Going back to analog days with this question

3db

3db

Audioholic Slumlord
This question is for those of us who had cassette decks and used them alot. Did you own and use a head demagnetizer? Have you noticed a difference with high frequency reproduction before and after use or is this one of those mythical audiophool ideas?
 
Last edited:
TLS Guy

TLS Guy

Seriously, I have no life.
This question is for those of us who had cassette decks and used them alot. Did you own and use a head demagnetizer? Have you noticed a difference or is this one of those mythical audiophool ideas?
No that is not mythical.

Tape heads and guides do get magnetized over time. This not only causes poor high frequency response, but also tends to erase the high frequencies on the tapes.

Now machines vary in their propensity for this. Machines with single record/playback heads are less prone to it than the more expensive three head machines with separate record and playback heads.

The reason is that the machine is supposed to be designed with some degree of auto demagnetization. This is done through the tape bias. A critical function during record is the AC bias signal to the head. This actually needs setting for different brands of tapes. It is best to set up a machine (this takes instruments on most decks) for one brand and brand type, of each of the different categories. Some very expensive machines had auto bias, or a means of easily setting bias and EQ, as they had built in instrumentation, like my pro TEAC machine.

Now the record bias is a high frequency AC signal and it tends to demagnetize the head to which it is applied. However on a lot of machines especially the cheaper ones, this signal would die too quickly or even instantly, leaving some magnetization on the head. On a good machine the bias should die slowly.

So yes, machines need regular head and guide cleaning with isopropyl alcohol and regular demagnetization.

Tape machines need lots of maintenance. That is one of their problems. This is especially true now, as tapes are aging and the binders failing. This results in excess oxide shedding and more fouling of heads and guides.

Now you need to demagnetize properly, or you make things worse. You start the demagnetizer away from the machine, and slowly bring it up to each individual part to be demagnetized, hold it close, but NOT touching for a few seconds, and then slowly withdraw it keeping the demag unit on, so the field dies away slowly and not leave the part/head with more magnetization.

Doing it correctly is very important.

The aging tape problem is huge now and getting worse with time. The fouling issue is only one part of the problem, the other is increased head and guide wear, as the binders which are failing are also the lubricant.

I have a tape baking system here for restoring binders, at least temporarily, to get a digital archive copy.

Tape machines are trouble, and not for the faint of heart. They get out of adjustment. Azimuth alignment of heads is crucial. Even very small azimuth errors indeed cause serious loss of high frequencies and degrade S/N. The high end NAKS had a complex auto alignment system. Otherwise to do the adjustments takes alignment tapes and instrumentation. The other critical adjustments are tape tension across the heads, bias and equalization adjustments.

Back in former times individuals who owned expensive machines like Revox took their machines into the dealers regularly for these complex adjustments. I remember years ago, Hi-Fi Sound in the Twin Cities had a long bench of techs, who did nothing else except tune up tape machines, mainly Revox as they were a dealer. I have had tape machines since my teens, and do my own maintenance. It is a highly skilled endeavor.
 
Dan Madden

Dan Madden

Audioholic
I could not have said it better than TLS guy. I had many tape decks over the years including reel to reel ones. I did have a tape head de-magnetizer as well and yes, it did improve hi frequency performance but it had to be done carefully, just like TLS explained.
 
3db

3db

Audioholic Slumlord
Thanks guys. I will look into Amazon and Ebay to purchase a demagnetizing wand for my Yamaha KX-800U 3 Head cassette deck.

TLS.. This unit has the added feature of DBX along with Dolby B abd C NR systems. I'm really impressed with DBX and wondered why it did not surpass Dolby as the NR standard. It clearly surpasses what Dolby offers.
 
TLS Guy

TLS Guy

Seriously, I have no life.
Thanks guys. I will look into Amazon and Ebay to purchase a demagnetizing wand for my Yamaha KX-800U 3 Head cassette deck.

TLS.. This unit has the added feature of DBX along with Dolby B abd C NR systems. I'm really impressed with DBX and wondered why it did not surpass Dolby as the NR standard. It clearly surpasses what Dolby offers.
I left out one vital piece of information. Always make sure the machine is off when demagnetizing, other wise you will blow it up.

The answer to your question is a simple one. Dolby B is tolerant to a degree of changed playback levels and frequency response errors.

The DBX problem is that frequency response errors between record and playback are double. So say an error of 3 db between record and playback signals will become 6 db. DBX is tolerant of level changes to a degree, but in my experience not as much as they claimed. Frequency errors combined with level changes can lead to "pumping" which was and is the Achilles heel of the DBX system

Now the professional Dolby A is highly intolerant of level and frequency response errors between record and playback. Everything must be aligned perfectly.

Dolby C is Dolby A light. Dolby C seldom played back properly when a tape was recorded on one machine and played back on another. The same can be said pretty much for DBX.

