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29 September 2011

Tetra Sans PS Phono Preamp

Well, in testing the new Tetra Sans PS, I have been
spinning a bunch of vinyl…and I don't want to stop. As I write this, I am
spinning Peter, Paul and Mary's (Ten) Years Together album, which
has never been a favorite, but dang if I am not being pulled into the
music. Even the dreaded Puff the Magic Dragon is altogether
compelling. I have to say again; it's amazing just how amazing LPs sound.
Yes, I know they tick and pop sometimes rumble, but dang it, they can
sound so...so dang real.

I was once staying a lovely bed and breakfast that
possessed an old, huge record player, a Victor Orthophonic Victrola
"Credenza" model (it might have been something even more expensive, as it
seemed far bigger than the Credenza I remembered) from the mid 1920s. The
manager noted my interest in the near antique, so offer to play it for me.
If remember correctly, it held an electric motor to spin the turntable,
but absolutely no electronics were involved in getting the sound off the
record into the living room. He placed shellac record in the Victrola and
dropped the needle. Wow! That purely mechanical player blasted, much
louder than I thought possible. I didn't expect this nor the surprisingly
immediate and urgent sound that poured forth from the folded horn. I had
always thought that those old ads showed everyone being fooled into
believing that live music was being performed were pure fantasy...now, I
was not so sure. Sure the there were no highs, no deep bass, but there was
music.

At the same time, to be perfectly honest, I hate the
LP's meager playing time per side and the ticks and pops can be
distracting; in addition, the whole ritual of getting up, replacing a
disk, cleaning, static removal, cueing up the cartridge—all are a pain.
(My wife complains of not having a track-skip button.) But as they say,
there are no roses without thorns...although there are plenty of
rose-less, thorn-covered stems... Just yesterday I was telling my kids
about Mahler's 8th Symphony, the symphony of a thousand, so
called because it requires nearly that many performers. An exaggeration,
but it does require many more performers than any Mozart symphony. (In
fact, I believe the largest ensemble for this composition was the one
gathered in on 15 March 2008, when Yoav Talmi led 200 instrumentalists and
a choir of 800 in a performance in Quebec City, to mark the 400th
anniversary of the city's foundation. But I have also heard that one of
the Swiss cantons held a comparably huge performance to celebrate its
anniversary. )

What equally impressed my kids was the 8th's one hour,
twenty minutes playing time. "How could anyone one listen to one song for
that long?" they asked me. I told them that listening to Mahler symphonies
has often been liken to climbing a tall mountain, which fatigues and
exhausts, but which, once surmounted, yields incomparable views. And the
whole ritual of record care is, in a small way, exhausting and fatiguing.
A friend once explained to me that within a gathering of music-lovers,
spinning LPs makes sense; whereas no one gets together to spin CDs. I
wasn't sure what he meant and I countered with the observation that
audiophiles get together to spin CDs all the time.

His answer was that while audiophiles do gather to
listen to speakers, amplifiers, and cables, they do not gather to listen
to music. Ouch. Still, I thought he was exaggerating a bit too much, so he
went on to explain to me that playing an LP was special, being a more
personal act than pressing buttons on a CD player's remote, as the LP
required its own special ceremony of preparation, which only the owner
could perform. Thus, the LP's extra effort and fragility made playing an
LP for friends something of a small, personal gift. Maybe he's onto
something; besides, the Eric Hoffer observation that I love to repeat is
that thought requires exaggeration and an unwillingness to exaggerate
often betrays an unwillingness to think.*

If nothing else, I love looking at LP cover art,
something impossible with CDs. Almost ten years ago, I went to an estate
sale of a demised jazz lover. There I found about 300 Blue Note LPs. Well,
he must have been a true fan, as every single LP was gray from hundreds
(or thousands) of playings with a cheap phono cartridge. Yet, every cover
was in perfect shape, which inclined me to believe that he had pulled all
the records from their sleeves and left them in tall stack, moving the top
LP to the record player and then to second stack, which once full, would
be moved one LP at a time back to where the old stack had stood; and that
someone else had returned the LPs to their covers, posthumously. I didn't
buy a single album, alas. What a fool I was! Such a painful regret.

