tape machine calibration

omaroski · 16th June 2008, 02:37 PM

following the manuals the first step is the INPUT LEVEL, my problem is with the reading i get back from the RMS voltmeter, here is a detailed description of the procedure i do:

- connect the built-in audio oscillator of the console to the voltmeter, set the rotary switch to the 3v +10db position (scroll down for a picture of the voltmeter)
-send the 1khz tone and adjust the fader to get 1.23v, which i suppose is the middle scale of the voltmeter(the one with 1 - 2 - 3 values). When it reads 1.23v the console's meters are reading 0VU (+4dbu) too.

- send the 1khz 1.23v tone to the tape machine set in INPUT mode and connect the machine out to the voltmeter
- the problem is here because with the voltmeter rotary switch always set on 3v +10db i can't get the needle to read 1.23, even if i turn the INPUT LEVEL pot all the way up i get a lower value.

Hope someone here can help me, sorry for my bad English but i'm from Italy.

Thanks!

Goreski · 16th June 2008, 11:05 PM

You may be measuring only one leg of a balanced pair - thus getting a reading 6 db less than normal. Check between XLR pins 2 and 3 if the output is balanced. If the output is unbalanced, you will have to try all combinations of XLR pins. Note that just because the machines has XLR connectors it does NOT mean the machine is balanced!

Also you did not say which tape recorder you are measuring... pro machines put out +4dbm (1.227 volts rms) but semi-pro/consumer machines put out only .3 volts (300mV) at 0vu.

Regards,

Goreski

Analog Rules!!! Pro-Audio Parts and Service Tons of info on Analog Recording !!

Pro Audio Manuals and Schematics Audio Manuals and Schematics -- hardcopies for sale / downloads for free !!

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16th June 2008, 02:37 PM	#1
omaroski Gear interested Join Date: Aug 2006 Location: Italy Posts: 12	tape machine calibration following the manuals the first step is the INPUT LEVEL, my problem is with the reading i get back from the RMS voltmeter, here is a detailed description of the procedure i do: - connect the built-in audio oscillator of the console to the voltmeter, set the rotary switch to the 3v +10db position (scroll down for a picture of the voltmeter) -send the 1khz tone and adjust the fader to get 1.23v, which i suppose is the middle scale of the voltmeter(the one with 1 - 2 - 3 values). When it reads 1.23v the console's meters are reading 0VU (+4dbu) too. - send the 1khz 1.23v tone to the tape machine set in INPUT mode and connect the machine out to the voltmeter - the problem is here because with the voltmeter rotary switch always set on 3v +10db i can't get the needle to read 1.23, even if i turn the INPUT LEVEL pot all the way up i get a lower value. Hope someone here can help me, sorry for my bad English but i'm from Italy. Thanks!

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16th June 2008, 11:05 PM	#2
Goreski Gear nut Join Date: Aug 2007 Location: San Francisco Posts: 83	You may be measuring only one leg of a balanced pair - thus getting a reading 6 db less than normal. Check between XLR pins 2 and 3 if the output is balanced. If the output is unbalanced, you will have to try all combinations of XLR pins. Note that just because the machines has XLR connectors it does NOT mean the machine is balanced! Also you did not say which tape recorder you are measuring... pro machines put out +4dbm (1.227 volts rms) but semi-pro/consumer machines put out only .3 volts (300mV) at 0vu. Regards, Goreski Analog Rules!!! Pro-Audio Parts and Service Tons of info on Analog Recording !! Pro Audio Manuals and Schematics Audio Manuals and Schematics -- hardcopies for sale / downloads for free !!