step by step instructions - boxed kit amps headphone amp kit stepby--step|"" 2! before you...

SOLOP HEADPHONE AMP KIT STEP-BY-STEP | 1

STEP BY STEP INSTRUCTIONS BASIC INFORMATION

The SoloP Portable Headphone Amp Kit was designed to sound great, look cool, and be fun to build even if this is your first kit project. Please follow these instructions carefully to ensure your safety and the best performance of your SoloP!

WARNING

Please read this BEFORE beginning! This kit requires soldering and the use of a soldering iron. Parts of the soldering iron get dangerously hot—including everything forward of the handle. You could hurt yourself or start a fire if you’re not careful. You must be instructed in the proper and safe use of a soldering iron. Do not use fingers to hold parts in place while soldering. You can be burned even though you are soldering on the opposite side of the board. All materials conduct heat, especially metal. Heat is quickly conducted through the metal leads. We strive to provide lead-free circuit boards and components. Everything in the kit is compatible with lead-free solder. Solder containing lead is toxic. We always use lead-free solder. It is readily available and no more difficult to use than the bad stuff.

The SoloP hardware is based on a very popular design for “A Pocket Headphone Amplifier” by Chu Moy. It’s also called a CMOY amp. For more information you can find his original article on headwize.com. Another excellent resource is the tutorial at http://tangentsoft.net/audio/cmoy-tutorial/ by Warren Young. The SoloP design is open sourced and the design files are licensed for just about any use CC-BY-SA. The project is archived at Github.

These instructions are copyright © 2014 by Boxed Kit Amps, Ltd.


BEFORE YOU START TOOLS AND SUPPLIES

Required

• Soldering iron • Solder - thin rosin core solder made specifically for electronics • Screwdriver - #00 Phillips-head • Small diagonal cutters (sprue cutters) • Pliers, regular or needle-nose • Metal file or emery cloth or sand paper • Wire strippers • Digital multimeter • Toothbrush (new is better, old ones are dirty) • Solid, stable work surface • Good lighting

Useful • Helping hands or PCB vise (Panavise Jr.) • Poster putty • Pencil eraser • Solder sucker and solder wick • Alcohol • Heatproof pad (Silpad) • Magnifying glass or close-up reading glasses


CHECK YOUR PARTS

Refer to the parts list, schematic, parts placement diagram, and the picture to identify all the parts.

Inspect the circuit boards for damage. Check for cracks, scrapes, holes drilled in the wrong place or plugged up.

Not shown: battery and case.


PARTS LIST

Part Description Quantity case w/battery compartment 1 front panel 3"x1" acrylic 1 volume pot 10K audio w/switch 1 RK09IF volume interface board 1 knob soft-touch, D-shaft 1 source & output jacks 3.5mm stereo, panel mount 2 LED 3mm 1

RLED 1K brn-blk-blk-brn-brn or 10K brn-blk-blk-org-blk 1

SOLOP main amp board 1 IC1 op amp, OPA2132PA 1 CS chip socket 8-pin DIP 1 C1, C2 470uF 25V electrolytic 2 C3, C4 0.47uF polypro film 2

R3, R6 100K brn-blk-blk-org-brn 2 R1, R2, R4, R7 4.7K yel-pur-blk-brn-brn 4 R5, R8 22K red-red-blk-red-brn 2 snap clip for 9V battery, with leads 1 battery 9V alkaline 1 foam spacer 3/8"x3/8"x3" closed-cell 3" rainbow ribbon wire 26 gauge 10 conductor 4"


PREPARATION

Read instructions first. Heed all warnings. Work on a solid flat surface. Use something like a Silpad to protect against scratches and burns. Clean everything before soldering. A simple pencil eraser, followed by alcohol works well. All the leads and the backs of the circuit boards should be shiny.

SOME GENERAL BOARD STUFFING NOTES Prior to stuffing any components, study the schematic, circuit board, and parts list—see how the same part is represented on each. Understanding the schematic will help you understand the circuit and the instructions, but it isn’t absolutely required to build the kit. Insert components from the top (printed side) of the circuit board and solder them on the bottom. As a general rule, start with the smallest components that lie closest to the board. The instructions start out very detailed and get less so as you get familiar with the process. Proceed at your own pace, skim stuff you already know, refer back to stuff you haven’t quite got yet.

SOME SOLDERING TIPS FOR THIS KIT These notes are meant to be helpful when you already know how to solder and do not substitute for instruction in the proper and safe use of a soldering iron. Get instruction!

• Clean, clean, clean! Clean is your best friend. Clean all the parts even if they don’t look dirty. The surface of the metal oxidizes. This oxidized layer not only makes soldering difficult, it is a significant insulator and can interfere with the electrical connection between the part and the circuit board. Clean the pads on the circuit board, too. Both sides! More on this below.