I didn't realize that the covers were valuable in
themselves, if to no one else to serious record collectors. Not that I
would have sold them, as I would have loved to display the covers as art
in 12.25-inch
frames. Imagine a wall with four LP covers on display, for example the
four above, which are then replaced each week by another four covers. Ah,
life can be sweet. Speaking of LP covers, if you haven't visited LPCoverLover.com,
you must.

One Wrong Turn

I thought that introducing a 16Hz high-pass
filter would be a good idea, so I used a tiny 0.01µF coupling capacitor in
between the Tetra's two gain stages. Why? Warped records. My view was that
16Hz was plenty low. It wasn't. It wasn't so much that the bass was thin,
although it was as well, but that the recording hall seemed to have gotten
smaller. Interesting. I replaced the tiny coupling capacitor with a
capacitor ten times larger (0.1µF ) and the room re-inflated. The
capacitors were the same brand, same type, same voltage (Jupiter beeswax
600V), so I assume that those who argue for subsonic frequency response
down to 1Hz are on to something. (If I remember correctly, Peter Moncrief
held that down to 0.5Hz was essential.) Three LPs revealed this anomaly
quite well, Benjamin Britten Noye's Fludde, The Mysterious Film World
Of Bernard Herrmann, and Andreas Vollenweider's Caverna
Magica.

Positive Feedback

Once again, I configured this new Tetra Sans PS phono stage to
utilize a bit of positive feedback. Not a lot of positive feedback, just
hint.

Originally, about 25 years ago, when I first played
with the above circuit, I simply sought to eliminate the need for a
cathode-resistor-bypass capacitor, but now I am convinced that something
extra results from the technique and I like it. The wee bit of positive
feedback seems to lend a restored vigor and liveliness to the sound,
almost as if a slight electronic expansion were being introduced. But it
might just be that nothing is being added; instead, pulled away was the
dead-hand grip of the electrolytic bypass capacitors. Whatever the actual
cause, I love it.

A right—but expensive—turn was to replace the four EH
12AT7WC with four NIB, NOS Amperex 12AT7WC tubes (the ones adorned with
the World symbol that were made in Holland late 1960s). I used own over
two dozen of these tubes, which I had bought at Quement Electrons in San
Jose, for $2.25 each back in 1974 (the junky newer versions cost more back
then, interestingly enough). Today, I am down to only six or so of them,
sad to say. This 12AT7, along with the Telefunken and Tungsol, was always
one of my favorites. Unfortunately, they sell for about $50 each (maybe
more) today, last time I looked. Of course, $200 worth of tubes is nothing
to some audiophiles, as they gladly pay twice as much for a single,
much-sought-after tube—but it does seem excessive to me. On the other
hand, I do have a few dozen NIB, NOS 12AT7s that are marked made in
Germany and boxed in a National Electronics box.

Click on image to see blowup

I believe that they were made by Siemens in the 1970s
(they have halo getters and gray, smooth plates) and I remember liking
them very much; I believe that these go for about $25 each these days,
which seems a bit more reasonable. In addition, I must somewhere have some
RCA black plates, which could prove interesting. And wasn't there a
special Sylvania 12AT7 with triple mica spacers that supposedly sounded
amazing? Blacker blacks and more extended highs, you know the sort of
adjectives used. One good thing about NOS tubes is that they tend to last
much, much longer than newly made tubes, so they may not actually prove
that much more expensive in the long run. (By the way, if you purposely
run the heater voltage slightly low, the
tube life is greatly extended; run them slightly hotter, greatly
diminished.)

Vs

One of the first things I noted was that the LP sounded
much more alive than its CD brother of the the same recording. I always
thought that this sonic effect must be due to CDs copies of historic
recording being made from old magnetic master tapes, tapes that have
slightly self erased over time, whereas the old LPs were pressed from
young master tapes (and received their signal through tube electronics).
Now, I am not so sure. For example, the CD and the LP versions of Dexter
Gordon's The Other Side of Midnight exhibit the same somewhat
deadened CD sound and the livelier LP sound—but both shared the same
digital master tape! Remember, digital is, as the ads told us, perfect
sound forever. Cough, cough.

