BUILD YOUR OWN AMPLIFIER
The increasing cost of high-end amplifiers has led many audiophiles to build their own or, at the very least, consider it. In this feature, Jason Rourke looks at the history of audio amplifier ‘kits’ and discusses what you should consider before taking the plunge into DIY.
Audiophiles have been building their own amplifiers for years. Indeed in the very early days of audio, the only way to get a low distortion, high-fidelity amplifier at a decent price was to build one yourself. Sure, you could buy a ready-made amplifier from the likes of Leak, McIntosh or Audio Research, but they were expensive — even back then. So many audiophiles built their own valve amplifiers, mainly using circuits supplied by the valve manufacturers themselves. Truth be told, many of the valve amplifiers you can buy today are still built using these self-same circuits. Nothing has changed in the past 100 years except that the quality and performance of the components — resistors, capacitors, diodes, transistors and so on — has improved. Not only has their quality improved; their cost has also dropped dramatically. Unhappily, the same can’t be said for valves, especially power valves. Once selling for around a dime a dozen, the cheapest KT-88 valve will now cost you around $60. And for a set of four matched Genalex Gold Lions, I’m afrid you’ll be paying around $350.
One of the most famous valve makers back in the day was Mullard. In 1954 it developed a brand-new valve design, the 9-pin EL84, so in order to ensure its popularity, it developed a mono amp that used two EL84s in push-pull configuration. In fact, the design featured five valves: an EZ80 for rectification, an EF86 for preamplification, an ECC83 for phase-splitting, and two EL84s in push-pull configuration for output. It had a rated output of 10 watts. Because of the number of valves and the output power, the amplifier was called the Mullard 5-10. It used the excellent Partridge output transformer and was highly regarded
for its excellent sound quality.
The Mullard 5-10 was highly popular because it was quite simple to build. There was a higher-powered, lower-distortion amplifier design available called the Williamson, which was named after its designer, Reg Williamson, despite the fact he’d actually based it on an earlier design by Walter Cocking… but I guess the Cocking amplifier doesn’t have quite the same ring to it! The Williamson was a complicated four-stage, push-pull, Class A triode output design that required expensive components (particularly the output transformer), was difficult to build, and was prone to instability as a result of having the four valve stages and the output transformer in a negative feedback loop. Nevertheless, many were built by hobbyists, and many more by manufacturers who had simply appropriated the circuit (which was published in full in Wireless World magazine) for their own use (and usually without attribution).
Famous US manufacturer Dynaco, which was founded by David Hafler and Ed Laurent in 1955, was probably the best-known supplier of kit amplifiers in the 50s and 60s, but it also made the same kits available as fully assembled units. Probably the most popular — and certainly the most famous
— of its designs was the Dynaco Stereo 70 designed in 1959. The ST-70 had four EL34 output valves, a GZ34 rectifier tube, two 7199 input driver tubes, two ultralinear output transformers and a power transformer.
Dynaco, now owned by Canadian outfit Radial Engineering, still makes the Dynaco Stereo 70 — albeit considerably updated from the original! — which is now in its ‘Version 3’ form. Rated at 35 watts per channel, the Series 3 is a Class A push-pull design, with 12AU7 dual triodes replacing the original 7199 pentodes, a new power supply with a larger transformer and improved line regulation, along with increased filter capacitance, and solid-state rectification rather than the 5AR4 rectifier valve that was used back in 1959.
Dan Fraser, the engineer who was responsible for the redesign, said that while he was planning the Series 3, he reviewed all the design modifications that DIYers had made to the Stereo 70 over the years, and incorporated several of them. You can read a full explanation of the new circuit here: www. tinyurl.com/dynaco-inside-story. (This links to Google’s cache of the story, as it’s currently not available on Dynaco’s website.)
And of course if you’d like to build your own version of the Dynaco Stereo 70, you can find a complete parts list and schematic diagrams here: https://tinyurl.com/dynacoST70 (https://hafler.com/pdf/dynaco/DynaST70.pdf.)
As you’d expect, you can also buy more modern amplifier kits, many of which are designed right here in Australia. One of these is a 5-watt stereo single-ended design called the ‘Red Roo’, which was designed by Phil Wait, who with Ron Keeley designed a 140-watt valve amplifier whose design was published in ETI magazine back in the 80s.
