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Poor Man's Cassette Deck Speed Calibration?

JamVal

JamVal

Addicted Member
I watched a youtube video that shows a procedure to calibrate a cassette deck's speed without having a calibration tape or a frequency counter. I'm just talking speed, not wow-flutter, or any other parameter.

Basically the guy had a known deck that he trusted the speed to be correct on. He generated a sine tone from his laptop using Audacity and recorded it on the known good deck.

He then played it back on the suspect deck to be calibrated. Simultaneously he played the same tone from Audacity on his laptop. If the speed of the suspect deck is off, a wha-wha-wha like sound is heard. The faster the wha-wha-wha the greater the speed is off. He adjusted the speed potentiometer on the decks motor and listened for the wha-wha-wha to slow down and when it disappeared completely he was satisfied that the suspect deck was running at the same/speed frequency as the tape he had made from his known good deck. The term 'zero-beating' was used.

It immediately reminded me of essentially using that procedure to calibrate the Collins R-390A receiver I used when I was in the navy.

So I did a little test using two computers with Audacity. I told my wife to generate a tone on one computer, but not to let me know what frequency she chose. Using the 'zero-beat' method I was able to duplicate the frequency tone my wife chose on my computer. She was impressed and told me I had won a dollar.

Has anyone else used this method? Is there a frequency that should be used to make the calibration tape from. Most manufacturer documentation I have seen shows 3,000 Hz as the speed calibration frequency. But the guy in the videos used 440 Hz.
 
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Many speed calibration tapes I've seen are duplicated at 330 or 333 hz, IIRC - close to the E4 note on a music scale (using 440hz as the A4 note).

I made my own "calibration tape" @ 330hz using an Audacity sine wave > DAC > tape deck, but I had to try and calibrate the deck by ear first using a pre-recorded tape, and matching the pitch as best as I could to a CD/digital version of the music. I'm happy to say that even though this is far from perfect, or the "right" way to do it, the results are very, very close. Good enough for me, at least.

I've been able to use the tape made on the first deck to calibrate other decks to the same speed using the sine wave in Audacity to match it to. Yes, you adjust the speed potentiometer on the deck playing the calibration tape while Audacity is playing the matching sine wave tone until the "beating", or "wah wah-wah" stops. In a way, it's sort of like tuning a guitar by ear.

I eventually plan to get "real" calibration tapes for optimum results, but this method works well in a pinch if you have a deck that's known to play at the correct speed.
 
Setting speed on a tape deck is very very difficult if not impossible without a 3k test tape and frequency counter due to the actual mechanical screw setting. Even the smallest touch on the screw has a pretty major effect. You can watch it on a freq counter. Even touching the screw sometimes effects the speed. So setting speed by ear or anything else is a crap shoot. BTW. Using 330 hz is inaccurate due to the high error rate of the low frequency. It will get you close i guess just by luck, but since there will be a speed deviation from the beginning of the tape to the end, what once was fairly close will be less fairly close. :)
You can buy 3k speed tapes for pretty cheap on ebay although i dont know how accurate they are. :)
And how do you know if a deck you have is on the money, to use to make a test tape? Only a test tape will tell you. :)
 
Taketheflame said:
Many speed calibration tapes I've seen are duplicated at 330 or 333 hz, IIRC - close to the E4 note on a music scale (using 440hz as the A4 note).

I made my own "calibration tape" @ 330hz using an Audacity sine wave > DAC > tape deck, but I had to try and calibrate the deck by ear first using a pre-recorded tape, and matching the pitch as best as I could to a CD/digital version of the music. I'm happy to say that even though this is far from perfect, or the "right" way to do it, the results are very, very close. Good enough for me, at least.

I've been able to use the tape made on the first deck to calibrate other decks to the same speed using the sine wave in Audacity to match it to. Yes, you adjust the speed potentiometer on the deck playing the calibration tape while Audacity is playing the matching sine wave tone until the "beating", or "wah wah-wah" stops. In a way, it's sort of like tuning a guitar by ear.