It's possible that the master's 48kHz sampling rate
(the standard audio sampling rate used by professional digital recorders
at the time the album was recorded) is just enough higher than the CD's
44.1Khz sampling rate to preserve a more lively sound. I doubt it. My
guess is that the phono cartridge, being an electro-mechanical device, is
contributing its own mechanical resonances and harmonics, which work to
restore a more natural timbre to the sound. I would love to hear a
laser-based LP playback, as it just may not sound as good as an
electro-mechanical cartridge.

And here is a crazy idea: maybe part of the reason
that LPs sound more alive is that they are psychologically live events in
a way that digital playback just isn't. If nothing else, the needle might
break off, while playing a record; large electrostatic pops appear out of
no where; new ticks mysteriously develop; and if nothing else, we must be
attentive to the needle having reached the end of the record and the tone
arm pestering us to raise it. In other words, we might be listening with a
different part of our brain to LPs, knowing that life is fraught with
mishaps and, to which, we must always be attentive.

In contrast, the digital recording is in "the can" and
not subject to life's uncertainties. (A CD's digital data could be printed
in a thick book, after all.) Think about how different our psychological
frame of mind is while we watch a live play than it is at a viewing of a
DVD recording of the same performance. Live acting is dangerous. Will all
the actors remember their lines? Will there be a staging mishap? Will
someone in the audience sneeze during the most romantic or suspenseful
part of the play? Such fears, small and large, loom in everyone's mind
while watching live acting, whereas we can happily clip our toenails while
watching the DVD performance.

Maybe a secret benefit we derive from owning high-end
audio gear is the concomitant fear that something will blow up or break,
which forces us to attend to the music more closely. I remember a friend
listening in an anguished fear that his old Quad electrostatics would slap
a diaphragm against a stator, thereby burning a hole in the thin film; he
listened quite intensely indeed.

Ripping LPs

I have a huge project ahead of me. First of all, the test that cries out
to be performed is to run the Tetra's signal out to a high-quality ADC,
then save the digital file to the hard drive. How much of this sonic
joie de vivre will survive? And at what cost in terms of storage
space?

I have ripped a few of my LPs before and I was neither
thrilled nor distraught by the results. One problem I encountered was
overloading the ADC; not pretty. Nonetheless, I am keen to get most of my
favorite LPs ripped, as the convenience of a server-based system is
compelling. I love being able to search out one song title and have six
covers of the song show up in the results column. (I even do this with
classical music; for example, I placed four different conductor's takes on
Beethoven's 7th Symphony's second movement placed in cue for playback.
Lots  of fun.) Here is the back cover of one LP that I have ripped.

Jazz
Reunion Backcover PDF

Note that the back cover has been OCR-ed, as the text
is selectable. My Barnes and Noble Nook
Color as a book reader is good; but as a remote control for my
Logitech Duet receiver, it's wonderful. I hacked the Nook so that runs the
Android OS CM7, which allowed me to download the Logitech app for their
Squeezebox units (works with both the Duet and the older Squeezebox).

The software isn't perfect, but it is a least one
hundred times better than the Duet handheld controller. (I have big hands,
so an iPod touch would be too small and an iPad too big—or is just too
expensive). But the Nook is just right, perfectly sized and perfectly
priced. One day, I hope to listen to WiFi streamed jazz LPs ripped to a
hard drive in another room and be able to read the liner notes on my Nook.
(By the way, I believe one of the reason Logitech's software is so lame is
that it was designed on the assumption that the average user only owned
100 recordings, not thousands.) I just wish that Media
Monkey software was available as an app ; they do offer a MonkeySqueeze
plugin that allows you feed music to the Squeezebox server, but I
would like the Media Monkey interface to appear in my Android powered
tablet.

Wait a minute, didn't you just go on-and-on about LPs sounding
wonderful? So, why are you back to icky digital sound?

Yes, LPs do sound wonderful, but my turntable is downstairs in my
listening room and I am often elsewhere in the house (or walking the dog
or driving). In other words, I still plan on playing a lot of LPs, but I
also want the option of an effortless playback. It is not a question of
either/or, but of both/and. Besides, most true, hardcore LP aficionados
always own two copies of their favorites, one for casual playing and one
for showing off, much like the bibliophile who own two copies of each
book, one for reading and one for worshiping. I will just make my second
copy a digital one.

