D.B. Systems - DB Systems DBP-6 Phono Capacitor Loading Kit

D.B. Systems



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Many moving magnet cartridges (the most common type by far) are strongly affected by the amount of capacitance load on their outputs. That is, it is not sufficient to connect them to a phono input with the typical value of 47.000 ohms input resistance without being concerned with the total capacitance load as well. This total is the sum of the cable capacitance from the turntable (probably in the range of 80 to 200 picoFarad, or pF) and the input of the capacitance of the phono preamp (0 to as high as 600 pF). If this total is less than the recommended load for the cartridge, then more capacitance is needed. With the proper value of capacitance loading, the flattest frequency response is obtained.

If such a cartridge has too little capacitance, it may dip in output at the 5 kHz range and peak in the 10~20 kHz range. The peak is an electrical resonance between the inductance of the cartridge and the total capacitance load and is not related to the mechanical resonance which is in about the same frequency region. The effect of increasing capacitance is to move the electrical peak down in frequency, filling in the dip in order to get the flattest response.

The sonic effect of too low a capacitance is a recessed quality to the upper treble, with a metallic edge to the very highest frequencies. This is most audible on brillant and forward recordings of percussion such as brushed cymbals.

There are three ways to determine the correct value of capacitive loading:

  1. Find out the cable capacitance of your turntable, add the input capacitance of your phono input (100 ohms for the DB-1A) and subtract from the cartridge manufacturers recommended load. However, cartridge to cartridge variation may mean that the optimum load will be different from the calculated one.
  2. Use a test record (such as the CBS STR-100 or STR-130 (RIAA pre-emphasized)) and an AC meter to obtain flattest response, after the capacitance is varied.
  3. Starting from 1., vary the capacitance to obtain the best sound. For the non-technical user this may be the best approach.

Using the DBP-6 KIT  Remove the turntable cables from the phono inputs. Plug the "Y" adapters into the left and right phono inputs. Plug the turntable cables into one leg of each of the "Y" adapters. The appropriate capacitor plug is then inserted into the unused leg of the "Y" adapter. The phono plugs are color coded to identify their value. Please note that each "Y" adapter has about 70pF of capacitance, so the plug for the 250pF actually contains a polystyrene 180 pF capacitor. The color coding is as follows:

150 pF       Brown

200 pF       Green

250 pF       Red

350 pF       Orange

450 pF       Yellow

A 100 ohm load plug (Black) is also provided for experimenting with matching moving coil cartridges as well as two additional empty plugs for custom loads.

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