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  • #46
    Originally posted by dminches View Post

    Am I correct in saying with the 10kHz tone you increase the bias until the recording sensitivity drops 3 dB?

    Also, what do you use to measure a 0.2 dB drop? I assume the deck's meters aren't accurate enough for that. A volt meter?
    As you increase the bias, it will reach peak level and starts to decrease using both methods. For 10Khz tone methods you increase the bias level beyond its peak and let it drop further per your tape manufacturers' recommended amount per speed.

    Correct, as you leave the 0VU region of the VU meter, its accuracy is not certain at best especially when I tried to obtain 0.2dB change. I use either the external millivoltmeter or the Sound Technology 1510A to hit the 0.2 dB drop.

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    • #47
      Originally posted by Bruce B View Post
      Ki..... don't show them all our tricks!!!
      Originally posted by Ki Choi View Post
      Oops, but we still have few more to get the interests in tapes stirred.
      Something tells me that the next time I'm in the Northwest around Seattle, I have to time it so Bruce and Ki are around.

      - Bruce for his museum of tapes.
      - Ki for his museum of tape decks.

      It's been at least 5 years since my last visit to that area. Yeah, I'm looking for a reason to book a flight.

      Dre
      **************************************************
      Every day is a good day to play analog.
      - 12" 33-1/3 RPM or 45 RPM vinyl
      - 10.5" 15ips or 30ips tape
      **************************************************
      Every day is a good day for live music.
      **************************************************

      Comment


      • #48
        Originally posted by dminches View Post

        Am I correct in saying with the 10kHz tone you increase the bias until the recording sensitivity drops 3 dB?
        I use SM900 where you look for about a 6dB drop, but I use a 4.5 - 5dB "sweet spot" !

        Comment


        • #49
          Originally posted by Bruce B View Post
          I use SM900 where you look for about a 6dB drop, but I use a 4.5 - 5dB "sweet spot" !
          For SM900, RTM recommends 6.5 dB overbias only for 7.5ips. For 15 ips, they recommend 4 dB overbias.

          -Tim Leinbaugh
          -Professional RTR restoration and modification for 45 years.
          Tim@MusicTechnology.com
          www.MusicTechnology.com

          Comment


          • Bruce B
            Bruce B commented
            Editing a comment
            that's why I use my "sweet spot"!! bias is determined by formulation, gap width, speed and your ears!!

            http://www.mrltapes.com/mcknight_biasing.pdf

          • Tapetech
            Tapetech commented
            Editing a comment
            RMG/RTM never recommended 6 dB overbias for SM900 at 15ips as you indicated ("I use SM900 where you look for about a 6dB drop"). That would be too much bias and would result in excess and possibly audible HF saturation.

            Their official recommendation for the typical pro record head (@ 15 ips) is 4 dB overbias.

        • #50
          Originally posted by Ki Choi View Post

          As you increase the bias, it will reach peak level and starts to decrease using both methods. For 10Khz tone methods you increase the bias level beyond its peak and let it drop further per your tape manufacturers' recommended amount per speed.

          Correct, as you leave the 0VU region of the VU meter, its accuracy is not certain at best especially when I tried to obtain 0.2dB change. I use either the external millivoltmeter or the Sound Technology 1510A to hit the 0.2 dB drop.
          Paul Stubblebine taught me the 1K tone method. He told me 0.25db drop. Fortunately I have 3 sets of audio cards for my ATR-102. So I have setups for three different tape types. Larry
          Analog- VPIClassic3-3DArm,SoundsmithZephyrII+MiyajimaZeroMono, 2xAmpex ATR-102,Doshi3.0 BottleheadPhonoPre,Herron VTPH-2A
          Dig Rip-Pyramix,IzotopeRX3Adv,Mykerinos,PacMicroModel2
          Dig Play-mchNADAC, LampiGG, Roon, HQP, Oppo105
          Electronics-Herron 360Pre,CJ MET1mchPre, Cary2A3monoamps
          Speakers-AvantgardeDuosLR,3SolosC,LR,RR
          Other-512Engineer/Marutani Symmetrical Power, ArtKelmGround1, AudioDiskVinylCleaner,AirTightRecordFlat, Scott Rust Interconnects,
          Music-15KRecs(90%classical),1KR2Rtapes,50TBrips

          Comment


          • #51
            Originally posted by Ki Choi View Post

            Correct, as you leave the 0VU region of the VU meter, its accuracy is not certain at best especially when I tried to obtain 0.2dB change. I use either the external millivoltmeter or the Sound Technology 1510A to hit the 0.2 dB drop.
            Last newbie question. How do you translate 0.2 dB into a change in voltage? What is the equivalence?

            Speakers: Vandersteen Model 7s, 4 M&K ST-150Ts, 1 VCC-5; Amplification: 2 Vandersteen M7-HPAs, CI Audio D200 MKII, Ayre V-6xe; Preamp: Doshi Audio Line Stage v3.0; Phono Pre: Doshi Audio V3 Phono Pre; Analog: Wave Kinetics NVS; Durand Telos and SME 3012R Tonearms, Lyra Etna SL, Ortofon Anna, Benz Micro LPS; Reel to Reel: Technics RS-1500; Doshi Tape Pre-Amp; Studer A810; Tascam BR-20; Multi-channel: Bryston SP-3; Digital: Custom PC> Lampizator Big 7 DAC

            Comment


            • #52
              I won't bore you with the formula and graphs to figure out the voltage representation of 0.2dB. As you might already know the dB scale is not linear, and it is logarithmic so the voltage difference from 2dB and 0.2dB is rather small.

              In short I would say if I were to measure the voltage difference of 0.2dB, it would be about ~1.02uV and 2dB swing will measure about ~1.26uV.

              This tape thing, like other analog media, nothing is an exact science. If you want bigger change to set your bias level, 10Khz method may work better for you. On average 10Khz method uses 3dB overshoot. Thus it would be better to use the recorders VU meter to make 3dB overshoot from the peak than try to hit 0.2dB adjustments, IMHO.

              Comment


              • #53
                Personally I find it easier to do this at 10k test tone. It's about the only time I use VU meters instead of PPMs. Fortunately the VUs on the Sony APR 5000 series and the Studer A820 are pretty good.

                Comment


                • #54
                  Originally posted by dminches View Post

                  Last newbie question. How do you translate 0.2 dB into a change in voltage? What is the equivalence?
                  You should not use a DMM (digital Multi Meter) to measure voltage when setting bias with the 1K method. It won't work due to small level fluctuations of the 1KHz tone. You won't see the .2 dB change (in voltage readout).

                  You need to use an external, analog dB meter with a high-rez scale (1/10th of a dB increments). My Sound Technology 1700A has that. Your typical VU meter on a deck is petty low-rez and won't let you see .2 dB.

                  Or use the 10K method where you look for a 4 dB level change if you use SM900 at 15ips (much easier to see 4 dB)
                  -Tim Leinbaugh
                  -Professional RTR restoration and modification for 45 years.
                  Tim@MusicTechnology.com
                  www.MusicTechnology.com

                  Comment


                  • #55
                    Originally posted by Tapetech View Post
                    Or use the 10K method where you look for a 4 dB level change if you use SM900 at 15ips (much easier to see 4 dB)
                    What level change would one seek at 30 in/s using SM900?

                    Vbr,

                    Sam

                    Comment


                    • Tapetech
                      Tapetech commented
                      Editing a comment
                      1.5 dB overbias at 10K for 30ips.

                    • c1ferrari
                      c1ferrari commented
                      Editing a comment
                      Thanks :-)
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