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Make your first Serious Amplifierby ynze on January 1, 2014

Table of Contents

Make your first Serious Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Intro:   Make your first Serious Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Step 1:   Links: Get a grip on the Gainclone Universe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Step 2:   Parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Step 3:   Size, footprint and design of the amp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

File Downloads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Step 4:   Circuit diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Step 5:   Prototype the Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Step 6:   Prototype the amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Step 7:   Volume control, connectors and wiring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Step 8:   Build the cases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Step 9:   Fitting the power supply in it's case . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Step 10:   Play it loud! . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Related Instructables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

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Author:ynze    YouTube channelAlso have a look at member Monster-Marit. She Rocks (I'm a bit prejudiced, though :-))

Intro:  Make your first Serious AmplifierI did it! I've always wanted to build my own amplifier, and now, finally, I made one. It's my first "serious audio" project ever.

Starting this project was daunting to me. There was a gap between buying the parts and actually making the amplifier... a two year gap, as a matter of fact. Although Iknow a thing or two about analog electronics and I can read and understand electronic diagrams, I never made something from scratch that connects directly to a walloutlet. And I usually make stuff with electronics either for kids or as a "proof of concept", where accuracy and details matter only little. In other words, I was just insecureabout me as a maker of Serious Amplifiers.

If you'd love to build an amplifier but are not sure about how to get it done, this Instructable is for you.

So what helped me to get started and overcome my reluctance? I just needed an amplifier. I love to play music and the best soundsystem I had was my iMac. And thatproved not good enough for me. So I had the choice between buying a cheap receiver while knowing I had all the parts for a much better amp or just get started buildingit. Oh boy, I am SO glad I did just that!

The amplifier I built is the best one I've ever owned (that claim isn't worth very much) and I'm really, really happy with it. Even with my secondhand (€10,-) loudspeakersit sounds pretty nice. In the video, the sound is recorded with the on-camera mic. What you hear is far, far away from the real life experience.

The amp is a so called Gainclone, using one LM3886 op-amp per channel. The power supply is based on a (way too large) 230VA toroid transformer. It took me about 32hours to build the amp and power supply.

In this Instructable, I'll describe how I made the power supply and amplifier. More important, I'll also describe what I would do different if I had to do the project again.

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Step 1: Links: Get a grip on the Gainclone UniverseI'm not an audiophile and not an expert on amplifiers either. So when I started to look around on "how to build a Serious Amp", I entered the universe of Gaincloneamplifiers. Looking at the sometimes gorgeous designs, I realised I wanted to build one of these babies myself. There are many different ways to build them, so browsearound and get yourself familiar with the world of gainclones...

Mark Hennesy's website: Very, very nice amps and great info on gainclones and powersupplies. Great pics and comments on how he built it. The most inspiringresource I found.Wikipedia article on Gainclone amps and where they come from.The Chill Amp: Well documented site, including schematics and parts list.Chipamp.com: I used their circuit diagram for the amplifier (the pdf is available on their site. Comes along with good tips on building amps). They also sell kits andparts.DIY Chip Amps: Nice listing of several DIY gainclone amplifiers.Audiosector.com: Stunningly beautiful gainclone amps.Decibel Dungeon (that's an audio-nerdy name :-)): Schematics for a gainclone amp and a power supply.Decibel Dungeon Gainclone Gallery: Nice collection of DIY gainclone amps.

You may have noticed that there are a lot of slightly different schematics and op-amp types that can be used. Not being an expert, I found it hard to choose. I turned to afriend who I consider to be an expert for advice. He convinced me just to choose something simple and trustworthy. The differences in the circuits are about details, whichare hardly relevant when building your first amp. Novice mistakes will be made and those will have much more impact for the worse than the refined details for the better.

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Step 2: PartsDepending on your configuration of choice, you need the parts. This is what I have used:

Power Supply:

1 toroid transformer with double secondary windings: at least 120 VA max output, 2x 12-18 Volt. I used a 230 VA 2x 18 V model, which is really too big for thisamp (over 300VA is considered overkill for any amp, so I'm pretty close to that :-))2x 10,000 uF / 35 V electrolytic capacitors1x rectifier module KBU10051x Anti-interference filter for mains supply: Kemo nr. M41 (I only used it because I had it lying around. I would have left it out otherwise)1x switch. I already had a very nice old model.1x male power plug, Euro model. These plugs are also sold with an integrated power switch, like this one.1x 3 Amp fuse with socket1x 10mm red LED1x 100 kOhm resistor to dim the LEDabout two meters of heavy duty power cable. I used loudspeaker cable for the power cord to the amplifier, and regular power cord for the internal wiring