Sans PS?

Why did I make power-supply-less Tetra PCB? What's wrong with including a
power supply? As I mentioned in the blog post, many already own or have
access to a power supply. For example, some own old tube equipment and can
jettison the old guts. Others own power supplies, such as the Janus and
PS-1 regulators. And others still own the All-in-One PCBs that hold both
a high voltage and low-voltage power supply, with extra solder pads for
just such an external-load use. Only four wires are needed to energize the
Tetra PCB from an All-in-One PCB.

One danger is taxing the existing power transformer or
overwhelming the heater regulator. For example, an Aikido line-stage
amplifier based on 6CG7 and ECC99 tubes will draw 1.4A @12.6Vdc; and the
Tetra based on four 6N1P tubes will draw 1.2A @ 12.6Vdc; thus, the total
will come to 2.6A, which still comes in under the LD1085's 3A maximum, but
it will generate a lot more dissipation from the regulator. In addition,
the heater power transformer winding will need to meet a 4.7A rating to
power the heaters. On the other hand, if the Tetra runs four 12AT7 tubes
and the Aikido runs four 12AU7 tubes, the total heater current draw will
be only 1.2A @ 12.6Vdc; much better, much cooler.

Somewhere in my garage, I have a new 19-inch rack-mount
chassis that is 2U tall, which should be able to hold both a Tetra Sans PS
PCB and an Aikido All-in-One HPA/LSA PCB (along with a power transformer).

Quatrode-2 with Gain

When I come up with a new circuit, my notepad fills
with an array of variations. So it was with the quatrode-2 topology. Over
twenty circuits blossomed from the three-device scheme. Not all seed
circuits are this bountiful and not all of the deviations from the initial
circuit worth keeping. One variation, however, I must look into further is
the B&B CF that has been forced to provide voltage gain.

The leftmost triode still sees its cathode faithfully
following its grid, which is only possible if the right triode's cathode
swings twice as far. I am sure this circuit might prove useful.

Remember the hybrid push-pull cathode follower from Blog No. 212?

The idea behind this circuit was get class-A, push-pull
operation out of the buffer. Well, we can apply the same technique to the
quatrode-2 topology.

Yes, both the transistor's base and the triode's grid
see the same voltage. To get 10mA of current flow through a 6DJ8/6922
triode with 100V of cathode-to-plate voltage requires a negative grid bias
voltage of -2Vdc. The PNP transistor, on the other hand, requires that its
base be about 0.7Vdc more negative than its emitter. Both of these
requirements are satisfied in the above circuit. The 103-ohm resistor not
only creates a 1.03Vdc voltage drop, it matches the 6922's output
impedance at its cathode, which better ensures good push-pull operation.
Of course, we could use other devices, such as a P-channel MOSFET.

The above circuit got me thinking about an OTL version
capable of driving 8-ohm speakers. Instantly, my mind exploded with ideas
of how such a hybrid OTL amplifier could be built. Imagine a burly stereo
power amplifier, adorned with two massive heatsinks and five 6AS7 dual
triodes per channel, with all ten triodes per channel effectively wired up
in parallel, each triode getting its own 10-ohm resistor. The following
schematic shows only the output stage, which is a unity-gain buffer, so a
tube-based valtage stage would have to proceed it.

It looks a bit complicated at first, but just ignore
the DC servo at the input for now. The ten triodes each draw 50mA, for a
total of 0.5A, which would yield 4 Watts of push-pull, class-A output into
an 8-ohm load. Wait a minute there are several 6AS7-based OTL amplifiers
that put out 60W of class-A power.

Actually, they don't.

An idle current of 0.5A means that 1A is the peak
output current swing before the tubes or the power MOSFET stop conducting
and the amplifier enters class-AB. And 1A peak into 8-ohms equals 1² x
8ohms/2 = 4W. Now, I know that many high-end audio companies have
abandoned RMS voltage and current readings, using peak readings instead,
as it allows them to use peak Watts, but even the cheating peak Watts only
comes to 8W, not 60W. (Maybe they are referring to Watts created or
saved.)

