Oscilloscope Project

I've found a use case for an oscilloscope. Dad has a nice, industrial scope from the 1960s, but being the size of a weekender suitcase, and weighing just as much, It was a little more than I care to have lying around the house. The next solution is the oscilloscope app for Android (of which there are quite a few). But when I found this one, I just couldn't resist. I picked it up from China (direct), and it only cost $21.00 plus shipping. Hard to beat that price, and to make things better, it's a kit, so I get to build it. This scope is a JYETech DS0138 scope.

Tools

I ended up using the following tools:

• Soldering iron (instructions call for a 20w. I used a 30w, and it worked just fine - I just took care not to linger, especially when working around the processors.
• Solder - good to have two sizes. I used one that was ~1mm in diameter, and the other ~2mm. The larger works really well for most components. The 1mm size was really useful on the USB and slider switch leads as they are really small, and close together.
• Multi-meter - I use a Fluke, but for this project, just about anything would work.
• Small Phillips screwdriver
• Wire cutters
• Small needle-nose pliers
• Solder remover (optional) - This should really be part of any project to aid in desoldering, if you make a mistake)

You will also need a 9v power supply (center positive), and for testing, something that can generate a signal (a cell phone with a tone generator app works really nicely), and a male-male 1/8" audio cable.

Building

Step one is taking stock of the contents (building kits is time consuming enough - no need to get knee deep into the build phase, only to find out there's a piece missing). Everything was there. There are two kits like this available from various Chinese resellers. The first is strictly the oscilloscope (board and LCD display). The second includes the Plexiglas case for $4 - $6 more (I opted to get the case, also).

One of the things to watch out for when inventorying components is that the resistors are VERY small, and they are all 5-band coded. This means it's very difficult to read the colors to validate the correct values. I ended up measuring them all with my multi-meter, rather than trying to read the color codes.

Next, we start soldering components. As a rule, secure resistors, diodes, jumpers and small capacitors first. These tend to sit lower on the board, and are more difficult to reach if there are larger components surrounding them. Next, hit the larger components on the inside of the board, and finally larger components and connectors on the edges of the board.

Once complete, you'll have a nearly finished board like this:

At this stage comes testing. This is really important. The instructions have you perform voltage tests before soldering over a set of jumpers. Important to follow the instructions so you don't damage the processors or display in the event something is not wired correctly.

Finishing

This was actually the hard part. You're provided 4 bolts with 8 standard hex bolts, and 4 rounded nuts (for the top). Use the 8 hex nuts to set the heights of the boards, and the 4 rounded nuts to secure everything together.

The case was shipped with three pieces of Plexiglas that were smaller than the two top/bottom pieces. You will need all three pieces. The one with the most holes goes under the display, and the display bolts on to it. The other two act as spacers (filling up the empty space between the display board and the top cover).

The time comes in making fine adjustments to the heights of each hex nut. If they are too low, you risk cracking the Plexiglas. If too high, the buttons will not stick out of the top. While yo are working on this part, take care, as the Plexiglas is rather brittle, and can crack easily.

Once you get the height set, you can start adding the Plexiglas layers. After the three inside layers are in place, drop in the red switch extensions (they must come before the top layer). Bolt on the top, and you're finished.

I added some labels to the finished product to make it easier to read.

1967 Fender Deluxe Reverb Restoration Project - Part 3

I've completed a few more items on the restoration. Before I jump in, if you are hitting this page first, you might want to check out PART 1 or PART 2.

Power Rewiring

OK, So one of the goals is to get the amp back to as close to the original as possible. There is a very real problem with this goal that I just could not ignore any longer. The original wiring called for a two-pronged plug with a polarity switch on the back. This is unfortunately unsafe, in that with the wrong polarity, you can easily shock yourself pretty good. So, in the interest of safety, I'm restating the goal to get the sound as close as possible to the original, but with safety first. As luck would have it, this rewiring job has no impact on the quality of sound, so here is the new power wiring arrangement:

I'm no electrical technician, so I'm not even going to begin to try to walk you through what I did (better to get the knowledge from someone that really understands this, and does it for a living). In short, however (no pun intended), I added the three-pronged cable, disabled the polarity switch, removed the Death Cap (yeah, you'll want to read up on that one), and brought the fuse inline with the hot lead. If you want to know step-by-step how to do that, check out Greg Perrine's website, Recycled Sound. He does a great job providing videos, reference documentation, and parts for your repairs.

Dating the Amp Redux

So as I was watching one of Greg's videos, he pointed out an interesting piece of information that I was not aware of. In the image above, there are some numbers stamped on the chassis (I circled in red to help you locate them easily). This is [drumroll] the manufacture date! Woohoo! So, from this number we look at the last 4 digits. They tell us the amp was assembled in the 22nd week of 1967. I was but a wee lad at only 6 months old when this amp was originally built. One more mystery cleared up.

New Speaker

I happened to locate a 12" Fender driver in Fort Wayne last weekend, and dropped a few bucks for it. It is a real fender, and it's in great condition. That said, it's neither the original, nor does it match the original Jensen specs. Quite honestly, I rather prefer the growl of the Peavy that used to be in there, but I have both, and since there's an External Speaker jack on the chassis, who knows? Maybe there is a second cabinet in its future.

