A U D I O... P A P E R
DESIGN NOTES on the original SE84CSP
2004 by Steve Deckert
It was a dark and rainy
October night when on an impulse I decided to make an unannounced
visit to a friends house who frequently gets the opportunity to
test anything new that we design in the way of electronics. We
call it the "Dennis Test" and it is a valuable part of
a network of field testers who run our new designs through the paces
before products become available for sale.
This is a
story about a type "B" preamp. If you don't know
what a type B preamp is, please read the following short article:
- Do they help or hurt the sound
learned from the above link, we have basically type A and type B
to work with. Type A being a circuit that you simply can't
hear requires a near perfect recording to achieve musical bliss.
Since most recordings being digital now days sound rather
anal or analytical type A preamps often get a bad rap and are falsely
labeled with these two adjectives. Nevertheless, hard core
audiophiles will often accept nothing less. Unfortunately
these "hard-core" audiophiles didn't get that way without
spending as much on stereo gear over the years as the average American
spends on their first house. They have the cost no object
sources and have spent years collecting nearly flawless recordings
so for them a type A is the only possibility worth considering when
choosing a preamp.
that, for the rest of us who still choke a little bit when we tell
people our CD players cost almost a thousand dollars because it
took some sacrifice to come up with that cash, welcome to the real
world. In the real world of majorities and averages the bottom
line involves listening to CD players and CDs where the recordings
are not all produced by Maple Shades, Chesky or Shefield Labs and
so on. So it goes without saying a large part of the music
we all listen to was not recorded live two-track using tube microphones
by skilled engineers who's sole objective is to impress fellow audiophiles.
this mean? Basically you can have the best tube amps and speakers
in the world and it's not going to change what's on that recording.
If the recording is dry, lacks dynamics, sounds compressed or
two-dimensional then that is exactly what you are going to hear.
TYPE B preamp - a magic device not unlike a good phono cartridge
that makes what comes out sound better than what went in. Is
this possible? Yup. In fact there has been many manufactures
who have addressed this goal with their products. Unfortunately
most simply came up with products that were so poor at resolving
detail and timbre that they veiled or homogenized the recording
to a point where all of the annoying things in the recording were
no longer emphasized and often missed entirely by the listener.
The result was - well, less annoying listening experiences
with sub par recordings.
(at least in my observation) the majority of audio gear today. You
may think it sounds pretty good but it all stems from a point of
reference. When you hear REALLY good stuff for a period of
time and go back to the mainstream audiophile crap that's been shoved
at you all these years you quickly realize that it actually sucked.
Whoops, I'm probably getting a little too honest there.
back to the story. I have been in the infamous (yes
that's what I mean) listening room at the Dennis test facility many
times. It's 1/2 glass with wood floors, no drapes, low ceiling,
no rugs, no furniture. Certainly it possess a huge potential
for poor acoustics. The only time the sound in this room impressed
me was one night when I inhaled a gas station sandwich and chugged
a couple beers. I got instantly sick, a cold sweat came over
me and down I went. While laying there on the floor roughing
it out for the next 30 minutes or so I was really rather impressed
with a 24 bit recording we listened to - but that was the only time
I really got off on the sound in this room. Of course in the
interest of fairness I have heard things sound respectable in there
at least a good portion of the time. This is what makes
this test facility so valuable to me.
night I arrived with a couple new toys to listen to, specifically
the new type B preamp we're selling called the SE84CSP. Prior
to hooking it up, I suggested we get everything that was already
there playing for a period of time - at least until it started sounding
good. Once it starting sounding good we would replace the
preamp in the system with the CSP and observe the changes. Of
course as always, the first 10 minutes of sound made me wonder why
I even wasted my time coming over. It was simply really bad.
But after the usual rotation of people checking how the speakers
were hooked up & playing with all the knobs and switches it
turned out to just be a dirty tube socket in the main amplifier.
Everything was going to be okay.
the next hour of listening I sat there as I usually do with fantasy's
about room treatments and how much better it would make things sound.
Now, this is important. The reason I often fantasize about
room treatments here is because just when you start to enjoy the
sound of something, a note or passage in the music comes up and
spanks you on the forehead. It's so annoying. And
the bass often never seems right, making you wonder if the speakers
are in the right location or perhaps just designed to always get
it wrong. Has this ever
happened to you? Well, I know it has, it does,
and probably will many more times before its over.
On this particular night I had formulated in my mind a specific
plan to address all these room issues and fully intended on making
a future unannounced visit with a truck load of treatments - if
for no other reason than to prove to myself that I was right.
main amplifier at the Dennis test facility is an original SE34-I
single-ended triode of around 7 watts per channel it is sometimes
easy after a few beers to run into volume problems. You know
the deal, it starts sounding really good so you push it a little
harder, it gets better, you go a little more, it starts to get worse.
