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Leader LDM-170 Operating Instructions Manual

Distortion meter
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NST
UMEN
s
MODEL LDM-170
DISTORTION
METER
OPERATING
INSTRUCTIONS
LEADER
ELECTRONICS
CORP.

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Summary of Contents for Leader LDM-170

  • Page 1 UMEN MODEL LDM-170 DISTORTION METER OPERATING INSTRUCTIONS LEADER ELECTRONICS CORP.
  • Page 2 CONTENTS SECTION PAGE DESCRIPTION General Specifications Panel Functions OPERATION Distortion Measurement Preliminary Notes 2.1.1 Preparation 2.1.2 Tuning and Balancing Adjustments 2.1.3 2.1.4 Measurements at 0.1 — 300mV rms input Use of an Oscilloscope 2.1.5 •8 Examplesof Measurements 2.1.6 S/ N Measurement Voltage Measurement 2.3.
  • Page 3 DESCRIPTION I .1 General The LDM-170 measures the distortion,S/N (signal-to-noise ratio),andsignal l evels in audiofrequency circuits. A highly selective balancing networkis usedto eliminatethe fundamental frequencyin the to 20kHzba: The distortionproductsarefed to a stable high-gain wideband amplifierfor indicationon the meter. Theamplif is effectiveup to 200kHz and measurements a repossibleup to and includingthe tenth harmonicof 20kHz.
  • Page 4 ouppry specurea voltage :r-1UYo, 50/6UHz; Input taps at 100, 115, 200, 215, and 23m approx. 5VA. Sizeand Weight 150(H) x 300(W) x 250(D) mm; 5kg. Accessory, furnished Input cord w/clips anddouble plug. Panel Functions A. Front Panel, Fig. 1-1. Fig. 1-1 Front panel controls. POWERswitch: Turnson the AC input for operation.
  • Page 5 OUTPUTterminals: For waveform monitoring with an externalscope,etc.; output proportional to the meter indication. BALANCE control: For nulling the fundamental during distortion measurements;outer and inner knobs respectivelyfor coarseand fine adjustments. FREQ. RANGE switches: Selectsthe range of the fundamental when measuringdistortion: x 10: 20 —...
  • Page 6 Sect. 2.1.4. Do not apply voltagesgreater than 125V, AC or DC, acrossthe INPUT terminals. If DC voltage is present i n the loadcircuit,usea blockingcapacitor w ith suitable voltage ratingin series with the "hot" lead, typically ().5gF correspondinglysmaller capacitancesat higher 20Hz, and frequencies.
  • Page 7 TABLE INPUT INPUT VOLTAGE RANGE SWITCH SEITING 0.35 — IV 3— 10 - After theINPUTVOLTAGEswitchhasbeenset,press theCAL switchanddistortionswitch. Advance t he SETLEVELcontrolfor full scale reading onthemeter N OTE: Thisstepisrequired when the input voltagehasbeenaltered. Press the switch of RANGE. Tuning and Balancing Adjustments 2.1.3 Tuning the fundamentalfrequency: The FREQ.
  • Page 8 An example is shownin Fig. 2-3. If the fundamental is at, say"6" (60Hz,600Hzor 6kHzdepending o n the range), t he dial is initially setat ''5" or "7" by over-running the ''6" marking. The vernierdrivewill cover the range between 5 and 7. Adjust the knob in the vicinity of "6"...
  • Page 9 TABLE SWITCH SCALE RANGE f.s. Use: 0—1 0.3% Useof anOscilloscope h 1.5 The use of a sensitivegeneral purpose scope,preferably the dual-tracetype, is recommended. Tuning and balancingadjustmentswill be speeded up; furthermore, waveformsof distortion components canbe observed. Typical connectionsareshownin Fig. 2-4. POWER RANGE : SET Level.
  • Page 10 FREQUENCY BALANCING MEASURE* TUNING INPUT _ENC OUTPUT * After repeatedadjustments; ideal condition shown. Fig. 2-5 Useof waveform display. Dual-trace method 2.1.5-B. With the OUTPUT connectionsas in A above,connectthe signalfrom the test deviceto the other channel input (in parallel with the INPUT leads);refer to Fig. 2-4. The upper traces in Fig.
  • Page 11 Power supply ''hum" Distortion due to or oscillation switching or crossover effects partial oscillation Higher harmonics Fig. 2-7 Distortion observed with Lissajous patterns. 2.1.6 Examples of Measurements 2. l. 6-A. Oscillator distortion When measuringthe distortion in audio amplifiers, it is advisedthat the oscillator (source)distortion be measured.
  • Page 12 Amplifier distortion 2.1.6-B. The distortion VS. output voltage at three selectedfrequencies is shown in ''A" of Fig. An exampleof distortion characteristics at three selectedfrequencies is shown in "A" of Fig. 2-9, in "B" of the samefigure, the overall distortion characteristic is shown. DISTORTION, (0%) —20Hz 1 kHz...
  • Page 13 SIN is the ratio of S (= signal + noise)to the noiseat the output Ofan amplifier. With the LDM-170, measurement i s madeat the sameinput levelsasin distortion measurement, i.e.,0.35 to 30Vrms. In general, t he S/N is measured at a specifiedlevel(at maximum)at the test circuit output.
  • Page 14 Control settings: INPUT VOLTAGE switch at 30. S/ N switch of function at on. CAL switch of RANGE at on. Adjustments: Amplifier output to specified level, or voltage. INPUT LEVEL switch andSET LEVEL control for full scalereadingon the meter. Oscillator frequency asrequired, 400Hz, etc. Disconnect the oscillator output and short the amplifier input to ground.
  • Page 15 2.3.2 Operation Switch settings: VOLTMETER of function at mV or V. RANGEdepending on the input voltage.If not known,setat a highrangeandwork down. HIGH PASS FILTER at off. Connect the input cord, or leads,to the INPUT terminals. Set the RANGE switch so that the reading is at least above 30% full scale(except when the IrnV range is used).
  • Page 16 2ND HARMONIC, 2fo Fig. 3-1 Distorted waveforms. In the LDM-170, the fundamental input voltage is used as the reference level (CAL operation). Then the fundamental suppression network is switched in, leaving only the harmonics whose level in % is indicated, seeFig.
  • Page 17 The input signal from an amplifier at a specifiedfrequency(400Hz, IkHz, etc.) is usedto set the referencelevel. Thenoise levelisdetermined b y removing thesignal s ource andshorting theamplifierinput. In the LDM-170, t he ratio S (signal i ncludingnoise)to noise, N , is calibrated in termsof dB(decibel), s eeFig.3-4. REFERENCE...
  • Page 18 The measurement is made in similar manner as that for distortion but with the filter network out of circuit. simplified block diagram is shown in Fig. 3-5. INPUT VOLTAGE LEVEL PREAMP INPUT RANGE 1 — 30V SIN RANGE METERING METER O —...
  • Page 19 The filtering characteristic is shown in Fig. 3-7. It is effective in eliminating low frequency noise, below 2kHz, (HIGH PASSFILTER switch at on), when usedin distortion and S/N measurements. —3dB -20dB 50Hz 500Hz Fig. 3-7 High-passfilter characteristic. DC Power Supply A regulatedsupplyfurnishesthe +18V requiredfor its operation.