The far more interesting aspect of the circuit is how
it works, not what a slick marketing department can do with it. First of
all, note the dissimilar rail voltages, with the tubes getting 120Vdc to
play with, while the MOSFET gets only 60Vdc. Also note that each of the
ten triodes sees a 10-ohm cathode resistor, which prevents
current-hogging by some of the triodes. These ten resistors are
effectively in parallel, with a combined value of 1 ohm. But the P-channel
MOSFET sees a 5.4-ohm source resistor. Why? The MOSFET must have its
transconductance weakened to match the triodes. The big question is at
what part of the triodes plate curves should we measure its
transconductance? At 0V grid volts, its transconductance is much higher
than at -50V grid volts. I choose the former, so 5.4-ohm resistor will
match the triodes at full output, not at idle. Had I chosen the latter,
the resistor would have been so large that the MOSFET would require a much
bigger negative power-supply rail voltage or suffer a large output-power
reduction.

By the way, the power supply such an OTL hybrid
amplifier is easy enough to create, as we can implement a voltage doubler
circuit.

An 88Vac CT secondary can create three rail voltages,
+60V, -60V, and +120V. The tubes get the 120V and the MOSFET gets the -60V
rail, which leaves the +60V rail for the heater elements and the DC servo.
Assuming that a stereo amplifier were built, the ten 6AS7 heaters could be
placed in series.

But the more I thought about this circuit, the more I
realized that something was fundamentally wrong. The quatrode-2 topology
had effectively greatly magnified the 6AS7's wimpy transconductance, but
the MOSFET was also getting a boost from the topology. In other words,
first we must diminish the MOSFET's transconductance and then we increase
it. But ideally, we want the quatrode-2 topology to encompasses only the
triodes, not the MOSFET.

I went back to my notepad and found this variation I
had come up with as a quatrode-2, push-pull, hybrid headphone amplifier
(actually buffer, as there is no voltage gain). In other words, instead of
many parallel 6AS7 triodes, this buffer uses just two 6DJ8/6922/E88CC
triodes per channel. Thus, the 17-ohm source resistor, whose job is to
reduce the P-channel MOSFET's transconductance to that of the quatrode-2
cluster, i.e. about 1/17 A/V or 59mA per volt.

Note how the MOSFET falls out of the quatrode-2's
scope. Well, with some adjustment, the above topology could be adapted to
create a big hybrid OTL. But the more I thought about, the less I liked
the idea of this hybrid, which lead me to envisage a quatrode-2-based
Circlotron, which used only triodes as output devices. (Although I have to
admit that big heatsinks and two phalanxes of tubes would look wondrously
cool.)

Quatrode-2 Circlotron

Click on image to see
closeup

This quatrode-2-inspired Circlotron OTL amplifier will
need twice the number of tubes that the hybrid would need, as negative
voltage swings will have to be provided by an opposing bank of tubes—but
then this design is much closer to pure tube (if you cannt see the
transistors, they do not count). Note how it is the output tubes that get
the coupling capacitors and AC input signal (and bias potentiometers) from
the MJE350, while the input tubes (the 6922) see the PNP collector's DC
voltage, but not its AC voltage swings. Also note, how huge the drive
signal to the output tubes can be, roughly +/-115Vpk.

The power supply is more of pain, as each channel must
have two floating, bipolar power supplies. Still, four smaller power
transformers (170Vac CT) might better fit in a sleek enclosure than one
large transformer. All in all, an interesting design. I ran some SPICE
simulations and the results were good, so crazy good that I won't show
them here, as I have a hard time believing them: they showed an extremely
low output impedance and vanishingly low distortion. On the other hand,
the 6AS7 is not a very linear tube and the quatrode-2 topology works to
iron it flat. Moreover, this is just a push-pull buffer, a brutal power
buffer true enough, but this circuit provides no voltage gain, so an input
stage's distortion would have to be added to the mix.

Click on image to see
closeup

What I must to do is build a small test version with
only two output triodes per channel and +100Vdc and -12Vdc rails—a
balanced tube headphone amplifier, in other words, as shown above. Wait a
minute, where are the two floating power supplies? Since the headphone
amplifier will work in pure class-A push-pull mode, we don't have to have
floating power supplies, as the two 330µF capacitors will function in the
same fashion.

