First, a little rantology: You may note that my designs break the KISS
rule. For what it's worth, I find the KISS acronym (Keep It Simple,
Stupid) offensive, it is both patronizing and in the use of the word stupid,
vulgar. There exists a plethora of simple amp designs. What
turns my crank is innovative topologies. I must concede that the best
innovation involves simplicity yet also, a level of brilliance which I lack the
ability to accomplish and to which, the aforesaid plethora of "simple"
designs also fall short of. And so I'd like to introduce a new paradigm,
IDEA: Interesting Design, Excellent Audio. For me, playing with
tubes is fascinating and so I aim for interesting designs that allow me to enjoy
both music and an excellent hobby. I would like
to think that my designs are creative but I realize that more truthfully, they
are perhaps tortured products of my fascination.
Top, Sota Star Sapphire with Benz LP11 / MK11 416 Phono-Stage / Meridian
508: Centre, Hot-Rod DV563a on top of Definitive Powerfield 1500 (the
integration of this unit is described on the 2A3 Line-Stage page) / (Upper) 2A3 Line-Stage (Separate PSU
is underneath) / (lower) 50-300B SE: Right, 845 SE. Cables are a mix of
Analysis Plus Oval 8s (speakers), Analysis Plus Solo Crystal Oval interconnects
and Canare Star-Quad. I use a home-brew power conditioner that is
described at the bottom of this page. Heavy rugs are hung on the walls to
control reflections. The sub has a concrete slab on top supporting a maple
platter on sorbothane pads that supports the DV563a. The Sota is on a
cabinet that is bolted to the wall, the cabinet has over 100lb of ballast in it;
On top of the cabinet is a maple platter on sorbothane, then the Sota turntable.
The maple platters are butcher's blocks from IKEA.
This is as near as I can get to a chronology of my system:
My return to tubes started with the original incarnation of my KT88 PPP
mono-blocks running from the variable output on a Adcom GCD 700 CD player.
The speakers were Energy C8s and the whole thing was a revelation!
So, I got the bug. I redesigned the
KT88 PPP amps using a cascaded
long-tailed-pair topology
with power supply regulators seemingly sprouting from every available space (and
not-so available space) on the chassis. I installed Sowter DAC 8347
transformers into the Adcom using 25ohm i/v resistors which results in around
560mVpk, so I needed some extra gain. This was provided with a
PP 6SN7
line stage, the (PP) line output transformer being Lundahl 1660s. By
then I had realised the limitation of potentiometers as volume controls and
came up with putting series resistors in each phase in the line stage and
hooking an Alps pot across them to form a shunt attenuator. I use the
variable shunt attenuator method still. It is convenient, sounds good (as
good as my switched attenuator, I think) and lends itself to remote operation.
It does have the drawback of variable input impedance. I minimised the
consequences of this by ensuring that the sources (CD, phono, tuner) have low
output Z (well, less than 2k anyway) so that the variation of load presented to
them has a minimal effect.
At this point, Kevin Kennedy gave me an AR turntable with a Merrill
platter. And so my thoughts turned to vinyl. I completed the
EL34 triode / UL
amp with a phono stage. I was astonished to discover that all
I had read about the superiority of vinyl over polycarbonate is true. This
TT came with an Audiocraft unipivot arm supporting a OL-2 (AT?) MM cartridge which Kevin felt was well past its'
best. Well maybe, but as a vinyl neophyte, it sounded good to me.
However, this was wiped out one sad day when I managed to drag a cable over the
TT, breaking the cantilever off the cartridge - thus the guards at each end of the arm in the
picture. I replaced it with the controversial Sumiko Blue Point
Special*. All this started a love affair with vinyl expressed in a number of somewhat derivative MM
and MC phono stage designs. The most recent of these being Calrad hybrid cascode MM
redesign. I have found that the high output cartridges perhaps not
surprisingly, sound best working into low capacitance. Simply using low
capacitance cables is insufficient, attention to low Miller
capacitance is also critical. *The Sumiko is sometimes criticized for a
confused mid-range and sibilance. I always enjoyed the dynamics and resolution
coupled with good tracking qualities. Coupling to the cascode seems to
retain these qualities while greatly diminishing any sense of confusion and
sibilance.
I
next embarked on a single ended voyage. (Actually, I do still play with PP
designs.) Always being a one to start at the end, first up was an
845
effort. I wound the output transformers, it was quite an odyssey! It
is also extremely heavy at more that 250lb.
To
complement this, I built a pair of two-way speakers which remain the centre of
my system, not so much due to exceptional merit but because I don't have space
to do anything else! As these broke in, I did quite a bit of crossover
re-tuning. They do most things quite well but I am anxious to move
on! More details of these speakers can be found on the Other
Projects page.
Next up is a
50 / 300B SE design: As with the
845, I wound the output transformers. I recently made some changes to
accommodate 50s. With the 50s, it has displaced the gargantuan 845 amp as
my favourite.
My
friend Walter Clay introduced me to the WE 416 planar triode with the potential
for multiplexing 19,000 signals which surely must find application in modern
recording set-ups with ever increasing numbers of channels.. (Err, just in
case, I am joking here - It is a telephone repeater tube used where the level of
multiplexing can reach 19,000.) It is a high Gm, low Ra device with
consequent high Miller capacitance, thus I saw potential for it in a low output
MC phono stage. The first of these is the "Adcom",
so called because I built it in a recycled Adcom power amp box. This was
followed by the MK11
416 planar triode MC a similar design to the MK1 but supported by individual
shunt regulation for each stage. The TT is a Sota Star Sapphire with
vacuum hold-down, equipped with a AQ PT6 arm and a Benz Micro LP11
cartridge. The table it is shown on (prior to my move) is braced and (was) bolted to the
wall. I added an additional floor support, under the front edge of the
table. The TT is stood on a concrete paving slab encased in a flannel
pillow slip, more to protect the table than anything else!
My
current system architecture uses a single sub-woofer. I built a
2A3 line
stage that has separate main channels and sub-woofer outputs. The main
channels have 50Hz high pass filters: The idea is to remove the large swing
sub LF signals
from the main amps and speakers, thereby simplifying the job of the amplifiers
and reducing the speaker cone movements. This implementation really
improved clarity and imaging. The left and right sub outputs are
integrated using a transformer signal summation (transformers shown in picture
on right) approach rather than simply using the L & R inputs on the sub
plate amp which, presumably, mix the signals in some parallel fashion. I
discovered that this approach causes some form of destructive interference
between the channels resulting in a "cracking" sound, audible when the
sub was played alone. I tried mixing the channels using an external
parallel method but the problem remained. The summation method (described
in more detail on the 2A3 line stage page) eliminated it.
Sources other than vinyl include a Meridian 508-20 CD
player (modified with separate psu for the analogue stages), a modified Pioneer DV-563A
multi-format player and Fisher FM-200B tuner.
LINE CONDITIONER
One fine day, I shall get around to developing a linear power
regenerator. Until then, I have built this simple line conditioner using a
re-cycled UPS (APC Back-UPS 600), based on Mike Vans Evers design from Sound
Practices, Vol 1:#4 The design uses the two heavy 8.5V secondaries as a
common mode line choke with 3uF/2000V capacitors across the line before and
after the choke. I had been lucky and picked up some low $ hospital grade
receptacles to replace the cheap units that came with the UPS. Does it
improve my system? I think so.