Amplifier:Electronics:

2x LM3886 op-amps1x 22kOhm potentiometer, logarithmic scale.Resistors: 2x 2.7 (2 Watt), 2x 680, 2x 1k, 2x 10k, 4x 22kCapacitors electrolytic: 2x 47 uF, 4x 100 uFCapacitors film (MKP type): 4x 0.1 uFSomething that can act as a heatsink for the op-amps. I used a piece of aluminium tube (square profile, 30x30 mm)

Connectors:

1 set of "audio-in" connectors. I don't know how they're called. In dutch, it's "tulip plugs". I'm not kidding.2 sets of lab connectors to connect the speakers1 set (male and female) 3-way XLR plugs, to connect the power supply to the amp.A piece of aluminium to mount the connectors in. I harvested a piece of 150 x 60 x 2 mm aluminium sheet from a discarded PC.

Casing:Anything you like, of course. I used birch plywood, 9 mm thick and alkyd-based clear varnish used foor floors and stairs.

Costs:All together, I spent around €100,- for the whole project. The toroid transformer is the most expensive part by far: €50,-. The op-amps cost around €9,- each, the bigelectrolyte capacitors are around €4,-. Please buy a decent potentiometer. I discarded two of these because they caused noise. The one I use now is so-so, for €6,-(which is PEANUTS for a potentiometer in audio, but I'm on a low budget).

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Step 3: Size, footprint and design of the ampI decided to make separate casings for the power supply and the amp. That way, I can choose to stack the casings or set them side by side.

I made the casings out of wood, because I'm more comfortable with woodworking than with metal. Besides that, I have a thing with clear lacquered birch plywood. I havea bookcase and my daughter sleeps in a bed made from birch plywood. So birch casings fit nicely in my home interior.

To get a grip on the size of the casing, the size of the power supply is leading (the PS has the largest components by far). I laid out the components on a sheet of paperand found out the whole thing can fit into a rectangle of 148.5 x 210 mm (that's the size of half A4, the document standard in Europe).

The top of the casings is a sheet of perforated aluminium. The sheet I used is 0.8 mm thick, which is a bit too thin: The sheets tend to sag a little. I'm looking out forperfed aluminium sheets of at least 1.5 mm.

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Image Notes1. Cut away to fix the mains filter.2. Heat sink for the rectifier.3. Connected secondary coils.

File Downloads

Lay-out-schematics-amp-v2.pdf (608 KB)[NOTE: When saving, if you see .tmp as the file ext, rename it to 'Lay-out-schematics-amp-v2.pdf']

Step 4: Circuit diagramsThese are the circuit diagrams I used. I built them without PCB's, all components of the amp are point-to-point soldered on the chip's leads. For the power supply I usedloudspeaker-cable and regular power cord to connect the components.

The secondary coils of the transformator must be connected. To do this right, you must find out which wires to connect. Connecting the wrong leads will result in a 0 Voltoutput. When connected the right way, you should read 40 to 50 Volts AC. I used an oscilloscope to find the right configuration, but it can also be done with a multimeter,set on AC Voltage.

The rectifier bridge (KBU1005) needs some cooling. I mounted it on a piece of aluminium.

For more info on the circuit: I added some comments with the pictures. Have a look.

Image Notes1. Primary coil2. Secondary coils3. These are mounted into a XLR male socket.-25 and 25 Volts? yes, don't ask me why, but the DC voltage is about 1.4 timeshigher than the AC current on de secundary windings...4. Mains.5. This is a tricky point. Two leads of the secondary windings are joined, but youneed to find out _which_ leads. I used an oscilloscope for that...6. I used MUR860 diodes because I had them lying around. The cap must be aceramic cap (it's purpose is to filter out radio signals, for that you need high freq.

Image Notes1. This circuit is taken from the ChipAmp LM3886 kit.2. Not necessary. Used as a way out when the amp is on without speakersconnected. If that happens, this will only last for a short while...3. This amp is best suited for 8 Ohm speakers. 4 Ohm speakers will pull a muchbigger current through the op-amps. Not desirable.

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ceramic caps...7. The indicator LED in the casing is connected to the 25 and -25 Volt leads. A100kOhm (!!) resistor is used to dim the LED to a not-annoying brightness.8. Entirely optional.