I eventually plan to get "real" calibration tapes for optimum results, but this method works well in a pinch if you have a deck that's known to play at the correct speed.
Click to expand...

zedex said:
Setting speed on a tape deck is very very difficult if not impossible without a 3k test tape and frequency counter due to the actual mechanical screw setting. Even the smallest touch on the screw has a pretty major effect. You can watch it on a freq counter. Even touching the screw sometimes effects the speed. So setting speed by ear or anything else is a crap shoot. BTW. Using 330 hz is inaccurate due to the high error rate of the low frequency. It will get you close i guess just by luck, but since there will be a speed deviation from the beginning of the tape to the end, what once was fairly close will be less fairly close. :)
You can buy 3k speed tapes for pretty cheap on ebay although i dont know how accurate they are. :)
And how do you know if a deck you have is on the money, to use to make a test tape? Only a test tape will tell you. :)
Click to expand...

Thanks for the replies.

This started as a result of playing a used "Dave Brubeck Time Out" tape I just bought. It started out OK, then slowed down to grossly distorted levels. I thought my deck had a problem until I played some of my other tapes that played back were fine. I read about old cassette tape cases with slip sheets that have lost their slip and transplanted the Brubeck tape into a new case. Problem solved. That led me to question whether or not my deck is running correctly and found the video mentioned in my OP.

I think my deck might be running a little slow and have tried timing some tracks on pre-recorded tapes against the same track from a digital source. The results are inconsistent. Which begs the question is it the deck or these old pre-recorded tapes suffering various levels of slow playback due to their mechanical condition.

Then I timed some tracks that I had recorded myself on this deck against their digital source and they are dead on. Of course they are, the record speed is the same as the playback speed, so even if my deck is off speed, anything I recorded on it will playback correctly. Yes?

After asking the question about what frequency to use for making my own test tape, I found that my DMM has a mode to measure Hz. So I measured the frequency of various Hz signals direct from Audacity --> Laptop--> DMM. There is a greater error at lower frequencies (<1,000Hz) than there is at higher frequencies as @zedex said.
All negative % error; examples 500Hz source -2.8% error on DMM, 1000Hz -2.0%, 3,000Hz -1.1%.

So, there can be error introduced from every possible variable:
Timing an old pre-recorded track against a digital source - the old tape case could be the problem.
Making a test tape on what I think is an accurate deck - big assumption.
How accurate is the tone generated from audacity and my laptop's sound card?
Accuracy of my DMM?

And I haven't even dared tweaking the deck's motor potentiometer yet.
 
You can tweak your Technics Deck and do it cheap. Buy the $10 3000hz tape from eBay and download a free sound spectrum analyzer for your cell phone, Tablet or computer.
Run the analyzer, plug in head phones. The adjustment pot is on the back of the capstan motor, the motor driving the large belt. You need a small flat screw driver like one used for repairing eye glasses. Wrap tape around the blade so only the end is exposed so you don't touch the pot and motor housing at the same time. Carefully insert the screwdriver and find the pot, just start turning to get a response. Ya can't screw it up, it's a simple DIY that you can do so don't be afraid.
 
even cheaper: Take the long way home.

the song, by supertramp. if you have a halfway decent ear you can nail the speed just listening to the opening harmonica.

btw- not all decks change speed on the motor. many modern ones mid 80-s up have a speed VR on the board...but point is taken.

tell me more about this $10 3Khz tape
 
I have a Tandberg deck that I 'trust' is running correctly, and spot checked some pre-recorded tracks vs the same tracks digital (spotify) time that checked out close enough for me.

Before recording a 3,000 Hz tone, I first measured the frequency output from my laptop with a DMM. There's about a -1% deviation between audacity and my DMM.
I played that tape back on the Tandberg and measured the output from the Tandberg deck. There is some variation from the start to the end of the tape 2970-3000Hz.

