Tape Biasing - Help Needed

Discussion in 'Tape' started by Bigerik, Jan 6, 2010.

  1. traf

    traf Active Member

    Messages:
    108
    One area of possible interest is how to upgrade/adjust some models in order to be able to reach the higher bias that is required for modern (high output tape) as many old models were set to work with lower output tapes, that are no longer available as new stock.
     

     

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  2. jan_stevns

    jan_stevns Super Member

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    Sounds strange - think the remaining producers do make tapes suited very well for all the tapedecks i can think of
     
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  3. dr*audio

    dr*audio Fish fingers and custard!

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    I don't know of any reel to reel decks that can't simply be adjusted for high bias tape. I had an Ampex 1260 tube deck that I had no trouble adjusting for Scotch 207 tape. The deck does not have to have a front panel switch with a high bias setting, the bias oscillators on reel decks put out enough voltage to work with high bias tapes. Regarding cassette decks, the early ones that are not made for high bias tape do not have good enough performance to be worth bothering with.
     
  4. Jonny Ramone

    Jonny Ramone Super Member

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    Nakdoc, are the record level pots used to adjust tapes for their sensitivity characteristics, for better noise reduction tracking?
     
  5. dr*audio

    dr*audio Fish fingers and custard!

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    The record level pots are to compensate for the sensitivity of the tape, so that when you record at 0dB, it plays back at 0dB. This is important for noise reduction tracking, as you said, but in general, to have the proper level settings is desireable. To get the proper dynamic range out of the recorder, you want to be able to record at the maximum level possible. If you set the record levels at 0dB, you don't want it to actually record at -3dB. Then you lose dynamic range. Conversely, you don't want to record at a higher level than you think you are, or you'll run into gain compression and distortion.
     
  6. SaSi

    SaSi Seriously Illogical Subscriber

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    I think we need to differenciate between cassette tape biasing and R2R tape biasing.

    In general the R2R tapes have similar biasing requirements and very little difference between them. With cassettes, there is a wider range of bias requirements and many more formulas (Fe2O3, FeCr, CrO2, Metal).
     

     

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  7. ricohman

    ricohman Adventure Rider

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    Reading all this is giving me a brain ache.
    I have messed around with my Pioneer CT-F650 enough to know how bias can effect the recording.
    But I would really like this deck to be "tuned" by a pro seeing as there is so much else to it.
    Any specific questions I should be asking before I drop it off? The deck functions fine but came to me with little high end.
     
  8. dr*audio

    dr*audio Fish fingers and custard!

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    Just get a good recommendation for a reliable Cannuck tech to send it to. He'll know what to do. If you do not have any other cassette tapes you want to play properly on it, have him align it to a standard tape. If you have some tapes made on another deck, send one with it, and have him align to that. If all you have is pre -recorded tapes, he can just align it to a standard tape.
     
  9. ricohman

    ricohman Adventure Rider

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    I have both pre-recorded and stuff I recorded a long time ago. I will start looking for a good local tech.
     
  10. knasty

    knasty Active Member

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  11. Old1625

    Old1625 Super Member

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    When I was doing service on tape recorders I used to use a function generator with a sweep feature that I would set to sweep from midrange up into the 20Khz range.

    Step one was always to spool in an MRL test tape and establish proper levels and reproducer frequency response.

    Then spool in the desired brand and series of tape. The three-head decks were easier to establish proper bias, as one could monitor the sweep envelope on the scope while gently tweaking the bias settings. The 2-head deck was more a trial-and-error process until a good sweep was verified on PB.
     

     

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  12. Rob-F

    Rob-F Likes Vintage Gear and DIY

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    I thought of a way to get across the concept of biasing a tape recorder, without all the technicalities. Let's say you want to look out of a window, at a view of some trees outside. But the window is not very large, and is set high on the wall--the window sill is above your eye level. So you get a stool, or a pedestal, to stand on. If the pedestal is too short, you won't be able to see the bottom of the trees. If it's too tall, it will cut off your view of the treetops. So you get an adjustable stand that you can set so that your eye level is just centered in the window--the same distance from the windowsill as to the top. Now you have a view that cuts off neither the treetops nor the bottoms.

    Tape biasing is like that. The bias provides a "pedestal" for the audio signal to "stand on" so that it is stronger than the minimum signal it takes to magnetize the tape (above the windowsill). Then we adjust the record level so that the strongest signals are still within the top of the "window"--that is, the tape's ability to accommodate the signal.

    How's that?
     
  13. JBryan

    JBryan New Member

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    7
    Excuse me for butting in... I have quite a few R2R blank tapes that came with my deck. They are Maxell UD35-180/B and they sound fine on playback. A couple of years ago, Guitar Center was selling out their stock of Quantegy reel tape but all they had was the 499 on 10" reels. I realized at the time that these tapes had different bias' but figured I'd cross that bridge when I got there. Well, I'm much closer now and I'm wondering if there's a good/proper way of biasing my deck (Akai GX-400D) to accommodate both tapes for recording and playback. Any thoughts would be most appreciated...Thanks
     
  14. Jon_Logan

    Jon_Logan Addicted Member

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    I can't remember the akai specifically, but if there's something like a "Bias Hi Lo" switch, you can adjust each position for a brand of tape.
     
  15. dorramide7

    dorramide7 New Member

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    My main deck (for now) is a 1984 Technics RS-B18 I got for graduation. 2 head with Dloby B,C, and DBX NR. Note the bias pots- there are also pots for gain, playback level, etc. A test tape and Dr. Audios info would have served me VERY well back in the day. I adjust mine with the power off. On a 3 head deck, I believe a plastic flathead screwdriver would be used while monitoring, but I'm not, REPEAT, not an electronics technician, so don't electrocute yourself! Clockwise to increase.
     
  16. Wilhem

    Wilhem Active Member

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    326
    BASF Explanation of Bias by Terence O'Kelly

    This explanation may help. The "curves" attachment shows how a change of bias affects output, sensitivity, noise, and distortion. The purpose of a bias current is to reduce distortion and increase output. The "proper" bias is a compromise between low frequency MOL and high frequency SOL. Too much bias increases low frequency output and reduces distortion (note the nadir of the distortion curve), but at that point the high frequency wavelengths are being recorded below the surface of the tape, and treble response drops off due to spacing losses--too far from the playback head gap. Too little bias causes too little low frequency output and dramatic increases in distortion.
     

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  17. Will S.

    Will S. Well-Known Member

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    Note that bias adjustments really shouldn't be performed in isolation. It's one step in the process of aligning a deck that starts with heads and ends with record eq. Here's a good article on performing full alignments: http://www.churchsoundcheck.com/tra.html It's pretty much exactly the way I used to do it.
     
  18. LAB3

    LAB3 AK Member Subscriber

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    I think he had a typo "GS-4000D" if so it does not have a Bias Hi Lo switch.
     
  19. KristianJ

    KristianJ Hillman owner

    Messages:
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    Location:
    Skåne, Sweden
    My TEAC 3340 has two switches: EQ and Bias.They have two positions: High and Normal.
    I have left it at "Normal" because I don't know better, and I can't hear any difference. (Anything wrong with me?) :)
     
  20. Arnold_Layne

    Arnold_Layne Member

    Messages:
    56
    The 3340 switches are used as such: High Bias and High EQ are for Low Noise High Output tapes

    Low Bias Low EQ are for normal tapes. Most tapes are LNHO type.

    Steve
     

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