• The tip of the soldering iron, as well as the solder already on the tip also oxidizes. That’s why

you need to clean the tip every time you use the iron. By the way, when you’re done for the day and you go to store the iron, clean the tip first, then coat the tip with a blob of solder. This will keep the oxidation off the tip and the next time you use the iron, you can just wipe off the coating of oxidized solder.

• The kit’s circuit boards are “plated through hole” (PTH), meaning that the holes in the board

are plated with metal all the way through. This plating pulls solder into the hole between the wall of the hole and the lead. Therefore, you don’t need much solder on the surface of the board. A good solder joint will have a tiny bit of solder showing on both sides of the board.


BUILD THE MAIN AMP BOARD Locate the SoloP main amp board.

SoloP Parts Placement Guide

The circuit boards are manufactured in panels where they are connected by small sprues. These need to be snapped off with pliers, and the scars smoothed with a file or emery cloth. Check all edges.


INSTALL THE CHIP SOCKET

Start with the 8-pin DIP socket. Be sure to align the socket such that the notched end matches the drawing on the board. Securely hold the part in place. Pictured is a “helping hands” — a very useful tool.

Carefully solder all eight pins. Start with a corner, then move to the opposite corner. After tacking the chip down by the corners, the rest of the pins can be soldered in any order.


IDENTIFY & STUFF THE RESISTORS

Eight (8) resistors go on the main board.

R1, R4 (2) 100KΩ brown-black-black-orange-brown

R2, R5, R7, R8 (4) 4.7KΩ yellow-violet-black-brown-brown

R3, R6 (2) 22KΩ red-red-black-red-brown

K stands for thousand so 4.7K is 4700 ohms. This is also written 4K7, to avoid any confusion over the decimal point.

This will leave one (1) resistor to go on the volume interface board. You will have one of the following two resistors in your kit depending on which front panel you have.

RLED (1) 1K brown-black-black-brown-brown

or

RLED (1) 10K brown-black-black-red-brown

The resistors supplied with the kit are manufactured to within 1% tolerance. This means that your reading on the multimeter may be off by a bit. There is also some error with affordable multimeters. So, for example, the 4.7K resistors can measure anywhere from 4.65K to 4.75K ohms. In this picture, the meter reads 4.71K ohms. That’s fine.

Resistors are marked with their value in colored stripes. You can use a color chart to pick a resistor out of the pile. https://www.google.com/search?q=resistor+color+code VERIFY that you have picked the correct resistor by measuring with a multimeter.

This is important because some resistor color codes make perfect sense when read backwards. For example 120 ohms backwards is 10K ohms. Both are common values. You may have gotten the wrong parts!


On each resistor bend the leads down at each end. This should just about match the spacing of the mounting holes on the board.

Insert half the resistors into the board. Use every-other resistor position (as pictured). You’ll see why when you flip the board. It get’s crowded under there. Spread the leads under the board to hold the resistors in place.


Flip the board and solder all the leads, trimming as you go (if any get in the way) or all at once when you are finished. Install the rest of the resistors in the same way.

The electrolytic capacitors are polarized and must be installed in the correct orientation. The positive lead is longer and goes in the hole marked with a plus (+) sign. This is important! Please double check: The wide stripe is on the side with the negative lead.


The film caps are not polarized and can be inserted in either direction. However, they have very short leads, so the trick with spreading the leads to hold them in won’t work. Poster putty works well to secure them in place until you can solder them. Be careful not to melt the putty!


BUILD THE VOLUME INTERFACE

Locate the RK09IF volume interface board.

RK09IF Parts Placement Guide

The edges of the volume interface board (RK09IF) need to be sanded smooth just like the main amp board. The last remaining resistor should be either 1K or 10K ohms. Install this in RLED.


Now, install the volume pot, being careful to line up all the pins. Install it on the top of the board—the side with the printing on it. It will only go in one way. Be sure it’s fully seated. Friction will hold it until all the leads are soldered.

The rainbow ribbon wire needs to be split into groups. Rather than tear it, which is hard to control and ends up ragged, use a blade to slice it apart. Be careful not to nick the inside colored insulation. This could leave a bare spot.


Make pieces that are 1, 2, 2, 2, and 3 conductors wide (as pictured). The color groups shown in the photo match the wiring diagram. black white+gray violet+blue green+yellow orange+red+brown

For each group of wires, split one end about 1/2” back. Then, carefully strip 1/16” off the individual ends. For the black singleton, strip 1/2” off one end. On each stripped wire end, neatly twist the bare strands together.


“Tin” the wire by applying the smallest possible amount of solder. The plastic insulation may shrink back due to the heat. It’s OK.

Take the green+yellow pair and insert the green wire into I 1 and

the yellow into I 2 .

