TORII SE DESIGN NOTES
STORY OF HOW THE AMP CAME TO BE
didn't sit around a table discussing marketing strategies...
resulting in the creation of another amp. In
fact no Decware amplifier has ever been created for
those reasons. Like this one, all were spontaneous
ideas that we built for fun. Of course when
the results exceed our expectations there is always
an overwhelming urge to want to share it! It is at this
point when we decide to take one into production.
Below is a little story of how this amp came to be...
is always a good time for new projects... around here
it gets dark at 4:00 P.M. so if not for the total immersion
of trying new things we would probably all go crazy. On
this particular early November night my creative alter
ego and good friend Paul Nibbelin and I were burning
the midnight oil building amps. We were trying to shrink the Christmas
bulge on the order board when Paul stopped soldering
and went to the truck.
Soon he slid back through the door (snow) with another
ugly little pull-out from a late 50's vintage console
or something like that. Cool, another show and
tell item, I thought. A tradition we've carried
on for 20 years that has created a collection of
odd tube amps that could fill the bed of a pick up truck!
set it on the bench and we both stared at it. "Well,
what is it?" I finally said. "I dunno",
he replied. "I've been using it for my center
channel and TV for the past 10 years and figured it
would be a good time to check it over." Indeed
it had no markings of any kind so we still don't know
what company made it. We hooked it up and
turned it on and proceeded to crack the top off a fresh
cold bottle of organic beer. As the evening progressed
we had it dated to between 1958 and 1960. Basically
the amp was as old as we were. Then we realized
the amp was actually in better shape than we were...
and noticed that it appears to have the original tubes.
In fact this thing hadn't been touched inside
or out as far as we could tell, yet it worked perfectly.
The NOS tubes in it still tested strong.
on my second beer I'm starting to become intrigued with
the fact that an amp can be 50 years old, be in service
for 12 hours a day for the past 10 years that we know of,
and still work with the original tubes. It was
a little mono amplifier with a single 6V6 output tube
and no feedback with a treble and bass control. We
think it was a harmonica amp. Naturally it sounded
a bit out there but with the tone controls we were able
to keep it from becoming too annoying hooked up to the
been on for a couple hours I noticed that nothing in
this amp gets hot, in fact the power transformer barely
gets warm. It was probably that moment when I
turned to Paul and said "Why can't we make an amplifier
like this... you know something small, light weight
that doesn't get hot and lasts forever?" It
truly seemed to defy physics from a heat perspective.
it sat on the bench hooked to the radio for a couple
days until I couldn't stand the sound of it anymore and decided to
add some feedback and convert it to a hi-fi amp instead
of a musical instrument amp. Took about a 15 minutes
and the problem was solved. No longer irritating
to listen to. In fact it sounded pretty damn good
as most amps do when you can count all the internal
parts on your fingers.
this time I was starting to think how nice it would
be to have a small little amp like this to set on my
desktop and or on my bench. Both places I use
my IPod touch to play non-compressed files from our
music collection and occasionally stream Internet radio.
An application like this would really favor an
amplifier that you can easily lift with one hand because
A) it was very light and B) the power transformer (or
handle) was cool enough to grab and hold.
was on the same page needing exactly the same thing
for the same reasons. My curiosity with how the
amp ran so cool and lasted so long had been satisfied
through some reverse engineering and testing. This
meant only one thing... we should build ourselves one
for Christmas. I suggested it would be fun to
see how good we could get one to sound with our parts
and techniques and then compare it to the original 1958
unit we modified. We have learned some things
in the past 20 years and it would be fun to have a sample
of it on our desks.
was also another very significant factor in justifying
our little pet project. Everything we've built so far
in the Decware line of amplifiers has been based on
the European family of output tubes, ie. EL84, EL34, KT88,
6550 etc. This amp would be based on the American
family of tubes instead and if designed carefully should be
able to accommodate the entire 6V6 family of tubes which
include a rather huge variety. With the new family of tubes
comes new signatures that could really be fun to manipulate
with some tube rolling.
the next week or two we figured out the best possible
layout and size only to discover the end result
was 8-1/2 by 11 inches, the size of a piece of paper...
that definitely means it will be small enough for a
desk top. We both looked at each other and smiled... and that's were the amp began.