Although ETI magazine no longer exists in Australia, the magazine’s intellectual property was purchased by Silicon Chip magazine, which has since developed many amplifier kits of its own, both valve and solid state.
One of the most popular of its valve designs is the ‘Currawong’, a two-channel amplifier rated with an output of 10 watts per channel, with each channel using two 12AX7 twin triodes for the preamp and phase splitter stages, and two 6L6 beam power tetrodes in the Class AB ultra-linear output stage. It’s available from Altronics as a complete kit of parts for $749.
Silicon Chip has also designed Class AB solid-state integrated and power amplifiers, such as its Ultra-LD 100W Stereo Amplifier, which it claims ‘is the best Class AB amplifier ever published’ but admits it does not sound as good as its 15 watt Class-A amplifier. Silicon Chip has also designed a Class D kit amplifier, the KC5514, which is rated at 150 watts into 8 ohms, and 250 watts into 4 ohms. It’s available as a kit of parts from Jaycar for $53.97, but you need two for stereo, and you have to add your own power supply and your own chassis. (The cheapest way to supply your own chassis is to buy an old, maybe non-working amplifier at a garage sale, and replace all its innards.)
Here in Australia we have an interesting DIY option thanks to a NSW-based company called TubeSoundAudio, which is the Australian distributor for England’s Elekit valve amplifiers. TubeSound Audio sells the Elekit amplifiers as kits that you have to assemble yourself, or fully-assembled. That said, there is a third option, which is that you can buy a kit, then also sign on for what it calls an ‘Amp Camp’, where you spend a weekend at TubeSoundAudio building your own amplifier under the supervision of experienced amplifier constructors. It’s based in the beautiful Blue Mountains of New South Wales, so although it will probably appeal to people living in Sydney and surrounds, it’s a great holiday destination at any time, so you may be able to interest your significant other in an interstate trip.
One of Elekit’s most popular designs is the TU-8200R KT88, which uses KT88, EL34 or 6L6GC output valves and can operate in Ultra-linear, Triode or Pentode modes. It’s rated at 8 watts per channel. Various upgrade options are available, but the basic version sells for $1,440 as a kit of parts, or fully assembled for $2,155. If you build it yourself at one of TubeSoundAudio’s regular Amp Camps, the total cost will be $2,155 [https:// tubesoundaudio.com.au].
Some of the amplifier ‘kits’ sold these days are not what most DIY amplifier builders would regard as a kit. An increasing number of manufacturers are building modules where all the resistors, capacitors and semiconductors required for that particular module are already soldered onto the printed circuit board. So one module will contain a power amplifier, another module a power supply, another a pre-amplifier, and so on. So to assemble a ‘kit’ all you have to do is order a pre-amp module, a power amp module, a power supply module and a suitable chassis to fit them all, after which you bolt all the modules onto the chassis and then wire them all together. Many of these kits don’t even require you to use a soldering iron; all you need is a screwdriver.
One such supplier is Class D Audio, a US company that specialises in Class D kits. Typical of its offerings is the CDA-120, a twochannel Class-D ‘kit’ amplifier rated at 60 watts per channel into 8 ohms. For US$185 you get the Class D stereo amplifier module, the power supply module for it and a toroidal power transformer. You have to supply a chassis, connectors and, well, quite a lot really, but you can purchase it as a complete unit. But how does it perform? At least one model didn’t appear to do very well when tested, as you can find out for yourself here: www.tinyurl.com/class-D-review-asr
Also, despite this kit being built by the manufacturer, know that it carries no testing or safety certifications.
Of course, now that China is into audio, some might question whether it’s worth building your own amplifier at all, either from scratch, or by wiring together modules. Chinese company 3e Audio is well-known for its many amplifier kits, but it also sells its DAP1002 Class-D integrated amplifier, with Bluetooth, completely assembled for AU$110 including shipping [www.tinyurl. com/DAP1002].
But of course its performance might be the
same as… or worse than!… the performance of the Class D amplifier measured by Audio Science Review.