A note about signal names The amp handles two channels. It doesn’t actually matter which is right or left, as long as they are kept consistent the whole way through. That’s why they’re simply marked 1 and 2 (S1, I1, O1). In this build channel 1 is right and 2 is left. Another point of confusion could be the difference between “source” (S1) and “input” (I1). It was necessary to distinguish the two wires and it made sense to name the wire that comes from the jack with the source of the music as the source (S) and the wire that goes to the input of the amp board as the input (I).


Flip the volume board assembly, keeping the wires inserted and securely in place. Solder the wires into the board. Make a good connection, but be quick so the plastic insulation doesn’t shrink back too far.

Install the triple group in the same way. These wires carry power—brown is V-, red is V+ and orange is 0V.


ASSEMBLE THE FRONT PANEL

Pictures below might show this better.

Attach a wire pair to each jack. Refer to the wiring diagram for color placement. It helps to tin the contacts on the jacks with a tiny amount of solder. Be careful, too much heat here can melt and ruin the jack. With both the wire end and the contact tinned, simply hold them touching and briefly apply the soldering iron just until everything melts together.

Carefully peel the protective paper from the front panel. You can do it dry, with just fingernails. Thread each wire pair through the front panel from the front. Seat the jack into the front panel, then thread the attaching nut up along the wire and onto the back of the jack. Tighten snugly, but don’t break the front panel.


The single black wire carries the common (CMN) signal. It attaches to the long, centered terminal on each jack. Solder the outboard connection (right jack in photo), then bend the wire down and solder the inboard (left jack in photo) connection.

Install the volume pot in the front panel by inserting the shaft from behind and placing the washer and nut on the front. The volume pot itself has a locating tab that fits into a slot in the front panel. Lining this up ensures everything is right side up.


Measure the length of the violet and blue wires from the source jack to the S1 and S2 holes on the volume interface board. Trim to length, split, strip, and tin.

Insert the end of the violet wire into S2 and blue wire into S1 from the top of the board. Be sure to keep the colors in the correct positions. Flip the whole assembly and solder from below. Attach the black common wire to the CMN hole in the same way.


INSTALL POWER INDICATOR LED

This step only applies to opaque front panels with a hole next to the volume pot. If your front panel is transparent it won’t have a hole and you can have the LED point wherever you like.

If you have a transparent front panel, then skip ahead two frames. If your front panel is opaque, then push the LED through the hole in the front panel from the rear. Be sure the cathode (shorter, negative) lead is toward the circuit board.

Smash the LED leads down onto the back of the front panel, into the corner, and along the side of the pot. This get’s the leads out of the way of one of the mounting posts inside the case.


With a transparent front panel: you can bend the leads so the LED points in any direction you choose. In the photo the LED lights up the back of the front panel. Be sure the leads don’t touch each other or anything else that could cause a short. You can use some tape to be safe.

In the photo the short lead appears to be longer due to it being on the inside curve.

The anode (longer, positive) lead goes in the last hole in the board. The cathode (shorter, negative) lead goes into the hole forward of the last hole. Trim, insert, and solder the leads.


COMPLETE WIRING

Layout the front panel and main board assemblies to match the wiring diagram. Note the PC board is backside up and the long edge with the notched corner faces the front panel. Measure the hookup wires for length. Trim the wires.

In the photo, the blue wire comes from the near side of the source jack and goes to S1 on the volume interface board. It’s difficult to see, but the yellow wire then comes out of I1 next to S1 on the volume interface board, and connects to I1, nearest, on the main amp board. The white wire then connects O1, nearest, on the main amp board

Prepare the hookup wires by stripping 1/16” off each end, tinning the bare leads, and twisting the input and output leads for each side. This is the most important place to get the channels consistent. Please double check the wiring diagram. As a second check, trace the wire from one side of the source jack (the jack with the arrow pointing in on front panel). Make sure that the channel number is the same as it routes from the source jack to the volume interface board to the main amp board to the same side of the output jack.


to the near side of the output jack.

Insert wires from the bottom side of the board and solder on the top.

Insert battery leads into volume interface board from the top. Be sure that red goes to B+ and black goes to B-. Solder in place from bottom of board.


The flux left over from soldering can conduct electricity. It has to be cleaned off both boards. Use a toothbrush and water to remove the flux. If the flux is being stubborn, you might have to use alcohol. Read the instructions that came with the solder.


PREPARE ENCLOSURE

Some of the turrets (bosses, nubs) inside the case interfere with assembly and have to be removed. The turrets to remove are the 4 shorter ones closer to the middle on both the top and bottom pieces. Be sure to leave the outer turrets in place. Use stout side cutters and watch out for flying debris.

Cut the foam spacer material at about 2”. The deeper half of the case is the top. Install the foam spacers inside this piece by simply sticking them to the side and rear walls. There should be a battery-sized space left.


