The OEM CD-38 uses a standard (low-cost) opamp. This opamp has a lot to do -which in
fact is also a part of its problem-. It has 3 functions at the same time: acting as an I-U
converter, taking care of the filtering and being the cd-players outputstage. The choice
for all this isn't strange as this machine was designed to be very cost-effective.
Anyway, this standard opamp is removed and replaced by the best available Burr Brown
opamp. In the AH! Tjoeb '99 modification this Burr Brown opamp has an easier life than the
standard opamp. The Burr Brown only has to take care of the I-U conversion and of a part
of the filtering. The other part of the filtering and the outputstage is found now on the
added tube-board. For maximum future flexibility the Burr Brown opamp is not soldered
direct to the pc-board, but it is placed in a high-quality ic-socket. This way eventual
future upgrades in this part of the circuit can be done by the owner without having to
send back the cd-player.
As with most standard cd-players the OEM CD-38 uses a transistor-designed muting-circuit. Such circuits have proven to be
bad influence on the soundquality. Most simple answer to this is to cut out this muting
circuit and leave it afterwards as it is. However than there is always a risk of damaging
other parts of the system. Reason why we introduced a relay-based muting circuit. This
circuit is only "touching" the signal at the moment there is a possible danger.
Most of the time the owner will only notice a small mechanical click of the relay at the
beginning and the end of the cd and between the different tracks. If you happen to play
home-recorded CDR's you might sometimes hear the click in silent parts of the music. This
is not a fault of the AH! Tjoeb '99 muting system, but it is a fault in the cdr-machine
which recorded a piece of silence as a change of track. As strange as it may sound this is
the case with some versions of the OEM manufacturer's DR-700. If you make a digital copy on this machine (digital is the system which
is supposed to say just Yes and No!) it should not be possible that a silent part on the
original creates a change of track on the copy. However it does. From the OEM
manufacturer (and eventually from us) an Eprom-upgrade is
available. We charge nothing for this Eprom exchange, what the OEM manufacturer charges we don't know.
The most obvious and important modification is the adding of the AH! Tjoeb '99
outputstage. This outputstage with its own dedicated powersupply is designed around 2
"old-fashioned" 6922 tubes which found their place between some "modern
times" SMD parts. The powersupply has been optimised for lowest possible noise and is
implemented in a dual symetric topology for lowest distortion of the single-ended buffer
stage. Because of the SMD parts the AH! Tjoeb '99 outputstage is fairly reasonable in
size. The analog tube stage is based on a feedback-less triode unit (half of a 6DJ8) with
passive first order anti-slewing filtering which is very important in all implementations
of r.f. related digital audio equipment. The outputstage is also based on a triode unit
(the other half of a 6DJ8) used as a Sallen-Key 2nd order filtering buffer, used for
impedance matching and consequent relative cable driving characteristics. The original
Tjoeb '98 was built with ECC88 Philips 6922 Jan tubes. Than we had to change to our 2nd
choice, being the same model from the Sovtek brand. However early '99 we have been very
lucky again to find a batch of 5000 military grade Philips 6922 Jan tubes, which have a
fantastic musical influence on the signal fed through. Due to the way these tubes are
used, it is expected that only after 2 or 3 years these have to be replaced.
Inside the OEM CD-38 critical
wiring has been replaced with high quality teflon-isolated signal wire. Wherever necessary
to solder, this is done with 2% silver solder. The standard RCA output connectors have
been replaced with goldplated ones.
Is that the maximum we can do? No way! We absolutely have a few more (proven) ideas to
make this machine sound better. But until now it has always been our goal to build the
best Tjoeb (this is the Dutch pronounciation of the English word "tube") under
HFL 1,000.-. We did not reach that point yet, as the retailprice is HFL 899,-, but we are
still investigating how we get the most improvement out of the last Hfl 100,-. Maybe you
consider this as being (typical?) Dutch or Scottish, but we think it is the only way to
give you the maximum quality for the given money. For your information: Hfl (which is
Dutch Guilders) 899,- is about US 425.- or UK £ 270.-.
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