I placed that tape into the Technics Deck (RS-M63) and played start, middle, end while measuring from that deck's output. Variation was 2970-3010.
Then I played it back through my speakers while playing that same tone from my laptop and heard some intermittent wha-wha-wha but nothing consistent to indicate that it was running at a slower/faster speed than the tone generated from the laptop.

I was ready to attempt an adjustment to the Technics. Yes @Furburger , the adjustment pot is on the back of the motor. Mine looks to have a cylindrical rubber plug with a slot in it. I'm assuming that is designed to insulate a metal screw driver, but to be safe I had painted the blades of my little screw drivers with enamel to insulate them. But with the results I got, I didn't bother making an adjustment.

My conclusion is the Technics Deck is running at just about the same speed as the Tandberg deck. Assuming that the Tandberg deck is correct may be a leap of faith, but like I said it sounds right to my ears.

I didn't find the $10 ebay 3000Hz tape, but found some for $6.99 plus shipping. This vendor makes his calibration recordings on either a Pioneer CT-F1250 or CT-A9 recently serviced decks. Recordings are made on new old stock Maxell UR60 (or other). He's got 100% feedback and most of his sales are for calibration tapes.
 
Attempted this recently using another method. Having replaced a belt on a recent Marantz cassette deck purchase , the speed on a TDK AD-90 that I had recorded on an Akai GX-52 was off by about a minute per side after replacement (and more than two minutes using the old belt) .
So , I went the maths route.
A TDK AD-90 says 135 metres on tape which works out at about 47 minutes and 16 seconds playtime on the Akai deck I used to record music on it. ( correct tape speed assumed to be 4.76cm second)
Basically I used the same two reference tapes and ran one through the Marantz and adjusted the motor pot via the small hole after each side played. I used an old mobile phone stopwatch. After several attempts..I was able to get the overall duration of the tape to within 2 seconds of 47 minutes-16 seconds. I did the same using the second cassette on a Technics RS-M270 that originally ran for 47minutes 18 seconds on the Akai Direct drive deck when I recorded it. Same again...managed to adjust the Technics direct drive to get within 2 seconds of that tape also.
The Technics has a better trim pot for adjustment that is easily accessible via the top of the cassette well than the marantz but they are both extremely twitchy so it might take 4 or 5 attempts to get the overall tape run duration within 10 to 15 seconds or so.
Once reasonably close ..then you can fine tune it down to under 5 seconds if you have the patience.
Obviously not the most scientific or accurate way of doing it...but it's nice to have 4 cassette decks that finish playing a side of the same tape within a couple seconds of each other and the 100+ tape collection that I have already recorded many years ago should (and does) sound pitch stable.
Getting within 2 seconds of the original run time works out to about 0.1% difference or thereabouts.
Good enough for me..

Decks used as follows:

2x Akai GX-52 direct drive ( on which two identical TDK AD-90 blank tapes were originally recorded and a note made of their run times several years ago )

One plays end to end of leader tape for 47m16s , the other 47m18s.
Both tapes say 135m on the J card ,unlike some Basf tapes of the era which were 132 metres long)

1x Marantz SD-45 mkII ( belt drive)

1 x Technics RS-M270X ( direct drive)
 
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I've done it by ear and by the "ebay sourced" test tape.

By ear was the same album on the turntable and on the cassette deck. I have an RCA switch that sends all my stuff into the same aux in, so it was just a matter or starting both and flipping back and forth. Once they both sounded the same to me, I stopped.

My ebay tape came from a guy in Spain. 3k hz, a PC oscilloscope and I adjusted from there.

Turned out adjusting by ear and switching back and forth was pretty close, but not exact on the 3k mark.

Thing about "test tapes" is if the source/recorder was "off" when it was recorded, so will your adjustments...
 
I use a speed tape made by Duplicators CA (No affiliation), and my DMM, which has a frequency counter function. The speed test tape is very reasonable cost.
 
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