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.

4

The pilot lamp on the front of the Phono 3C chassis indicates that the preamp is active. It

12SC7

(L)

Phono input selector switch

Power out to Line 2C preamp

takes about 30 seconds for the tubes to reach operating temperature ready for use. During
operation, is it normal for the power supply chassis to become quite warm to the touch.

The PSX power supply is protected by a 20mm, 1 A, 250 V fast-acting fuse that can be
accessed by removing the fuse drawer from the ac receptacle after disconnecting the ac
line cord. Under normal conditions, it should not be necessary to replace the fuse. If
power fails to come on, you can check the fuse and replace with a spare if necessary. A
spare fuse is also located within the fuse drawer. If the fuse blows a second time, you
should not try to operate the unit. Contact Mapletree Audio Design for information
regarding service.

Input/Output Connections______

12SC7
(R)

Power cutoff switch
(normally left in ON position)

Power In

Power in from PSX power supply

ON

OFF

Line 2

(if sharing PS 2C power supply)

12SN7

GndOut

Ph 1

Ph 2

RCA jacks are provided for two stereo phono inputs, selectable using the toggle switch
located between them, and one stereo output. The same ground binding post is used for
both inputs. Left channel jacks (white) are uppermost.

Tubes____

The vacuum tubes supplied are new-old stock (NOS) and have been pre-tested. A burn-in
period of several hours may be needed to achieve the best sonic performance. Tube life
should be thousands of hours. Aging tubes may result in a reduced gain in one or both
channels or an increase in noise levels. Infrequently, a heater may burn out which is
indicated by total loss of sound. Replacement tubes can be obtained from several
suppliers in the U. S. and Canada. Some listeners enjoy trying different brands and
variants of tubes. The highly regarded 12SX7GT is equivalent to the 12SN7GT.

Warranty___

Mapletree Audio Design warrants the materials and workmanship (parts and labor) for a period of 2 years
to the original purchaser. Tubes are warranted for 90 days. Electrolytic capacitors are heat sensitive with

lifetimes that vary with usage and are not covered by the warranty. Warranty service does not include
shipping costs.

5

Phono 3C Specifications______

RIAA equalization: 20 Hz–20 kHz ? 0.5 dB (typically ? 0.3 dB)
Gain: 40 dB ? 0.5 dB with 470K load (connected to Line 2B)
Output impedance (1 kHz): 2.5 k?
Input impedance: 47 k??for both inputs

Hum and noise at output: less than 2 mV rms
Phase: inverting
Power requirements: 30 W (12 VDC@0.6 A; 200 VDC@10 mA)

Phono 3 Equalization (average of L and R)

Gain = 40 dB +/- 0.5 dB

Hum and Noise: < 2 mV

30

20

10

0

dB

-10

-20

-30
1 10 100 1000 10000 100000

Frequency (Hz)

6

Mapletree Audio Design

(if sharing a PS 2 power

L. Phono

inputs

Gnd.

R. Phono

inputs

© Copyright Lloyd Peppard 2009-15

Ph 2

Ph 1

47,5K

chassis

Ph 2

Ph 1

1%

47,5K

47,5K

1%

47,5K

1%

1%

12n

3.3M 1%

12n

332K 1%

+61 V

3

6

332K 1%

3

3.3M 1%

0.1u/400V

2

1

0.1u/400V

2

6

Phono 3C Preamplifier

47.5K

+

L. Output

1M
1%

R. Output

22.1K

100u

400V

+166 V

820p

820p

7.8n

221K

1%

4

221K 1%

4

7.8n

5

4

Gnd. Bus

400V

5

4

12SC7

432K 1%

1

432K %

3.3M 1%

12SC7

432K 1%

1

1

432K 1%

3.3M 1%

0.1u

400V

0.1u

½ 12SN7

221K

1%

1

1M
1%

½ 12SN7

221K

1%

4

1M

1%

3

6

5

2

1.5u/400V

47.5K
1%

1M
1%

1.5u/400V

Rev. June 13/15

+

100u/400V

2.2K

+

7

7

12 VDC

8

8

_

12SN7

12SC7

12

½ W

5%

5.1K 2W

7

8

12SC7

+200 V

Power

4

3

Power In

4
1

23

Power Out

to Line 2

suppl;y)

1

2

1

Gnd. Bus

7

Mapletree Audio Design Preamplifier Power Supply PSX

© Copyright Lloyd Peppard 2012-15

Rev. June 22, 2015

120AC 60 Hz

1A/250V

L

N

Chassis

Power

115

VAC

115

VAC

115

VAC

115

VAC

115

VAC

115

VAC

10

VAC

10

VAC

230 VAC

25 mA

10 VAC

2 A

100 V

6 A

MUR180

100/400

+

10000/25

+

6.8K/5W

100/400

LED

2.2K

+

330K/1W

1

4

23

Power Out

rear view