To get the best results for all NR systems both record and playback machines have to be obsessionally set up. Only Dolby B is at all tolerant. Only Dolby B could handle the huge errors incurred by high speed tape duplication. Dolby C and DBX can not cope with that.

By the way there are two version of DBX. There is DBX 1 and DBX 2. DBX 1 was for professional reel to reel recorders, and that is what I used for my on site recordings for outside broadcasts of symphony and choral concerts. You pretty much had to run at 15 ips, which I did.

DBX 2 was introduced for mass produced reel to reel tapes. I do have a DBX 2 decoder also, and my TEAC has Dolby B, C and DBX 2. I have to keep my Revox A77 4 track in top shape to play DBX 2 4 track reel to reel tapes, and I have a few.

I also have an old Advent Dolby B decoder. The reel to reel tapes had test tones for properly setting the decoder for each tape.

The DBX 2 decoders also came the with DBX noise reduction for LPs. I have a few of those, and they have silent background. You must have a turntable with pretty much zero frequency response errors, as again they are double. With everything properly set up those DBX LPs are really impressive. Groove modulation is markedly reduced. They have full dynamic range (wider than CD) and no bass roll off. The background is totally silent.

If you think working in the digital domain is much easier you are dead right.

I think the plug and play convenience of digital media has contributed to Audiophoolery. Back then we had far too many serious problems to worry about. I think you can see from these posts there were lots of them. Relived of all those, all manner of imaginary problems had to be created to satisfy idle hands!
 
3db

3db

Audioholic Slumlord
I left out one vital piece of information. Always make sure the machine is off when demagnetizing, other wise you will blow it up.

The answer to your question is a simple one. Dolby B is tolerant to a degree of changed playback levels and frequency response errors.

The DBX problem is that frequency response errors between record and playback are double. So say an error of 3 db between record and playback signals will become 6 db. DBX is tolerant of level changes to a degree, but in my experience not as much as they claimed. Frequency errors combined with level changes can lead to "pumping" which was and is the Achilles heel of the DBX system

Now the professional Dolby A is highly intolerant of level and frequency response errors between record and playback. Everything must be aligned perfectly.

Dolby C is Dolby A light. Dolby C seldom played back properly when a tape was recorded on one machine and played back on another. The same can be said pretty much for DBX.

To get the best results for all NR systems both record and playback machines have to be obsessionally set up. Only Dolby B is at all tolerant. Only Dolby B could handle the huge errors incurred by high speed tape duplication. Dolby C and DBX can not cope with that.

By the way there are two version of DBX. There is DBX 1 and DBX 2. DBX 1 was for professional reel to reel recorders, and that is what I used for my on site recordings for outside broadcasts of symphony and choral concerts. You pretty much had to run at 15 ips, which I did.

DBX 2 was introduced for mass produced reel to reel tapes. I do have a DBX 2 decoder also, and my TEAC has Dolby B, C and DBX 2. I have to keep my Revox A77 4 track in top shape to play DBX 2 4 track reel to reel tapes, and I have a few.

I also have an old Advent Dolby B decoder. The reel to reel tapes had test tones for properly setting the decoder for each tape.

The DBX 2 decoders also came the with DBX noise reduction for LPs. I have a few of those, and they have silent background. You must have a turntable with pretty much zero frequency response errors, as again they are double. With everything properly set up those DBX LPs are really impressive. Groove modulation is markedly reduced. They have full dynamic range (wider than CD) and no bass roll off. The background is totally silent.

If you think working in the digital domain is much easier you are dead right.

I think the plug and play convenience of digital media has contributed to Audiophoolery. Back then we had far too many serious problems to worry about. I think you can see from these posts there were lots of them. Relived of all those, all manner of imaginary problems had to be created to satisfy idle hands!
I tried DBX twice, once from a CD and once for vinyl and I noticed no audible artifacts "pumping" that you described. What I did hear was no high frequency roll off like with Dolby B and no tape hiss. It truly works well from my limited experience.
 
highfigh

highfigh

Seriously, I have no life.
Thanks guys. I will look into Amazon and Ebay to purchase a demagnetizing wand for my Yamaha KX-800U 3 Head cassette deck.

