Hafler DH-110 manual Additional Information, Rl Value Kohms Desired Load Kohms

ADDITIONAL INFORMATION

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

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:

-93.1

Rl =

1 - 93.1/RT

To simplify, the following standard 1% values of Rl will provide desired loads RT as shown (all in Kohms):

Rl Value Kohms	Desired Load Kohms
11.3	10
17.8	15
24.9	2 0
34.8	2 5
44.2	3 0
56 .2	3 5

Metal film type resistors are recommended for lowest noise.

So far we still need			140 pF
Subtract the DH-110 input capacitance			= - 3 0
Compensation	capacitor	required	=110 pF
This is close enough to	the 120pF	supplied that	Phono 1 can

be used without change.

16