In this article
we will finally make some REAL progress in dealing with
a transport digital signal S/PDIF going to the DAC. Did I
mention a green marker pen - ? NO Do you think it
is about VRDS clamp system? NO Is it about belt
drive transport ? NO (oh I am sure the belt helps a
lot !) Is it about the
air pump suspension ? ? NOOOO. Do you suspect
it is about WADIA 10.000$ bargain transport? Anybody? Golden
cones? Silver/gold digital cables with plugs machined
from one block of solid beryllium?
I have read
hundreds of reviews of transport players, some of them
costly toys for boys. I read in Stereophile, in Hifi Choice, in FI, in
What hi-fi, in various Polish rags - and NONE of them, I repeat not a
single article if memory serves me showed the scope trace. The
most basic fundamental
test - see on the scope if square looks like square. But NO. Nobody
did. Hey writers
RETURN YOUR SALARIES BACK. If they didn't,
I did. I took the scope and looked at over 10 different
players, most of them costing A LOT of money back then when they were
new.
I analysed over
25 schematics and I reached the conclusion that all
these player's digital trace and all schematics of outputs look
BAD. Some of them better than others, some - so-so, and some just plain
bad.
What
particularly annoyed me is that the signal trace is so sensitive
to
small changes of the load - resistance, capacitance and inductance.
That's why digital cables sound different from one another - because
the transmitter is not optimized. It is weak. Its output impedance is
10 times too high or even more.
THIS IS ALL
WRONG. No amount of "price" no wooden cheeks, no marble
slabs and no siltech gold cables can make wrong S/PDIF signal good
again.
Only dealing
with the problem can do it. Thinking can do it.
Engineering can solve a lot of problems. Lets try to design the damned
S/PDIF from scratch. In fact, perhaps
the transport engineering and marketing has the
HIGHEST content of bullshit from any other hi-fi product. And
almost no practical information.
LET'S LAMPIZE
S/PDIF !
(a
disclaimer for people who take things too seriously: this is a funny
experiment done just for fun and I do not suggest that you should do
the same although you may.) Ladies and
gentlemen (what Ladies ? Women don't come to these
pages anyway) this is the WORLD'S FIRST - THE REAL DEAL - DIGI-LAMPIZATOR. This is purely
my own invention, my dearest baby. This is my greatest
contribution to Hi-Fi so far.
MY REASONING was
this: if all the problems which distort the signal on
the way to the DAC are arising from too weak generator - the Philips
SAA7220 chip - leg 14th, why not make what an engineer should and add a
buffer. The chip will be happy working into virtually no load at all,
just the grid. The square will be perfect as hell. Then the tube will
have infinitely better output impedance (single hundreds of
Ohms) and it will send the signal nice, pure, sharp , stiff and
INDIFFERENT to cable and plugs. No more bullshit about "quality"
of transport and cable - costing a fortune. The quality means sending a
proper signal not deploying voo-doo and mythology. To have a world's
best transport does not mean buying Wadia, Levinson or Theta. It is
about making a good player - a great transport by adding a
DIGI-LAMPIZATOR.
I took the tube
which is good for high frequencies - the Russian 6N14P,
which has a frequency response good till 200 MHz. Our signal needs
circa 20
MHz bandwidth so the tube is ten times "too good" for the job. Any
other radio tube is good, The parameters like amplification etc. do not
matter because it is a cathode follower. The audio tubes are no good
because the frequency range is too low. There are tons of these tubes
around and they are dirt cheap because nobody needs them today. I paid
1 Euro for 5 tubes brand new NOS. TV tubes are good too.
DIGI-LAMPIZATOR
I created a
simple mono triode amplifier in cathode follower. The anode supply
is circa 90 V as should be, the heaters are just
6,3 V AC, no rectification. The cathode is a 75+75 Ohm resistor divider
(150 Ohm cathode load. Output is a 1,5 V DC square from 75 Ohm
resistor. Fully aligned to 75 Ohm characteristic impedance of the
S/PDIF format (and cable). After assembling
the DIGI-LAMPIZATOR I connected the leg 14th of
SAA7220p/B to the tube grid directly. I added a 15 K resistor to ground
the grid and to load slightly the transmitter chip.
BINGO. The
square wave is PERFECT. It beats the stock signal without
sweat. The difference on the scope is night and day. There is no
ringing, no rolloff, all is just excellent. Forget about the expensive
transports. I have yet to see the output trace as clean as this one!