1967 Fender Deluxe Reverb Restoration Project - Part 2

This is a continuation of a restoration project I undertook for a 1967 Fender Deluxe Reverb amp. You can find Part 1 HERE, and Part 3 Here.

New Tubes!

So after a bit of a break, I got back to work. My dad (a retired electronics technician for what was once Bethlehem Steel) called me from a hamfest and said there's a guy with tubes. He asked if I needed any, and after a bit of Q and A, he was bringing home a spare 12AX7, and a matched set of GE 6V6 tubes.

 

Now, these are the originals, in the original boxes (they really are pristine), which makes them 'new old stock' (NOS) tubes. I've done a good bit of reading about these elusive NOS tubes, and although they fetch a pretty high price, it's not really clear that they improve the sound of the amp. Either way I do get the benefit of having a matched set (something the amp was lacking before).

A New Reverb Tank!

This one was a long time coming. I ended up picking up an Accutronics 4AB3C1B reverb unit. It's a two-pring unit with 8 ohms input, and 2250 ohms output. This is as close to the original that would have come with the amp back in the day. I also picked up a cable to go with it. Here are some build notes:

I installed some tie-downs along the left side to keep the wire out of the way. I can still throw some things in the back, without too much concern of tugging on the connector cable.

I ended up having to scour the Internet for how to connect these, as installing was more than trivial, and I didn't want to have to pull it back out to look as the back side of the cover to see which color was input, and which was output.

 

I did cut a piece of cardboard to fit under the tank. After a good bit of trolling the forums, it seems the originals produced by Fender back in the day had cardboard underneath, so this was just trying to keep in the tradition of 'as close to original as possible'. That said, since the screws are tightly affixed to both the cabinet, and tank cover, I doubt that there is much difference in the sound of the reverb with or without. (I'm working on a post about sound quality that should be out in a few weeks.)

TubeScreamer+ Project - Part 5: Seeing Sound

INTRODUCTION

A few weeks ago, I became curious what sound passing through the TubeScreamer+ would look like. Fortunately, I have two cell phones, and the cables in hand already. I used a Samsung Galaxy s4 mini and an app called ToneGen for tone generation. As the scope, I used a Google Nexus 5x with an app called Oscilloscope. I also used a screenshot app to capture the images of the scope. Between the two phones, I have the pedal connected to each phone using two cords and two adapters (1/8" stereo-to-1/4" mono). Next, I fired up the apps, and started sending a nice clean tone (about 1000hz) from the tone generator to the oscilloscope.

NOTE
For those that did missed my earlier posts during the building project, refer to a photo of the pedal below. The H/L switch under the GAIN indicates High and Low. The original Tube Screamer TS-808 used the H position. The L position activates a capacitor mod that ends up giving the output much more low-end (for a heavier rock style). The lower switch describes two different distortion methods. The left side (with the diode symbol) is the original asymmetric diode clipping style used in TS-808. Flipping the switch to the right changes the clipping technique to one that uses both transistors and diodes.

A CLEAN SIGNAL

Above is the clean signal. The peaks and valleys are symmetrical, and have a nice logarithmic bow. In addition, the distance is exactly the same from one crest to the next. These are all traits we would expect to see from a signal generated by a tone generator.

THE ORIGINAL SOUND

In the image above, we see the effect of running the same clean signal through the pedal. Notice the nice even curves now have a slight shark-fin look. The audio for this would sound significantly distorted, and somewhat high-pitched.

ADD A CAPACITOR MOD

The capacitor mod (flipping the top switch to the right) shown above shows an increased amplitude but the wave is shaped slightly differently, as well. In audio terms this would sound similar to the previous, but with more low frequencies (for that heavy rock sound).

A CAPACITOR MOD WITH LESS TONE

In this image, you can see the effect on the wave of changing only the tone control in the upper left corner. I dialed the tone down to about 50%. The wave now has a slightly more subtle curve in the crests and valleys. Audio-wise, this translates into the same low-end distortion from above but as though someone threw a blanket over the speaker. Much of the higher frequencies have been filtered out.


This was a really fun exercise. I want to do more playing to see how different clipping styles compare, and how changes in the GAIN affect the shape.

PART 1 ~ PART 2 ~ PART 3 ~ PART 4 ~ PART 5

TubeScreamer+ Project - Part 4

THE UNVEILING

All the parts came in, the last bits of solder have hardened, and the paint is dry. And here is the final product:

The design was laid down with nothing more than a pair of gold and black permanent markers. Once the design was finished, I threw two coats of automotive clear coat down to protect the ink.

It plays like an absolute dream. The extra range in tones I get from the two mods was totally worth the extra effort (both switches flipped to the left provide the closest to the original TS-808 sound).

