How to make audio measurements on stereo receivers and amplifiers

Transcription

1 How to make audio measurements on stereo receivers and amplifiers

2 HOW TO INCREASE YOUR SALES Many dealers are using performance tests on the sales floor to sell customers up to a more expensive item. Such performance tests also impress the customer with your store's technical competence. In addition, more and more retailers are running clinics as sales promotion events. And clinics do increase sales. They also build your service volume. MAKING MEASUREMENTS We've prepared this booklet to assist you in making up-to-date receiver and amplifier measurements and in running sales clinics. The information here assumes that you have available the following Sound Technology instruments: (a) Model 1000A FM Alignment Generator (b) Model 1200A Stereo Test Panel (c) Model 1700A/B Distortion Measurement System These instruments are arranged as indicated by the following diagram. More details are given in the instruction manuals for these instruments, particularly the Model 1200A Manual. SCOPE S/T1000A ALIGNMENT GENERATOR S/T 1100A SIGNAL CONDITIONER S/T I700A/B DISTORTION ANALYZER S/T 1200A STEREO TEST PANEL RECEIVER BEING TESTEO (OR DEMONSTRATED) BENCH RECEIVER LOADS SPEAKERS CLINIC FORMS On the last two pages are forms that are useful in recording measurements for your customers. These forms are of a quality that permits direct reproduction by your printer. A space is provided for adding your name. This can easily be done by affixing your letterhead on the master. While the forms are copyrighted, Sound Technology releases them to users of its equipment. 2

3 AMPLIFIER MEASUREMENTS TO MEASURE VS. FREQUENCY AT RATED POWER (6) Reset 1700 F U N C T I O N s w i t c h t o D I S T O R T I O N. Read the amplifier's right channel distortion on the m e t e r o f the (2) Adjust 1700 O S C I L L A T O R L E V E L until amplifier rated output p o w e r (read o n 1700 meter) is reached. (7) Set 1200A M E A S U R E M E N T t o L E F T C H A N N E L. Read amplifier's left channel distortion. (3) Adjust oscilloscope controls for convenient display of amplifier output signal and distortion. N O T E : If amplifier output p o w e r rating is unknown, increase 1700 OSCIL L A T O R L E V E L until " c l i p p i n g " o r other signs of a m p l i fier overload become evident. Then reduce O S C I L L A T O R L E V E L slightly until signs of overload disappear. (8) Repeat above measurements at other frequencies, and plot a curve showing amplifier distortion vs. fre quency at rated power. N O T E : The test may also be r u n w i t h a 4 or 16 o h m load by pressing the appropriate but t o n o n the 1200 front panel. (4) Reset 1200A M E A S U R E M E N T to R I G H T C H A N N E L. (5) Adjust TEST S I G N A L R I G H T L E V E L control until right channel amplifier output matches the left channel output. Recheck scope display for signs of overload f r o m either channel, and reduce oscillator level i f necessary. The output p o w e r measured at this point may be used as the r a t e d p o w e r output of the amplifier. CAUTION: Before switching loads, turn d o w n 1700 O S C I L L A T O R L E V E L. A f t e r switching loads, repeat steps (2) and (3) above. TO MEASURE VS. POWER AT 1 khz (4) Reduce amplifier output p o w e r in 3 db { % p o w e r ) increments, recording left and right channel d i s t o r t i o n at each step. N O T E : The m i n i m u m output p o w e r level at w h i c h distortion need be r e c o r d e d is 250 mw. Also, i f desired, the amplifier may be driven slightly above rated p o w e r to r e c o r d the increase in distortion as o v e r l o a d occurs. (2) Set 1700 to 1 khz, and drive amplifier t o rated p o w e r output f r o m b o t h channels as described in steps (2)-(5) above, (3) R e c o r d (plot) distortion of b o t h channels o.25 V S. P O W E R A T 1 khz II! DC O t- cn Q O H II II I // < I BRIGHT o I 0.1 T y p i c a l curve POWER OUTPUT PER CHANNEL 3 (WATTS) 100