Step 5: Prototype the Power SupplyNot very hard, this step. The power supply has only a few components and is easy to prototype. I connected the parts with connectors and crocodile clamps and hookedit up to an oscilloscope. It worked right away for me.

Step 6: Prototype the amplifierI found prototyping the amp's difficult. That might have something to do with my choice for point-to-point soldering. Although p2p soldering is not very difficult, it doesmake the wiring a lot more complicated. I almost had to build one entire channel to be able to test it. If you're reading this: I'd love to have some advice on this...

Here's how the op-amp looks like with the soldered parts:

If I had to make an amplifier again, I would use PCB's instead of the point-to-point soldering. But I never made custom PCB's before, and the op-amp's pins don't fit in theveroboard I normally use.

Cut away leads 2, 6 and 11 from the op-amp (picture 1)I used a third hand and non-hardening clay to fixate the parts to be soldered.Start soldering the parts directly on the pins:Solder the 22k resistor from pin 3 to pin 9 in pictures 2 and 3 (it's the feedback path. The connection should be as short as possible). Cut away the protrudingleads entirely.Solder the 10k resistor between pins 4 and 8 (picture 4). This time, let the resistor protrude from the op-amps chassis. You need the length of the resistor's leadsto mount other parts on. Pins 4 and 8 are pretty crowded.Solder the 100uF cap's minus side to pin 8 and the 10k resistor (picture 5). Try to make "solder-time" as short as possible. By heating up the resistor it tends toget loose from pin 8.Connect pin 7 to the plus-side of the 100uF cap with a piece of bare solid wire (I used jumper wire from a breadboard) (picture 6).Solder the 680 Ohm resistor to pin 9. Take care not to un-solder the 22k resistor on pin 9 (pic 7).Solder the 47uF cap's minus lead to the plus-side of the 100uF cap. Connect the plus-lead of the 47 uF cap to the 680 Ohm resistor (pic 8).Solder a piece of solid kern copper wire to pins 1 and 5 (pic 9). I bent the pins into a small arc so the copper wire wouldn't roll away too easily. Let the wireprotrude.Finally, solder the wires to +V, -V and ground to resp. pins 1 and 5, pin 4 and pin the plus-side of the 100uF cap (pics 9 and 10).

Repeat this for the second op-amp. But again, my advice is to do this on a PCB if you know how to. I would, however, solder the 22k resistor directly between the op-

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amp's pins 3 and 9. PCB or not.

Image Notes1. 10k resistor connecting pins 4 and 8. Let the resistor protrude as much aspossible from the op-amps chassis.

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Step 7: Volume control, connectors and wiringNow that you have the amps, it's time to connect power, ground and signal on the plate. I found this the hardest part of the project. That might have something to do withmy choice for point-to-point soldering instead of using PCB's. It's wisdom that comes with hindsight, but if I ever make another amplifier I'll use PCB's for sure. Thedrawing in picture 1 is an attempt to show how I set it up.

I'm not very happy with the result. I'm confident that the wires and connections will not cause shorts, but boy, what a mess! If I ever make another amp, this is the partthat I'll want to do better.

Here's how I organised the wiring:See pics 1 and 5. Grounding: At first, I wanted to ground all components in one place. I read about "ground star-configuration" over here , and it made sense to me. Butthere's a price to pay: The many wires to the central ground cause a true spaghetti incident in wiring. So after a failure or two, I decided to ground the parts in twodifferent but close spots.

Volume control:Start easy. See picture 2. The middle lead goes to the amps through a 1k resistor. One other lead goes to ground, the remaining lead must be connected to the input. It'sa matter of paying attention and soldering two resistors per channel onto the potentiometer.

Connectors:I mounted the connectors to an aluminium back plate. The trouble with wiring starts here: All connectors must be grounded, resulting in 6 leads to the "star ground" M4bolt in the back plate. Try to cut the grounding wires as short as possible. Loopy wires take up space. See pic 3. Start with choosing one of the XLR-plug's pin as groundand connect it to the star ground. Also connect the star ground in the back plate with star-ground 2 on the "floor".

V+ and V-:See picture 5: I made leads for the V+ and V- connections with solid kern electrical wire. The wires are mounted in 16 amp connectors which are screwed onto thewooden floor. Solder leads from the XLR plug to the V+ and V-.

