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SERVICEMAN'S LOG Remaking a ‘vintage’ guitar FX pedal Dave Thompson Ask any guitar player (or just hang around one for a couple of minutes), and they’ll soon tell you everything about their ‘sound’ and the lengths they’ve gone to in order to achieve it. But for many of us, finding our tone can be frustrating. Most beginners (a group in which I include myself) start by wanting to emulate an existing player’s sound and style, with the likes of Buddy Holly, Jimi Hendrix, Hank Marvin, Eric Clapton and Eddie Van Halen all being popular role models back in my day. Of course, the sound I want my own guitar(s) to make is influenced by the musical direction I want to go in. I recall trading a skateboard for my first electric guitar; the last in a long line of musical instruments I’d tried my hand at as a schoolboy. While proudly showing it off to another friend, he asked a question I had no answer for at the time: “Why doesn’t it sound like guitars on all the records we listen to?” At that stage, I hadn’t even considered what I wanted to sound like; all I knew at the age of 16 is that I’d likely be far more popular with girls as a guitarist rather than a clarinettist! (As it turned out, it made no difference…) 62 Silicon Chip My quest to answer that question plunged me into the world of guitar amplifiers, speakers and effects pedals. It was typical of me to think of hardware before even learning to play! In my defence, all the glossy magazines and peer pressure at the time emphasised having the ‘right’ gear rather than actual playing, so I can blame at least some of that for my early decisions (how’s that for a rationalisation?). Another school chum said he had an old valve amplifier I could have if I wanted it. At the time, my hobbyist electronics experience had been limited to relatively simple transistorbased projects gleaned from 1970s electronics mags, so the world of valves was alien to me. I was soon to learn that this mono ‘hifi’ type amplifier, salvaged from an old radiogram, wouldn’t be any good as a guitar amp anyway. Australia’s electronics magazine What I really wanted was something with a bit of gain and bite to emulate the popular lead guitarists’ tone of the time; with mismatched input impedances and lack of a high-gain stage, without significant mods (far above my pay-grade at the time), this amp wouldn’t be much chop at all. At least I could now hear what I was trying to play, though the ancient speaker burgled from the same wrecked radiogram was about as suitable for guitar reproduction as the amp itself. But it was loud enough to elicit the ubiquitous “turn that thing down!” command from my parents that all aspiring guitar players will be familiar with. My usual retort was that they should be glad that I didn’t want to learn to play the drums! An expensive hobby This process gave me my first taste of being what is now colourfully siliconchip.com.au Items Covered This Month • • • • Pedal to the heavy metal An 1890s Weston voltmeter repair Idle-stop-start-system fault Fisher & Paykel “French door” fridge repair *Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz called a ‘gear slut’. It is a natural human tendency to try to overcome a perceived deficiency by throwing money or resources at it, and I am no exception. However, the more I learned, the more I discovered that anything worth having in the guitar-playing business cost a lot more than the average pimply teenager could scrape together. While it’s true that buying a topquality brand-name guitar is as prohibitive today as it was then, I’d still have needed to work my after-school job for years to be able to afford something like a Fender Stratocaster or a Gibson Les Paul, arguably the two most sought-after models in history. I ended up with a reasonably good Strat clone, but still had to plug it into a proper amp to get any real sound out of it. At the time, transistor amps were very much in-vogue and becoming far more affordable than tube amps, due to the proliferation of increasingly- siliconchip.com.au inexpensive and ever higher-powered transistors and hybrid amplifier modules. This, coupled with a concerted campaign by the marketing people to portray valve amps as being old-fashioned, heavy to cart around, expensive to repair and all but superseded by the miracles of modern electronics, led to a boom in solid-state amplifier sales. The ever-diminishing stocks and increasing cost of suitable valves and transformers also made going solidstate appear to be the sensible option. However, more-savvy guitar players knew the truth; transistors didn’t sound as good as valves when used in guitar amplifiers. Making transistor guitar amps sound better To combat this, manufacturers of solid-state amps soon started using a variety of circuits to try to emulate the much-desired ‘valve sound’. This sparked another sales boom, this time in effects pedals. Ironically, many of these floormounted units were solid-state, yet all manner of electronic jiggerypokery was used to try to capture the ‘warm’, harmonic-rich and more pleasant-sounding distortion that valves naturally exhibit when pushed outside their normal operating parameters. These days, sophisticated solidstate ‘modelling’ amplifiers that can make any guitar sound fantastic are highly regarded (and very expensive!) but in general, transistor guitar amps Australia’s