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Author Topic: Help with Technics RS-1520 playback level calibration issue  (Read 5605 times)

Offline tkintp

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Help with Technics RS-1520 playback level calibration issue
« on: March 10, 2017, 03:14:46 PM »
I recently picked up a Technics rs-1520 deck, and am trying to set playback level using the Technics service manual spec and an MRL cal tape.  The MRL cal tape is the 250 nWb/m 7.5ips multifreq tape.  The deck was originally manufactured to show 0db at 185 nWb/m with balanced output of 1.228 Vrms.  When I play the 1KHz tone from the 250 nWb/m tape I measure aabout 2.3Vrms with the VU meters reading a hair over 0db.  Should I be adjusting the output voltage to 1.228Vrms, or somehow compensating for the difference in recorded flux density in the output voltage?  My instincts are that the greater recorded flux density of the test tape would cause a greater output for a given VU reading, but I'm not sure what or how to adjust here.
Any help would be appreciated.

Offline Detech

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Re: Help with Technics RS-1520 playback level calibration issue
« Reply #1 on: March 15, 2017, 08:56:07 AM »
Hi Tom.
In  brief, if you wish to set to original playback level.
adjust replay level to Approx +3 vu.
However that standard is the original Ampex operating level.
Dating back to the early 1960's.
Tape stock improved greatly over the years.
In the last days of professional recording always being done on tape.
Ampex and other manufactures produced tape stock that could record at operating level 9 db above "Ampex"spec'
And still maintenance same distortion figures, but increasing signal to noise level to a point to compete with Digital recorders .
For machines like B77 , pr 99 etc . They should be able to operate  at 250 nW at 7.5 i.p.s.
Problem will be record drive and or Head saturation in record. So you loose front end on any sudden transient.
I use to have to do the calculation to convert test tape level to desired operational level all the time.
You can calculate the db difference in the same manner you calculate the difference in voltage.
20 × log (Flux ratio)
20 x log(185/250) =2.61db.
I think I would be trying to get machine to record at 250 nW/m if I was in your situation.
Just one question, if you play back the test note, adjusted back to 0 VU, is it distorted ?
I think I had some machines, that the replay head would distort, in my case 320 nW/m .
I  that case for me, the tape machine was not suitable for the task required.
For you, just go back to manufacturer spec.

I hope that help somewhat.