Write down the XLR's pin numbers that are now connected to Ground, V+ and V-. You will need that when you connect the other side of the XLR plug to the powersupply's power cord!

Heat sink:I glued a piece of alu tube (30x30 mm) over the width of the floor with epoxy. I made some halfway cuts in it to improve ventilation and add some area. The disadvantageof this configuration is that the line-in wires and a ground wire must go through the heat sink. I covered the wires with heat shrink tube to protect them against the heat.Better safe than sorry.

Connect it:All is ready to be connected now. Connect the potentiometer to the lines-in and ground through the heat sink. Then mount both amps on the heat sink. Start connectingthe wires one by one, cutting them as short as possible. Use shrink wrap to isolate the soldered connections where possible. The spaghetti incident is happening rightunder your hands! With some patience and a decent soldering iron, you'll get there.

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Image Notes1. To left and right speakers2. 2.7 Ohm and 0.1uF caps. It's an optional safety, in case the amp is on withoutspeakers attached.3. two lines in.4. RTX connector, provides ground, V and V- from power supply.

Image Notes1. Heatsink: a piece of square 30x30 mm aluminium tube.2. Ground 13. Ground 24. To pin 3 of the right op-amp5. To pin 3 of the left op-amp.

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Image Notes1. This was my first attempt for wiring: Forget it, it doesn't work. I trashed this andstarted over.

Step 8: Build the casesThe wooden cases are fairly easy to make. However, it's easy to mess it up.I made the cases from 9mm birch plywood. They had three coats of clear lacquer.I added many pictures of the making of the casings. I think the pics are pretty self-explanatory...

Here are some tips. I learned some of them the hard way...

Use decent tools: Sharp saw and drills, screwdriver that actually fit into screws, etc.DON'T RUSH! It will not save you time in the end.I remembered just in time to label the panels before sawing them. With the labels on the panels, I could make the grain of the panels continue from one panel intothe next when the power supply and the amp are stacked.Drill all holes before glueing the panels together.I don't have a cutter. I used the table saw to make the groove in the panels for the aluminium sheets. It works well, but the groove is a bit wide (2.5 mm).Clamping the panels while maintaining the angles straight is always difficult for me. This time, I made an extra panel with the same size as the bottom and usedthat as a placeholder for the clamped panels. It worked pretty good.Apply the coating in broad daylight! Especially with the second and third layer, it's sometimes hard to see whether parts are missed.My first layer of lacquer was too thick. It started dripping after I was finished. It took me careful sanding to get rid of the drips.

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Step 9: Fitting the power supply in it's caseCompared to the amplifier, wiring the power supply is a piece of cake! I mounted the parts on a separate wooden floor. The mains plug, the fuse, the switch and theindicator LED are fitted in the case itself.Browse through the pictures to see what I did. It's not a hard job.

The toroid transformer is mounted on the floor with a 60 mm bolt. I drilled a 20mm hole in the bottom of the case, so that the floor can ly flat on the case's bottom.

In the floor, I drilled two 35mm holes to fit in the big capacitors and I cut away a rectangle to fit the mains filter.

I used a tie-rap around the power cord on the inside of the box as a strain relief. Just in case someone decides to lift the power supply by the power cord...

Image Notes1. Cut away to fix the mains filter.2. Heat sink for the rectifier.3. Connected secondary coils.

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Image Notes1. Fuse holder. Will be screwed to the inside of the casing.

Image Notes1. Yuk! The drill breaking out of the wood!

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Image Notes1. I used a tie-rap on the inside as a strain reliever, when pulling the powercord.

Image Notes1. Two MUR860 diodes are part of the filter for the ground wire from mains.

Image Notes1. The completed filter for the ground wire. I screwed the upright diode on theinside of the case.

Step 10: Play it loud!That's it! As said, my first Serious Amp is the best amplifier I've ever owned and I'm very happy with the result. It's not perfect, though. When the volume is turned upwithout music playing, a soft noise comes up. It's inaudible when playing music, but it's there. I think it comes from my cheap potentiometer, but a small cap in the line-inmight fix it as well. I'm going to have a look at it when I find some time. For now, I totally enjoy playing music. Loud!

For people reading this who never built an Amp but always wanted to: Do it! I hope this I'ble gets you the motivation and confidence that you can. If you have questions,write them down in the comments. I'll try to answer them as good as I can.

For people who made Serious Amps before: Please leave your comments and tips for others. It'll be appreciated by me and hopefully a lot of future Amp-builders.

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