Specifically certain notes or passages in the music become
hard or brittle, so you reduce the volume to a more sane level and
everything gets fine again. Well last night was no exception
and even though I've heard it get substantially louder in the past,
I can't say that it ever did with the recordings we were listening
to at the time. I probably said, or at least thought, "put
in a decent recording so we can crank it up". I usually
Time to swap
in the new preamp. Do not change the selected recordings,
lets just see what it can do with what we're listening to. The
preamp was installed, someone pushed play, the volume adjusted to
the same level we had been struggling with all evening and suddenly
it got really really good. I knew it probably would be, but
I didn't know that my fantasy's about installing room treatments
would simply and abruptly end.
was really shocked because each and every note, and "dangerous"
passages in these non-audiophile recordings was suddenly balanced
and well behaved. Nothing would fall apart. It wouldn't
shout at you. It sounded good. (For the first time I
realized that this room didn't require room treatments) After
a short time of amazement we realized we could turn up the volume
without negative consequences and did. Then after a bit, we
turned it up some more. Amazing - it just wouldn't sound bad
and was now playing way louder than should even be possible at 10
times the power level we had. This was another epiphany for
me as I realized just how valuable this preamp actually was. It
had a way of making music out of pure crap. It let the notes
hang there in the air with long articulate decays that were to put
it mildly, seductive. Of course I knew it would do that and
was anxious for Dennis and Paul to witness it. But I had no
idea it would regulate and govern recordings with such grace as
it did. And I think everyone would agree it did it with no
loss of detail, in fact quite the opposite. We were simply
hearing WAY more music come out of these recordings and with the
best overall balance I've heard in this type of system. The
only thing that I can say I have heard with this type of finesse
is my reference vinyl rig in my personal
listening room. And I have to say that the rich harmonic
content that oozed from every CD we played was much closer to analogue
than it was to digital.
Now, you might
be thinking, okay, the preamp that was swapped out for this new
CSP must have been a real piece of crap to evoke such a contrast
and I would accept that assumption in most cases if this story was
told to me. But the shocker is that the preamp we replaced
was good. It was one of my own SE84CSP type B preamps!
folks, it's always a point of reference equation. We all thought
the original CSP was good. Me, Dennis, Paul, and quite a large
number of customers who own one are raving about it. Damn,
here's more honesty - fasten your seatbelts. The original
CSP was and is in fact very good, this new one is just better. Better
sonically and more user friendly. The problem with the original
CSP was that because of it's rather esoteric SRPP output stage,
you have to run really GOOD spec tubes in it. Once a customer
starts tube rolling with it, it can develop noise and or hum problems.
You might say, well,, so, just run the factory tubes in it.
Many still are I'm sure. But once a person who is into
tube rolling finds a particular 6DJ8 or whatever that he or she
likes the sound of better, the added noise or hum is overlooked.
My feelings on this are A) DECWARE has never produced a product
that hums, and B) Someday someone will visit these original CSP
owners who did roll tubes and bring them a preamp that sounds just
as good, but doesn't hum. Wow! The customer is impressed
and buys the other preamp. He then sells his CSP on Audiogon
or ebay. The new buyer always wanting to try a Decware
product purchases it. He finds it hums and somewhat annoyed
gets on the Internet and blows off some steam about how he or she
tried the supposedly great CSP preamp and it hummed. You can
see my concern. So since this is a brand new product and it's
still early in the game I decided to completely redesign it so that
you can stick any damn tube in it and never have a noise problem
- ever. The result was a rock steady design with an average
hum of 0.7 millivolts which is as good as it gets, and superior
to most. I didn't know until I started voicing the new design
that it would sound better than the original, but it simply did.
I could tell that within 30 seconds even out on my test bench.
I personally gutted 6 brand new CSP preamps before they went out
the door and rebuilt them on my dime. And of course if anyone
with an original CSP and is not happy with it I will update
them too. I should warn anyone in that position that
the two units do not sound the same. The original was more
dynamic, perhaps slightly more detailed. On a really good source
the original is wonderful sounding. Even though it was
a type B designed to make things sound better, I now have to update
the definition of type B to the revised model. By comparison,
the original falls between a type A and type B, while the revised
is solidly and completely a type B.
a type A is usually all I will use in my reference system with the
vinyl, I have spent many hours in my listening room listening to
this new type B and nothing is lost. The music, like I said,
hangs in the air longer. The decays are clearly heard and sustain
is noticeably longer. It's incredibly musical with my 10,000.00
source, and was incredibly musical with a 500.00 CD player. In
my 30 years of this hobby I have never had a preamp that would do
both so well.
Design changes between the original CSP (serial numbers below 020
or so) and the updated model are as follows:
A more classic
circuit design with a straight gain stage feeding a cathode follower.
The original was a cathode gain stage driving an SRPP output stage.
The two output
tubes like before are dual triodes, but now are wired using only
one side of each tube. And the left tube uses the left side,
while the right tube uses the right side. This means that
after your tubes wear out you can simply swap the left for right
channel and you have a fresh set of tubes again! Twice the
driving each stage in the new design have been reduced from around
300 volts to 80 and 90 volts, and the current increased by the same
because of the 62 % drop in supply voltage changing rectifier tubes
will make about 32% more difference on the signature of preamp.
Specifically, the 5Y3GT has the largest voltage drop (around
30 volts more than a 5U4 in this circuit) on the B+ supplies for
each stage. A 5AR4 has less of drop and consequently when compared
to a 5Y3GT increases the B+ supply voltage. A 5U4 has the
least voltage drop so it raises the B+ supply voltage even more.
A 30 volt increase of a supply voltage that was only 90 volts
to begin with is large change. As the voltage changes on this
circuit the signature changes from very euphoric and smooth to having
more force and weight. Think of the 5Y3GT giving you the most
type B signature possible and a 5U4 tilting the scale to somewhere
between a type B and type A, similar to the original circuits signature.
This should make tube rolling with different rectifiers
EXTREMELY rewarding. Of course, as before, the CSP is not
hard on tubes, does not create much heat and can still be left on
24 hours a day 365 days a year with no worries.
Decware is a trademark of High Fidelity Engineering
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2007 2008 by Steve Deckert