electronics magazine are thought of as sounding ‘harsh’ and discordant when over-driven. While not ideal for certain guitar sounds, transistor-based amps have found favour for those desiring lowergain but still-powerful ‘clean’ sounds, such as in country or jazz music and for keyboard or bass guitar amplification (although many bass players do like to add a little ‘fuzz’ too!). One of the earliest attempts at making any amplifier sound better is a device called a “Tone Booster”, or “Treble Booster”. This is essentially a low-gain preamp and filter that was intended to add some extra sparkle to an overdriven valve amplifier, due to the tendency of the sound to ‘darken’ when the amp was pushed into clipping. They typically also boosted the output of then-weaker guitar pickups, which added a hint of overdrive and colour to the sound. Many different companies made these units, some of which are now prized and highly collectible. There were also local companies and savvy individuals making clones of these boosters, hoping to cash in on the popularity and scarcity of overseas models. My assignment, which I chose to accept This brings me to my current assignment; a customer called at the workshop bearing one such Tone Booster clone and wanted it refurbished so that he could use it. He’d acquired it from someone’s estate, and it appeared to have been sitting in a garden shed for the last 50 years. August 2019  63 There was no name on the nowshabby and rust-spotted metal case, and the faded panel labels had been simply-but-neatly drawn on. But it was quite well-made with tidy, point-topoint wiring evident among the cobwebs and dead earwigs inside. It was anybody’s guess who’d made it, or when, but with a battery attached, it still worked, though the pot was shot and the jack-plug connections dodgy. Now, this is the point where things get contentious amongst gear-heads; the Booster could be termed a vintage pedal, and though not strictly a collectible (or even all that desirable or valuable), swapping out components just isn’t the done thing. Working or not, this clone might be worth something to someone, so it didn’t feel right to be messing with it. While the owner didn’t care so much about that side of it, I pointed out some potential problems with what he intended to do with it. He’d been doing some internet research and like many guitarists, had been swayed by the fact that many of his heroes had used a similar device in their recording and stage setups. He wanted to add this Tone Booster to his existing pedal-board effects chain and have it powered by the board’s ‘daisy-chained’ 9V power supply. I informed him that while this could likely be achieved, it would mean overcoming considerable electronic hurdles, and the benefits of doing that were probably not as desirable as he might think. 64 Silicon Chip For a start, this effect was either on or off, and turning it off would kill the signal from that point onwards. Modern effects use a bypass system, where stomping on a heavy-duty DPDT (or 3PDT) switch adds or removes the effect from the signal loop; this box only had a small, case-mounted on/ off switch, unsuitable for switching with one’s foot anyway. Plus, adding a bypass system would completely ruin the original aesthetic of the Booster. Then there was another more complex issue; this device uses a germanium PNP transistor; therefore, the circuit could be termed ‘positive ground’, with the battery positive terminal connected to the case. Running it from a negative-ground power supply wasn’t going to be simple, especially if it is connected to his other pedals, as the input and output would essentially be shorted to ground. Again, while this could be overcome, it would completely change the Booster’s original look. Over the years, I’d met several constructors and heard of many others who had successfully modified vintage pedals, or made their own versions. So my advice to the customer was to leave the original as-is and create a whole new pedal using a more modern case, negative-earth supply and a bypass system but using period components and circuitry. The idea was to try to achieve the same overall sound. He went away and thought about it and came back with the mandate to go ahead, although he had some reserva- Australia’s electronics magazine tions about being able to get the same sound as the original Booster. Designing a new old pedal I reverse-engineered the circuit and found it was a clone of the much-coveted Dallas Rangemaster, a widelycopied 60s-era Tone Booster supposedly bearing mythical powers. Just what made it so great is up for debate, as it is generally accepted that every Rangemaster gave a slightly different sound due to the ‘use-whateveris-in-the-parts-bin’ approach to manufacture and the relatively wide component tolerances of the era. What is known is that almost all the great guitar players over the years have either used one at some point in their careers, or raved at length about it in magazines and videos. As most of the industry tech guys I knew who’d done this kind of work have long-since settled down into middle-aged obscurity, I hit the web and was gratified to discover that there is a thriving sub-culture dedicated to the Rangemaster, and they’d already done all the research and development into modernising the pedal. As there was no point re-inventing the wheel, I cherry-picked what I wanted and drew up a circuit