by Nick Guppy
Once upon a time, Boogie only made one amp – now
it’s a big family. Taking the F-50 as an example, when
you design a new amp, how do you come up with something new and
yet still retain the family sound we all know and love? Does
the concept of a different tone come first with a blank sheet
of paper, or do you start with existing building blocks and modify
them until you find something new?
“All of the above, some new, some old; an idea
of the sounds we’re looking for but a willingness to let
a design develop its own identity. If I didn’t enjoy the
creative process I would have stopped long ago. But building high-performance
vacuum-tube guitar amplifiers is my passion and my life’s
work. For me, amp design is an evolutionary process, and I approach
it a bit like music: I want to continue playing, learning and expanding.
The process itself is artistically satisfying (if you ignore all
the frustration and tedium!). And just as we assemble musical improvisation
and speech by linking together known phrases, so too are amplifiers
created using many previously developed circuit elements put together
in new combinations.
“The F-50 uses one of my favourite sounding
front-ends and I finally figured out how to get it quiet enough
to use in a powerful rig. Plus it’s got a new pair of oldtime
tone controls, a pre-set EQ for the Contour, a twisted hi-fi driver
and the 50- watt output section. The trick is to get everything
working happily together. It’s a surprisingly versatile and
familiar sounding amp for deviating so far off the usual path.
“Most of my favourite amplifiers – including
vintage Marshalls – can trace their lineage back to old Fender
designs, not only because they established the tonal standard but
because they just sound so musically right. But as I came up 30
years ago, I wanted to take what I had been repairing for years
and try to kick it up to another level and satisfy the wishes I
kept hearing from the players I knew. They weren’t all that
stoked with what we would now consider vintage treasures. They
saw sonic limitations and they wanted more from their amps. That
quest led to the Mark I and to the introduction of highgain from
cascading preamp stages. There I did have a sound in my head, a
sound more like a sax than a guitar. It didn’t go ‘plink,
plink’, it had sustain and rich harmonic overtones to arrive
at a lead voice. The Mark I, of course, lead to the Mark II, which
introduced channel switching so that both the new high-gain lead
sounds and the traditional clean response were presettable and
easily footswitchable.
Many Players, including some jaded "vintage
only" guys, have raved about the clean sound, calling it the
best ever from a Boogie
The basic architecture of the F-50 originated around
1980 and first appeared in our Studio .22 – a great sounding
but noisy amp. It’s simpler and more stripped down than the
Mark II and the basic arrangement more resembles the Mark I. But
while the Mark I sounded great, it didn’t footswitch very
well and this patented new circuit sought to overcome that limitation.
And it did so partly by placing a huge attenuation pad right in
series with the incoming guitar signal, a very bizarre thing to
do. That’s the source of both the tone and the noise. This
pad increases the clean headroom of the input stage and cultivates
a curvaceous tonal response, bursting with freshness and bouncy
dynamics.
“When switched into the high-gain mode, the
front-end operates largely like an original Mark I, except for
that attenuation pad, which now adds an out-of-phase component
that is surprisingly vital to the overall sound. After that, anyone
familiar with amp circuits could see a pair of different tone controls,
one for each channel, where credit must be given to old Fender,
because those tone stacks are unsurpassable even today, in my opinion.
The clean channel uses the spankier Black Face type while Channel
2 uses the older tweed Bassman configuration altered to Dual Rectifier
values, which contributes mightily to the F-50’s gain sounds.”
THE PRINTED CIRCUIT board layouts in all
your amps have a very distinctive look. We believe they were
once drafted by hand – are they still?
“Yes. Thanks for noticing that ‘distinctive’ look.
I still do them entirely by hand. Something like the Road King
board can take a year or more to complete, but I think that process
is part of the art. You’ve got to live with it. I use the
old-fashioned black tape and donut pads on sheets of clear mylar.
A typical board requires six clear overlays: the main three, the
pad master, component side traces and solder side traces are connected
together. The others are the nomenclature, hand-printed to identify
each part; the drilling schedule for hole diameters and the routing
layout showing the cut-outs, perforations and breakaways of sub-boards
from the main board.
“All of our boards are ‘plated through’ and ‘double-sided’.
That means there are circuit traces on both top and bottom sides
and, most important, each hole where a component lead is mounted
is ‘plated through’ using a platinum alloy to form
a small eyelet inside the hole’s circumference and connecting
the top and bottom traces. This gives great strength and allows
for easy service compared to the ‘single-sided’ boards
normally used in guitar amps. There the mounting of parts relies
mostly on the strength of the glue holding the foil to the board.
They’re weak and hard to work on because you need access
to both sides at once. I think some of the scepticism regarding
circuit boards in amplifiers is the result of boards poorly done
and not anything intrinsic.
“Our ‘flying lead’ construction
of hand-wiring pots and switches from the main circuit board blurs
a lot of the distinction between point-to-point and our way – except
we can achieve greater consistency because all parts and conductors
are precisely located (part of the design process) and don’t
vary. All Mesa/Boogies, from the very first, have used circuit
boards and something like our flagship Road King would be nearly
impossible to do at any price without circuit board construction.
Curiously, I still use the very same X-Acto knife I’ve had
for over 15 years. I haven’t even changed the blade because
it’s been worked down to the right level of sharpness, dullness
really, so it can work the tapes around corners in aesthetically
pleasing curves without cutting through them.