4 TO MEASURE INTERMODULATION DISTORTION VS. POWER (2) Set 1700 to P K E Q L W V / P W R. (3) D r i v e amplifier t o rated p o w e r output f r o m b o t h channels. N O T E : Refer to 1700 Instruction Manual for d e t e r m i n a t i o n o f I M output p o w e r as compared to a single frequency p o w e r level. (4) Set 1700 to I M D and r e c o r d left and right channel distortion at amplifier's rated p o w e r output. Reduce p o w e r in 3 d B (% power) increments, recording distortion at each step. N O T E : The m i n i m u m p o w e r level at w h i c h distortion need be measured is 250 mw. If desired, the amplifier may be d r i v e n slightly above rated p o w e r t o r e c o r d the increase in distortion as overload occurs. (5) The test may be repeated w i t h other loads by pressing the appropriate b u t t o n on the 1200 front panel. CAUTION: Before switching loads, t u r n d o w n 1700 O S C I L L A T O R LEVEL. TO MEASURE SIGNAL-TO-NOISE RATIO REFERRED TO RATED POWER MEASUREMENT: CHANNEL: RIGHT A preferred (B, C, OUT, may be used as desired) (A) T o measure using A U X Input: (2) D r i v e amplifier t o rated p o w e r as described in step (2)-(5) at top o f p. 3. TEST S I G N A L : C H A N N E L : O F F (5) Range 1700 R A T I O switch d o w n until on-scale reading is obtained. Read right channel signal-tonoise ratio directly in d B. (3) Reset 1700 controls as follows: db V O L T S 0 db Set for full scale meter reading (6) Reset 1200A M E A S U R E M E N T to L E F T C H A N NEL. Read left channel signal-to-noise ratio. (B) T o measure using P H O N O input: (4) Reset 1200A controls as follows: (1) Reset 1200A TEST S I G N A L to P H O N O and re peat above test. TO MEASURE RIAA PHONO EQUALIZATION ACCURACY (5) Reset 1700 controls as follows: (2) Reset 1200A controls as follows: db VOLTS MEASUREMENT: AMPLIFIER OUTPUT: RCDR 0 d B range TEST SIGNAL: B U F F E R E D 1700, M O N O I N V RIAA, PHONO Set for - 3 d B meter (6) P r o g r a m 1700 F R E Q U E N C Y switches over the R I A A phono equalization range noting any change in reading at each frequency. Changes in meter readings are e r r o r s i n phono p r e a m p equalization. Record (plot) meter devia tions. (3) Reset 1700 controls as follows: 0.3 V range OSCILLATOR: F A S T RESPONSE (4) Reset amplifier to P H O N O input, and drive that input to o b t a i n a reading o f approximately 0.15 volts o n the 1700 meter. (7) Repeat test for left channel. m +1-0r RIAA EQUALIZATION ERROR VS. F R E Q U E N C Y LEFT RIGHT o reading F R E Q U E N C Y (Hz) 10K 20K

5 TO MEASURE AMPLIFIER TONE CONTROL RESPONSE NOTE: This section describes example of all bass and treble treble cut response as an boost or cut responses. (1) Set controls as stated in SET UP 1 on p. 7. (2) Reset these 1700 controls as follows: Proper range to measure 1/10 rated power output of amplifier OSCILLATOR: FREQUENCY: FAST RESPONSE 500 Hz (3) Set amplifier treble control for maximum cut. Drive amplifier to 1/10 rated power output. If 1700B meter reading goes off scale, turn INPUT switch one position clockwise. Now the 10 db point on the meter is 0 db. For example, an indication of 8 db on the meter is actually + 2 db. (4) Reset 1700 controls as follows: db VOLTS Set for 0 db meter reading (5) Increase 1700 FREQUENCY in a sequence such as 1:2:5, plotting meter readings as a function of frequency. (6) Repeat measurements for left channel. m LU a. h- -15 I I I I I I I K 20K Typical cu,»e FREQUENCY (Hz) TUNER MEASUREMENTS TO MEASURE HARMONIC DISTORTION AT 65 dbf (1) Set controls as stated in SET UP 2 on p. 7. (3) Set 1200A to RIGHT CHANNEL and repeat test. (2) Measure THD using NOTE: IEEE/IHF test requirements specify repeating test at 100 Hz and 6 khz. Test may also be repeated in Mono. TO MEASURE SIGNAL-TO-NOISE RATIO (1) Set controls as stated in SET UP 2 on p. 7. (2) Reset 1000A to MONO. (3) Set receiver to MONO. (4) Reset 1200A controls as follows: FM MOD: LEFT BAND PASS (5) Reset 1700 controls as follows: (6) Reset 1000A to CW. db VOLTS Set for full scale meter reading. (7) Range 1700 RATIO switch down to obtain an onscale meter reading. (8) Read signal-to-noise ratio directly in db on 1700 meter. 5