As for other ‘kits’ sold by Chinese outfits, I have seen close-up photographs of the
PCBs and in most cases have been very disappointed by the quality of the layouts and the components used, as well as the standard of the assembly. They are certainly cheap, but it is glaringly obvious that you get what you pay for. And if one does something nasty, like bursting into flames and burning your house down, or — worse — frying your loudspeakers, you haven’t really saved any money at all, have you?
Local Australian designer Allan March, who uses ready-made modules in several of his designs, says that many amplifiers — both kit and ready-made — that use
Class D modules are poor designs. “The ready availability of Class D modules has led to many companies taking shortcuts with how they integrate the modules into their amplifier designs,” he says. “I won’t be specific — but some of them don’t know what they’re doing. They don’t have the background knowledge of electronics, signal integrity, and so on. Practically every single competitor to us does not even put r.f. filters on the front of the amplifier, they just connect them straight out to the outside world… and with Class D, that’s a problem, because r.f. noise getting into the amplifier can intermodulate with the switching signal, and then you get ‘birdies’ and noise in the background. So it’s having a deeper fundamental understanding of electronics and signal processing and signal integrity that helps us differentiate ourselves.”
March also claims that the prices for his amplifiers are so low that they’re comparable with the price of a kit build using the same modules he’s using himself. “If you look at the total cost required to build an amplifier yourself, it’s not economically worth it. We’re charging not much above do-it-yourself prices, and for that you get an amplifier that’s professionally assembled, fully tested and guaranteed for three years, and all in a nice enclosure milled from a solid block of anodised aluminium that looks great.”
HAVE A GO
But let’s say you are interested in building your own amplifier, by yourself, in your own home. Is there anything you should be looking out for?
The first thing to be war of is that despite many amplifier kit suppliers advising that their kits can ‘be assembled in just two evenings using only simple tools such as a screwdriver, cutters, long-nose pliers and a low-wattage soldering iron,’ this is usually true only if you are experienced at building electronic kits.
The second thing to watch out for — and one that’s far more important than the first — is that ultimately the product you are building will involve you getting right up close and personal with some very dangerous voltages, particularly if you are building a valve amplifier or a high-powered solid-state amplifier. It is absolutely essential that you take all the necessary precautions, including using properly insulated tools.
All amplifier circuits, but in particular those involving valves, can retain the potential to deliver a potentially lethal electronic shock even after the power has been switched-off and the amplifier is disconnected from the mains socket! It is crucial to make sure an amplifier’s power supply is completely and fully discharged before working on any part of a circuit. And if you don’t know how to do this, you should not be building an amplifier at all!
KIT OF PARTS
Many amplifier kit manuals suggest you inventory all the parts you have been supplied. My personal advice is not to bother. Just assume that the supplier has a pretty good system for ensuring you have received everything you paid for. If it does turn out that you are missing a part, I am certain any reputable supplier will send it to you. Or, if it’s only something simple that’s missing, such as a resistor or a capacitor, just buy it yourself from Jaycar or Altronics.
I would, however, suggest that you set aside a very clean, very well-lit area in your home where you can build the kit, and leave all the parts out during the build process.
This will minimise the chance of you losing a part. Nearly all the parts you will be installing will be small, and many will be round, which means they’ll roll easily. Stating the obvious here, but if they fall off the bench they could be difficult to find. With regard to this, I would suggest always keeping the box that all the parts came in until you’ve finished building the kit, because I have in the past found components that have slid between the two layers of cardboard that make up the bottom of the box.
A GOOD IRON
...the product you are building will involve you getting right up close and personal with some very dangerous voltages... it is absolutely essential that you take all the necessary precautions
Many kit manuals imply that a cheap, low-cost soldering iron is all that’s required. Nothing could be further from the truth. Proper soldering of components on a printed circuit board requires the speedy but concentrated application of heat to the junction between the PCB track and the component lead end, without the possibility of any high-voltage spikes, and to do this you will need a high-quality, temperaturecontrolled low-voltage iron, plus a selection of tips. Pointed tips are used for soldering components to the PCB. Chisel-shaped tips are for soldering directly wired connections, such as wires to terminal strips and to socket terminals. For really heavy soldering that doesn’t involve fragile components buy and use a cheap, mains-powered 60-watt iron.
