Line 2B SE Stereo Line Preamplifier
Contents
1. AUDIO DESIGN Line 2B SE Stereo Line Preamplifier User s Manual Revised Nov 18 13 Mapletree Audio Design Lloyd Peppard R R 1 Seeley s Bay Ontario Canada KOH 2NO 613 387 3830 www mapletreeaudio com info mapletreeaudio com Copyright Lloyd Peppard 2002 2013 Introduction The Mapletree Audio Design Line 2B SE Stereo Line Preamplifier is part of the MAD Modular Series of preamp power supply components It offers the audiophile a number of desirable features Compact chassis layout for use with separate power supply for low noise Exclusive use of NOS 12SN7GT octal tubes known for low distortion and musicality Heater voltage switch for use of 6SN7GT tubes if desired Low output impedance less than 500 Ohms Parallel output jacks User specified gains of from 0 to 22 dB Premium Auricap polypropylene film signal coupling capacitors Alps volume control Power Supply Connections The Mapletree Line 2B SE consists of a preamplifier chassis with a separate power supply This allows separation between the two units and eliminates induced hum originating from power supply circuitry and components The Mapletree PS 2 or PS 2a power supplies provide 12 VDC regulated at 0 6 A for the heater supply and 200 VDC at full load 12 mA for the B plate supply The PS 2a has dual power outputs that allow the Phono 3 phono preamp to share the power supply with the Line 2B The power conn2. insulated from chassis VAC 3 F Power Supply Parts List Reference No Description 6A 200V diode bridge Dual 50uF 50uF 500V electrolytic capacitor 10000uF 25V electrolytic capacitor 1N4007 diode 10 mA LED MUR180 high speed diode 800 V 1A 250V fast action fuse 3 pin chassis jack IEC ac line receptacle TL780 12 voltage regulator 6 8K 5W 5 wire wound resistor 220K 1W 5 metal oxide resistor 1 8K 1W 5 carbon film resistor SPST power switch 250 V rated 230 VAC 25 mA power transformer 14 VAC 1 4 A filament transformer 6 3 VAC 0 9 A filament transformer 6X5GT rectifier tube
3. on how you ordered your Line 2B SE the line input gains may be different The standard configuration is 10 dB for all inputs Consult the invoice included with your shipment to verify the gains for your unit The upper jacks are the left channel The line input impedance resistance is normally 100 k which provides minimal loading of any line source such as CD DVD player tape deck tuner or PC sound card If one or more inputs have been configured for other than the 10 dB standard gain the input impedance will be affected See the schematic diagram for details The line output impedance is less than 500 which is suitable for connection to a power amplifier through cables up to 10 ft in length The heater voltage switch located next to the power input jack allows you to accommodate either 12SN7GT supplied or 6SN7GT tubes in your Line 2B Note that operation in the 12SN7 position with 6SN7 tubes installed will most certainly damage the tubes E 9 9 9o Eu 9 e o 9 Preamp Controls The front panel controls of the preamplifier include a three position source selector switch to select between one of the three line inputs balance control and volume control that acts on both channels a EH LINET LINE2 LINE3 BALANCE VOLUME Mapletree Audio Design Line 2B SE Stereo Preamplifier zi EN Tubes The vacuum tubes supplied are new old stock NOS and have been pre tested A burn in period of sever
4. al 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 Mapletree Audio Design will attempt to provide replacement tubes to customers at cost plus shipping Some listeners enjoy trying different brands and variants of tubes The highly regarded 128 X7GT is equivalent to the 12SN7GT The heater voltage switch permits the use of 6SN7GT tubes including the 5692 variant and currently manufactured types Parts List Part No Description C2a b C4a b 1 0uF 200 V polypropylene film capacitor C3a b 0 1uF 400 V pp film cap C5 100uF 400 V electrolytic cap D1a b 10 mA red LED J1a b J5a b RCA gold plated phono jack J6 chassis jack power in P1a b 100K dual audio potentiometer Alps P2 100K linear potentiometer R1a b 100K 0 6 W 1 metal film resistor for 10 dB gain see schematic R2a b 511K 0 6 W 196 metal film res R4a b 47 5K 0 6 W 1 metal film res R6a b 511K 0 6 W 196 metal film res R7a b 1K 0 6 W 1 metal film res R8a b 10K 0 6 W 1 metal film res R9a b 1M 0 5 W 196 metal film res R10 5 1K 2 W metal oxide film res Swi 3 position 2 pole rotary switch SW2 DPDT toggle switch hea