(A power amplifier for driving 8-ohms speakers might be
made along the same lines, if the 4.3k ohm resistors were replaced by a
two chokes a much higher negative power supply rail were used or,
possibly, replaced by a canter-taped choke.)

As I look at the schematic above, I anticipate that
many will be instantly turned off by the four constant-current sources.
They are not essential, just convenient. Thus, with a wave of mouse, here
is the same circuit sans constant-current sources. The DC
voltages derive from SPICE simulations. The important point to observe is
that the negative power supply (-12V) is not used in powering the external
load, as the two output 6922 tubes do all the hard work; in fact, the two
1k resistors are a small drag on the output tubes, which is why
constant-current sources area better idea. But we must have one or the
other, as this circlotron uses only two power supply rails (for a stereo
amplifier, no less), not two independent floating power supplies per
channel. Thus, the B+ voltage must have a current path that runs all the
way down to the -12Vdc rail to complete the circuit.

Click on image to see
closeup

Here is a simplified schematic that shows the DC
relationships with this circuit.

DC means direct current: that is, steady, unwavering
current flow. The two 330µF capacitors pass no DC flow of current, so they
do not exist in this filtered viewpoint. Putting on a different pair of
eyeglasses, the AC-only kind, we see the following view of the
circuit.

Note that here are no power supplies, nor DC voltages
displayed. They do not exist from this perspective. The two 330µF
capacitors now are seen as being effectively dead shorts to audio AC
signals and the two 4.3k resistor that connected to the B+ are now seen as
just being in series and constituting a parallel load to the 300-ohm
headphone driver. Even the 30µF coupling capacitor can be seen as dead
short. Wait a second, tubes and transistors cannot conduct without voltage
across them. True, but the two above schematics are NOT
FUNCTIONAL in reality; they present two different perspectives on
the circuits functioning.

I remember how I once intensely disliked seeing
schematics like the following in old electronic textbooks, as they were
obviously nonfunctional.

Where is the coupling capacitor, the power supply? Then
I got it, realizing that in terms of AC signal, they did not matter.
Effectively, the power supply and coupling capacitor were dead shorts. And
if we assume a perfect power supply, one that produced the purest DC, then
it would be the exact equivalent to ground, save for its big DC offset,
which we can ignore in AC analysis. (Unless, of course, we were analyzing
a circuit's PSRR.)

Speaking of coupling capacitors, some might query the
need for the 30µF coupling capacitor at the output in the original
schematic, as the 2.34Vdc DC offset is equal on each side, which means
that the 300-ohm voice coil would see no voltage differential and, thus,
suffer no damage. Perhaps, just perhaps nothing ill would happen, but I
would want to do a lot of testing before I removed the capacitor.

I am keen to see how well this circuit works, then I
will return to dreaming about 200W Circlotrons (say twenty 6AS7s or 6080s
per channel).

*Eric Hoffer Quote

This is the third time that I have used this quote here in the
TCJ, so I thought I better look up the actual words he used. I
remembered the quote being in his wonderful book, The Passionate State
of Mind. But where? I have a strangely good memory (or ability) to
quickly find sentences that I am looking for in books that I read decades
ago; I often know exactly which side of the book the sentence is on and
its position on that page and roughly how far into the book the page is
located. Well, in far less than a minute, I found it. (When this happens,
I am both pleased and distraught, as it seems impossible.)

"186
It is impossible to think
clearly in understatements. Thought is a process of exaggeration. The
refusal to exaggerate is not infrequently an alibi for the
disinclination to think or praise."

page 114 of The Passionate State of Mind (1955) by Eric
Hoffer

My view is that if Eric
Hoffer wrote it, it's worth reading. Born in either 1898 or in 1900,
in either Europe or here in America (no one knows for sure) and died in
1983 in San Francisco, his life was amazing. His parents were immigrants
from Alsace. He was nearly blind up until the age of 15, when his sight,
amazingly enough, returned to him. Fearing a return to blindness, he read
all that he could and never stopped. He was an only child and he never
attended any school. In other words, he was largely, if not entirely, self
taught. He left the East Coast and arrived in California in 1920. He
worked as a migratory field worker, a gold miner, and, finally, as a
longshoreman in San Francisco. He lived in a single-room apartment,
without a radio, TV, or telephone. His collection of books was small. He
never married. He did write a best seller, The
True Believer, but continued to work at the docks. Above all, he
was an original, powerful, and penetrating thinker, who wrote
epigrammatically and aphoristically in a simple, but sharp, wry, style.
For example, also from his book, The
Passionate State of Mind.