You will find that a high-quality temperature-controlled low-voltage soldering iron will cost you around $60 for a basic
model, up to around $200 for one that would be used by a serious kit-builder. As you can see, if you’re building a one-off, this adds considerably to the ‘cost’ of your kit… which is, of course, the reason that kit manuals imply that a cheap iron is all you need! And although I’d be the first to admit that it’s not essential, you should also considering purchasing a PCB holder with a magnifying lens and built-in illumination. It will make your life easier and reduce the possibility of making mistakes when it comes to component identification — particularly the values of resistors!
Of course, you also need solder and, while this might be supplied, it’ll likely be lead-free, in order to comply with Australia’s regulatory requirements. The problem here is that it’s really difficult to get good joints with lead-free solder. So if the solder supplied is lead-free (or you don’t know what type has been supplied), my advice is to buy standard 60/40 rosin-cored solder. This solder is made as a round ‘wire’ comprised from tin (60%) and lead (40%) down the centre of which is a rosin that acts as a flux to allow the solder to ‘grip’ to the PCB track and the lead of the component you are soldering.
Solder is available in two diameters (1.0mm and 0.7mm) to suit the component you’re soldering and the width of the PCB track. Buy a small roll of each, at around $15 per roll. If you’re good at soldering you won’t need additional flux, but if you’re having trouble with larger terminals a bit of flux paste should help ($20 for more than you’ll ever use in a lifetime), though I would not recommend it for soldering components.
CAUTION, WILL ROBINSON!
If you are truly a novice kit builder, please make sure that you insert the components onto the correct side of the PCB, and that in situations where a component is polarised — that is, there’s a (+) lead and a (–) lead — the component is correctly oriented. This would seem to be an unnecessary caution but I know of several kit suppliers who have had ‘non-working’ kits returned for repair where the fault was that the kit builder had inserted every single part on the ‘copper’ side of the PCB rather than the fibreglass side. This most likely occurred because some kit manufacturers show board layouts as viewed from the copper side of the board, while others show layouts from the component side, with an ‘X-ray’ view of the copper below. So make sure you understand the presentation in your kit manual before you start or it could happen to you.
You also need to insert components onto the PCB correctly. Some components need to be pushed down flush with the PCB whilst others need to be positioned a precise distance above the PCB. It’s essential to get this right.
WATCH OUT FOR FAKES
If you purchase a kit of parts from a reputable supplier (Altronics, Jaycar, RS Components, etc) you can be assured that all the small parts (resistors, capacitors, transistors and other semiconductors) will have been sourced directly from the manufacturer and are genuine parts.
However, if you decide to source your own components, which would be necessary if you’re building a design for which printed circuit boards are available, but not a kit of the individual parts (Silicon Chips’ Class A amplifier for example, or Rod Elliot’s Death of Zen amplifier), you will need to be very careful to ensure you are buying genuine components, particularly when it comes to transistors and large-value capacitors. There are many ‘fake’ components out there that will quickly fail after a few hour’s use.
For example, this is a note from Rod
One way to ensure a ‘professional’ end result is to buy a secondhand — preferably nonworking — amplifier in good condition... and replace all the innards
Elliot’s website (https://sound-au.com) concerning the output transistors he recommends for use in one of his designs: “Although I have shown MJL4281A and MJL4302A output transistors, these have been available for more than six years and are still hard to get. The recommended alternatives are MJL21193 and MJL21194. Note: it is no longer possible to recommend any Toshiba devices, since they are the most commonly faked transistors of all. The 2SA1302 and 2SC3281 are now obsolete, and if you do find them, they are almost certainly counterfeit, since Toshiba has not made these devices since around 1999~2000.”
As for capacitors, counterfeiters make these by inserting a small low-voltage capacitor inside the much larger case that’s necessary for a high-voltage capacitor. So if you measure the capacitance of the fake, it will test at the correct value, say 47,000μF, but if you apply the voltage shown on the exterior of the case, it will explode (literally!).
Again, choose a reputable supplier: Altronics, Jaycar, RS Components, Wagner Electronics, Digi-Key, and Mouser are the first that spring to my mind, but there are others as well.
