Additional Information - Hafler DH-110 Instructions For Assembly And Operation Manual

RACK MOUNT END CAP INSTALLATION
Every DH-110 is supplied with front panel accessory end
caps which adapt it to a standard 19" rack panel, and with a
5/32" Allen wrench which fits the mounting screws.
Remove all power and signal connections from the DH-
110. On a protected surface such as a towel, remove the
two cover screws on each side of the bottom, and slide the
cover back. Remove the screws in each corner of the front
panel. Exchange the end caps-they slide outward. If you
are careful, you will not dislodge the LEDs from the panel.
Replace the cap screws and nuts only finger tight at first.
Check the alignment of the panel around the knobs before
tightening fully. Then replace and secure the cover.
PHONO CARTRIDGE CAPACITOR LOADING
The cartridge manufacturer usually specifies in their
instructions the optimum 'load' or termination for the car-
tridge. The needed capacitance is expressed in picofarads
(pF). The DH-110 is supplied with pairs of two values of
capacitors plugged into the sockets behind the rear circuit
board at the Phono inputs (one for each channel). One of
these values is likely to accommodate the majority of
available cartridges with most high quality connecting ca-
bles within the accepted tolerance of ±5OpF If no informa-
tion is available, we suggest first trying the 120pF which is
installed in the Phono 1 input.
The total capacitive load is the sum of three numbers:
Turntable cable capacitance (from its manufacturer)
+ Preamp input capacitance (DH-110 = 30 pF)
+ Compensation capacitor (value you desire)
= The specified load (from the cartridge manufacturer)
You need to know the cable capacitance, from either the
turntable maker, or the cable supplier, if they are separate.
Unfortunately, this is not always readily available, and it
can vary widely, but lower capacitance cables invariably
are more expensive. If you must guess, use 60pF per foot.
If your turntable accepts plug-in cables, you can usually
overlook its internal wiring capacitance, as it will likely be
within the 50pF tolerance. Short cables are desirable
because total cable capacitance can itself be higher than
the total specified load. The lowest you can go in compen-
sation is to leave that capacitor out. It is why a good
preamp design has a low input capacitance.
As an example: Recommended cartridge load= 320 pF
The turntable has a three foot cable, and
they say it is 60pF/foot. Subtract 3 X 60 = -180
So far we still need
Subtract the DH-110 input capacitance
Compensation capacitor required
This is close enough to the 120pF supplied that Phono 1 can
be used without change.
16

ADDITIONAL INFORMATION

If you require new capacitors, we suggest that you
purchase, if possible, either polypropylene or polystyrene
types. These premium grades have been selected for all
critical circuits in the DH-110 because of their superior
audio performance. Their leads should be formed like
those presently installed, and they must extend at least ¼",
but not more than 3/8" beyond the capacitor body to avoid
a short circuit to the back panel.
Some fastidious users prefer to solder the compensation
capacitors in place once a final value has been determined,
to preclude any less-than-perfect socket contact as time
passes.
PHONO CARTRIDGE RESISTIVE LOADING
As supplied, the phono load resistance of the DH-110 is
46.55K ohms, which is accurate loading for most car-
tridges. This value may be changed if need be, by replacing
Rl and RlOl on the main circuit board. See the board dia-
gram in the center of the manual.
The input resistance is determined by the parallel com-
bination of Rl (101) and R2 (201), each of which is 93.1K
ohms (white, orange, brown, red). A different value of Rl
(101) will change the desired load to the value RT in accor-
dance with the formula:
To simplify, the following standard 1% values of Rl will
provide desired loads RT as shown (all in Kohms):
Metal film type resistors are recommended for lowest
noise.
140 pF
= - 3 0
=110 pF
-93.1
Rl =
1 - 93.1/RT
Rl Value Kohms Desired Load Kohms
11.3
17.8
24.9
34.8
44.2
56.2
10
15
2 0
2 5
3 0
3 5