6 T O M E A S U R E S E N S I T I V I T Y F O R 30 d B Q U I E T I N G (3) Reduce 1000A RF L E V E L until distortion reading rises to 30 db. Sensitivity for 30 db (3%) quieting is the RF L E V E L dial reading in microvolts or dbf. N O T E : This test is very sensitive to receiver tuning. Receiver may be m o r e sensitive in M O N O. (1) Set controls as stated in SET U P 2 on p. 7. (2) Reset 1700 controls as follows: DISTORTION 3 % ( - 30 db) range T O M E A S U R E H U M A N D N O I S E A T 65 d B f (1) Set controls as stated in SET UP 2 on p. 7. db V O L T S (2) Reset 1000A to M O N O. (3) Reset receiver to M O N O. Set for full scale m e t e r read ing (4) Reset 1200A controls as follows: FM M O D : (6) Reset 1000A to C W. LEFT (7) Range 1700 R A T I O switch d o w n t o obtain an onscale m e t e r reading. L O W PASS (5) Reset 1700 controls as follows: (8) Read h u m and noise at 65 d B f directly in d B o n 1700 meter. T O M E A S U R E S E N S I T I V I T Y F O R 50 d B Q U I E T I N G (1) Set controls as stated in SET U P 2 on p. 7. (2) Reset 1000A to M O N O. Set for full scale m e t e r read ing (6) Reset 1000A to C W. (3) Reset receiver t o M O N O. (7) Reset 1700 R A T I O switch to - 5. (4) Reset 1200A F M M O D U L A T I O N to L E F T. (8) Reduce 1000A RF L E V E L until meter reads full scale. 50 db quieting is the RF L E V E L dial reading in m i c r o volts or dbf. (5) Reset 1700 controls as follows: db V O L T S T O M E A S U R E C H A N N E L S E P A R A T I O N A T 65 d B f scale reading on 1700 meter. Read left separation directly in db. (1) Set controls as stated in SET UP 2 o n p. 7. (2) Reset 1200A F M M O D U L A T I O N to L E F T. (6) Reset 1200A F M M O D U L A T I O N to R I G H T C H A N NEL. (3) Reset 1700 controls as follows: db V O L T S (7) Reset 1700 R A T I O switch to. Set A D J U S T control for 0 db meter reading. Set for 0 db meter reading (8) Reset 1200A M E A S U R E M E N T to L E F T C H A N N E L. (9) Range 1700 R A T I O switch d o w n to o b t a i n an onscale reading o n 1700 meter. Read right separation d i rectly in db. (4) Reset 1200A M E A S U R E M E N T to R I G H T C H A N N E L. (5) Range 1700 R A T I O s w i t c h d o w n to obtain an on- TO MEASURE SUBCARRIER REJECTION (1) Set controls as stated in SET U P 2 on p. 7. (2) Reset 1200A FILTERS to H I G H PASS. (4) Press 1700 S I G N A L O F F button. Range R A T I O s w i t c h d o w n t o obtain an on-scale reading on 1700 meter. Read subcarrier rejection directly in db. (3) Reset 1700 controls as follows: db volts Set for full scale m e t e r read ing 6

