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Author Topic: Bias for RMG - Technics 1506  (Read 11009 times)

Offline Soundproof

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Bias for RMG - Technics 1506
« on: December 31, 2011, 04:20:41 AM »
I have bought the 911 and LPR35 tapes from RMI.

As I believe the 911 uses the old BASF formula, I have been using the bias settings for BASF when recording (2-2).
But would like to know what experience/recommendations members have for these tapes on my Technics?
« Last Edit: January 02, 2012, 02:05:58 PM by Soundproof »
Stein Leikanger
TD124/Beogram 3000, Technics 1506, Beolab 5000 amplifier, Helsinki Gradient 1.5 speakers.
http://www.hifisentralen.no/forum/index.php?action=dlattach;topic=62965.0;attach=290514;image

Offline ironbut

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Re: Bias for RMI - Technics 1506
« Reply #1 on: December 31, 2011, 12:53:30 PM »
Hi Soundproof (btw, we use our real names here, please read the "Forum Rules),

Welcome to the forum.

It always best to have your machine biased for using a specific tape rather than hoping that the factory settings will work well. Also, unless you bought the machine new, you never know if a previous owner has changed those settings and if it was done correctly.
Bear in mind that some of the advantages of having your machine biased for a particular tape is to take full advantage of what that tape is capable of.

If you're an old hand at this, find yourself a service manual.
If you're kinda new to all this, it's a good idea to find a tech in your area and have him do an alignment and bias one of the setting for the tape you want to use. Someone with all the right equipment and test tapes do this will establish a base line of machine performance (many will provide print outs of record/playback results).

I have my 1500 biased for 911 and I've been pretty happy with it. I don't do very much recording but having the option to use the "longer play" LPR35 is a big plus IMHO. Another practical consideration is it seems to be the most widely distributed tape.
If I was planning to do critical live recording work, I'd bias my machine for the new ATR Magnetics tape since it has the most headroom of any tape.
steve koto
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Offline Soundproof

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Re: Bias for RMG - Technics 1506
« Reply #2 on: January 02, 2012, 03:27:07 AM »
Thanks.
The player has been serviced and calibrated by a professional studio tech to Technics' RT-10B218, and that should give proper EQ and BIAS for BASF at 2/2.

However, I have subsequently read that the RMG 911 is not based upon BASF but on Maxell, and my question could have been clearer.

Anyone know for certain what established tape-formulas one can compare the RMG 911/LPR35 tapes to?
« Last Edit: January 02, 2012, 02:07:05 PM by Soundproof »
Stein Leikanger
TD124/Beogram 3000, Technics 1506, Beolab 5000 amplifier, Helsinki Gradient 1.5 speakers.
http://www.hifisentralen.no/forum/index.php?action=dlattach;topic=62965.0;attach=290514;image

Offline ironbut

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Re: Bias for RMI - Technics 1506
« Reply #3 on: January 02, 2012, 01:41:36 PM »
Hey Stein,

If your tech adjusted your machine for 911 then that's all you really need to know.
A decent tech would have downloaded the data sheet from RMG and used it to bias the machine.
If he hasn't, here's the link;

http://www.rmgi-usa.com/page4/page4.html

You'll notice that there is a data sheet for each formula.

911 is a formula that was used by Emtec. I never heard that Maxell had used it but it could be that they had a tape that had similar bias requirements.
steve koto
 Sony scd 777es(R. Kern mods)> Vpi Aires>Dynavector XX-2mkll>Bent mu>CAT ultimate>CJ premeir 140>Magnepan 1.6qr(Jensen xover)Headphone Eddie Current Zana Deux>AT ad2000,HD800 ,Metric Halo ULN-2 (battery powered),
 HE Audio Jades

Offline Soundproof

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Re: Bias for RMG - Technics 1506
« Reply #4 on: January 02, 2012, 02:08:20 PM »
Thanks, that should help. Not that I plan to do much recording, but it's good to get it right when one does.

Cheers.
Stein Leikanger
TD124/Beogram 3000, Technics 1506, Beolab 5000 amplifier, Helsinki Gradient 1.5 speakers.
http://www.hifisentralen.no/forum/index.php?action=dlattach;topic=62965.0;attach=290514;image

Offline Phil_in_CA

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Bias - Technics 1500
« Reply #5 on: January 05, 2012, 11:55:18 AM »
Hi Steve,

Finally got back to working on my 1500.  I am trying to bias my deck to take advantage of some reel ends that I got from the Tape Project, back when they were selling them...  I can't remember the type just now, but anyway, I was attempting to set the bias only to find that my machine won't peak!

When I rack the bias control from end to end, the output tracks from low to high, and never peaks.  It seems that the machine won't generate enough bias to actually over bias this tape...

I wonder, and it has been suggested to me, that the coupling caps are shot and there isn't enough bias reaching the heads to have a peak.  Does this speak to you?  I expected a peak at least at the high end of the bias setting.

I want to get this set up so I can record with my new heads and now it looks as if I am going to have a huge re-capping project on my hands first!!  Not something I am looking forward to, since I do not have a desoldering station... argh.  I hate reworking pc boards!  Removing components is my least favorite part of electronics.

Before I forget, I hope you have had a great holiday.  We stayed home, where it was warm and quiet...

TTYL,
Phil

Offline Tim

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Re: Bias for RMG - Technics 1506
« Reply #6 on: January 05, 2012, 12:50:13 PM »
I don't think it's a defect cap problem. The 10Khz peak occurs with a "too little" bias setting, so perhaps the control can't turn down the bias enough. Since this deck has no real record EQ adjustments, you can't set bias "by the book" anyway.  (book would be to peak 10K, then increase bias so that 10k drops 3db, then set record EQ for a flat response.  This for 15ips.)  Also don't assume CW on the control is more bias.  May be less.

-Clean the EQ and bias switches (they could be defective)
-set bias so that 1k and 10k are the same level
-try this for all 3 bias/eq switch positions
-use position that give you best results as for as distortion at peak record level (peak level is 6 db higher than 0VU.  Should be less than 3%)  Or use a listening test for each switch position if you have no test equipment.
Tim Leinbaugh
Service Technician
with RTR specialty.

Offline Phil_in_CA

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Re: Bias for RMG - Technics 1506
« Reply #7 on: January 05, 2012, 06:57:21 PM »
Thanks for the reply, Tim.

Yes, "By the Book" I know.  I cut my teeth on Ampex AG-440 in the 70s but could never afford one, at my "Assistant to the Chief" pay grade! LOL!  Biasing them was a snap, as it was just a tweak...

Anyway, these Technics decks are a breed apart from the 440s.  I have the service manual and can say that the biasing procedure uses the voltage drop across a 1 ohm load resistor in the record head circuit.  All this does, unless I am asleep, is to put the machine back to factory spec's, which is not what I want; unless the TP pancake tape I have (SM468, I believe) could be optimized with one of the factory settings (bias 1,2,3).  Hmmmm, probably not; most likely not!

Maybe someone here will chime in with their best idea on how to bias the Technics 1500 to Tape Project Tape.

Offline Tim

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Re: Bias for RMG - Technics 1506
« Reply #8 on: January 06, 2012, 03:14:50 AM »
I already posted how to bias the Technics RS1500 for Tape Project tape (SM468). See reply #6.  Adjust the internal bias cal pot so that 1K and 10K are the same level.  Your only control of record EQ is the front panel selector, so try adjusting the bias for each front panel EQ setting (1,2 or 3) and see which one works best. After that, set your record level cal and meter cal as per service manual instructions.
« Last Edit: January 06, 2012, 05:42:35 PM by Tim »
Tim Leinbaugh
Service Technician
with RTR specialty.