Test before Final Assembly

Attach the battery. It only snaps in one way, but it’s best not to even touch the terminals the wrong way around. Twist the volume switch clockwise until it clicks on. The LED should light. If not, see the Troubleshooting section.

With the notch on the socket facing up, pin 1 is at the upper-left corner. Pins are numbered going down, 2, 3, 4, and then across to the lower-right corner 5, then turning upward 6, 7, 8 at the upper-right corner.

Although the numbering scheme will always be consistent, the function of each pin will vary for different types of chips.

Check for proper voltages at the op amp chip socket. Set your digital multimeter (DMM) to measure DC voltage in the range up to 20 volts. Attach the negative lead of DMM to the middle of the 100K resistors just south of the chip socket. It’s OK if this shorts them together; they are connected here. Pin 4 = –V = -4.5 Pin 8 = +V = 4.5 Values to within +/-0.5V are acceptable. Turn off the power.


FINAL ASSEMBLY

Safe handling of integrated circuit (IC) chips

The circuits inside the chip are microscopically small and easily damaged by static electric shock. Be sure to get rid of any static electricity you may have built up on your body. Ground yourself by touching something large and metal – the leg of your desk, for example. You can also be safer by touching all the pins at once. This is the idea behind the black conductive foam. It shorts all the pins to each other, ensuring that they are all at the same voltage and no current can flow.

Make sure the power is off. Orient the notch in the chip with the notch in the socket and make sure both notches are aligned with the picture on the circuit board. You may have to squeeze the pins to get them to go into their holes. Don’t push too hard – you could bend the pins.


Install the main amp board and front panel assemblies into the top half of the case. The top half is deeper and has a slot for the main circuit board. The front panel also fits into a slot at the front of the case. Route the battery wires over the corner notch in the main circuit board and then behind the screw boss (a.k.a. turret or tower).

Snug the battery into its space next to the foam filler. The battery terminal goes on the end away from the corner notch. Carefully line up the bottom half of the case and install four screws. Open the battery compartment and make sure the battery wires are not pinched and that the battery can be easily changed.


To install the knob, find the flattened part of the hole in the knob, line it up with the flat on the shaft, and push the knob home.

You’ve done it! Take a moment to admire your handiwork. Now, be brave and plug it in! [See Hookup diagram for help with this.] For the first test, you probably shouldn’t use your expensive mp3 player as a music source or your very best headphones to listen.


HOOKUP DIAGRAM

!

SOLOP HEADPHONE AMP KIT STEP-BY-STEP | %!!

Wiring Diagram


Main Amp Board Schematic

Volume Interface Board Schematic


Troubleshooting Smoke, sparks, oozing, bad smell. *** If safe, disconnect battery!!! ***

If the electrolytic capacitors leaked and the board looks salvageable, remove and replace capacitors double-checking polarity. Clean the board, of course. If the capacitors had correct polarity, check polarity of power supply. Go through steps for electrical problems. Replace any burned out components. Check the music source plugged into the amp, especially if chip or socket is charred.

No sound. Check that the battery is installed correctly and has a charge, on switch is “on”, and volume is turned up. Make sure music source plugged into amp is actually sending a signal. Make sure headphones are working. Go through steps for electrical problems.

Case won’t shut all the way. Make sure no wires are being pinched. Especially check under the amp board. Remove everything and make sure the case closes when it’s empty. If not, see if you can’t fix it. It may need to be replaced. Insert front panel backwards so everything else remains outside. Take it back apart and trim edges with file if necessary. Assemble with amp board in place, but front panel hanging out the front. Disassemble and trim edges with file if necessary.

Power voltages are wrong. Make sure battery is good. Measure its voltage. Should be at least 8.4 volts. Be sure it’s snapped in all the way. Volume switch is turned past its “on” click. Inspect wires for pinching. Go through steps for electrical problems.


Electrical problems. Terrible scratchy sounds, static, buzzing, squealing, etc.

Go through wiring diagram making sure all components are installed in correct position, orientation, and value. Make sure all wires are connected properly. Double check that the op amp is installed in the right direction. The chip socket could be installed backwards, so be sure to align it according to the circuit board. Inspect boards using an illuminated magnifying glass. Look for short circuited or broken traces or leads. The solder flux can actually conduct enough current to cause short circuits. Remove all flux with alcohol and toothbrush, cleanroom swabs, and toothpicks. Look for what’s called cold solder joints. That’s where the solder didn’t stick properly. A good joint is pretty. It is smooth and joins smoothly into lead and board. Anything that looks ugly or suspicious should simply be remelted. Failing everything else, melt all the joints just to be sure.

Still doesn’t work. Drive to coast. Huck amp into water. Consider a new hobby, like fishing. Just kidding. You should have a look at Chu Moy’s original article on headwize.com

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