“I was paid a funny compliment by a new technician
in the photo lab that generates composites of the various layers.
Up until then his only experience was with computergenerated circuit
boards. He looked at my pile of mylars and said, Hmm, now I see
why they call it art.”
THE F-50 MAY look simple from the front panel,
but there are all kinds of things going on behind it. Could you
explain what the contour effect is actually doing on Channel
2, and what other tricks, if any, are happening with the EQ?
“You’re right. We wanted to keep the
F-50 as simple-looking as possible, but there is a fair amount
going on inside. I started to discuss the pre-amp layout, and I
think you could say it’s one that deviates most from a traditional
Fender as far as the circuit and the arrangement of the main elements.
“The way in which the reverb circuit interfaces
with the dry signal chain is also unique, as is the phase-splitter
stage driving the output tubes. That was something I worked up
long ago for hi-fi use: it’s real warm sounding and the way
it works with the bias supply delivers a lot of ‘envelope’.
When you hit a note, you can hear a complex morphing of harmonics
that gives it that elusive and interesting character. As far as
the contour, that’s another carefully voiced EQ circuit that
has been in Boogies for decades except this time – to keep
it simple – it’s not useradjustable. It’s preset
in our classic ‘V’ curve, like the setting we’d
use on an old Mark II-C for example. It’s there to help deliver
a modern, aggressive overdrive from a sweet little old amp! I should
mention also that the negative feedback changes too, depending
on which channel is selected, and that’s part of it also.”
WHAT’S WITH THE op-amps and discrete
transistors on the F-50’s PCB? And what’s your opinion
of mixing solid-state stuff with valves in guitar amps in general?
“The two op-amps are parts of the recording/headphone
circuit and the reverb circuit. Most of the transistors you see
are there to drive the channel switching relays, or are for signal
muting to mask the noise of the relays’ switching. Over the
last several years I’ve been favouring relays over all other
types of switching devices because they are so reliable and so
predictable. Fully on or fully off there’s no signal loss
and no bleed-through. And, unlike FETs, there is no amount of signal
voltage they can’t handle.
“The problem is, they make huge popping noises
when switching on and off (remember the old Mark II-Bs?). To solve
this problem, I came up with a mute circuit (patent pending) triggered
by the relays themselves, that cuts off the amplifier just at the
moment the pop would occur. I don’t think you can even detect
the moment that the amp is silent, it’s that brief. And it
sure beats a huge pop!
“In the F-50 the main signal path uses four
12AX7 dual triodes with two 6L6s for power. It’s all-tube
from the input to the speaker jack except for the pre-set contour
circuit and that goes all the way back to the Mark I. This isn’t
one of those hybrid amps that are all solid-state except for a
single ‘alibi’ tube. I’m pretty fanatical about
tubes – in fact it’s all I know. I couldn’t even
design a transistor amp. Yet I don’t see any sacred reason
NOT to use some solid-state devices within a vacuum tube circuit… as
long as they don’t compromise the tonality.
“For example, the rectifier diodes in the high-voltage
supply are solid-state. As you know, some of our more expensive
amps let you select between silicon and vacuum tube rectifiers
because there is a big sonic difference between those two: however,
neither one is automatically ‘better’. But the only
solid-state stuff that ever comes in contact with the actual signal
path in our amps either contributes selectively to the voicing – like
the contour or the reverb – or is sonically neutral, like
the mute FETs. They’re ‘not there’ until that
moment of switching.
“Any part a designer uses, no matter what the
type, should be totally neutral or actually contribute to the overall
musicality. If it doesn’t, then it’s wrong. Period.
Don’t accept compromises! And yet you can make a lousy sounding
amplifier using nothing but tubes, so that by itself is no guarantee.
I guess what I do is a combination of American hot-rodding and
Italian cooking, using tasty, musical ingredients. Give me a super-charger… give
me lots of fresh garlic, and a little red wine!”
WHAT EXCITES YOU about the F-50 and how does
it differ from previous stripped-down designs like the Caliber
or the Subway?
“What excites me about the F-50 is the way
it sounds. It may be simple, and we’ve tried to make it affordable,
but there’s been no compromise on the performance. Many players,
including some jaded ‘vintage only’ guys, have raved
about the clean sound, calling it the best ever from Boogie and
saying it gives their precious old amps a run. I like the low-end
breath with that morphing harmonic complexity I described earlier.
Doug (West, resident Boogie tonemeister) can make a musically satisfying
event out of plucking a single note. But it also rocks hard, especially
in Channel 2 with contour. It’s a little more mainstream
than a Rectifier, a little less aggressive, but not a lot. After
all, we already make the Rectifiers for players who want total
sonic annihilation, including the Single Rec. So, if that’s
what you’re looking for, it’s available. This is more
rock and hard rock rather than overthe- top Recto. The other cool
thing is that Channel 2 without contour really plays the blues
in a way that just wasn’t possible with either the Caliber
or the Subway amps. Here, in the F-Series, the rotary tone control
circuit is different from either of those and has the further refinement
of switching the treble frequency between contour and straight – just
to provide some bluesy treble sting.”
WILL THERE EVER BE A MARK V?
“Yes, there will probably be a Mark
V… but not for a long time. And it will probably sound
just like the Mark IV but with a simpler control layout. It’s
not next on my palette because the Mark IV is still going strong
after 12 or 13 years. But who knows? By the time that bad boy
comes around, anything could happen!”
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