TLS.. This unit has the added feature of DBX along with Dolby B abd C NR systems. I'm really impressed with DBX and wondered why it did not surpass Dolby as the NR standard. It clearly surpasses what Dolby offers.
To go with what Mark wrote, all of which made me shiver because these are questions & issues that I had to deal with on a regular basis when I worked at a stereo store, is the fact that a dbx encoded tape sounds terrible when played on a machine without it, so it's not as simple as using a Dolby-encoded tape on a machine with Dolby and things are basically hunky-dory. For most people, it was close enough and they were more interested in making tapes for the car, boom box or as an "archive copy" to save the LP from wear, as if their $129 cassette deck could come close to the sound quality of a clean LP played on a decent turntable with a good cartridge. Then, they used tape that was cheap, which was similar to passing sandpaper over the heads. No highs, bad S/N ratio and they didn't last long.

dbx is/was called a 'compander', which stands for (it's probably obvious) 'compressor/expander', working with the dynamic range of the music and that's where it differs from Dolby, which is an equalization system, used to reduce the noise floor. By tilting the mid/high frequency response upward during recording and using the inverse tilt on playback, the noise floor being inherent in the tape, tilting the response downward on playback results in the noise floor of the recorded material being lowered on playback. It's also the reason that mixing and matching Dolby types doesn't work well in the vast majority of cases and if Dolby B is used on record, Dolby C shouldn't be used on playback. Dolby A, Dolby SR and Dolby S were used in Pro applications (SR is often shown in movie credits) and HX/HX Pro weren't used in many machines- B&O licensed it first, with a delay for release to other brands.

One thing I liked about three head cassette recorders was the ability to hear the recording while it was happening (or better, taking the time to actually do some setup) and even better, were the three head decks with variable bias. It was possible to hear the input, output and switch to the actual source to compare and make the playback sound as close as possible to the original without needing to record, play it back and find that it's not a good copy (for a variety of reasons). Using the input signal wasn't a good way to compare because that was WITH the equalization going to the tape, so the high frequency response was exaggerated.
 
highfigh

highfigh

Seriously, I have no life.
TLS- where do you buy belts? Now that almost nobody here services audio equipment, nobody stocks parts. Not a fan of paying $1 for a belt and $2 for shipping.
 
TLS Guy

TLS Guy

Seriously, I have no life.
I tried DBX twice, once from a CD and once for vinyl and I noticed no audible artifacts "pumping" that you described. What I did hear was no high frequency roll off like with Dolby B and no tape hiss. It truly works well from my limited experience.
You think it is OK, because you are recording back on the same machine. If your buddy made the tape, and you played it or vice versa, then more likely than not there would be big problems.

In addition it looks as if your machine in in relatively good shape right now, although if it has not been serviced foe some time, it would likely benefit from the restores hand.

You will find out soon enough that tape machines are trouble with a big T. Three head ones like yours need particular attention, as azimuth errors between playback and record are a big problem. In a two head machine, the playback and record will have the same azimuth error and will only be manifest when the tape is played on another machine. Very small azimuth errors indeed have a huge impact on frequency response errors and distortion. Having said that I only own three head machines and one four head one.
 
TLS Guy

TLS Guy

Seriously, I have no life.
TLS- where do you buy belts? Now that almost nobody here services audio equipment, nobody stocks parts. Not a fan of paying $1 for a belt and $2 for shipping.
So far I have only needed the tape counter belt for the A700. I got that from an old Studer/Revox engineer in Nashville, who has lots of parts.

All my reel to reel machines are direct drive servo controlled units, except the Brenell which is idler drive to the capstan. Apparently they were made by Durex and don't fail like on other brands! All are three motor.

The cassette units are dual capstan three motor. So the only belts are to the dual capstans from the capstan motor. So far so good.

Cassette machines I think are my least favored contraptions. In fact I have little good to say about the cassette medium and I have very few cassette tapes actually. They are way, way inferior to reel to reel machines, though I admit more convenient. At only 1/32 track width and running at 1/7/8 ips is just not Hi-Fi which ever way you look at it. 1/8 inch track width and 15 ips and you have a chance at quality.
 
3db

3db

Audioholic Slumlord
You think it is OK, because you are recording back on the same machine. If your buddy made the tape, and you played it or vice versa, then more likely than not there would be big problems.
I get that a dbx recorded tape can only be played back on a deck with dbx. I tried to play a Dolby B tape back with dbx engaged and turned it of right away because of the noise so I know from that little experiment that there is definately a compatability issue big time. :oops: Panasonic and Marantz are the only manufacturers I know of that produced Walkmans with DBX. I can't find any on EBay and I would think they would be prohibitively expensive. For every day tapes (ie going into the Walkman) I will be resigned to use Dolby B.

In addition it looks as if your machine in in relatively good shape right now, although if it has not been serviced foe some time, it would likely benefit from the restores hand.
I bought this 2nd hand for $40 and its sound better than any deck I've owned previously. It could use a really good cleaning for sure. I bought this deck as I still have some cassettes I can't fine online or on CDs. I also have some vinyl that is prohibitively expensive to replace via CD and they are definately not available online. To save these albums, I will record one set of tapes using dbx for playback at home only and another set of tapes with Dolby B so that I can listen to them while commuting back and forth to work.
 
TLS Guy

TLS Guy

Seriously, I have no life.
That unit is fine. I have one of those.

