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Studer A80mkII calibration REPRO EQ
Old 28th January 2009
  #1
Gear Head
 
Stefbossa's Avatar
 
🎧 15 years
Studer A80mkII calibration REPRO EQ

Hello !

I have a question regarding tape calibration for a 1/4inch stereo analog recorder Studer A80 MKII.

I use MRL reference tape, looking for a operating level of +9 with 499 tapes.

So I put the MRL 1K test tone for REPRO level. Set the meter VU to -9db in order to get an operating level of +9.

Then there is trims for TREBLE and BASS REPRO to be set on the Studer. For this I use respectively the test tape 10k and 100hz.

QUESTION: do I have to put these TREBLE and BASS REPRO levels to -9VU (same as desired operating level) or at 0VU???


Anybody familiar with this?

Old 28th January 2009
  #2
Lives for gear
 
nosebleedaudio's Avatar
 
🎧 15 years
What is the test tape level?
250nWb?
If so your levels should be -6dB on the VU.
For all frequencies.
Did you demag the heads?
Make 100% sure you do the alignment in the correct order, if you have never done it before...
Old 29th January 2009 | Show parent
  #3
Gear Head
 
Stefbossa's Avatar
 
🎧 15 years
You are right it should be -6 since it is a 250nWb.(+3)

Yes, I demaged it. Azimut is fine. It is just for the REPRO EQ TREBLE and BASS level I'm not sure. Do I adjust it same as REPRO LEVEL (-6) or 0VU using the 100hz and 10k tone of ref tape?
Old 29th January 2009 | Show parent
  #4
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nosebleedaudio's Avatar
 
🎧 15 years
Quote:
Originally Posted by Stefbossa ➑️
You are right it should be -6 since it is a 250nWb.(+3)

Yes, I demaged it. Azimut is fine. It is just for the REPRO EQ TREBLE and BASS level I'm not sure. Do I adjust it same as REPRO LEVEL (-6) or 0VU using the 100hz and 10k tone of ref tape?
Yes..
when you do the bias I would reduce the record levels, its more accurate...
Old 1st February 2009 | Show parent
  #5
Gear Head
 
Stefbossa's Avatar
 
🎧 15 years
Thanks for the info...

If you lower your recording level while adjusting bias, what range do you try to stay in? Should the bias highest reading be +3 before you lower 3.5 db over bias for 456 formula tape?
Old 1st February 2009 | Show parent
  #6
Gear Addict
 
AnalogBrain's Avatar
 
🎧 10 years
Hi,

I try to keep my bias peak around -1VU. Also, Studers do better (in my opinion) when the low test tone is 50hz. But what you have should be fine.

Yes, repro gain, repro hi EQ, and repro lpw EQ should all be at -6VU (with a 250nWm MRL tape).

-Neilthumbsup
Old 25th June 2009 | Show parent
  #7
Lives for gear
 
🎧 10 years
Hi

I have aligned and calibrated A 80 and everything is working fine .
I did some experimenting with the repro amp EQ and level settings by recording the sine wave signal at different levels and came up with some interesting results .

When recording sine wave to tape at -30 dbfs to - 20 dbfs i get pretty flat response on the output of the deck. Then i did some testing by recording the sine wave at - 6 dbfs to tape and i got:
1.5 db less at 100 Hz and almost 2 db less at 10 Khz on the output .

So i decided to set the EQ on the repro amp based on the - 6 dbfs sine wave ( which is NO-NO i know ) just to hear the results , and i like it . It sounds more open ,live ,interesting and overall better then setting the repro amp at -20Dbfs which sounds more ... flat .

Do you guys fool around with your repro EQ settings ? Would you like to share some of your experimenting results ?

Thanks
Old 25th June 2009 | Show parent
  #8
Gear Guru
Never "mess around" with tape machine settings unless you know what you're doing.

Low frequency EQ is done during the record alignment, not during the playback alignment due to tape fringing.

Bias points are determined via a distortion analyzer if you want to nail it. Record/play EQ is best done with an analyzer like Audio Precision with a frequency response function to smooth out the response. Otherwise, it's a guess, a bad thing to do with an analog machine. All the recommended tape bias points are wrong and will vary for every track of every machine. They are only useful as a starting point.

A precisly aligned tape machine is a wonder to hear, a miss aligned tape machine is torture.

Jim Williams
Audio Upgrades
Old 25th June 2009 | Show parent
  #9
Lives for gear
 
BradM's Avatar
 
🎧 15 years
Jim,

I've seen you recommend using the AP analyzer to align tape decks in many threads. Obviously 99.999% of us don't own an AP system. Is there another acceptable way that you would recommend for achieving good results?

thanks,
Brad
Old 25th June 2009 | Show parent
  #10
Gear Guru
I've used the AP since 1992. The other common technique is using a low frequency sine wave at 20 hz and adjusting bias for lowest modulation noise. I found after checking a machine aligned with that technique it was very close. Do a google search on it for more details.

Jim Williams
Audio Upgrades
Old 25th June 2009 | Show parent
  #11
Lives for gear
 
BradM's Avatar
 
🎧 15 years
Yes, I know exactly what you are talking about. That's how I've been adjusting my bias. I've been using a 30Hz tone though.

Brad
Old 26th June 2009 | Show parent
  #12
Lives for gear
 
🎧 10 years
Quote:
Originally Posted by Jim Williams ➑️
Never "mess around" with tape machine settings unless you know what you're doing.

Low frequency EQ is done during the record alignment, not during the playback alignment due to tape fringing.

Bias points are determined via a distortion analyzer if you want to nail it. Record/play EQ is best done with an analyzer like Audio Precision with a frequency response function to smooth out the response. Otherwise, it's a guess, a bad thing to do with an analog machine. All the recommended tape bias points are wrong and will vary for every track of every machine. They are only useful as a starting point.

A precisly aligned tape machine is a wonder to hear, a miss aligned tape machine is torture.

Jim Williams
Audio Upgrades
Hi Jim

My mashine is aligned by a tech guy with proper instruments , the guy knows what he is doing .
After that i had some issues with repro amps on my studer A80 so i had to get another pair of the repros and change them . When i did that i checked the sine wave at - 6dbfs and realized that i have drops of 1.5 db at 100 hz and almost 2 db at 10Khz . So i called my tech and he told me i should make it flat at all freq. by using -30 dbfs sinewave . After i did it step by step i just recorded the same track back to the PC
1. take - repro amps set by -30 dbfs sine
2. take - repro amps set by -6 dbfs sine

i like the sound of my mashine set flat at all freq. by using the - 6 dbfs sine wave - thats all .

BTW i didnt touch the recording amp bias , level or eq ....

Do you have any explanation for this ?

Thanks
Old 26th June 2009 | Show parent
  #13
Gear Guru
First off, you can't swap repro cards willy-nilly. They too have adjustments for levels and playback EQ. They must be precisly aligned via a MRL test tape. You cannont fix record errors by playing around with repro settings. Your tech is wrong when he said to adjust the repro electronics via a recorded signal. That's the opposite of what you're supposed to do.

Put up the MRL tape and look to see if the playback is aligned. That assumes of course that your meters are also calibrated. Most I find are not, that's usually the first thing to check.

Jim Williams
Audio Upgrades
Old 26th June 2009 | Show parent
  #14
Lives for gear
 
nosebleedaudio's Avatar
 
🎧 15 years
I know TOP engineers that have aligned their tape machines for YEARS with OUT a distortion meter and have hit records...
You do NOT need a AP to check distortion on a tape machine, the low end distortion meters will be just fine, and MOST tape machines will have .2% or higher anyway...

My .02cents...

I still use the old 10KHz tone, you either have MORE or Less bias, heard of the 1KHz alignment ect..don't see it making a huge difference...

One thing I have noticed is this: the harder you hit the tape the MORE bias you need for the same distortion level...
It's a compromise in my book..
Old 26th June 2009 | Show parent
  #15
Lives for gear
 
🎧 10 years
Quote:
Originally Posted by Jim Williams ➑️
First off, you can't swap repro cards willy-nilly. They too have adjustments for levels and playback EQ. They must be precisly aligned via a MRL test tape. You cannont fix record errors by playing around with repro settings. Your tech is wrong when he said to adjust the repro electronics via a recorded signal. That's the opposite of what you're supposed to do.

Put up the MRL tape and look to see if the playback is aligned. That assumes of course that your meters are also calibrated. Most I find are not, that's usually the first thing to check.

Jim Williams
Audio Upgrades
Jim i totally agree with you and understand what you are saying .
I was playing with adjustments for levels and playback EQ ON the repro cards cos there is no other place on studer where i can adjust the repro amp. I know that's "wrong" but it sounds so much better now .
My studer was aligned the way you described , the playback first with MRL tape etc ... So you are saying after the repro is set right with test tape then i should adjust the record cards levels and EQ to get the linear freq. response over the whole spectrum by recording the sine wave - its clear . My question is what level of the sine wave should i send ? Since i was sending sine wave from my PC i noticed that when sending -20to -30 dbfs sine wave ( 100 hz , 1Khz and 10 Khz) my output was linear -so what came in came out but then when i sent the - 6 dbfs sine wave i had 1.5 db less at 100 hz and 2 db less at 10Khz and 1khz was linear . So i guess the drops are caused by tape saturation or maybe i am wrong ?
Another thing is that I don't have the VU meters on my studer so i am reading my signals over total mix ( rme ) and yes we have measured the output and input of converters and set the input and output level of the machine so that i can control it from my DAW . We made the - 14dbfs from my DAW going out from my apogee rosetta to be 0 dbVU on my studer aligned for RMG SM468 tape. This way my mixes are peaking at - 2 dbfs in my DAW and i also have 2 db extra ( before i hit 0 dbfs) to hit the tape harder without overloading my DAW .I went true this method step by step with Bob Katz couple of months ago on this forum .
So everything is pretty clear except how comes it sounds better now ?