amplifier is dual mono with a 6V6 output tube wired
as a single ended pentode
with a tube regulated grid. The input stage consists
of a 12AU7 or 12AT7 to drive the 6V6 where both sections
of the tube are used for gain. A defeatable tone
control consisting of a simple capacitor shunted to
ground lives between the stages, and the final stage
has a small amount of feedback.
takes advantage of the same output transformers used
in our Zen Triode amps. The power transformers
on this amp are 50 mils each and use an indirectly heated
6X4 rectifier tube in the mini 7 pin socket. Of
course there is one for each side. The 6X4 is
a real sleeper of a rectifier tube sounding better than
the 5Y3GT, 5U4's we've always used in the past. The amp was
built with the same attention to layout as our original
Zen Triode amp, using point to point construction with
the least amount of nodes possible.
OA3 tube regulation on the output tubes is taken from
our Torii MK II amplifier because it works so well
to improve linearity. Since the goal with this
amp was to see how good we could make it sound we also
added OC2 tube regulation for the entire input stage.
It is wired on a bypass switch so the amp can
operate without it. However the difference it makes
in locking everything together sonically is rather amazing
so it gets used all of the time. The switch is
there because listening to the amp with and without
the regulation is truly eye opening and educational.
It demonstrates the true value of using tube regulation
on the input stage.
nest where the amp was hatched - taken seconds
after it's first flight.
both instances, where the grids of the output tubes
and the input stage are regulated, they are not regulated
in the typical way. Instead the regulator
tube is wired in series with the load. The tube creates
drop and acts as a filter that seems to block much
of the nasty harmonics and noise that seeps in from
your AC power. Rather than resistors or chokes which
provide a direct conductor for the high voltage, the
regulator tube creates a condition where all the high
voltage must jump between the cathode and plate through
a vacume, so hey folks, look no wires! It simply
amazes me what doesn't make the jump. In fact
even ripple rejection is many times higher that it would
be with the equivalent voltage dropping resistors. Off
all the tube amplifiers available on the market today,
very few use tube voltage regulation so it's realistic
to think this amp will be somewhere in the top of pack
sonically. NOTE: If you wire the regulator
tubes the normal way as a shunt to ground, they actually
inject noise that must be later removed.
amplifier has 3 stages and 2 coupling caps and is blessed
with being able to use very small cap values, ie., a 0.1uf
and a 0.0022uf which is a huge advantage for keeping
the speed up and maintaining a good phase angle. We
seriously considered using transformers instead of caps
but elected not to because A) good ones are too big
and effect the layout in detrimental ways on this amp,
B) good ones cost too much, C) I couldn't get the desired
drift in the phase angle that I was looking for, or
should I say, listening for. Changing the value
of the smaller cap alone will yield as many variations
on the phase angle as you have time to try, so I played
with this for a few weeks. For anyone wondering
what exactly the phase angle effects, ... well everything,
but the most obvious is sound stage focus and size.
the day at work we find ourselves listening to the radio
and Internet radio such as Pandora etc., and while it
sometimes sounds almost hi-fi, most of the time it makes
a guy like me suffer. Putting a treble dampening
circuit in the amp that is fully adjustable, not in
the direct signal path and fully defeatable makes it
possible to listen to sub-par sources or recordings
with far less
distraction. At the same time many high efficiency
speakers are fairly tipped up in response, having significantly
more treble than bass. If it weren't for this
trait everyone would probably love single driver full
range speakers but the majority develop a love/hate relationship with them. This amp allows
you to damp the top end as much as needed, and on the
fly. So it has a dual purpose and I think many
people will find it more than valuable.
is the first amp we've done with more than one gain
stage driving the output tubes which means it basically
has a preamp built in. This was done for two reasons.
A) Since the volume control only gets to the half
way point before the amp starts clipping on a 2 volt
source, there is a better sense of acceleration. You
could think of it as a muscle car with higher compression.
B) Using sources like computer sound cards, IPods,
and other portable devices means lower than 2 volt sources
will be regularly encountered, so the additional gain
will restore the drive and weight that these sources
this is a dual mono amp it is simply two matching mono
amplifiers each with their own power supply, on/off
switch, and volume control. The only thing that
is tied to both amps is the tone control - which is
defeatable. Dual volume has two advantages, 1)
better stereo separation and 2) It allows you to raise
the level of one speaker first and then raise the level
of the second to match. It might seem like a less
than easy way to adjust volume but unlike a balance
control, it gives you deeper control to lock in your
sound stage. The amp can be built with a
single volume control and even a conventional balance
control as a custom option.