PART 1 ~ PART 2 ~ PART 3 ~ PART 4 ~ PART 5

TubeScreamer+ Project - Part 3

CAPACITOR MOD

Before we get on to the mounting work, I thought I might follow up on one of the mods I referred to in the previous post. The folks at DIY Effects offered a suggestion of changing out one of the capacitors to provide additional low-end on the output signal. I liked the idea (and it's really a very simple mod), but I was concerned about losing the 'original' Tube Screamer sound. So as a compromise, I did both. By soldering the leads of both caps together, and connecting the other two leads to a switch, I could select between the original sound, and the extra low-end. Here's what that looks like (the switch is connected to the red, yellow, and black wires underneath the board).

After the photo was taken, I dropped a small amount of hot glue on the capacitor leads to provide a little stability, and to ensure they never touch.

PREPARING THE ENCLOSURE

I picked up this enclosure from Pedal Parts Plus. They have a good selection of enclosures (all cast aluminum), but more than that, they have made ordering the finish a breeze. You just add the case, and a paint charge to your shopping cart, then add a finish to the shopping cart. They have a few finish pricing models (based upon the complexity/cost of the finish), so you do have to make sure the finish charge you add to your cart is appropriate for the finish type that you add. I ordered this on a Sunday night. Monday morning I received an e-mail saying that the case shipped, and had a tracking number. It arrived on Friday.

Step 1 is to mark the holes. There's nothing too complicated here: just draw the lines, mark your holes, then, using a punch or nail, tap a dent in the center of each hole to keep your drill bit from 'walking' along the surface as you're starting to drill.

WARNINGS

A few items are worth mentioning at this stage. DIY provides a diagram of where the holes should go, including diameters. It's a 1-page PDF file. The first time I printed this out, the dimensions all lined up perfectly on the box. The second time I printed it (on a different printer), the output was slightly smaller than the enclosure surface. To be safe, use the measurements; don't rely on the size of the printed output as an accurate guide. Also when you look at the diagram, the top face appears as you would expect: the controls are at the top, and the foot switch is at the bottom. As you look at the front face, however, it is actually upside down, relative to how the pedal sits. It shows the in/out jacks at the top, when in fact, they should be at the bottom. There is even the word "TOP" printed on what should be the bottom, further inviting you to drill holes in the wrong place. Check, recheck, then check one more time.

Once the holes are marked, it's time to drill some guide holes. I like a 1/8" drill bit for this. It's large enough to force the step drill bit in the right direction, but small enough that if the bit shifts, you can recover with some manual effort. (The cases are cast aluminum, The nature of casting metals is that some areas will be more dense, and some less. As a result, even if you properly tap the holes as described above, the bit can still shift as you are drilling.)

After drilling guide holes, it's time for the actual holes. All of the hole diameters specified in the enclosure prep guide provided by DIY Effects matched up nicely with the sizes of the actual components, but you can't undrill a hole, so be sure to recheck the actual components before you start. If in doubt, since we're using a step drill bit, make the hole a little smaller, and have the components on hand to check the fit. To keep myself from drilling the holes too large, I placed a piece of tape above the final step. This gives a really good visual cue to help you know where to stop. One last tip: if you have access to a drill press, that makes life much easier. You can do it with a regular drill, but the press helps with straightness, and preventing some of the issues with the bit moving above.

Once your holes are drilled, you have a box ready for mounting the board and components. If you go with the DIY Effects plans, you'll notice some changes to the original layout. I added the second switch above the original for the capacitor mod, and I moved the hole for the power indicator LED up a little to give the second switch some extra room.

Mounting the components was pretty simple, though I've left out an important step. It's a good idea, before you get to this stage, to set the board up on a bench and test it out. There are a number of steps at which a mistake could happen:a cold solder joint, a drop of solder touching an unintended contact, a bad component, etc. Troubleshooting the pedal in the case is no fun, and with this design, getting the board in and out means soldering, and desoldering the 9v and ground wires to the power receptacle each time. As it happens, with this one, I discovered that the power receptacle has a short in it. So, my final assembly will have to wait until I get a replacement.

PART 1 ~ PART 2 ~ PART 3 ~ PART 4 ~ PART 5

TubeScreamer+ Project - Part 2

I'm a few hours into the project. Below is the current progress. I discovered that I am short one diode so there will be some delay (no pun intended). Image below shows the components, and the stomp switch.

CLIPPING CIRCUITS

Here, I've highlighted the clipping circuits. Circled in red is the standard clipping circuit found in the original TS-808. It's basically just a set of diodes reversed. One mod to this is for asymmetric clipping, which is achieved by adding a third diode. I opted to keep this circuit the same as the original, so instead of adding the third diode, I just ran a jumper in its place. The section surrounded by blue is an option for clipping using two LEDs. Since the design supports only two clipping mods, I opted out of this one. In green is a third option, using two MOSFET transistors and two diodes.

CAPACITOR MOD

Looking closely on the lower right, there is a spot for a capacitor with nothing in it (C11, upside-down). There is another optional mod that allows for changing out this capacitor with others in order to boost the lower frequencies. DIY Effects offered three possible replacements for the stock capacitor. This will be my second mod, but before I decide which capacitor to put into place, I need to hear them. I can't play through the unit without the second missing diode, so this will have to wait.

Next up will be drilling the case so I can get the pots, jacks, and switches mounted.

PART 1 ~ PART 2 ~ PART 3 ~ PART 4 ~ PART 5