"Naiveté in grownups is often charming; but when
coupled with vanity it is indistinguishable from
stupidity."

and

"There are many who find a good alibi far more
attractive than an achievement. For an achievement does not settle
anything permanently. We still have to prove our worth anew each day: we
have to prove that we are as good today as we were yesterday. But when
we have a valid alibi for not achieving anything we are fixed, so to
speak, for life. Moreover, when we have an alibi for not writing a book,
painting a picture and so on, we have an alibi for not writing the
greatest book and not painting the greatest picture. Small wonder that
the effort expended and the punishment endured in obtaining a good alibi
often exceed the effort and grief requisite for the attainment of a most
marked achievement."

Here is another sample from a notebook that he wrote in
1950 and it echoes the first quote:

To think out a problem is not unlike drawing a
caricature. You have to exaggerate the salient point and
leave out that which is not typical. "To illustrate a
principle," says Bagehot, "you must exaggerate
much and you must omit much." As to the quantity of
absolute truth in a thought: it seems to me the more comprehensive and
unobjectionable a thought becomes, the more clumsy and unexciting it
gets. I like half-truths of a certain kind—they are interesting and they
stimulate.

Amen.

Next Time

I hope to return to power supplies and regulators.

//JRB

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shipping
speed.

Wanted to let you know that this is simply the best PCB I have had in
my hands, bar none. The quality is fabulous, and your documentation is
superb. I know you do this because you love audio, but I think your
price of $39 is a bit of a giveaway! I'm sure you could charge double
and still have happy customers.

Looking forward to building the Aikido, will send some comments when
I'm done!

Thank you, regards,
Gary.

And

Mr Broskie,

I bought an Aikido stereo linestage kit from you some days ago, and I
received it just this Monday. I have a few things to say about it.
Firstly, I'm extremely impressed at the quality of what I've been sent.
In fact, this is the highest quality kit I've seen anywhere, of
anything. I have no idea how you managed to fit all this stuff in under
what I paid for it. Second, your shipping was lightning-quick. Just more
satisfaction in the bag, there. I wish everyone did business like
you.

Sean H.

High-quality, double-sided, extra thick, 2-oz traces,
plated-through holes, dual sets of resistor pads and pads for two coupling
capacitors. Stereo and mono, octal and 9-pin printed circuit boards
available.

Designed by John Broskie & Made
in USA

Aikido PCBs for as little as
$24

http://glass-ware.stores.yahoo.net/

Only
$9.95
to start
designing
tube-based
crossovers
and much more...

TCJ Filter Design

The Tube CAD Journal's first companion program, TCJ
Filter Design lets you design a filter or crossover (passive, OpAmp or tube) without having to check out thick
textbooks from the library and without having to breakout the scientific
calculator. This program's goal is to provide a quick and easy display not
only of the frequency response, but also of the resistor and capacitor
values for a passive and active filters and crossovers.

TCJ Filter Design is easy to use, but not lightweight, holding
over 60 different filter topologies and up to four filter
alignments:

Bessel,

Butterworth,

Gaussian,

Linkwitz-Riley.

While the program’s main concern is active filters, solid-state
and tube, it also does passive filters. In fact, it can be used to
calculate passive crossovers for use with speakers by entering 8 ohms as
the terminating resistance. Click on the image below to see the full
screen capture.

Tube crossovers are a major part of this program; both buffered
and un-buffered tube based filters along with mono-polar and bipolar power
supply topologies are covered. Available on a CD-ROM and a downloadable
version (4 Megabytes).

Download or CD ROM
Windows
95/98/Me/NT/2000/XP

For more information...

To
purchase , please visit our Yahoo Store:

http://store.yahoo.com/glass-ware

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