going to show you how to set up a Fender Telecaster-style guitar. We are only going to do a basic setup, which is enough most of the time, but occasionally more is required, such as filing the nut, or doing some fretwork.

If you're setting up a Stratocaster-style guitar, you might prefer to have a look at this blog post:
Alternatively, if you're setting up a Les-Paul-style guitar, you should have a look here:
So what does a basic setup involve? Let me break it down for you, as follows:

  1. Checking and adjusting neck bow (how straight the neck is)
  2. Checking and adjusting saddle height
  3. Checking and adjusting the intonation (how far back or forward the saddles need to sit at the bridge to keep your guitar as in tune as possible no matter what fret you’re playing)

Those three steps will have a dramatic effect on your guitar and none of them are very difficult, or require particularly specialized or expensive tools. Here's today's patient:

1. Check and adjust neck bow (how straight the neck is)

Since we only want to check how straight the neck is, we need to isolate this aspect of the guitar. In other words we don’t want the height of the nut or the placement of the saddles to confuse us, so we take them out of the equation. Don’t worry; we’re not going to remove any of these components, just circumvent them.

I use a ruler to do this, but you can do it using only strings. I’ll describe both methods below.

Method A: Using a ruler

Get a ruler (or straightedge if you want to be all fancy) that is at least as long as the neck, but not so long that it reaches all the way from the nut to the saddles. If you can’t get one between these lengths, and are willing to sacrifice a ruler, get one that’s too long and cut it to length. Alternatively, you can just cut a little out of one edge so that you can still make full use of the other edge of the ruler.

Now lay the edge of the ruler along the frets (don’t rest it on top of the nut or the saddles).

Method B: Using the strings

First, put a capo on the first fret. This stops the nut from having any influence, say from being too high/low.

Next, hold down the low (thick) E string on the bridge side of the highest fret. This stops the saddles from having any influence.

No matter whether you used method A or B, you can now go about measuring the neck bow. This is done by measuring the string height (the gap between the ruler/string and the top of the fret) at about the 8th fret. There is a lot of debate over how straight a neck should be, and in fact it really is personal choice, but a height roughly the same as the thickness of a B string is a good starting point. Personally, I use a 0.012” feeler gauge to do this, but you could use a B string. Simply slide the feeler gauge/B string into the gap to see if it is too big/small.

If the gap is perfect, congratulations – you may now move on to step 2.

If the gap is too large, then you need to tighten the truss rod a little (similarly, if the gap is too small, you need to loosen the truss rod). Locate the adjustable end of the truss rod. On this guitar it is at the head of the guitar and requires a 4 mm Allen key, though your guitar may be different.

On some Teles, it is located at the other end of the neck. This is a pain, because every time you want to make an adjustment to the truss rod, you will need to loosen the strings, remove (or partially remove) the neck, adjust the truss rod, re-attach the neck and tighten up the strings again to check the neck bow.

Anyway, here’s how you adjust the truss rod. This must be done with the strings tuned to whatever pitch you usually use. If your neck is too bowed (the gap you just measured is too big), you tighten the truss rod by turning the Allen key (Allen wrench), screwdriver, or socket (the tool required depends on your guitar) clockwise. It is recommended that you only turn the tool a quarter turn (or even an eighth turn) at a time and then give the neck some time to settle. You will also need to make sure the strings are still properly tuned after each adjustment.

CAUTION: If you find that the truss rod is very difficult to turn, then stop now and take your guitar to the guitar shop. It may be that there is a problem with the neck or the truss rod and you may damage the guitar by forcing it. Believe me, you do not want to damage the truss rod.

If, instead of tightening the truss rod, you need to loosen it, do so by turning it anti-clockwise (counter-clockwise). Again, a quarter turn at a time. Once you have got the gap to 0.012” (or whatever gap you prefer), you will have finished this step. Feel free to remove the capo at this stage if it is attached.

2. Check and adjust the saddle height

Firstly check and, if necessary, adjust the low (thick) E string height. Do this by adjusting the height of the saddle on the bridge (on this guitar, a 1.5 mm Allen key is required, though your guitar may require something else). Then this is done by screwing the outermost screw in or out. Since Telecaster’s generally have three saddles (each supporting two strings), rather than six individual ones, you will probably end up with them being at a bit of an angle, rather than parallel to the guitar. This is fine (if you happen to have six individual saddles, then for each one, I recommend that you try to keep the two screws at the same height as each other, although some people would disagree with me).

The question here is how high to make the saddle. Well, this is personal choice. Find somewhere were the string doesn’t buzz on any fret from being too low, but low enough that you can play up and down the neck easily. There’s usually a sweet spot where you can just start to detect some buzzing and you can leave it just a tiny bit higher than that.