7 FORMS YOU MAY Below is a form useful for a mini-clinic. On the next page is a larger form suited to more detailed testing. These forms can be easily reproduced by your printer. REPRODUCE Just have him place your name, address, etc., in the space provided (your letterhead can serve as a suitable master). While the forms are copyrighted, Sound Technology releases them to users of its equipment. Customer Name Datp Street City on : M,m: IMPRINT YOUR NAME HERE) State 7in Phone Receiver Make Moripl Nn. 3 SOUND TECHNOLOGY T PERFORMANCE EVALUATION FORM AMPLIFIER PERFORMANCE AT RATED POWER OF WATTS AT 1 khz Left Channel % Right Channel. % INTERMODULAR ON DISTORTION AT RATED POWER Left Channel % Right Channel % SIGNAL-TO-NOISE RATIO REFERRED TO RATED POWER ('A' WEIGHTED) TUNER PERFORMANCE IN 970,J.V (65 dbf) SENSITIVITY FOR 30 db QUIETING,u,V dbf SEPARATION Left db Left Channel db on aux input Right Channel db on aux input Right db The undersigned hereby authorizes the company to perform the above tests and assumes the risk of loss or damage to the equipment being tested. Comments. Signed - Sound Technology, Inc., 1978 Test Technician's Signature. WARNING FOR YOUR SAFETY, THE CHASSIS OF THE RECEIVER OR AMPLIFIER UNDER TEST SHOULD ALWAYS BE CONNECTED TO THE 1200A CHASSIS (rh ) BEFORE CONNECTING THE RECEIVER/AMPLIFIER TO A POWER SOURCE. THIS CHASSIS CONNECTION SHOULD BE MAINTAINED AT ALL TIMES. BASIC SET UP 1 CAUTION: Reduce all signal levels to minimum before connecting equipment. Set Model 1200A controls OSCILLOSCOPE: MEASUREMENT: TEST SIGNAL: LOAD: > follows: EXT. TRIGGER: 1700 INPUT MON, 1700 A-INPUT/B-DIST AMPLIFIER OUTPUT: SPKRS, CHANNEL: LEFT, OUT BUFFERED 1700, AUX/TAPE, CHANNEL: BOTH 8 (ohms) Set Model 1700 controls as follows (see 1700 Manual) FREQUENCY: 1000 Hz 80 khz VOLTS/POWER To desired power range AUTO SET LEVEL position OSC LEVEL. Minimum OSCILLATOR: LOW DISTORTION Set controls of amplifier under test as follows: BASS/TREBLE: FLAT LOUDNESS: OFF AUX BALANCE: Approximately centered SPEAKERS: ON VOLUME: Maximum BASIC SET UP 2 CAUTION: Set receiver volume at minimum before switching to FM band. Set receiver controls as follows: FM STEREO MUTING: OFF LOUDNESS: OFF BASS/TREBLE: FLAT SPEAKERS: ON AFC: OFF SENSITIVITY: DISTANT OUT TUNING: Dead spot in FM band Set Model 1200A controls as follows OSCILLOSCOPE MEASUREMENT: FM MOD: LOAD: EXT. TRIGGER: 1700 INPUT MON, 1700 A-INPUT/B-DIST AMPLIFIER OUTPUT: SPKRS, CHANNEL: LEFT, BAND PASS 1700 L-R 8 (ohms) Set Model 1000A controls as follows RF LEVEL: PILOT LEVEL: FREQUENCY: 65 dbf (970 microvolts with a S-T Model 100 Transformer) STEREO 9 *o (see 1000A Manual) EXT Set Model 1700 controls as follows: FREQUENCY. OSC LEVEL: OSCILLATOR: Tune lo receiver setting VOLTS/POWER Proper range to drive amplifier to 1/10 rated power 1000 Hz 80 khz Set for 100% modulation as read on 1000A meter AUTO SET LEVEL position LOW DISTORTION Set receiver VOLUME for 1/10 rated power output. 7

8 Customer name_ Date Street City_ State Zip. _Phone_ IMPRINT YOUR NAME HERE) Receiver Make.Model No. S O U N D T E C H N O L O G Y r PERFORMANCE EVALUATION FORM AMPLIFIER PERFORMANCE TUNER PERFORMANCE AT JUST BELOW CLIPPING LEVEL WATTS AT RATED POWER OF WATTS AT 1 khz Left 20 Hz 2000 Hz % Right 20 Hz 2000 Hz % INTERMODULATION DISTORTION AT RATED 20,000 Hz 20,000 Hz 970 (65 dbf) % SENSITIVITY FOR 30 db QUIETING fiv dbf SIGNAL-TO-NOISE 970,uv (65 dbf) _db SENSITIVITY FOR 50 db QUIETING Left 1 Watt 10 Watts Rated Power % Right 1 Watt 10 Watts Rated Power % <uv STEREO dbf SIGNAL-TO-NOISE RATIO REFERRED TO RATED POWER ('A' WEIGHTED) Left Channel db on aux input Right Channel db on aux input RIAA EQUALIZATION ACCURACY SEPARATION Left db Right 970 (65 dbf) Left db Left Channel ± db Right Channel _db Right db The undersigned hereby authorizes the company to perform the above tests and assumes the risk of loss or damage to the equipment being tested. Comments Signed. c Sound Technology, Inc., 1978 Test Technician's Signature