incorporating all the various mods required for modern stage use, whilst retaining as much of the original circuitry as possible. Nutting out the design That meant sticking with a germanium PNP transistor and using vintage carbon-composition resistors siliconchip.com.au and polyester or film capacitors. This posed no problems for me, because I have drawers packed with NOS (New Old Stock) components collected over the last 40 years, many of which are from dad’s collection and date back to the 60s. I have many AC and OC-series transistors that will do the job, along with hundreds of various values of old capacitors, resistors and potentiometers. All I needed from my stash was one PNP transistor, four capacitors, one pot and two resistors for the basic booster circuit. I also decided to add three different-value, switchable input caps to offer a wider range of tone choices, since modern pickups are typically hotter and sound different from those from the olden days. I also added input pull-down and output resistors, which are not necessary when the Booster is used as a stand-alone effect but are preferred when used in conjunction with other pedals, to match impedances and minimise switching noise. Another modification I made is to use a trimmer pot instead of one of the originally fixed bias resistors, to help with fine-tuning the transistor operating point and hopefully enable us to dial in the perfect tone. I also decided to use a transistor socket, so I could experiment with other transistors to get different sounds. I also included a foot-operated total bypass switching system, which completely removes the booster circuit from the signal loop, without affecting anything else. By today’s standards, this is a flawed circuit, with non-optimal input and output impedances and noisy, ‘oldtech’ components, all expected to interface with modern, high-gain electronics. Regardless, many guitarists will put up with noisy pedals (or use gates or other methods of minimising noise) to get a better overall tone, so this isn’t a show-stopper. A different power supply arrangement Nonetheless, I still had to modify the original circuit slightly to use a negative ground, so we can plug in other pedals and use the customer’s existing power supply. This modification should not affect the tone. Initially, I thought I would simply be able to switch the existing ground siliconchip.com.au and signal points at the jack sockets while keeping the rest of the circuit above ground. But this turns out not to be a good idea as it can cause circuit instability and add more noise. The solution was to use a powerconverter board to manipulate the voltage polarity instead; this ensures the circuit functions as originally intended, while still making the Booster compatible with the modern power supply and other pedals in the signal chain. In case the customer wanted to use the pedal as a stand-alone effect, or off-grid, I added the ability to run it off its own 9V battery. I utilised the power socket’s second set of contacts to take the battery out of circuit when external power is plugged in. I also used a stereo jack socket for the signal input, so power is switched on when the mono input jack is plugged in; this is standard with newer pedals. I chose a solid, cast-aluminium enclosure for the case as this will stand up well to the ‘rock-and-roll’ life of a floor-mounted effects pedal. It also supplies a stable platform for stomping on the heavy-duty bypass switch. These cases are now inexpensive and widely available from many vendors. Putting it all together Construction was very straightforward; much of the hard work is drilling the case for the various components. It is certainly far simpler to build than the DAB+ Radio I’ve just assembled (siliconchip.com.au/Series/330). That project is a real test for constructors! Setup is also easy, with nothing much to do. To start off, I plugged a recommended OC44 transistor into the socket. I then hooked up a power supply, my guitar and a 15W valve amplifier, so I could tweak the bias voltage by adjusting the bias trimmer to get the most pleasing sound. The Booster certainly makes a big difference; through it, my Telecaster sounds bright and punchy. The Booster at full volume drives my 12AX7 preamp into a very pleasant crunch. Switching the input capacitor selector to other values made quite a tonal difference, but I think this will vary widely depending on what guitar is used. Regardless, the customer was delighted when he heard me playing through his new pedal, and later Australia’s electronics magazine called to tell me it sounded fantastic, if a little noisy, through his setup. But that’s all part of the vintage charm. Job done! Weston voltmeter repair D. V., of Burpengary, Qld, got a very unusual request lately. He was asked to repair a Weston voltmeter. Haven’t heard of Weston? I can’t blame you. The Weston Electrical Instrument Company existed from 1888 to 1954. They were one of the early electrical pioneers and this is the greatgreat-grandfather of the multimeter which we all use today. This is what happened next... Being an old and long retired electrician, the request to repair the Weston voltmeter aroused my interest. I was keen to see how it was made and whether I could get it working. So I duly agreed and waited for the instrument to show up at my door. It arrived carefully packed in an aluminium carry case. Inside was a neat, polished timber box, possibly American redwood, measuring 200 x 180 x 100mm deep – or should that be 8 x 7 x 4 inches? The label inside the lid described it as a “WESTON Standard Portable Alternating and Direct Current Voltmeter, No: 123” with an accuracy of 1/5 of 1%! The date it was tested in the Weston Laboratory was August 20th, 1891. The label states (paraphrased): “This instrument indicates Legal Volts. It has been standardized for use in a HORIZONTAL position, and to obtain the most accurate results, should be used in that position. It is absolutely permanent, and if properly used, its indications may be relied upon to within 1/5 of 1%. Resistance of 60 volt coil at 70°F: 1107.72 Legal ohms Resistance of 120 volt coil at 70°F: 2224.11 Legal ohms Standardized at Weston Laboratory, Newark N. J., U.S.A. Date: August 20th, 1891 By Wallace Hill, Certified: Edward Weston Do not handle this instrument roughly. Rough usage is liable to injure the jewelled bearings, or pivots, and thus cause friction and diminish the sensibility of the instrument. Avoid wiping the glass cover just before making a reading. Neglect of this rule frequently causes great discrepancies in the readings of electrical measuring instruments, owing to the August 2019  65 The Weston Voltmeter dated at 1891, with a view of its internals directly below. The paper sleeve remarks that the glass cover should not be wiped before testing as the rubbed parts become electrified. fact that the rubbed parts become electrified and the moving parts are electrified by induction, and are therefore subjected to forces other than those they are intended to measure. Carefully read the instructions for use accompanying the instrument before attempting to use it.” Well, the instructions had disappeared long ago as the instrument was acquired somewhere in the 1940s. Nobody knew where it had spent the previous 50 years of its life. The meter movement sits behind a thick glass panel, held in place with a single screw. I thought it would be a moving iron meter as the scale is cramped at the beginning. But removing the works revealed a rather large moving coil assembly with two wound field coils. There is a timber bobbin with silk-covered resistance wire wound on it, to provide for the two voltage ranges, 120V and 60V. Mounted on the glass panel is a small multi-position rotary switch with small wire resistors between the contacts. The scale is marked 60° to 105°, no doubt in Fahrenheit! The switch was very stiff with age and a few of the resistors and switch contacts measured open-circuit. A mercury thermometer is mounted under the glass, with its bulb curved around so that it is close to the field 66 Silicon Chip coils. You set the knob to match the temperature on the thermometer to compensate for the change in the resistance of the coils as they warm up. The moving coil is wound in a ring with the jewelled pivots glued on. There is no metal former as in a modern moving coil instrument, so there is no damping of the meter movement. The stator coils are wound on Bakelite formers. The moving coil pivots are mounted between the two coils with the hairsprings which carry the current to the coil. Also, it has a disc brake. Because the meter has no damping, a change in reading will cause the pointer to swing like a pendulum. By easing the pressure on the Operate button a little, a small brake pad touches the disc and steadies the pointer. Press the button Australia’s electronics magazine right in and the pointer will settle at the correct reading within 1/5 of 1%, apparently! The original wiring was rubber insulated, and after 127 years it had crumbled away, so I replaced it with plastic-insulated wire. I checked the meter accuracy against a Fluke 87 multimeter as my calibrator couldn’t provide the required current. It takes 50mA for full-scale deflection! Initial testing showed an error of about 2% on the 60V range and about 4% error on the 120V range. This was better than I expected for such an old instrument. I decided to shunt the bobbin resistors with wire-wound resistors to improve the accuracy a little. These could be hidden, tucked away inside the instrument. The accuracy was then siliconchip.com.au about 2%, which was deemed good enough for a museum piece. How did Mr Weston achieve the stated accuracy of 1/5 of 1%? Probably by setting everything up in ideal conditions in his laboratory. The meter would have had only the curved lines on the dial. A precise voltage would have been applied and a small mark put on the scale. This would have been repeated over and over until all the major marks were made. Then a very talented and neat artist would mark up all the necessary calibration points. So the accuracy would be within 0.2% of his instruments, at least initially. How long it remained that accurate, it’s hard to say. Having gotten it working satisfactorily, I popped it back into the carry case and sent it back to the museum, where it will no doubt fit in nicely. Car start-stop battery bodge A. K., of Armidale, NSW had to use some lateral thinking to overcome a design flaw in his car. You have to wonder why the engineers who designed it didn’t think of this in the first place... I purchased a new SUV five years ago. While gazing into the engine compartment, I noticed that it had a big 12V battery – much larger than I was expecting it to be. I was to find out why that was the case shortly. This car has a feature called the idle stop-start system (ISSS), where the motor shuts down if the brake pedal is held down for more than a few seconds. It starts up automatically as soon as you take your foot off the brake again. This is starting to become more common, and some people hate it. But it does explain why the vehicle needs such a large battery – to allow for the frequent cranking that results. The ISSS feature is designed to save petrol and reduce car emissions in cities. It’s OK in a city when you’re frequently stopping at traffic lights but in a small town with lots of roundabouts, it can be a problem! Three years after I purchased the car, the ISSS fault lamp started blinking. I was told by the service department that this indicated when the battery was down to 75% of its full charge. They told me to make sure the battery electrolyte was topped up and take it for a long drive, or use a mains charger and that would fix it. And it did, for nine months, then the lamp started flashing again. This siliconchip.com.au time, the service department gave the battery a thorough test, which it passed with flying colours. However, within six months, the flashing was back to stay. The service department’s answer was for me to buy another battery! But the batteries had lasted much longer than five years on my four previous cars, so I took exception to this. I have worked extensively with 12V lead-acid batteries used for emergency power over my 40-year career as a broadcast technician. I always refilled them with distilled water, using a hydrometer to check the cells and I do the same with my car batteries. The car doesn’t crank long before it starts and it starts every time. I never saw a battery voltage below 12.3V. So it should still be in good condition. I started wondering why I was having this problem and decided that the ISSS system must be especially hard on the battery or especially fussy about its condition. Perhaps the battery’s impedance had increased as it aged and that was causing the problem. So I needed a way to reduce the battery’s impedance to a more normal level. Then I remembered my old mentor technician (boss) soldering a 1000µF capacitor across a 9V radio battery, extending its life by quite a bit. Perhaps a capacitor across my car battery would do the same. But it would need to be much bigger than 1000µF! Back in the 90s, one Farad capacitors were all the rage for use with car sub-woofer amplifiers. I dropped into the local car hifi shop and luckily picked up an old one off the shelf for a good price, as new 1F capacitors are $150-200. I attached the capacitor to the car battery holder as close as possible and wired it in parallel, keeping the leads short. I was disheartened that after starting the car, the ISSS lamp was still flashing. But the next day, the ISSS lamp didn’t flash and for the past six months, the flashing has not returned. I consider that a success! I have more recently become aware that some car manufacturers (mine in particular) manipulate the battery charging voltage. I checked my battery voltage with the engine running and got a reading of just 12.55V. I was expecting at least 13V, so what is going on? Then I remembered a letter in MailAustralia’s electronics magazine bag (Silicon Chip; September 2018), where a car owner found his car would only properly charge the battery when the lights were on. I then turned on the headlights to main beam and lo and behold, the battery charge voltage went up to 13.8V. Even switching on the parking lights did the trick. Perhaps this was the other reason my car battery was not aging well. I don’t drive much at night and with the lights off, perhaps it was never being fully charged. I suggest readers who own newer vehicles may want to monitor their battery charging voltage, to make sure it is getting charged adequately from time to time. Fisher & Paykel fridge repair D. M., of Toorak, Vic made a simple repair which saved his friend hundreds of dollars and no doubt, lots of frustration. He’s very annoyed at the situation, and we can’t blame him… I have a friend with a Fisher and Paykel “French door” fridge. It was giving an F20 error code. A Google search explains this is due to a broken wire that goes from a door to the body of the fridge. The wire is evidently for a heating element. The wires are located under the upper-left hinge cover which snaps off. She had previously had this problem repaired several times by a technician sent by F&P, and she paid $400 each time. She wanted me to look at the fridge and see if I could stop it from failing repeatedly. It only took me a few minutes to get to the wires in question, and they appeared to be ordinary wires, not a type specially designed to be fatigue resistant, as you would expect in a situation where they can be repeatedly bent and unbent dozens of times per day. Multiple breaks in these wires had been repaired with wire joiners. I removed all evidence of the previous repairs and soldered new high-quality wires of similar thickness in their place. I think my repair will last a long time. It took me about thirty minutes in total, and I think it is outrageous that she paid $400 on multiple occasions to the same person for essentially the same repair. Especially since the fault appears to be due to a design flaw, ie, using an inappropriate type of wire for this application. SC August 2019  67