Another thing is that i am using only the tapes which i recorded on the very same tape machine , i mixdown to tape so basically its not the worse thing in the world if i make up on repro amps a bit .
When you sent the tapes to ME you are recording the sine waves anyway for him to be able to align his machine so that your tape sounds right on his machine too right ?
Old 26th June 2009 | Show parent
  #16
Gear Guru
Quote:
Originally Posted by nosebleedaudio ➑️
I know TOP engineers that have aligned their tape machines for YEARS with OUT a distortion meter and have hit records...
You do NOT need a AP to check distortion on a tape machine, the low end distortion meters will be just fine, and MOST tape machines will have .2% or higher anyway...

My .02cents...

I still use the old 10KHz tone, you either have MORE or Less bias, heard of the 1KHz alignment ect..don't see it making a huge difference...

One thing I have noticed is this: the harder you hit the tape the MORE bias you need for the same distortion level...
It's a compromise in my book..
Doesn't have to be if you see what's happening on the analyzer. Dolby HX was developed to overcome the increased bias effects of hitting tape harder with lot's of high frequency content, it added energy to the bias waveform and increased bias and lowered hf response.

.2% is not typical. I measure .5% typical on a stock recorder at 250 nw at 1k hz. The THD curve is not linear, it appears as a smiley face, with lowest THD at 1k with 100 hz and 5k hz passing 4% THD. One can optimize THD vs frequency with bias. You can lower it in the bass at the expense of the tops. Or do the opposite.
I like to get it pretty even.

A modified record/play tape machine can do much better. I have reached .15% at 1k hz at +9 db (520 nw) on an MCI JH-110C. That's far better than the stock measurements of .55% at +3 (250 nw).

As to frequency response accuracy, just pin pointing 1k and 10 k leaves the rest to chance. That's were the frequency response sweeps on the AP help out. You can see the bumps and maybe smooth them out a bit IF you can see what you're doing. Otherwise, it's a crap shoot. Yes, many hits were done with crap shoots, still, it doesn't make it right.

Then you can use the AP for other set ups like tension and wow and flutter measurements. You can use it to phase align the stereo heads. You can use it to calibrate the recorder's meters.

That is if those things are important to you. I've never tested an analog recorder that didn't have some or most perameters set incorrectly. Even a new machine needs a complete going over after transport.

Jim Williams
Audio Upgrades
Old 26th June 2009 | Show parent
  #17
Lives for gear
 
🎧 10 years
Hey Jim why skipping dont you have any comment on my post ?
Old 26th June 2009
  #18
Gear Nut
 
@ΒΆ,*Ζ’Ζ’Ζ’&β„’'s Avatar
 
🎧 10 years
Quote:
Originally Posted by Stefbossa ➑️
Hello !

I have a question regarding tape calibration for a 1/4inch stereo analog recorder Studer A80 MKII.

I use MRL reference tape, looking for a operating level of +9 with 499 tapes.

So I put the MRL 1K test tone for REPRO level. Set the meter VU to -9db in order to get an operating level of +9.

Then there is trims for TREBLE and BASS REPRO to be set on the Studer. For this I use respectively the test tape 10k and 100hz.

QUESTION: do I have to put these TREBLE and BASS REPRO levels to -9VU (same as desired operating level) or at 0VU???


Anybody familiar with this?

Jim, what level is the MRL? +2 (185 nwb) or +3 (250 nwb)? Aligning 1 kHz to -9 VU is not where you want it for a +9 alignment. You want to align it to -7 VU if it's a 185 nwb tape and -6 VU if it's a 250 nwb tape. You make up the gain on the record side of the alignment.

As for your main question, yes, repro alignment will put the appropriate tones to the levels I just described. The unity gain alignment of feed from console to '0' on the meter will be done when you perform the record alignment.

Also, this alignment situation is not unique to the Studer A-80...it's for all machines...
Old 26th June 2009 | Show parent
  #19
Gear Guru
Quote:
Originally Posted by bass man ➑️
Hey Jim why skipping dont you have any comment on my post ?
Your machine doesn't have meters. That is a problem. Record alignment and low frequency playback EQ should be done at 0 VU. If your machine cannot reproduce that signal at 0 VU, you have larger fish to fry. On that MCI that I got .15% THD at +9 levels (520 nw) recorded flat to 32k hz at 30 IPS with 996 Scotch.

Jim Williams
Audio Upgrades
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