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P1000 STEREO TURNTABLE AMPLIFIER OPERATING AND MAINTENANCE MANUAL © Copyright 1997-2005, Audio Technologies Incorporated - Printed in USA Audio Technologies Inc. | 154 Cooper Road #902 | West Berlin, NJ 08091 | Voice 856-719-9900 | Fax 856-719-9903 | www. audio.com GENERAL A turntable preamplifier is a deceptively simple device and has been the subject of an amazing amount of poor design. The seemingly simple matter of attaching a high capacitance load (in the form of the RIAA feedback network) onto a preamp stage which does not have adequate current drive capacity, guarantees Slew Rate Distortion, Transient Intermodulation Distortion, rising high frequency harmonic distortion and probably a few other distortions we haven’t named as yet. This problem is common to almost all existing preamps. A second common fault is designing too much gain into the input equalized state to compensate for a mediocre noise figure in the following output stage with the result that the input headroom is severely limited. Since groove stylus velocities of digitally mastered and direct disc recordings exceed 50 cm/sex peaks regularly with even greater dynamic range expected in the future, a high output cartridge can readily strain the typical 80 mV maximum input limit of typical preamps. ATI has eliminated these two problems by use of a new integrated circuit developed for the European professional audio market and recently made available to the US market through two major manufacturers. This chip incorporates a low noise input stage designed for use with the low source impedances typical of phono cartridges. In addition, this chip has an output stage free of crossover distortion and of sufficient current swing capability to drive 600 ohm loads to full supple voltage. An inherent slew rate capability of 13 volts per microsecond, a 50 KHz gain bandwidth product and 100 db open loop gain make this chip an ideal device for audio applications. Excellent low noise performance in both input and output stages allows to the MicroAmp to operate at reduced input stage gain yielding an input swing capability of almost 1 V p-p at 1 KHz while preserving excellent noise performance. The high Push Pull output capability allows the first stage to drive the RIAA equalization network with ease and without slew rate limiting to degrade high frequency performance. The high open loop gain provides 46 db loop gain for 200 to 1 distortion reduction even below 50 Hz where the equalized stage is operating at maximum gain. The high output also allows the output stage to drive the load directly on through a simple 1:1 isolating transformer. ATI proves three models of each MicroAmp; Transformer outputs for high RF field environments. A balanced, differential output stage version (bridge circuit) is also available. It is suitable for low RF environments where balanced output lines are required for hum rejection in long runs and the minor performance degradations of an output transformer are not desired. In addition a simpler, lower cost single ended output model with full 600 ohm drive capability is designed for use for short runs in low RF environments. Audio Technologies Inc. | 154 Cooper Road #902 | West Berlin, NJ 08091 | Voice 856-719-9900 | Fax 856-719-9903 | www. audio.com Another design consideration is the presence of large low frequency input signals, which originate in record warp and seismic pickup from people walking, bumping studio desks etc. The signals are strongest in the neighborhood of the cartridge/tone arm resonant frequency, typically 6 to 10 Hz. In studio applications these signals can overload subsequent amplifiers, overdrive limiters and damage loudspeakers. Previous attempts at Rumble Filters noticeably roll off low frequency audio when operated and therefore must remain switched out of the circuit most of the time. The MicroAmp incorporates an active two pole, subsonic filter bridged around the RIAA equalization network. The Q of this filter is designed to allow the preamplifiers response to follow the RIAA curve precisely to approximately 28 hz, drop only 3 db at 20 hz then plunge quickly to –18 db at 10 hz and achieve approximately 30 db rejection at 6 hz. Thus, excellent subsonic rejection is attained without low frequency degradation. Hi Boost and Hi Cut switches are included. Our power supply incorporates a couple of unique regulation devices called zener diodes. In contrast to most fancy three terminal IC regulators these devices will live through line transients and simultaneously protect your expensive circuitry. INSTALLATION MOUNTING Your MicroAmp may be desk mounted on its suction cup feet and left out for everyone to see since it is so pretty. If you want to keep knob twirlers away, you can bury it inside your turntable cabinet using the two angle brackets provided. Place them at diagonal corners under the lower cover mounting screws. Avoid magnetic fields from the turntable motor. Make sure your cartridge leads reach the preamp before permanently mounting. Rack Mounting Kits are available. P/N 20021-501 mounts a single MicroAmp. P/N 20024-501 mounts two MicroAmps side by side in 1 ¾” vertical rack space. WIRING The