You did not understand what I was saying. When you made cassette DBX tapes or Dolby C tapes, invariably they would not play back on another deck that also had Dolby C and DBX. In addition Dolby C and DBX were quite useless for high speed copies even if the decks had the encoders, as there was too much frequency response and level difference.

You have to go 2 track quarter inch at 15 ips to not have tape saturation at high frequencies at full 0db modulation. All cassette tapes suffer from severe HF losses as the level progresses to 0db (full) modulation. High speed copies had to have much greater HF equalization (boost) than real time copies and so tape saturation and distortion are much greater on manufactured high speed transfers than real time tapes.

For these reasons I have never considered the cassette tape a Hi-Fi medium, but a mid-fi at best, with most machines distinctly low-fi.

Thank goodness for the digital age!
 
WaynePflughaupt

WaynePflughaupt

Audioholic Samurai

That unit is fine. I have one of those.

You did not understand what I was saying. When you made cassette DBX tapes or Dolby C tapes, invariably they would not play back on another deck that also had Dolby C and DBX.
In my experience that was an issue with the cassette medium in general, even using Dolby B or no NR at all: Tapes sounded best when played back on the machine they were recorded on. Perhaps TLS can confirm, but I expect that the issue (or at least part of the issue) was variances in head alignment from one machine to the next.

Regards,
Wayne A. Pflughaupt
 
WaynePflughaupt

WaynePflughaupt

Audioholic Samurai

3db, one of the nice things about 3-head decks is that if you can get the well door off, you can use one of your old tapes to get optimal alignment of the playback head. Just set the monitor to “Tape,” play the tape and adjust the azimuth screw to where the highs sound best.

Regards,
Wayne A. Pflughaupt
 
TLS Guy

TLS Guy

Seriously, I have no life.

In my experience that was an issue with the cassette medium in general, even using Dolby B or no NR at all: Tapes sounded best when played back on the machine they were recorded on. Perhaps TLS can confirm, but I expect that the issue (or at least part of the issue) was variances in head alignment from one machine to the next.

Regards,
Wayne A. Pflughaupt
The problem with the Cassette is that it is super critical. The tape width is so small and the tape speed very slow. So minute changes in head alignment have enormous effect.

One of the big issues is that the tape runs both ways, and you always get a different skew and therefore a slightly different alignment for each side of the tape. That is why the NAK Dragon turned the tape over so it always ran the same way. My machines do not run in reverse, you have to take the cassette out and turn it.

Now if I aligned two machines you could get DBX and Dolby C to play properly if they were decent machines.

I do not like your method of Azimuth alignment. That will lead to major errors, as you have peaks and nulls as the tape is aligned, and very likely you will set it to a side band.

When aligning the heads, you need a certified laboratory tape. You align the heads for maximal output and make sure the channels are in phase. The most important is you find the max output when both channels are perfectly in phase on a 10 KHz signal

You need to set the playback level to be at -10 db. You can not do measurements on a tape machine at 0db unless it is at least quarter inch tape at 15 ips, because of tape saturation. All other speeds are done at -10db. You need to set playback level by instrument and set the EQ pots for flattest response. Again you need a laboratory certified tape for this.

Then you can do record, and set the the azimuth by monitoring off the playback head. You have to feed the machine from a signal generator. Then you set record bias, for best output and lowest distortion with a high frequency signal. The lowest distortion is usually just as output begins to fall. Then set the EQ pots, and repeat the bias adjustment. The bias adjustment is different for every brand of tape, and for every type of tape within the manufacturers offerings. So once you have set up a machine it will only work properly with the type of tape it was set up with. If you change tapes you need to go through the set up adjustment process again. This applies to record only. Every tape has a unique record bias signal requirement.

For servo, oscillator driven decks, you need to check the capstan drive with a frequency counter and set it to spec.

This all takes some time and has to be done carefully. All instruments used around the heads must be demagnetized before each use.
 
3db

3db

Audioholic Slumlord
Well time will tell shortly to see if my new used cassette deck lives up to Yamaha quality as I expect from that company. I've ordered a Walkman from EBay and will be using it to play cassettes recorded from the Yamaha.
 
lovinthehd

lovinthehd

Audioholic Jedi
While I did have a cassette deck or two and a few walkmans and used a demagnetizer like yours I cannot imagine wanting to revisit any of it.....
 
TLS Guy

TLS Guy

Seriously, I have no life.
While I did have a cassette deck or two and a few walkmans and used a demagnetizer like yours I cannot imagine wanting to revisit any of it.....
3db is recently retired and needs something to do!
 
3db

3db

Audioholic Slumlord
While I did have a cassette deck or two and a few walkmans and used a demagnetizer like yours I cannot imagine wanting to revisit any of it.....
Its the only way I can get some music off of some vinyl I own as I have some albums that simply are not available in the digital domain or are prohibitively expensive. Besides, I will be really cool again ;)




 
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