Download Line 2B SE Stereo Line Preamplifier
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Modular Series 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, K0H 2N0 (613) 387-3830 www.mapletreeaudio.com [email protected] © 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 connections 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 2 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 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. 1 Line 12SN7 2 Out 1 3 In 2 1 L R 6SN7 3 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. 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. 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 12SX7GT is equivalent to the 12SN7GT. The heater voltage switch permits the use of 6SN7GT tubes including the 5692 variant and currently manufactured types. 4 Parts List______ Part No. C2a,b, C4a,b Description 1.0uF/200 V polypropylene film capacitor C3a,b 0.1uF/400 V pp film cap. C5 D1a,b J1a,b–J5a,b J6 P1a,b P2 R1a,b R2a,b R4a,b R6a,b R7a,b R8a,b R9a,b R10 SW1 SW2 V1a,b 100uF/400 V electrolytic cap. 10 mA red LED RCA gold plated phono jack chassis jack (power in) 100K dual audio potentiometer (Alps) 100K linear potentiometer 100K 0.6 W 1% metal film resistor for 10 dB gain (see schematic) 511K 0.6 W 1% metal film res. 47.5K 0.6 W 1% metal film res. 511K 0.6 W 1% metal film res. 1K 0.6 W 1% metal film res. 10K 0.6 W 1% metal film res. 1M 0.5 W 1% metal film res. 5.1K 2 W metal oxide film res. 3 position, 2-pole rotary switch DPDT toggle switch (heater voltage) 12SN7GT tube 5 Mapletree Audio Design Line 2B SE Stereo Line Preamplifier © Copyright Lloyd Peppard 2002-2013 Rev. Nov 4/13 Gain 1 1.8 3 4 5.6 8 10 dB 0 5 10 12 15 18 20 R1 340K 182K 100K 68K 47K 24.6K 22.1K B A Input resistance ~ R1 +185 V R2a 511 1% +210 V V1a 6/12SN7GT R4a 47.5K 1% J3a 3 J2a R1a-3 L. Line inputs 2 J1a R1a-2 1 +75 V 2 SW1a Source C2a 1.0/200 Auricap XO 1 R1a-1 R1a 100K 1% C3a 0.1/400 Auricap XO +49 V 4 P1a Volume 100K 5 L. outputs C4a 1.0/200 6 Auricap XO +54 V 3 chassis R6a 511K 1% R1a replaces R1a-1,2,3 if custom gains are not required D1a 10 mA red LED J4a J5a R7a 1K 1% R9a 1M R8a 10K 1% 1% P2 Balance 100K V1b 6/12SN7GT B A +185 V 3 R. Line inputs 2 1 J3b +210 V R4b 47.5K 1% R2b 511K 1% R1b-3 J2b R1b-2 +75 V 2 SW1b Source J1b 1 R1b-1 chassis R1b 100K 1% R1b replaces R1b-1,2,3 if custom gains are not required C3b 0.1/400 C2b 1.0/200 P1b 100K 3 5 +49 V 4 R6b 511K 1% R. outputs 6 +54 V C4b 1.0/200 J4b J5b R7b 1K 1% D1b 10 mA red LED R9b R8b 1M 10K 1% 1% Ground bus B +185 V A +210 V R10 5.1K 2W C11 100/400 B- + _ 12 VDC + 12 V 7 7 8 8 A+ 4 3 A- 1 2 B+ J6 Power In Rear View 6V SW2 Heater Voltage 6/12SN7s 6 Circuit Operation______ Both channels are identical as shown in the schematic diagram. Operation will be described for the left channel. The selector switch (SW1) 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 commoncathode 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 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? ?for 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. 7 Mapletree Audio Design Preamplifier Power Supply PS 2 © Copyright Lloyd Peppard 2003-13 Rev. Nov 18/13 SW1 Power FU1 1A/250V 1 L G J2 120 VAC 50-60 Hz R1 6.8K 5W 3 5 115 VAC V1 6X5GT D3, D4 MUR180 TR1 2 115 VAC 25 mA 6 4 8 8 + 5 + C1a 50/500 C1b 50/500 N Chassis 4 330K 1W 115 VAC 115 VAC 1 2 3 7 3 Rear View TR2 1 D1 1N4007 5 115 VAC IC1 2 6 3 7 14 VAC 1.4 A BR1 6A 3 + 4 TL780-12 12 V/1.5 A 1 R3 1.8K + 2 C2 10000/25 115 VAC D2 LED 8 1 2 3 TR3 5 6 4 8 6X5 2 7812 2 115 VAC 3 D1 7 6.3 VAC 0.9 A IC1 1 115 VAC Mounting tab connected to pin 2 insulated from chassis 7 Power Supply Parts List ______ Reference No. BR1 C1a,b C2 D1 D2 D3, D4 FU1 J1 J2 IC1 R1 R2 R3 SW1 TR1 TR2 TR3 V1 J1 Power Out 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 8