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Messages - reelnut

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Tape Tech / Re: What are the effects of bias current?
« on: November 20, 2008, 11:12:16 PM »
I thought this thread had been pretty well covered, until I came across what I've pasted in below. It's a direct quote from the bottom of page 11 of the MRL paper "Choosing and Using MRL Calibration Tapes for Audio Tape Recorder Standardization". (, one of my favorite papers to read. (I guess I should read it more often, since I had forgotten about this). The paper is a dandy, since it's written in a language that I can understand, and completely explains levels, eq, and more. The paragraph below prescribes a method of biasing for anyone (besides myself) who still is unsure of where to set the bias point when using an unfamiliar tape. I can't wait to try it. Read the whole paragraph- the best part comes at the end!

  "An old, simple, and effective method that we use for setting bias with all kinds of tape is to use a 1000 Hz test signal. First set the bias current for maximum recording sensitivity. Then, for 15- and 30-in/s recording, increase the bias current so that the recording sensitivity drops by 0.2 dB. For 3.75- and 7.5 in/s recording decrease the bias current so that the recording sensitivity drops by 0.1 to 0.2 dB. Another method, recommended by tape manufacturers, uses a 10 kHz test signal. We find this method more complicated ? you need toknow the gap length of the recording head, and the amount of signal reduction for each kind of tape and each speed ? and without any redeeming social value."

Tape Tech / Re: What are the effects of bias current?
« on: November 20, 2008, 07:58:32 PM »
Well, I know I haven't got it, but I get some of it!

Thanks again to George for his knowledgeable comments on this subject, and to all of the pros who are educating the rest of us!!

Reel to Reel Tape Machines / Re: Studer A810 reel tables
« on: November 20, 2008, 02:42:40 AM »
Arian & Steve:
Thanks for your interest in this. Arian opened my eyes to the obvious fact that the hubs could not affect the height of the reel. FYI I examined the Studer and Darklab hubs- they appear to be perfectly identical, except for the slaves. They appear to have been made in the same plant. They look like they come from the same mold. I don't know what to think. I did have both motors out of the machine roughly a week before I got the Darklab hubs, but didn't have the drums off of the motor shaft. I am certain the table height was correct prior to that point. Since the tape is packing about 1/16th inch from the front reel flange, that means the reel tables need to come up by approx. the thickness of a CD. Maybe some day I'll figure this out. Or, I could put about one precision machined washer on the shaft under the drum to shim it out correctly. Thanks to Arian for that info!

Reel to Reel Tape Machines / Re: Studer A810 reel tables
« on: November 19, 2008, 05:15:07 PM »
OK, I see what you're saying and you are absolutely right about the reels being pressed against the tables in both cases. But I noticed this misadjustment the very 1st time I used the Darklabs. I dunno what's goin on here, but I'm working on it and will get back to you on this! Thanks very much!

Tape Tech / Re: What are the effects of bias current?
« on: November 19, 2008, 04:51:22 PM »
What a wonderful in-depth reply to my question! There is much there to think about- Thankyou George!

Re your 3rd paragraph: I do the same when I'm adjusting the bias. I usually input the 10kHz at a level which brings the VU meters up in the middle of the scale. It's then much easier to over-bias by the amount you want, since you can accurately see the change on the meters. (The A810 manual say to input 10kHz @ -20db, and I always wondered how they expected you to see for instance, a -4.5db change from -20db!). I am familiar with RMGI's website and refer to it when using their tape. Ive also read JM's paper, which, as you indicated is an excellent reference. However, it's so technical I found it really hard to digest!

Man, I gotta tell ya the reference to BASE's website at is a real gem! There is a TON of info there pertaining to R2R's! I've already spent literally hours going through it all! Thanks again for taking the time to provide us with these insights George!

Tape Tech / What are the effects of bias current?
« on: November 19, 2008, 12:19:16 AM »
Hello readers! The reason I have this question stems from the fact I am using an A810, which has a digital interface to calibration, and that I am not an expert. This kind of hardware makes it extremely easy to set all recording parameters for every single tape you might record. Thus, if you are a tweak freak (I am one), there is no reason not to check and set your bias, level and freq. response for every single tape you record. The manual shows a table listing different types of tape and lists an "over-bias" amount for each one. So how does an expert bias a tape that's not in the table, and what are the effects of an incorrect bias setting? I know some will say just put it wherever you think would be best, but I need to know specifically what to listen for in order to do this. My understanding (meaning I may easily be wrong) is that as bias current is decreased treble sensitivity increases, but IM distortion also increases, and vice versa. What is IM distortion? Does it translate into muddiness or distortion on the low end of the freq. spectrum? Thanks for any help on this matter!

Reel to Reel Tape Machines / Studer A810 reel tables
« on: November 18, 2008, 06:00:05 PM »
Does anyone know how to change the height of the reel tables on a Studer A810? I recently purchased some NAB hub adapters from Darklab. They look EXACTLY like the Studer originals I have (except that the slaves are bonded directly to the hub, rather than being a screw-on affair). But when using them they cause the tape pack in the reels to be way off-center. The tape packs about 1/16th inch, or less, from the front flange of the reel, so it's actually acceptable, but it sort of drives me reelnutty that I can't figure this out. I have disassembled the tables down to the motor itself and can't see how to correctly adjust anything. Placing a CD disc on the table before putting on the NAB hub provides the added height that I need, but this is an unacceptable solution. The original Studer hubs provide a perfectly centered tape pack.

Suggestion Box / Re: Joan Baez
« on: November 17, 2008, 11:51:02 PM »
I also would vote for Joan. Most definitely. Or Judy Collins!

Tape Project Albums - general / Re: Before you play those tapes!
« on: November 17, 2008, 11:04:32 PM »
Good explanation and very worthwhile points! Thank-you for that info! However, here is where I believe the danger might lie: during fast wind, if there is no power in the tape tension assemblies the reels would not slow down and stop at the same rate. The reel with the least amount of tape on it would stop first, and the reel having the most tape is heavier, so it would keep on spinning and spilling its contents all over the place!

Tape Project Albums - general / Re: Before you play those tapes!
« on: November 17, 2008, 01:59:36 AM »
Has anyone ever thought about what'd happen to their prized tape if a power outage was to occur??? I pulled this tidbit
off of usrecordingmedia's website. It's a real gem:

You may want to consider using a UPS, or uninterruptable power supply, on your open reel deck. Why? If you're rewinding a tape to play it and the power goes off, even briefly, it can be a mess. You can possible ruin your tapes depending on the transport.

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