Now do the exact same procedure for the high (thin) E string.

There are two ways that you can go about adjusting the other strings.

Method one: Adjust each string the same way as you just adjusted the two E strings.

Method two: Use a radius gauge, as follows:

Lay a radius gauge across your strings, close to, but not touching, the saddles. Adjust the remaining strings only (A, D, G & B) until every string is just touching the radius gauge. Radius gauges can be bought from numerous sources ( I got mine from, or you can make your own. Feel free to use Google at this point if you don’t know about radius gauges. Just make sure that you use a radius gauge that matches the neck of your guitar. Not all Teles have the same neck radius, so the best way is to rest a radius gauge on the neck of your guitar (with the strings removed if necessary) to find out which radius you should be using, as follows:

Incidentally, I use these snazzy radius gauges that can go either above or below the strings (below gives a slightly more accurate result, although the difference is arguable).

Please don’t take these measurements as the absolute final string height, but more as a good estimate. You can adjust them a little to your own personal tastes after this.

OK, that’s step 2 finished. Your guitar should be nice and playable now. However, it may not seem to stay in tune very well. That’s because the intonation might be off.

3. Check and adjust the intonation

The intonation here refers to the forward/backward position of the individual string saddles. By moving the saddles forwards or backwards, we are actually adjusting the length of the strings. Without going into too much detail, if the string is the wrong length, the positions of the frets will not be correct and the guitar will be out of tune on some of them. Adjusting the intonation is not difficult. All you need is a guitar tuner and a tool to move the saddles forwards or backwards.

Play an open low E string and make sure it is in tune (using the guitar tuner).

Now play the 12th fret of the low E string.
It should also be in tune. If it is too high, then you need to move the saddle back. This increases the length of the string. If the note is too low, then you need to move the saddle forwards. This decreases the length of the string.

Now check both the open and the 12th fret notes again. You’ll have to tune the open string again because by moving the saddle, the tension of the string will have changed and so will need to be retuned.

Once you have correctly moved the saddle so that both the open string and the 12th fret are in tune, you can move on to the A string. Ordinarily, you would repeat this step until all of the strings have been done. However, if you have three saddles rather than six, you may have to compromise a little and find the position where the pair of strings passing over each saddle are as well intonated as possible. One may end up being a mm too short and the other a mm too long. You will notice that I use “staggered” saddles on this particular Tele. They help minimize the compromise you will have to make, and if you’re lucky you’ll end up with something close to perfect.

That’s a basic setup done. Hopefully your guitar will now be easy to play and appear to be in tune no matter where you play the note.

Also, if you want to change the neck pickup height on your Tele, check out this post:

Tuesday, April 21, 2015

Making a reverse/inverse RIAA attenuator

A couple of blog posts ago, we made an RIAA preamplifier ( Hopefully you understand what that is now, but if you don’t, maybe have a look at that post now.

As part of the process of making that preamp, I found it useful for testing purposes to have an inverse RIAA attenuator on-hand. Wait, a what? An inverse RIAA attenuator. It's basically the opposite of an RIAA pre-amp.

If we refer back to the RIAA Equalization Curve graph that we used on the RIAA preamp post, you'll see that it has two lines (see below). One is called the recording curve (dotted blue line) and one is the playback curve. The RIAA preamp follows the red curve. The Inverse RIAA attenuator follows the dotted blue one. If you were to put one after the other, you would end up with a flat horizontal line running right across the middle of the graph at 0dB.

So why would you want one of THOSE? Well in my case, it made it possible for me to take the line-out of any device, send the signal through the attenuator, and then feed its output into the RIAA preamp I was building at the time. If the output was back to line level, then I knew the preamp had no major problems (though I would still test it later with a record player for sound quality, etc.)

Now I understand that most people would not be in this situation, and therefore this attenuator would seem to be of little use. However, it does have one other fantastic use, and I wish I’d had one when I encountered this exact problem a few years ago. Imagine the situation—you have an amplifier with just a few inputs. One of those inputs is labelled “phono”, but you don’t have a record player, so it’s basically wasted. Well, with a reverse RIAA attenuator, you can plug just about any device with a line-out connection into the phono input using this attenuator as a go-between. In fact you’d probably get away with the headphone output of many devices, though you may have to play with the device’s volume levels to get a decent sound quality/frequency response—in fact I tested this with an iPod and it worked just fine.

