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Author Topic: Full calibration of TEAC X2000R  (Read 1920 times)

Offline Petronel

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Full calibration of TEAC X2000R
« on: August 24, 2015, 11:41:45 PM »
Dear Friends,

I will highly appreciate if you'll help me with the following issue:
I intend to full (Play & Record) calibrate my TEAC X 2000R.
I don't have any calibration tape. Instead, I have a tone generator and a digital oscilloscope.

Please help me with a step-by-step calibration procedure for my machine.

Looking forward for any reply, I will highly appreciate yours support.

Kind regards,

Petronel

Offline stellavox

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Re: Full calibration of TEAC X2000R
« Reply #1 on: August 25, 2015, 02:16:50 PM »
Petronel,

This is a VERY good question, and I'm trying to come up with an understandable answer as to why it CAN'T be done. 

Let's try this.

The audio information on tapes, like records, have a "built in" pre-emphasis "boost" added to the signal to boost the high frequencies relative to the lows.   This boost, in "cooperation" with a corresponding cut when playing back the prerecorded medium, was done to "subjectively" reduce the amount of high frequency noise and "tape hiss" added during the transcription process, that you might hear on the finished record or tape.  The amount of boost/cut was decided upon long ago, and incorporated into industry standards - RIAA for records, NAB (USA) and IEC (Europe) for tape.  When tapes are played back, The tape reproduce pre-amplifier subjects the desired signal to a corresponding "de-emphasis", so that the frequency response of the material you ultimately hear appears "flat". 

Because tape decks can both record and playback; and probably due to the fact that you can use differing brands of tape and that tape heads/electronics can wear and loose high frequency response, tape deck manufacturers added the ability to "adjust" BOTH the amount of high frequency boost in their record amplifier circuitry and low frequency cut in their playback preamplifiers. 

You have a consumer deck that somewhere along the line was set up for a certain amount of record boost and playback cut corresponding to the NAB standard.  The person who did that undoubtedly started with a "playback calibration tape" that had tones recorded with a "known/calibrated" playback characteristic that correlated to the standards.  Your machine now is not new; it has seen (a lot of?) use and we DON'T know how "accurate" either the record boost or playback cut is.

So when you play a PRE-RECORDED tape, you don't know and can't really demonstrate that the playback characteristic of your current preamplifier matches the NAB/IEC standard.  To verify this you need a playback calibration tape.

However, If all you want to do is record your own material and play it back, you could record tones of equal volume/intensity from say 30hz to 20khz onto a tape, play the tape back and measure the volume/intensity of the recorded tones.  Then if the frequency response is NOT flat, start adjusting the "tone" controls on either the record or playback circuits to get it as flat as you can.  BUT which ones do you adjust? 

"Standard practice" for aligning a tape deck is to first play a playback calibration tape and, using some means to monitor the output, adjust the high (and on some machines, low) frequency response adjustments on the playback preamplifier to produce as flat response as you can get.  Then take the calibration tape off; put a "blank" tape you wish to record on the deck; record a series of frequencies and adjust the frequency adjustments in the RECORD electronics for as flat an overall response as you can get - the playback response being  'previously calibrated".  Note that the amount of record BIAS also effects the frequency response  but that is another story!

Hope this makes some sense - others PLEASE chime in!!!

Charles   
« Last Edit: September 08, 2015, 11:56:49 AM by stellavox »