Correct me if I
am wrong, nobody ever did something like that before. The cost of the
tube plus socket plus 3 caps is in total in the single
Euros. The transformer adds 20 Euros. But this makes ANY PHILIPS /
Marantz or Grundig CD PLAYER WITH SAA7220 AN ABSOLUTE CHAMPION OF
TRANSPORTS. Add one os-con in 5V power supply of the
SAA7220p/B chip, add a super-clock- and
you have the best transport that any money can buy. Some people
asked me why is DIGI-Lampizator necessary if in the
Transport article I demonstrated that resistor tweaking and transformer
removal can give already grat results. The answer is that this signal
was good without load. Any different cable, different dac, longer cable
etc would distort the signal again. Because it was produced by the
source which has high output impedance, low damping factor and no
possibility to hold square stiff. The lampizator
makes signal stiff - will be MUCH more tollerant
to variances of what is AFTER the output.
I will play a
little with the system and I will optimize the circuit
and I will post then the final version and the sound description. I
will compare two identical players, one modded and one stock. The first
impression, before comparison to stock player, is very good.
It is easily the best transport I ever had at home. Difference is
audible. Things became
more solid, the sound is very tight and lively, but the
most shocking aspect is the hallucination thing. The accoustic of
recorded event more that ever before produce believable realistic
soundscape. My guess is that
because the datastream is mono, carrying left and
right information alternating in the data packets L and R , The timing
to send them both to stereo DAC is critical. When the timing is really
perfect, the sound of L and R becomes better synchronised. Our brain is
fooled better - it can detect time differences between L and R as
small as single milliseconds - thats how we can "see" with our ears
where the fly flies with eyes closed. Left and righ ear detect
differences in timing of sound arrival to our ears. With precise
digital
signal - time allignment of L and R is much improved. The pleasure of
listening increases by a factor that is easy to detect in few seconds
after hitting PLAY.
I will go to
friend's house and compare my transport with world's best
machine in my opinion - Audiomeca Mephisto (also employing Philips CDM
mechanism, although only low model number 4.)
My schematics -
first revision but already working very well.
The test drive
before making everything nice and neat. (short leads are
critical)
Signal tapping
from the SAA7220p/B chip - leg 14-th.
Original signal
from Grundig 9009 Fine arts and the sameone -really
identical -
was from Marantz CD94 MK2. Both have Philips CDM1 mk2 mechanisms but
very
different schematics. Both use SAA7220p/B for S/PDIF.
The best trace by far was from Sony 555 ESD but that is a really good
machine all around.
I have over 15 different traces waiting to be posted here below when I
crop the jpegs.
Digi-Lampizator
trace of the same machine pictured above - the Grundig Fine Arts 9009.
Just look at the level of improvement.
pp voltage level is 1V
Try to beat that! Anybody? Hey CEC are you there
? Accuphase ?
FInal word and
conclusion about digi-Lampizator:
This experiment was fun. Tube can work as digital transmitter. System
is very stable and provides a lot of pride of ownership. WHAT WE ACHIEVED
SO FAR: We learned, that REGARDLESS OF THE PRICE - be
it 20 Euros or 2000 - all players have basically the same kind of
S/PDIF
output. They use same cheap transformer for separation which corrupts
the signal and which is unnecessary. Regardless of
the price, all players can become good transports if the
signal is cleaned up. The super-clock will
help to avoid jitter - data timing problems, as well as it eliminates
the
high frequency modulations of signals, power supplies and earth in the
player. Superclocks are good to have. On top of that
the digi-Lampizator gives us clean and stiff signal, no more
problems with cables distorting heavily. This output will drive any
cable, even a totally wrong lamp zip cord. No more need for exotic
silver Gucci cables. Of course Gucci cables are nice to have.
The combination of clock, stiff S/PDIF buffer and some anti-vibration
measures give us all we need to have good transport. Adding a super DAC
with lampizator takes us to Nirvana right away (source wise of course)
A side comment -
Sony and Kenwood have best stock form signal traces -
no wonder - they use transistor buffers doing just what my buffer does.
But having tube output is so much more cool !!!!
but for those pragmatic people I have a solution! here comes ...
THE DIGIFETISHIZATOR
As usual with transistor technology, I referred to someone else who
knows this "sand" technology well.
Mr. Dietmar suggested his beloved J-FET to act as my tube - as a
cathode follower.
This circuit is easy to build and easy to fit inside CD player.
It will remove the load seen by the output chip S/PDIF (making trace
much sharper) and it will make output impedance significantly
lower. The circuit will drive any cable and any DAC out there without
sweat.
Remember to use twisted pair from CAT5 cable or just screened coax to
take the signal to the output socket.
