Revox A77 Calibration Tape

[algarcia]

Hi all,

I have a 2-track standard speed (7.5&3.75ips) Revox A77 that I'd like to calibrate. I know that I need to buy an MRL tape, but I'm confused as to which one I need. I think this one fits the bill: https://reverb.com/item/34268186-1-4-7-5-ips-mrl-four-frequency-calibration-tape

The four frequencies of the tape are 1 kHz, 10 kHz, 16 kHz, and 50 Hz.
This tape will be at +3db (250 nWb/m) at 7.5ips speed.

Do I need a tape with both speeds?
Maybe I'm overthinking it, but I'm still new to open reel decks and just wanted to make sure I bought the right thing the first time. Would I also be able to use this same tape on a 4-tack machine?

 

[KentTeffeteller]

Call Jay McKnight at MRL, he can walk you through what you need, and is very knowledgeable about what he sells, and what is best for your needs. He's friendly, a gentleman of the highest, and respected heavily in this industry.

 

[D_Zoot]

I think you might want MRL part # 21T204. Based on description the one in your link is the "short" tape, cost savings in minimal, I'd suggest the full 6 minute multifrequency tape #21T204. It has what you need to set repro level to +3, set head azimuth and perform repro frequency response checks at 7.5ips. No, you won't need another tape for 3.75ips. Speed/flutter tests are a second tape, but unless you suspect a speed problem you can skip this, it isn't needed for general alignment and calibration tasks.

 

[mateusfig]

How can I calibrate 3.75ips with a 7.5ips calibration tape?

 

[twiiii]

You will need a 3 and 3/4 inch calibration tape to as it has a different EQ curve and is calibrated at different levels.

Buy a Revox service manual. Its not a simple process and you will need the appropriate test equipment. You cannot trust Revox VU meters for calibration. And you are going to need to know the capabilities of the tape your record on to calibrate the record section after you get the playback sections right.

After you calibrate a R2R machine you will understand why most cassette machines are a compromise.

 

[mateusfig]

I have received the calibration tape. It has a aditional section for speed/flutter checking in the end (not showed at the image). All I have is a multimeter and the Nak T-100 software. I don't have osciloscope and milivoltmeter. Can I make some reasonable calibration? I'm not looking for perfection at this moment.

 

[jlb2]

Since the input and output levels of your sound card are not calibrated, the first step of any calibration job is to adjust them, and you cannot do that unless you have an instrument that tells you the actual voltage, namely an oscilloscope or an audio millivoltmeter. So unfortunately the answer to your question is no.

 

[jlb2]

Buy a Revox service manual.

Why buy one when you can have it for free from (the mirror of) the official Studer/Revox FTP site?

https://www.reeltoreel.nl/studer/Public/Products/Revox/Revox_A77/Manuals/

 

[D_Zoot]

How can I calibrate 3.75ips with a 7.5ips calibration tape?

That depends on the specific machine we are talking about. Different machines have different adjustment capabilities and calibration steps. In many cases, such as the Revox A77 the original poster was referring to, there are no separate repro adjustments for the 2 speeds, repro adjustments are made at 7.5ips and then due to the design of the repro circuits 3.75 should end up in specs as well. One may use a 3.75ips tape simply to verify there isn't a fault in the EQ circuitry, but this wouldn't be a necessity most of the time. Now, there are some machines that allow for separate repro adjustments, and in those cases you would want a tape for each speed to adjust the levels and EQ for each speed, but this isn't common with consumer level decks. Record calibrations at the 2 speeds are referenced back to the repro calibration, not the calibration tape, so the speed of the calibration tape isn't a factor for record calibration. What machine are you attempting to calibrate?

All I have is a multimeter and the Nak T-100 software. I don't have osciloscope and milivoltmeter. Can I make some reasonable calibration? I'm not looking for perfection at this moment.

In order to calibrate any deck you need a known point of reference. The calibration tape is used in conjunction with an appropriate scope and/or a meter to establish that point of reference. You need a meter that is a True RMS meter and accurate in the audio frequency range and at low voltages, most multimeters don't do this well and if you don't have a proper point of reference the whole calibration will be off.