12SN7
12SC7
(R)
Phono 3 Phono Preamplifier
User’s Manual
12SC7
(L)
Revised Dec. 22/13
Mapletree Audio Design
Lloyd Peppard
R. R. 1, Seeley's Bay, Ontario, Canada, K0H 2N0
(613) 387-3830
hollowstate.netfirms.com
info@mapletreeaudio.com
© Copyright Lloyd Peppard 2013
2
PSX Power Supply
Introduction _
The Mapletree Audio Design Phono 3 Phono Preamplifier is part of the modular series of
components that includes the Line 2B line preamp, the Ultra 4B phono/line preamp, the
LR 1 line router, and the PS 2/2a/X power supplies. The features of the Phono 3 include:
? ? Compact chassis layout and separate power supply for low noise. The Phono 3 can
share one PS 2a power supply with the Line 2B preamp if desired.
? ? 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, 50 Hz – 20000 Hz.
? ? Use of polypropylene film signal coupling capacitors.
? ? 38 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_______
For operation with a separate line preamp or integrated amplifier, the Phono 3 is supplied
with the PSX power supply, which provides high voltage (B+) 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. The preamp and power supply are connected by a special interconnect
cable that plugs into the 4-pin sockets on the rear of the two chassis as shown below. 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
3
possibility of ground loops forming between the two chassis, through the signal
AC Line cord
interconnect shield and the ac line ground circuit, which can produce hum.
12SC7
(R)
Power In
Ch 1-2/LF Level
12SN7
ON
Out Gnd Ph2 Ph1
OFF
Power interconnect cable
12SC7
(L)
PS 2a Power Supply Connections______
PSX Power Supply
If you purchased your Phono 3 with the Line 2B SE line preamp and are sharing a
common power supply, you will be provided with the PS 2a power supply. The PS 2a
power supply provides high voltage (B+) and heater voltage (A) for both the Line 2B and
Phono 3 preamps. It differs from the PS 2 only in providing two power output jacks. The
physical separation of amplification and power supply units eliminates induced hum
originating from power supply circuitry and components. The PS 2a provides 12 VDC
(regulated) at 1.2 A for the tube heaters and 200 VDC at 20 mA for the B+ plate voltage.
Separate 4-pin jacks are provided for the Line 2B and Phono 3 power connections via
special 4-conductor cables. Pin assignments are as follows: Pin 1: B–, Pin 2: B+, Pin 3:
A–, Pin 4: A+. In order to prevent a ground loop from forming through the common B–
connections (signal ground), the B– feed for the Phono 3 is isolated from that for the Line
2 by a series 12 Ohm resistor in the power supply. In practice, either power output jack
can be used with either preamp.
4
Line 2
123
4
AC Line cord
2
Power interconnect cable to Line 2B
6X5GT
12SC7
12SC7
(R)
(R)
Power In
Power In
12SN7
ON
Out Gnd Ph2 Ph1
OFF
12SC7
(L)
Power interconnect cable
Phono 3
1
3
4
Power Supply Operation______
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(s) are securely attached between the power supply
and Phono 3 and the line cord is plugged in, the ac power switch may be turned on. A
separate power switch is located on the rear panel of the Phono 3, adjacent to the power
input jack. The Phono 3 can be powered off with this switch, which disables both the
plate and heater voltages. Pilot lamps on both the power supply and Phono 3 chassis
indicate that the power supply is on and when power is being supplied to the Phono 3. It
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 power supply is protected by a 1 A 250 V fast-acting fuse which can be accessed by
removing the bottom cover of the power supply. Remove this cover only after powering
down for at least 60 sec. 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. If the fuse blows a second time, you should not try to operate the unit. Contact
Mapletree Audio Design for information regarding service.
5
Input/Output Connections______
Ch 1-2/LF Level
12SC7
(L)
Out Gnd Ph2 Ph1
12SC7
(R)
Power In
On
Off
12SN7
RCA jacks are provided for two stereo phono inputs, selectable using the toggle switch
located between them, and one stereo output. The centre position of the source selector
switch is a mute position. The same ground binding post is used for both inputs. Left
channel jacks 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.
6
Phono 3 Specifications______
RIAA equalization: 50 Hz–20 kHz ? 0.5 dB (typically ? 0.3 dB)
Gain: 38 dB ? 1 dB with 30 k? - ? load
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 (PS 2a or PSX power supply): 30 W (12 VDC@0.6 A; 200
VDC@10 mA
7
© Copyright Lloyd Peppard 2009-13
Mapletree Audio Design
Rev. Dec. 22/13
Phono 3 Preamplifier
47.5K
0.1u
400V
Gnd. Bus
0.1u
400V
4
½ 12SN7
221K
1%
1
1M
1%
½ 12SN7
221K
1%
4
1M
1%
2
3
1u/400V
47.5K
1%
5
6
1M
1%
+166 V
820p
820p
6.8n
221K
1%
4
221K 1%
4
6.8n
5
4
5
332K 1%
1n
47,5K
1%
47,5K
1%
10n
3.3M 1%
1n
10n
L. Phono
input
Gnd.
chassis
R. Phono
input R. Output
chassis
+61 V
3
6
332K 1%
3
6
3.3M 1%
0.1u/400V
2
1
0.1u/400V
2
1
1
1
12SC7
432K 1%
432K %
3.3M 1%
1n
12SC7
432K 1%
432K 1%
3.3M 1%
1n
L. Output
1M
1%
1u/400V
22.1K
+
100u
400V
1.8K
7
8
12SN7
5.1K 2W
+
100u/400V
+
7
12 VDC
8
_
12SC7
12SC7
Gain = 38 dB @ 1kHz with 33K load
Noise < 2 mV
Output impedance < 2.5K
+200 V
7
4
8
3
Power In
1
2
1A/250V
L
N
Chassis
Power
120AC 60 Hz
115
VAC
115
VAC
115
VAC
115
VAC
Gnd. Bus
PSX Power Supply
Hammond
229A230
115
VAC
115
VAC
10
VAC
10
VAC
230 VAC
25 mA
10 VAC
0.6 A
100 V
6 A
MUR180
100/400
+
10000/16
+
6.8K/5W
100/400
LED
1.8K
+
330K/1W
1
4
23
Power Out
rear view
Triad FS20-300
8
Mapletree Audio Design Preamplifier Power Supply PS 2a
© Copyright Lloyd Peppard 2012-13
Rev. Nov 4/13
L
N
1A/250V
G
120VAC 60 Hz
Chassis
Power
115
VAC
115
VAC
115
VAC
115
VAC
115
VAC
115
VAC
115
VAC
25 mA
115
VAC
14VAC
14VAC
MUR180
14VAC
1.4 A
6.3 VAC
0.9 A
6X5GT
3
5
6.8K 5W
8
7
2
6X5
+
50/500
6A
+
10000/25
+
50/500
330K/1W
1N4007
+
12 V
1.5 A
12
1 W
1
4
2
3
1
4
3
Line 2 Power Out
Rear View
2
Phono 3 Power Out
Rear View
7812
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