Now, as I'm sure you know, an attenuator is the opposite of an amplifier. Since we’re not actually amplifying anything, we can do this circuit completely passively (no power supply required). In fact, it’s an incredibly simple circuit once you’ve worked out which resistor/capacitor values you need. This is no mean feat, but luckily there’s almost always someone else on the Internet that has already worked this kind of thing out. In my case I used this circuit, which I got from here:

I highly recommend visiting that site if you want a little more information about the circuit and how it does what it does.

The schematic is extremely simple, requiring only four (or even three--see below) capacitors and three resistors for each channel. So simple in fact, that you don’t require a circuit board.

These are the values I ended up using:

R1 = 909k
R2 = 75k
R3 = 1.5k
C1 = 3.3nF
C2 = 270pF
C3 = 1nF
No need for C4

I boxed them in a fairly small project box with a couple of RCA jacks at each end.

Then covered it up and marked which end was which (don’t mix this up).

And here’s an action shot of me using it to test out the RIAA preamp I made in the previous post:

This ended up being a simple, cheap and fun project and I ended up with a very handy little device.

Wednesday, April 15, 2015

Building a Bazz Fuss fuzz pedal

Hey, what should we do today? How about making a fuzz pedal?

Cool, I knew you were up for it.

As you may be aware, I’ve recently been helping my friend Adam with a few guitar projects and he was keen to get started on pedal making (specifically a fuzz pedal). I suggested the Bazz Fuss as an easy starter project. It’s only 5 components (and a pot) and it sounds good too. It's designed primarily for a bass guitar, but it sounds great with a normal guitar too.

Here it is (note that I laid mine out slightly differently, and I eventually swapped the 10k resistor for a 100k one):

And here's my very professional layout:

Since I hadn’t already made a Bazz Fuss myself, I decided it might be fun to do so. Apart from having one for myself, it would be handy to have one to refer to if Adam ran into any issues while he made his.

I decided to challenge myself a bit and see if I could fit it into a Hammond 1590A enclosure. They’re pretty hard to find round these parts, but I did manage to find an enclosure that had almost the same dimensions. In fact it’s slightly tighter than a 1590A, but hey, that’s just part of the fun, amirite?

Just for reference, a Hammond 1590A enclosure measures 93 mm x 39 mm x 27 mm. Mine measures 90 mm x 36 mm x 30 mm. The walls are a bit thicker and there are some extra bits inside which will make it even more cramped.

Here’s the enclosure in question: 

And here’s the inside. You can see some additional metal in there that you would ordinarily screw a ground screw into, as well as some circuit board slots (which I won’t be using).

Here’s a bit of a test fitting just to see if I can even get the main mechanical parts in there:

The answer is “just about”. So we start drilling very carefully.

First the switch:

Then the first jack:

Second jack in place:

I’m testing the jacks with something plugged in, just to make sure I can still do that without any contacts banging up against anything they shouldn’t. In a normal-sized enclosure this would be less of an issue, but things are very close together in here.

Next to go in is the DC-in jack, since there’s really not much flexibility there. Once that’s done we’ll be able to see what space is left for the pot and the circuit.

OK, the pot can just about fit in here, with the legs bent up (in fact I ended up cutting off parts of the legs to help them fit).

Just one more item and that’s the LED. I decided to go with a smaller 3 mm LED. And I also decided to make use of one of the little grounding threaded holes I mentioned earlier. 

This (little) one, which I drill all the way through so the LED can sit in it:

Here’s how that looks from the front:

And we’re done (apart from the circuit and wiring of course):

Here’s how THAT looks from the outside:

When you’re trying to fit a circuit into something this small you really have to think about how big your circuit board can be and still physically fit. Not only that, but things like whether the capacitors can sit vertically without hitting the back of the enclosure (they couldn’t, which is why they’re lying flat).
Anyway here’s the board done, and wired to the pot:

I stick some insulating material between the pot and the board so there are no short-circuits:

Before we wire this up, I’m going to paint the enclosure. How about blue?

And here it is wired up. Not the easiest pedal wiring job I’ve ever done.

I’ve put some insulating tape anywhere where there was a danger that something might touch something it shouldn’t, and that included the inside of the back cover.

Finally it’s time to put it together.

As you can see above, my "Sharpie" decal didn't turn out as well as I'd hoped, so I made something up in Illustrator, printed it out on normal paper, stuck some Scotch tape on top to make it look laminated, and then put double-sided sticky tape on the bottom. Et voilĂ , a cheapskate decal.

The first time I tried it out, it sounded bad. It worked, but not well. I replaced the 10k resistor with a 100k one and it sounds great now. You may want to do the same.

Here's a quick and dirty (see what I did there?) demo of the pedal: