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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…)
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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.
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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.
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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
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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
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