OTHER PARTS YOU WILL NEED
You will certainly need other tools if you are planning on doing a good job. At the very least you will need a pair of side cutters ($20– 40), a pair of long-nose pliers ($15–35), and a pair of wire strippers (approx $30). I would also strongly suggest you invest in a silicon or PVC work mat (around $30) because this will make solder splashes easy to remove and prevent small parts from rolling away. Some mats have magnetic sections so you can’t lose metal nuts or washers, and some have indentations so you can store small tools (jeweller’s screwdrivers etc).
FOLLOW THE INSTRUCTIONS!
Being in the writing business as well as the electronics business, I have to say that back in the days when we sent our words to typesetters, whose job it was to transcribe them into a photo-typesetter, there was a ‘golden rule’ for typesetters: ‘Follow the copy, even if it flies out the window!’ This simply meant that the typesetter was never — ever — to change a word or wording, or even spelling; they had to type in exactly what they were given.
The same applies when you are building an amplifier kit. You will always be provided with a manual that tells you, step by step, what to do and the order in which it needs to be done. Do not try to ‘jump ahead’ or anticipate what might need to be done and do it. If you do, you will usually find yourself having to unsolder a component, which could end up damaging it or a nearby component due to excess heat. That said, I would always suggest that if the kit manufacturer has a website, you should double-check that there are no ‘errata’ or ‘corrections’ listed on it that apply to your kit. Forums may also contain helpful advice from fellow kit-builders who have built your exact kit, of course.
ALIGNMENT AND TESTING
Most modern amplifier kits can be aligned either with no test equipment at all or with a fairly basic low-cost ($20–35) digital multimeter. If alignment is required (setting bias on a valve amplifier, for example), follow the alignment instructions word by word, double-checking everything as you go. If it transpires that an oscilloscope and a signal generator are required, you’re either going to have to buy them yourself (prices start at around $400 each) and learn to use them, or find someone who owns them and will do the alignment for you — preferably a friend who’ll do it for free!
IT’LL LOOK LIKE A KIT
Internally, your amplifier will likely look pretty crude and nothing like one that’s been assembled by a professional. This is because the insertion of components will have been done by a robot, the soldering by a machine and the wiring by a person who does it eight (or more!) hours a day, five days (or more) a week, 48 weeks (or more) of the year and has special jigs to ensure perfect symmetry.
Externally, your amplifier will likely also look like a kit, because the metal won’t be finished to an industrial standard and the front panel lettering will be crude, unlike the lovely silk-screened lettering you see on commercial components. That said, there are exceptions out there.
As mentioned earlier, one way to ensure a ‘professional’ end result is to buy a secondhand amplifier in good condition from eBay or Gumtree (or a boot sale) and replace all the innards with your own. You may find you can even use, for example, the volume control from the second-hand unit. If there are any controls or switches on the front panel you don’t need (balance control, tone control etc) just cut the wires at the back and leave them there. After all, only you will know they’re not connected.
You can also buy pretty a good-looking empty chassis on eBay (usually from China). You need to make sure this is big enough to house your project, and if heatsinks are fitted that they’re efficient enough to dissipate the heat from your output devices, especially if you’re building a Class A amplifier. Chassis quality varies, however, and what you receive may bear little resemblance to the photo shown. Prices can also be steep and freight is usually very costly. I sometimes wonder whether the latter is simply to discourage returns from dissatisfied customers.
TAKE TINY STEPS
If you have decided that you might like to have a go at building your own amplifier, I’d say the safest way is to do it is via an ‘Amp Camp’ as mentioned earlier. Alternatively, you may be able to find an experienced kit builder who lives nearby. You may be able to do this via DIY amplifier building forums, or just by putting up a ‘Help Wanted’ sign at your local Jaycar or Electronics store. Most kit builders are happy to help other kit builders.
But if you lack experience and are 100% determined to fly solo, I would suggest that rather than taking a 747 for a transatlantic flight, you should instead hop into the cockpit of a Cessna and take a few loops around the airfield by starting out with a simple, proven, low-cost kit, such as the ‘Champion’ amplifier designed by Silicon Chip ($24.95 RRP) or maybe that magazine’s ‘Nu-Tube’ Valve Stereo Preamplifier.