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G8MNY  > TECH     04.03.24 16:40l 125 Lines 5360 Bytes #999 (0) @ WW
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Subj: Marconi 2331A Distortion Factor
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By G8MNY                              (New Jan 21)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)
I bought this quite old large 19" 4U unit, made around 1975. It is an AF
Distortion meter, noise meter (weighting option) & an AF volt meter.

                 Frequency     Freq Band    Cal       Power
      _____________________________________________________
     ³ÚÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ¿³
Input³³            /~~~~~\         .        ( ) -~~~~- ( )³³
Level³³ (  )      /  .-.  \       (  )         / /    \   ³³
     ³³          ³  ³   ³  ³                  / /      \  ³³Meter
     ³³  .        \  '-'  /                  o~--.__.--~  ³³
Input³³ (  )       \_____/                                ³³
Range³³   '                        .               .      ³³
     ³³         (  )     (  )     (  )           (  )     ³³
  AF ³³ o o  ß                      '         ß       o o ³³Output
Input³ÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ³
      ~ÜÜ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ÜÜ~
          600R  Fine Freq  Phase  Mode    LF cut  Range

Although with 20 germanium transistors & a -15V PSU, it works fine. Main issues
are large dirty switches & scratchy wire wound pescision pots.

SPECIFICATION
Volt Ranges: 1-3-10, 7 in all from 30V down to 1mV FSD or in dBm. 1M Input.
Built in voltage calibrator.
Input: 1-10 (10K) & 10-30V (10-100K) & 600R term (some models AM RF det option)
Notch Freq: 20Hz-20kHz in 6 bands, Fine trim for Freq & Phase to notch -80dB.
Bandwidths: 20Hz-100kHz, or 20Hz-20kHz @-3dB.
Weighting: one filter option for Comms, Broadcast, or other is fitted.
LF Cut: -3dB @ 400Hz steep roll off hum filter.
Power: 95-130V or 190-260V AC 40-500Hz 3VA, or -18 to -45V 25mA DC.
Output: up to 150mV @ 1K of what is being metered, for oscilloscope.

USES
AF Voltmeter measures a wide range on average reading meter.

Distortion measuring & seeing Oscillator's & Amplifier's figures, adjusting for
min distortion on FM discriminators.

Noise measurement, with filters as needed for accurate assessment of kit noise.

A modern way of doing this might be with a laptop soundcard & suitable (free)
AF spectrum analyser/scope program!

There are 3 main parameters to Audio quality....

 FREQUENCY RANGE
 Here is the approximate frequency plot for some audio sources. Note that the
 old disk system was not really limited & special equipment can do Quad audio
 with high frequency sub-carriers!

 ³Sub Sonic³<- - - - -Young Human ear response - - - - - - ->³Ultra Sonic >
 ³I            BASS                MID              TREBLE
 ³N    <- - - - - - - - - - -Disk H i F i- - - - - - - - - - - >
 ³F       < - - - - - - - - -C.D. H i F i- - - - - - - - - - >
 ³R          <- - - - - - - Broadcast HiFi - - - - - - - - >
 ³A             < - - - - - Original Cassette- - - - - ->
 ³               <- - - - - Ä A.M. Radio - - - - - ->
 ³ F E E L I N G              < - - COMMS - - ->                B A T S
 ÀÄÄÄÂÄÄÄÄÂÄÄÂÄÄÄÂÄÄÄÄÂÄÄÄÄÄÄÄÂÄÄÄÂÄÄÄÄÂÄÄÄÄÄÄÄÂÄÄÄÂÄÄÄÄÂÄÄÂÄÂÄÄÂ>Frequency
 DC 10   20  30  50  100     300 500   1k      3   5   10 15 20 30kHz

 CDs are the best source most people are familiar with, its frequency range is
 limited by the 44kHz sampling rate & the requirement to filter off all the
 frequencies higher than 22kHz to stop aliasing mixes caused by the sampling
 rate.

 SIGNAL TO NOISE RATIO
 This is the measure of unwanted noises below the wanted sound..
 e.g. Hiss & Hum, or windage/engine noise, Neighbours/street noises etc.

  0dB´ Noisy Conversation
  10 ´ Poor Comms, NORMAL CAR
  20 ´ Fair Comms
  30 ´ VERY QUIET CAR                        AM RADIO
  40 ´ Typical Cassette Tape, Living rooms
  50 ´ Reel-Reel tape, Dolby Cassette
  60 ´ New Vinyl Record                      FM RADIO/TV SOUND
  70 ´ Mini disk (unmasked noise)
  80 ´ Dat tape.                             DAB
  90 ´ Perfect Digital CD, apparent Minidisk
 100 ´
 110 ´
 120 ´ Ear Threshold Signal : Silence to Pain ratio

 With Digital sources there is also "Quantization Noise/Distortion", which is
 due to the sample step size, & is a set No of dBs below any sound level for
 logarithmic level sampling.

 HARMONIC DISTORTION
 This is the amount of unwanted signals generated in harmonics of the wanted
 signal, in the audio pass band of interest. It is usually very dependent on
 the level, except for digital systems where it is a mathematical design
 feature. Note the ear generates these too!

 It is measured as a % of the signal, so 10% = -20dB in harmonics.

   %    dB
  10 Å -20 Cheap AM Radio at high Volume, Comms Audio
   5 Å -26 Film Optical Sound
   3 Å -30 Cassette & Reel Tapes (peak)
   1 Å -40 Quality Valve Amps                AM BROADCAST
  .5 Å -46 High Quality Disk                 FM BROADCAST
  .3 Å -50 Most Loudspeakers (not loud)
  .1 Å -60 Most AF Amps,                     DAB
 0.05Å -66 Good modern AF Amps.
 0.03Å -70 Most Digital AF sources.          CD ~MD ~Mpeg3?

 Sometimes the above parameters are joined together in a "Signal In Noise And
 Distortion" (SINAD) rating for measured RF signal level of a Rx.



See Tech bul "Marconi Distortion Meter TF2337", "AF Waveform Generator (RS)", &
"FeelTeck Dual DDS Osc FY6600-60M".

Why don't U send an interesting bul?

73 de John, G8MNY @ GB7CIP



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