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Calibration tutorial

Can I do it?
In short, you can.

What you will need

First of all, for a complete adjustment, you need a service manual for your deck. Without it, you can only perform basic head alignment. You need alignment tapes, and you have several options. Find yourself a set of Nakamichi originals (difficult task). Grab a new set of TEAC calibration tapes (however not quite the same, as these comply with IEC Standard “Prague 1981”, to which Nakamichi does not completely adhere) [May 2013 Update: This TEAC link hasn’t been working for a long time now. All TEAC Cal Tapes are gone 🙁 ]. Alternatively you can get a nice set here.

Some measuring equipment too. Ideally, you would need a wide-band true RMS voltmeter. Some older manuals refer to a VTVM (Vacuum Tube Volt-Meter), being high input impedance the most important spec, so you don’t load the circuit while measuring. Most modern Digital Multi-Meters (DMM) will do the job properly. These usually have also a frequency counter, always handy for speed measurement. An oscilloscope is always a good idea, but you can do without it.

A tone generator. This is specifically used to align the record head. If you don’t have one, you can use your PC to generate a tone. Several free tone generators are available out there. I, however, have created 4 6-minute test tones, which are available for download to my calibration tapes customers. These are 0dB 400Hz, 1KHz, 3KHz and 15KHz, compressed with Apple Lossless Codec. If you have an iPod, they can be played from it, or with the help of iTunes, you can record them on a CD.

The all-in-one tool is the Nakamichi T-100 Audio Analyzer, still available today at reasonably prices (400-500€ range) from eBay, which comprises level and peak metering, wow & flutter, distortion, etc.

If you only can get hold of a DMM, I would recommend looking at this software: Audio Level Meter, developed by Paul Marshall and specifically the QUAD version. I have contacted Paul and he is about to do some mods to the program so it can fit better for the purpose. Right now, it provides metering for L and R channels, as well as mono signal and stereo only (difference) readings. This is quite useful, because a properly aligned signal will be “in-phase”, thus making sum maximum and difference reading minimum. An “out-of-phase” signal will make difference maximum, and sum minimum. May 2013 update: For a Mac alternative, please check out ProLevel, by Katsura Shareware. Thanks to Andy de los Reyes for this useful link for Mac users!

You can connect the deck to the input jack of your PC and use the program to monitor the alignment process. These reading will only mean relative values (i.e. higher or lower values), as no absolute readings can be performed.

Use of this program is free and unrestricted. However, if you find the program useful, please consider making a small contribution via PayPal to Paul. See his website for details.

I am about to explain the basics of alignment, and this should only serve you as a guide. Before attempting to do any work on your deck, make sure you have cleaned and demagged all parts. USE AT YOUR OWN RISK. IF WHILE FOLLOWING THIS GUIDE YOUR DECK BLOWS AWAY YOUR ENTIRE NEIGHBOURHOOD, DON’T BLAME ME.

Calibrating the deck

Speed adjustment: Load the 3KHz tape, and connect your DMM with Freq. Counter to the output of the deck. If an output pot. is available in your deck, leave it at maximum. Play the tape. Read the freq. from the DMM and adjust speed to get 3.000Hz, or as close as possible. The speed adjusting pot can be located in several places, refer to your deck’s service manual. If you have a wow and flutter meter, use this tape to read it. If you get a reading say lower than 0,1% you deck is in good shape. Newer decks should not read more than 0,07%, while older or very used machines can peak at around 0,12-0,15%. No wow and flutter meter? Listen to the tape. If a constant tone is heard, your are OK. However if you hear fluctuations in the tone, dips or pops, you may be facing W&F problems. You will need to check belts and lubrication. This is beyond the scope of this guide.

The following is a picture from a CR-7, showing the usual location of the 4 adjustments on a 3-head Nakamichi deck. Note the red marks I placed before adjustment. This can help should you need to go back to the initial setting.

CR-7

Playback level adjustment: A reference level is very important – among other things – for the Dolby circuits. This is done with the 400Hz level tape, and provides an accurate level reference to adjust the playback gain and the Dolby circuits. Measure signal at point of playback amp specified by the service manual. Adjust to obtain reference voltage. Some modern decks use a 1V playback reference value, while older models use 580mV at output terminals. Always check your service manual for details.

Playback head height: (not adjustable in all decks – for example 500 or 600 series) This adjusts the head heigh position with respect to the tape, making sure it is right on top of the tape’s recorded path. Start the Audio Level Meter (PPM) on the PC. Load and play the 1KHz tape. Adjust head height screw (refer to SM for details) until you get maximum levels on the meters (please be aware that, with the Nakamichi original track alignment tape, this adjustment should be minimum as referred to in the service manual!). Do the following: Turn the screw slowly (no more than +/- half a turn, otherwise you may be facing other severe mechanical problems!) until you get max green and red (L and R) readings (of aprox. same reading). When you think you are close, fine tune using the white and yellow needles. Look for maximum white and minimum yellow. If you get a lot of red / green difference and the needles don’t come close at maximum levels, your may need to repeat the playback level adjustment 😉

PPMquad
Green: Left
Red: Right		 White: Sum
Yellow: Difference

Playback azimuth alignment: This adjustment rotates the head to make sure head is parallel to tape’s recorded path. Slight azimuth errors lead to poor high frequency response. Start the PPM (check input level, this is a -20dB signal!). Load and play the 15KHz tape. Adjust head azimuth screw – always refer to SM for details – until you get maximum levels on the meters. Do the following: Turn the screw slowly (no more than +/- half a turn, otherwise you may be facing other severe mechanical problems!) until you get max green and red (L and R) readings (of aprox. same reading). When you think you are close, fine tune using the white and yellow needles. Look for maximum white and minimum yellow. If you get a lot of red / green difference, your reference level may be be out of tune. If your deck has recorded a lot of tapes while azimuth was not spot-on, your pre-recorded tapes may sound dull. If you don’t have playback azimuth adjustment (Dragon, CR7 or cassette deck 1, among others), you should seriously consider leaving your head slightly misaligned so most tapes sound fine. If you intend to do so, play a pre-recorded tape, and adjust azimuth “by ear” until you get the best treble performance.

It is very important to repeat these last adjustments (PH height and azimuth), as they are always complementary. At least 2 or 3 iterations until perfect alignment!

Record head height and azimuth adjustment: Only for 3-head machines. Load a Type IV metal tape (ideally a reference Nakamichi tape, but most will do fine). Check your service manual for details. Record-play the 1KHz tone, at about 0dB level, and monitor the recorded signal. Adjust RH height to obtain maximum levels on the PPM, and minimum signal difference (yellow). When done, record-play the 15KHz tone, adjust to aprox -20dB, and proceed to adjust RH azimuth screw until you get maximum levels on the PPM, and minimum signal difference (yellow). Repeat both head height and azimuth adjustments.

Once you are there, you most probably have a nice, aligned deck. Congratulations!