5
PHONO STAGE SET-UP
CONT’D
CONNECTING EXTERNAL EQUIPMENT & EXTERNAL ADJUSTMENTS
Connect the turntable to the Phono 1 input RCA jacks (F) and
using a suitable length of interconnect cable, connect the
PHONO 1 outputs (E) to your Sonic Frontiers Line 1, 2, or 3, or
other line level preamplifier input. If there is a ground or earthing
wire on your turntable, connect it to the binding post (H) on the
chassis rear. It is very important to ensure that all connections are
solid and that the RCA plugs on your interconnect cable are of
good quality. It is also preferable to have the same metal to metal
contact on the connectors. Your Phono 1 phono stage uses cus-
tom made gold plated RCA jacks so it is recommended that gold
plated RCA plugs be used. Dissimilar metal to metal contacts can
have galvanic reactions that could cause low level noise, particu-
larly in humid climates. Periodically clean your RCA plugs and
jacks to ensure optimum sonic quality.
THE PHONO CARTRIDGE TO PREAMP INTERFACE
Most phono cartridges have been carefully designed to provide
the flattest and widest frequency response into a specific load
impedance, most commonly 47000 Ohms. Due to mechanical
and electrical design constraints or other special characteristics,
some cartridges require additional resistive and or capacitive
loading to achieve optimum performance.
The Sonic Frontiers PHONO 1 provides the user with the ability to
adust the optimum load values beyond the default 47K5 ohm
input load impedance. Adjacent to the input RCA jacks (F), are
the phono cartridge loading switches (G). Activation of these
switches either individually or in various combinations allows the
user to optimize cartridge frequency response by placing addi-
tional parallel resistance and capacitance (RC) across the phono
inputs. The loading options provided should be satisfactory for
most if not all currently available moving-coil phono cartridges.
The switches are 10 position per channel precision gold DIP
types. Four switch positions provide resistance, four positions
provide capacitance and two are spare user positions. The spare
user positions allow a custom value of resistance and capacitance
to be conveniently switched in. Custom component values may be
easily installed by persons with reasonable electronic soldering
skills on internal terminals provided on the rear panel printed
circuit assembly.
To select a loading value, it is necessary to refer to the position
number on the loading switch(s), (G). The values are as follows:
pF = picofarads = X .00001
K ohms = X1000
Position 1 - 10 ohms (RL1 and RL2)
Position 2 - 100 ohms (RL3 and RL4)
Position 3 - 1K ohm (RL5 and RL6)
Position 4 - 10K ohm (RL7 and RL8)
Position 5 - 47pF (CL1 and CL2)
Position 6 - 47pF (CL3 and CL4)
Position 7 - 100pF (CL5 and CL6)
Position 8 - 100pF (CL7 and CL8)
Position 9 - User 2
Position 10 - User 1
These positions apply to both left and right channels.
Any combination of resistance and capacitance may be selected
by depressing various switch combinations, and will be added in
parallel to the 47K5 nominal input impedance. Resistors divide
when added in parallel and capacitors add. eg., if positions 2,
3, 5, and 6 were selected, the loading value would be 90.73
ohms resistance and 147pF capacitance. As can be seen by the
above example, combinations of resistance result in relatively
minor changes in total resistance. It recommended that for major
value changes, the “user 1” and “user 2” positions be used. To
order alternate resistor types and/or values, please contact the
Parts Connection*. To calculate the possible combinations, use
the following formula:
R1 X R2
R total X 47500 ohms
——————- = R total, and then, ————————–––––– = R load
R1 + R2
R total + 47500ohms
Capacitors simply add in value, eg., 47pF + 100pF = 147pF.
The capacitor values provided may also provide some relief from
RF interference which can occur in urban areas, particularly in
apartment buildings.
The phono cartridge manufacturers’ recommended loading values
is a good starting point. Do not be afraid to experiment with
loading values. This is a controversial issue among audiophiles
and our view is that generally, the loading value is dependent on
several system variables, such as tonearm type/brand, type and
capacitance of the lead out wire, type and location of turntable
grounds, input capacitance of the phono preamplifier, as well as
the systems’ overall sensitivity. All these system variables will effect
the loading value to some degree, and as all systems are differ-
ent, no hard and fast rule holds for a loading value for a given
phono cartridge.
Figure 5
- The internal CUE/MUTE switch is located in the rear
right of the main circuit board.
CUE/MUTE
two position DIP switch
* The Parts Connection Toll Free Order Line 1-800-769-0747
Tel: (905) 829-5858 Fax: (905) 829-5388
E-Mail: [email protected] Web Site: http://www.sonicfrontiers.com/TPC