PREAMP OUTPUT FOR BIAMPING
we could, we added a preamp output that is actually
driven off the output transformers. That makes
it a low impedance output that is some 20 times lower
than most preamps so it is absolutely guaranteed to
drive even the most difficult amplifiers and do so with
a correct frequency balance / translating to good
weight and dynamics.
would be ideal for a sub woofer or a pair of stereo
subwoofers, but the exciting application of such an
approach is applied to speakers such as open baffles.
Those with more than one driver would normally be bi-amped.
Biamping always has mixed results because the
differences in the two amplifiers used and the preamps
ability to control both amps equally.
our approach you can use the Mini Torii SE as your preamp
and use it to drive a second amp. This way the
second amp closely follows the signature of the Mini
Torii and will respond to adjustments in the volume
and treble settings of the Mini Torii.
ensure that the signature of the second amp is as close
to the first as possible, the even order harmonic signature
of the Mini-Torii is embedded into the output signal.
This will not only make subwoofers disappear more
easily, but anyone with an open baffle or similar high
efficiency full range speaker that uses two drivers
is certain to have better results when the signature
of both amps are matched. This means the second
amp can be either tube or solid state.
amp uses a small amount of feedback on the output stage
that makes it ideal for single driver speakers
that benefit from a little more control. Remember
this amp is a pentode design. Triodes are linear
without feedback so why bother with a Pentode amp? Pentodes
have more speed and spank than triodes and if properly
controlled can come off sounding more like real music
via better dynamics and tighter bass control. The
operative word there was "properly". It
is much easier to get a triode to sound "right"
than it is a pentode, however if you're successful the
pentode can sound "more right" in many systems.
this comes together to ideally serve all of the single
driver high efficiency speakers such as Lowther, Fostex
and others by giving them a smooth frequency balance,
an adjustable top end, and flatter more extended bass.
is the frequency response of the Mini Torii SE as indicated
by the white line, and THD as indicated by the green
line. The -3dB point is 28 Hz which is perfect for a
lower power amplifier.
graph below is showing the THD with the first harmonic
at -52dB. This also shows us the 60 cycle hum
at an impressive -55dB. This puts the dynamic
range of this amplifier without distortion at 52dB and
with a tolerable amount of harmonic distortion it benches
much higher. This is a very a quiet amplifier.
last graph shows the frequency response double the division
as indicated by the white and light blue lines that
are on top of each other. The violet line shows
the effect of the treble control and the green line
just for kicks shows what happens without feedback.
designed in some flexibility to allow for custom options
including but not limited to dual inputs for two sources,
EX output transformers for high impendence speakers,
different volume control configurations, knob choices,
hardwood choices etc.
SOUND AND PERFORMANCE
hoped this new amplifier serves a dual purpose. It
makes it possible to listen to Internet radio during
the day while you work without going mad... and it brings
a new light into the listening room when compared to
all of the other Decware amps.
we have to look at the sound for each amplifier, since
it can be made (like our Zen Triode amp) to drive a
dead short OR made to favor high impedance loads depending
on which output transformer we use.
original two Mini-Torii's were built like the Zen, and
excel into lower impedance loads. When the first
one was completed and tested on our 4 ohm DM944 bookshelf
speakers were stunned at the performance. It made
the speakers get plenty loud, and it made them HIT.
The bass was simply breathtaking. However,
once placed on my reference 8 ohm corner horns, it clearly
struggled, just barely getting the job done. Rather
than just decide it needs 4 ohm speakers, we left it
on the corner horns for the next several weeks and listened
to it anyway. As we did so, I continued to
tweak and adjust the circuit until the performance was
equal to what we heard on the DM944's. A tremendous
amount of progress was made during that stage and the
end result was wonderful on both speakers. Basically
the higher 8 ohm speakers lowered the power on the amp
enough to be barely workable at first. The problem was
corrected by raising the overall power level of the
amp by fine tuning it's clipping characteristics.
any case this is when we considered the amp finished,
built the second one, got identical results, and proceeded
to listen to it on the 8 ohm corner horns for many weeks.
