CD94 MK2
balanced XLR mod with a clock and snip-it output bypass.
February 2008
My second encounter with the 94/2. This player, especially in
champaigne finish - is visually irresistible. 10 out of 10 for visual
design in my book.
Inside, what I appreciate is that the DAC -holding PCB is easily
accessible and removable, so I can work on it easily from both sides.
This time I will try to find out what happens if:
1. I use both "phases" of the DAC output and make this player really balanced
2. I add a super-clock
3. I use my snipit technique and use the available signal BEFORE it
gets destroyed by the analog output stage although without using
any tubes whatsoever.
Concerning 1. - I have no comments. The balanced signal works as
expected (before some fool at Marantz decided to sum it into SE ). If
you have a truly fully balanced amp (like I do) you have no choice but
to take the only logical step and convert the CD into balanced.
The two DAC chips are stereo ones, both have left output as well as
right output, but their respective digital inputs is phase reversed 180
degrees (the chip that does that sits in the small PCB mounted on side
wall which has optical toslink output on it.)
So our job is not really a CONVERSION TO BALLANCED but rather
un-winding - removal of single ended summation which takes place in the
second op-amp after dac chip outputs. This happens on main PCB, after
the signal goes from DAC pcb to main pcb by means of 6 steel rods.
Concerning 2 - I added the clock with separate power supply and
transformer, but I can't swear that this is audibly superior. It
surely does not hurt.
Concerning 3 - First op-amp must be kept because the output of DAC is current type - not readily usable for driving the amp.
SO what we do we first trace down the 6th and 25th leg of TDA to
respective opamps mounted close by, and we identify the output leg of
that op-amp.
If the input is number 2 or number 3 - the output is no. 1. If the
input is leg 5 or 6, the output is 7. One dual op-amp will be then
channel left, pos and neg, and the other dual op-amp will be right pos
and neg.
While doing this we may observe that the signal from DAC to op-amp will
have additional UNNECESSARY filter of RCR type. We should get rid of it
by means of lifting the resistor - the first R in this RCR. See photo
for details.
After cutting away the HF filter, we will have good signal on the
op-amp. To make this signal GREAT we must cut the following second op-amp
away. This is tricky - we cant just cut the first op-amp near its outputs,
because we must keep the first op-amp feedback loop. We can not simply
pull out the second op-amp, because it would still present the second
feedback loop in passive mode to our signal.
So to get rid of the second op-amp, we must carefully break the link in
between them. We do it by lifiting resistors Rxx and Ryy.
Since the first op-amp which we decided to keep has DC offset present
on the output leg (usually circa 2,5 V DC) we must block it by
using a capacitor leading to the new solid RCA and XLR outputs. We must
buy 4 good caps, I recommend of course copper foil paper in oil caps
from Jensen or Audionote. In this case we can use 0,22 uF or 0,33 or
max. 0,47 uF. If we use MKP polypropylene cap, we can go up to 4 uF or
so.
This player does not have much room for XLR outputs (remember these are
male) but we can fit them . Don't try to drill the 24 mm holes
with rear panel installed. You MUST detach it and drill
against the solid wood support.
The sound quality resulting from the above described one hour mod is
nothing short of spectacular. This is very very close to perfection, as
far as redbook CD format is concerned.
Highly recommended.
In the future, if you wanna go for Lampizator, all the work will pay
off. Just mount lampizator in place of the first op-amp - and all will
be super!!!
That is what I will use as my new reference player which will superceed the Grundig 9009.
P.S. While doing all this I advise to:
1. mount the op-amp sockets and experiment with different, newer types
of chips, usually better than the stock one (it is 22 years old,
remember)
2. replace all electrolytes on the DAC pcb with os-cons or blackgates or 10 uF MKP's
3. As a final touch - you may want to convert this player to non-oversampling, which will elevate it from superclass to absolute top elite. Thats what I will do for myself. (see the NOS mod HERE: the Marantz mod description in detail.
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