Re: Gullible Audio Design Strikes Again
- From: Bret Ludwig <bretldwig@xxxxxxxxx>
- Date: Mon, 06 Aug 2007 19:11:05 -0700
On Aug 6, 2:49 pm, François Yves Le Gal <fle...@xxxxxxxxxxx> wrote:
On Mon, 06 Aug 2007 16:30:22 GMT, Patrick Turner <i...@xxxxxxxxxxxxxxxxxx>
wrote:
Well done point to point IS BETTER for ALL tube amps and
especially appropriate for the hobbyist.
The key words are "well done"...
A very interesting view on various board techniques:http://www.aikenamps.com/PCBorPTP.htm
Is Point-to-Point Better Than PCB?
General
Which is better, point-to-point (PTP), or printed circuit board
(PCB)? You will find manufacturers arguing both sides, some quoting
outlandish claims to support their argument, others claiming PTP is
much better, then, when they start using PC boards, they claim PCB is
better. What is the truth?
First, exactly what is point-to-point?
Point-to-point wiring is the term given to a style of construction
where the components are mounted on the tube sockets and/or terminal
strips, and the connections between components are then hand-wired
together to complete the circuit. Perhaps the best-known example of
point-to-point is the Matchless amplifiers, which had the parts
mounted on terminal strips and wired together. Carr amplifiers also
use this type of construction. The term is also commonly used when
referring to amplifiers with parts loaded on eyelet boards or turret
boards, with the connections hand-wired between them, although these
are technically not "true" point-to-point. Old Fenders are examples
of eyelet board construction, with the eyelets installed in a wax-
impregnated cardboard board. Hiwatts are examples of turret board
construction, with all the components neatly layed out between two
rows of turrets on a piece of phenolic board.
Matchless John Jorgensen (point-to-point using terminal strips)
Hiwatt DR504 (turret board)
Fender '65 Vibrolux Reverb (eyelet board)
(Click on images for larger view)
What is a printed circuit board?
A printed circuit board is a piece of copper-clad phenolic or
glass-epoxy board with portions of the copper etched off, leaving
copper traces that connect the components together. The components
are soldered to "pads" at the ends of the traces. This type of
construction is well-suited to high-volume production, because the
components can be auto-inserted by machines, and all connections can
be soldered at once by passing the loaded board through a wave solder
machine. Most of the cheaper modern amplifiers are PCB construction,
including all new amps by Mesa Boogie, Peavey, Fender, Marshall, etc.
Surprisingly enough, some very high priced "boutique" amplifiers, such
as the Soldano SLO-100, are also PC board construction.
Soldano SLO-100 (PCB)
Peavey 5150 (PCB)
(Click on images for larger view)
Okay, so which is better?
Either construction method can be good or bad, depending upon the
way in which it is done. Neither is inherently good nor bad on their
own.
Properly layed out, a point-to-point amplifier is a work of art,
and is virtually indestructible. Improperly done, they are a veritable
"rat's nest" of wires, impossible to troubleshoot. The main advantage
to point-to-point is ease of maintenance and modification. Components
are simply desoldered from their eyelets or terminal strips and new
ones are put in their place. There is no disassembly of the unit, and
the repair is quick and easy. The main disadvantage of point-to-point
is the intensive labor needed to construct the amplifier. This is why
it is only used by low-volume boutique manufacturers who have lower
overhead costs, and whose amplifiers usually command a premium price
that allows them to cover the cost of the extra labor involved.
Properly designed, a printed circuit board can be every bit as
reliable as a good quality point-to-point board. However, most
manufacturers do a very poor job of designing the PC board. They
skimp on quality in order to lower costs, by doing such things as
making the board single-sided, where the traces are only on one side,
which means the pads tend to be rather flimsy, and usually pull up the
first time a part is replaced. In addition, these types of boards
tend to have solder joints that break loose very easily under
vibration, as there is only a very poor mechanical connection on one
side of the board. A proper PC board should be double-sided, with
plated-through holes, which allows the parts to be soldered in much
better. In addition, some manufacturers also skimp on the soldermask,
which is an insulating coating (usually dark green, gold, or blue)
that protects the bare copper traces from solder shorts and other
unintentional short circuits. Some manufacturers even go as far as
not providing a silkscreen, which is the ink layer that indicates the
component reference designator as an aid to troubleshooting. The
hallmark of a very cheaply built amplifier is one that uses single-
sided boards with no soldermask and no silkscreen. Incredibly, some
very high priced amplifiers use this type of PC board construction.
PCB-mounted tube sockets and pots are also indications of cheaply
constructed PC boards amplifiers.
The best of all worlds, in my opinion, is to use a thick, 1/8" G10/
FR-4 epoxy circuit board, but instead of plated holes to mount the
component leads in, turret terminals are mounted in the holes. If the
board is manufacturing using heavy 2-oz double-sided copper, with
plated-through holes, the turrets can be swaged in to allow a tight
mechanical connection on the top and bottom pads, and then soldered to
the bottom pads for absolutely reliabable conductivity. This type of
construction allows for extremely consistent wiring, a full ground
plane on top of the board if desired, and ease of component removal or
servicing or modification. Components can be soldered and desoldered
from the turrets indefinitely without the possibility of lifting a
circuit pad trace, because the swaged-in turret itself holds the top
and bottom pads and inner plated-through core in place. In addition,
a soldermask can be added to protect the traces, and a silkscreen can
be added to allow easy identification of components during servicing.
The disadvantage to this type of construction is that it is still time-
consuming, and cannot be automated for machine-assembly, so it is not
suitable for mass-produced amplifiers. It is also expensive to have
the turret boards manufactured, so smaller companies may not be able
to justify the added cost.
Aiken Invader MK I
(turret boad with full ground plane, soldermask, and silkscreen)
As to which is better, PTP would be the obvious better choice from
a repair/modification/reliability standpoint, but a properly designed
PCB amplifier will also be just as reliable, but more difficult to
work on. Ignore the hype put forth by the "gurus" who claim PTP
"sounds better" than PCB for various unsubstantiated and unprovable
reasons. You will find many of them extolling the virtues of PTP,
claiming PCB amps "rob tone", then, when they start making PCB amps to
improve their profit margins, suddenly PCB amps no longer "rob tone".
Make an informed decision on which to buy based on quality of
construction, not hype.
.
- References:
- Gullible Audio Design Strikes Again
- From: Bret Ludwig
- Re: Gullible Audio Design Strikes Again
- From: Patrick Turner
- Gullible Audio Design Strikes Again
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