third amp built is the one in the picture above, and
it was done with the EX transformers to see what would
happen. Theoretically it should make another huge
improvement on the reference 8 ohm speakers. It
took some additional tweaking on this amp because the
lower impedance output transformers drop the B+ voltage
across the board which changes the signature of the
amp. Once completed, this amp was evaluated
on the Corner horns for sound quality (and other 8-16
ohm speakers for performance). The result still
has me shaking my head. The Corner horns sound
better with this amp than any other Decware amp to date,
including the Torii Mk II.
brings me to the commonalities between each version
of the amp... the bass. Anyone who's owned a good push
pull amp and a single-ended amp is well familiar with
the advantages one has over the other. I've heard
a lot of single ended amps, both large and small that
have more than OK bass performance! However, in
our own line up of amplifiers, going between the single
ended models and our push pull Torii, the Torii has
the hit that makes music, especially Rock and Classical
fun to listen to. You would think that's largely
because of the difference in power between 25 watts
and 5 or 6 watts but it's really not the case. It
is the signatures of the amps that are responsible.
Mini Torii SE was appropriately named because it has
the signature, weight, and hit of it's much larger sibling,
the Torii Mk II. Yet the Mini Torii SE is single
ended giving it superior low level performance and detail
- meaning it will sound more involving at lower volumes.
On my corner horns the bass from the Torii MK
II is impressive and impossible to ignore, yet on the
same speakers the bass from the Mini Torii SE is actually
better, tighter, flatter, and equal in amount.
this magic quality of the Mini Torii SE seems to come
almost completely from the OC2 tube voltage regulation
applied to the input stage. When it is turned
off, the signature of the amp "returns to normal"
in that it sounds very much like all of the other Single
Ended amps... still very good, but no longer the coherent
hit in the bass.
going between say our Zen amp, or Taboo (both single
ended) and the Mini Torii during the day with (high
bandwidth) Internet radio, the Mini comes off smoother,
warmer, fuller making it the new choice for listening
at work. The other amps all sound like they
have slightly less solid footing, and make a national
ordeal of everything that is not perfect with the recording
and or source.
its perch as the center piece of the listening room
with a really good source, the amp is musically involving.
It gives you the low level detail of a great Single
Ended amp but with the signature of an equally great
push pull - a rare combination that gives you the best
of both worlds when efficient speakers are used.
of these observations so far have been made with what
will be the stock configuration, a 6V6 output tube and
the OA3 regulator tube. Changing to one of the
4 different regulator tube choices will change how the
6V6 (or any other output tube) sounds.
different output tubes in the Mini Torii SE was exciting
because the variety of tubes you can use is so large
and the differences in sound were so distinct it was
possible to make the amp sound pretty much any way you
like. Some combinations were harder sounding which
served less efficient speakers well. Some were
softer, even pastel sounding with completely different
sound stages so it doesn't take long before a tremendous
feeling of empowerment comes over you. It really
brought the theme of this transparent and flexible little
amplifier to be about the tubes themselves. If you thought
the amp had a particular signature it was only until
you rolled some different tubes in it. One night
we stuck a pair of original G.E. 6L6 coke bottle shaped
tubes in it from circa 1950's and they sounded just
like a classic 300B amp!
final comment about tube rolling... as a designer we
can only make an amplifier so good. To push it
past this point we would have to voice it in your listening
room with your supporting components and with you there,
over the course of several weeks getting the bass, midrange,
top end, sound stage depth, width, height, rhythm, pace,
delicacy, transparency, low or high level detail etc.,
etc., until it became virtually impossible for anything
you buy in the future to sound as good. Well,
obviously this can't happen unless you put the designer
up for a few weeks and are willing to pay 100 times
what the amp actually would have cost. Tube rolling
makes it possible (on the right platform) to do just
that - voice your own amplifier. The Mini
Torii is the right platform. You can invest in
and explore the variety of tube choices this amp will
run without fear of it blowing up or prematurely burning
up your investment. Remember, we have a working prototype
that is 50 years old with the original tubes still in
good shape and new looking despite the fact they have
at least 20,000 hours of idle time on them that we know
of this amp is somewhere between 3 and 6 watts depending
on the tubes used and the speakers you connect it to.
But wanna have some real fun? Use it to
drive the bigger Torii MK II in a bi-amp arrangement.
Mini Torii SE's big brother - the Torii MK II.
MK II is exactly twice the size with 4 times the power.
back to the Mini Torii SE product page.
Decware is a trademark of High Fidelity Engineering
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2007 2008 2009
by Steve Deckert