Mapletree Phono 3C User Manual

12SN7

12SC7

(R)

Phono 3C Phono Preamplifier

12SC7
(L)

User’s Manual

Revised June 22/15

Mapletree Audio Design

Lloyd Peppard

R. R. 1, Seeley's Bay, Ontario, Canada, K0H 2N0

[phone]

hollowstate.netfirms.com

[e-mail]

© Copyright Lloyd Peppard 2013-15

2

Power switch

IEC AC receptacle

Introduction _

The Mapletree Audio Design Phono 3C Phono Preamplifier is part of the modular series
of components that includes the Line 2C line preamp, the Ultra 4C phono/line preamp,
the LR 1 line router, and the PS 2C and PSX power supplies. The features of the Phono
3C include:

? ? Compact chassis layout and separate power supply for low noise.
? ? Exclusive use of New Old Stock (NOS) 12SN7 and 12SC7 octal tubes, known for

low distortion and musicality.

? ? Low output impedance (<2.5K? ).
? ? RIAA equalization within 0.5 dB, 20 Hz – 20000 Hz.
? ? Use of polypropylene film signal coupling capacitors.
? ? 40 dB gain suitable for all MM cartridges when used in conjunction with a line

preamp with at least 10 dB gain.

? ? Selector switch for two separate phono inputs.

PSX Power Supply Connections_______

Pilot

Power Out jack

For operation with a separate line preamp, headphone amplifier or integrated amplifier,
the Phono 3C is supplied with the PSX power supply, which provides high voltage (B+)

3

and heater voltage (A+) for the preamp. The physical separation of amplification and
power supply units eliminates induced hum originating from power supply circuitry and
components. The PSX provides 12 VDC at 0.6 A for the tube heaters and 200 VDC at 15
mA for the B+ plate voltage. A power interconnect cable provides power from the PSX to
the Phono 3C chassis (“Power In” jack) as shown below.

Power In

12SC7
(R)

ON

OFF

12SN7

GndOut

Line 2

12SC7
(L)

Ph 2

Ph 1

The power supply chassis is connected to the AC line ground but is otherwise isolated
from the preamp chassis, which is connected to the signal ground. This eliminates the
possibility of ground loops between the two chassis, through the signal interconnect
shield and the ac line ground circuit, which can produce hum.

Note: The power output jack labeled “Line2” on the rear panel of the Phono 3C is
used only when sharing a PS 2C power supply with a Line 2C preamp. Separate
user instructions are provided for this operation, which are not needed if you are
using the PSX power supply.

CAUTION: Do not operate a power supply when it is not connected to a preamp.
Damage to components may result from operating the power supply with no load.

Once the interconnecting power cable is securely attached (use of the locking rings is
recommended) between the PSX power supply and Phono 3C and the line cord is plugged
in, the PSX ac power switch may be turned on.

A separate power switch is located on the rear panel of the Phono 3C, between the
two power jacks. The Phono 3C can be powered off with this switch, which disables
both the plate and heater voltages for the Phono 3C but maintains the power feed to
the Line 2 (if applicable). When using the PSX power supply, it is recommended that
the Phono 3C power switch be left permanently in the “On” position.