third wire ground can cause a ground loop with your station ground. If you are sure your station ground will provide adequate protection to personnel in case of an AC line short to the chassis, a 3 to 2 AC line adapter can be used to isolate the power line ground. We recommend that the adapter be removed and the power line ground reconnected prior to any service work requiring removal of the station ground connection from the MicroAmp chassis. Audio Technologies Inc. | 154 Cooper Road #902 | West Berlin, NJ 08091 | Voice 856-719-9900 | Fax 856-719-9903 | www. audio.com The four inch copper strap which you are, of course, using for your station ground is not going to fit around the #6 chassis ground screw on the MicroAmp rear panel. Run strap to within a few inches of the chassis and jump to the chassis ground with shield braid. Connect the tone arm ground lead to the same point (or any other place that works better). Plug cartridge leads into the phono jacks. Convention is white for left channel, red or black for right channel. Output wiring is indicated on the rear panel label. HI outputs are in phase with each other and are in phase with the input signal. Transformer output MicroAmps (1000-1) may have either HI or LO outputs grounded (but not both). Single Ended Output MicroAmp (P100-3) has the Lo output internally grounded. Do not ground the HI output as this shorts the output. CAUTION Balanced differential output MicroAmps (P1000-2) has active drivers for both HI and LO output terminals. Do not ground either HI or LO terminals. To drive an unbalanced (one side grounded) load connect it between HI and GND terminals and let the LO terminal float. Two separate 600 ohm unbalanced loads can be driven from each output without interaction by connecting one between HI and GND and the other from LO to GND. The two loads thus driven will be out of phase with each other. Individual grounds are provided for left and right outputs. ADJUSTMENTS The MicroAmp has sufficient gain and output capability to overdrive some console inputs particularly those providing preamps for high level input channels. Two o’clock on the level pot will provide +8 dBm for 0 VU (5 cm/sec) recording level with typical cartridges providing 1 mv/cm/sec, 12 o’clock is approximately 0 dBm, 10 o’clock is approximately –10 dBm output. Operation with the MicroAmp pot below 10 o’clock degrades noise performance and a fixed attenuator pad should be placed between MicroAmp and output and console input to allow operation around two o’clock. MAINTENANCE NOTES Power supply voltages are + and – 20 VDC nominal, dropping to +\- VDC under full output. Maximum allowable voltages are +\- 22 VDC (limited by IC). If zeners are replaced remove A1, A2, and A3 ICs and check output voltage before plugging ICs back into the circuit. Remove power when inserting or removing ICs. Audio Technologies Inc. | 154 Cooper Road #902 | West Berlin, NJ 08091 | Voice 856-719-9900 | Fax 856-719-9903 | www. audio.com IC output DC voltages (no signal conditions) should measure OVDC +\- .5 VDC. Significant deviation indicates IC or circuit problem. Measurable DC difference between +\- amplifier inputs (other than due to meter loading) indicates IC failure. MODIFICATIONS 230 VAC OPERATION Your MicroAmp is wired for 115 VAC 50/60 Hz operations unless otherwise requested at the time of ordering. It can be modified for 230 VAC use by removing the Power transformer primary jumpers W1 and W3 and inserting a jumper in the W2 holes. 150 OHM OUTPUT IMPEDANCE Transformers output MicroAmps are converted to drive 150 ohm audio lines by removing jumpers W4 and W5 located adjacent to output transformers T3 and T2 respectively. Insert two new jumpers for each output transformer between the original jumper terminals and the empty terminals immediately adjacent to and in line with the original terminals in order to parallel the secondary windings. Balanced differential output and single ended output MicroAmps will drive 150 ohm loads without modification but will current limit before full supply swing is reached. Audio Technologies Inc. | 154 Cooper Road #902 | West Berlin, NJ 08091 | Voice 856-719-9900 | Fax 856-719-9903 | www. audio.com TECHNICAL SPECIFICATIONS MODELS P1000-1 DUAL/STEREO OUTPUTS P1000-2 DUAL/STEREO DIFFERENTIAL OUTPUTS +22 dBm (P1000-1-3) +26 dBm (P1000-2) OUTPUT CLIPPING LEVEL TRANSFORMER BALANCED DISTORTION @ +20 dBm OUTPUT P1000-1: .2% 30 Hz to 20000 Hz P1000-2: .05% 20 Hz TO 20000 Hz EQUIVALENT INPUT NOISE SHORTED INPUT, .5 MICROVOLTS RMS. Cartridge Input, .8 micovolts, RMS. 1000 ohms + .5 Hz SIGNAL TO NOISE RATIO 80 db unweighted, ref. 10mVrms, 1 KHz 20 KHz bandwidth FREQUENCY RESPONSE RIAA Curve +\- .25 db, 30 to 20000 Hz. INPUT SENSITIVITY Adjustable, 1.0 mVrms at 1 KHz for +8 dBm output INPUT OVERLOAD 320 mVrms at 1 KHz. INPUT IMPEDANCE 47K ohms and 220 pf. SUBSONIC WARP AND ARM RESONANCE FILTER -3 db max @ 20 Hz -18 db @ 10 Hz. HI CUT SWITCH -3 db @ 10 kHz HI BOOST SWITCH +3 db @ 10 kHz SYSTEM SLEW RATE 13 V/Microsecond POWER REQUIREMENTS 115/230 VAC +\- 10% 47-63 Hz. 8 ½” W X 1 ¾” H X 7” D, 2 ½ lbs. Audio Technologies Inc. | 154 Cooper Road #902 | West Berlin, NJ 08091 | Voice 856-719-9900 | Fax 856-719-9903 | www. audio.com