5. dB Maximum input voltage 5 V rms Voltage Gain 100 k load 1 kHz 10 dB standard configuration Output impedance 1 kHz 450 Input impedance 1 kHz 100 k Tor 10 dB gain configuration Hum and noise at output max volume less than 200 V rms Phase Inverting Power consumption 30 W Warranty Assembled MAD components are warranted for 2 years to the original purchaser for failure of parts excluding tubes and workmanship Tubes are warranted for 90 days exclusive of shipping cost Service including parts and labor but excluding shipping is free within the warrantee period Mapletree Audio Design Preamplifier Power Supply PS 2 Copyright Lloyd Peppard 2003 13 BR1 C1a b C2 D1 D2 D3 D4 FU1 J1 J2 IC1 R1 R2 R3 SW1 TR1 TR2 TR3 V1 Rev Nov 18 13 Sw FU1 D3 D4 1 Power 1A 250V TR MUR180 6X5GT R1 f 1 5 3 6 8K 5W e a AN O 115 115 VAC 8 H S eC J2 VAC 25 mA o gt l Cia Ctb O 120 VAC 50 60 Hz e 5 IT 50 500 50 500 Reece a ge I pe e Lx m7 ow tes l 4 8 EZT 4 330K 1W Chassis 115 ae O 01 Ji VAC 30 o amp Power Out 3 7 e Rear View TR2 D1 1 5 1N4007 115 VAC 2 6 14 VAC 4 LAA BRI y 6A R3 3 2 lt C2 2 1 8K 115 10000 25 LER VAC 4 e 4 8 La TR3 e 1 5 d 115 7 VAC AAT 6X5 2 6 i 7 4 8 Mounting tab connected to pin 2 115
6. ections to the preamplifier chassis are made through a special power cord that plugs into jacks located on the rear panels of the power supply and preamplifier chassis This manual refers to the PS 2 power supply Operation with the PS 2a is identical CAUTION Do not operate the power supply when it is not connected to the preamp Damage of components may result Once the interconnecting power cord is securely attached between the two chassis and the line cord is plugged in the toggle switch on the front panel of the PS 2 is used to activate the power supply The pilot lamp indicates that the unit is on 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 warm to the touch The power supply is protected by a 1 A 250 V fast acting fuse located inside the power supply chassis 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 Wait 60 sec with the unit unplugged before removing the bottom cover 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 The signal input output jacks are located on the rear panel of the preamplifier chassis RCA jacks are provided for three stereo line inputs and two stereo line outputs Depending
7. ew oT S Loo o 12V 6v 9 8 8 Sw2 6 12SN7s Heater Voltage 6 Circuit Operation Both channels are identical as shown in the schematic diagram Operation will be described for the left channel The selector switch SW 1 selects from one of the three line inputs jacks J1 J3 Series resistors R1 determine the gain of each line input The maximum gain with zero resistance is approximately 22 dB The selected signal is applied to the grid of the first section of the 12SN7GT which is configured as a common cathode voltage amplifier with current feedback The output from this stage is capacitor coupled through C2 to the top of the volume control potentiometer P1 The signal at the wiper of the level control is capacitor coupled through C3 to the grid of the output stage comprising the second section of the 12SN7GT configured as a cathode follower stage The grid bias voltage is established by R7 and the plate voltage by the sum of R7 and R8 The operating conditions are chosen to provide the maximum possible output voltage swing around 13 V rms The output voltage is taken from the cathode of this stage capacitor coupled to the output jacks J4 and J5 through capacitor C4 The gain of this stage is less than unity but the output impedance is sufficiently low less than 500 to enable driving capacitive interconnect cables without high frequency loss Specifications Frequency response 100 k 50 pF load 1 V output 10 Hz 20 kHz 0 2
8. ter voltage 12SN7GT tube Mapletree Audio Design Line 2B SE Stereo Line Preamplifier Copyright Lloyd Peppard 2002 2013 Rev Nov 4 13 Gain dB Ri 1 0 340K 18 5 182K B 3 10 100K A 4 12 68K Input resistance R1 4185 V 5 6 15 47K 210V 8 18 24 6K R4a Via 10 20 221K En 7 5K 1 6 12SN7GT J3a 3 G O J2a mid sWia 75V 4 Pla C3a L Line inputs 2 QU AN o Source i Volume 0 1 400 JiaR1a 2 7 100K Auricap XO 16 Onto AA 1 1 0 200 49 V L outputs R1a 1 i ia Auricap XO A IN 4 C4a 100K 1 1 0 200 O J4a chassis i er FiG 6 Auricap XD areplaces R1a 1 2 3i 54V I custom gains are not 511K C J5a I required 5i 196 Z R7a a 1K1 l 10 mA red LED T X R9a l R8a 1M I 10K1 1 J l J l P2 Balance 3 6 12SN7GT i l 185 V R4b I R2b 47 5K 1 Bites l 511K 196 J3b 3 Q VWN o 1 SWib 75 V SB R Line inputs 2 O o Source C2b 0 1 400 Jib 16 AN 1 1 0 200 m l 49 V R outputs R1b 1 Rib IX 4 C4b 100K 1 on 1 0 200 J4b R1b replaces R1b 1 2 3 if a L custom gains are not O chassis required J5b Dib 10 mA red LED R9b R8b im 10K1 1 Ground bus LG B O 185V A 4210 V R10 5 1K 2W e 7 AAA B C11 A 100 400 E 12 VDC gt d Power In e s Rear Vi
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