What causes "hiss"

[MCS Guy]

This question has been bugging me all day, so I figured I ask the guru's.

What causes tape hiss in cassettes or reels? If you go out and buy one from wally world, there is hardly any hiss in the tape. But if you record a CD or LP on tape at home, there is a whole lotta hiss.

And what is this dobly crap? My deck can record and playback in dobly, but it ends up making the recording worse by removing the highs in the right channel. Also changes the "sound" too.

 

[danj]

Tape hiss is a characteristic of analog recording and is caused by the interaction of the magnetic particles on the tape and the electrical currents used in the tape heads and electronics. It's a complex subject but the general rule is that each time you make a recording of an analog recording you increase hiss by about 1.5 to 2 db. Each time you halve tape speed you increase hiss by 3 db. Each time you decrease the track width you increase the hiss by 1.5 to 3 db (all this depends on the quality of the electronics and tapes). Conversely, when you increase speed or track size, hiss goes down by the same amount.

Dolby B and S will not decrease treble when the machine is properly aligned and the tape is correctly biased to the machine. If you underbias a tape you get increased hiss AND dolby mistracking. If you overbias a tape, you get decreased highs and Dolby mistracking. If you get decreased treble on one channel, the Dolby circuit is misaligned OR the tape head is worn OR very dirty. Make sure the following circuits are all properly aligned for best results on all tape decks but especially on cassettes: 1. BIAS 2. Equalization (record AND playback) 3. Dolby "0" VU levels 4. Dolby tracking.

Mechanically, make sure the heads are not too worn, are aligned, set for correct azimuth, and demagnetized and cleaned. Make sure the capstan(s) and pinch roller(s) are clean and straight. Make sure the tape door and holders are not bent.

A cassette deck needs everything to be just right or performance will suffer.

Dolby DOES NOT REDUCE TREBLE when the circuits are properly aligned, the tape deck is mechanically and electrically sound, and the deck is properly biased and EQ's for the tape being used. Don't believe me? Try a properly set up Dolby B or S in an A-B comparison with the source. When everything is right, it works spendidly. Yes, when you switch off the Dolby on an encoded tape, it does sound brighter and, to some listeners, better. That's fine but that does not mean a properly functioning Dolby unit is cutting highs, it just means you prefer the brighter sound. However, a misaligned or malfunctioning circuit will sound worse.

Go to the Dolby Labs website for a tutorial on how Dolby works. It's a complicated process but a great boon when used properly.

I personally have little use for Dolby C. It works great on some decks but poorly on others AND is so deck dependent that a "C" encoded tape that sounds great on one machine may sound positively awful on another. Dolby B and S are much less sensitive to machine differences and, when not overused, can sound fine on many different machines.

 

[stereofisher]

Several Things

There are many things that can cause hiss. The easy ones are poor quailty tape. A poor quality cassette deck. A poorly aligned tapehead on a tape deck. A magnetized head. Also, a combination of the above. Are your heads clean? Another easy to fix problem. I once owned a Panasonic 8 track that sounded crappy when I recorded with it when the heads got slighty dirty. It needed cleaning every time I recoorded with it.

The quality of the deck is a big issue. My recent auqusition of a TEAC 450 and a 460 showed how dramatic better decks can be. You are right about loosing high end frequencies with Dolby on. I had a lot of cheap decks that did this. On the TEAC's I leave the Dolby on and have no high end loss what so ever. My one Nakamichi also did not hurt the highend frequencies. You would not beleive how good these cassettes sound in my car. Beats the crap out of my new Sony CDR. I only keep that damned CDR for my friends. Can't get it not to skip on record. That piece of crap if it were not for my friends I put a bullet through it Hope this helps. Good quality decks are cheap.
Had loads of fun fixing up the TEACS and have enjoyed the great sound they put out! See pic.

Eric

 

[visitor]

Everything causes hiss.

but it ends up making the recording worse by removing the highs in the right channel.

At least if you did not understand the Dolby system you should have said it removed the highs on both channels. It sounds to me like your deck needs a service.


If you have the manual, read and look at the graphics of how the Dolby system works. Graphics will help you much more to understand it than just written words.

 

[danj]

Re: Several Things

That's one fine looking 450, one of the finest decks of its era. In 1974 I had a 360S, which had the exact same electronics and heads as the 450 but had the conventional sloped design then popular. I sold it and then immediately regretted having done so.

I currently have two Naks - an LX-3 and a CR-1a - and a nearly new Sony TCKE400S, which has Dolby S. "S" is a big improvement over Dolby C. Still, especially with the LX-3 and the Sony, Dolby is not a requirement for making a good quiet recording as long as I use a type II or IV tape. The electronics and heads are better than average.

Hiss was very noticable back in the early days when tape formulations were not so good. Since the advent of Chromium Dioxide and cobalt-doped type II tapes the tape-induced hiss problem hasn't been a big problem. I still do use Dolby B for general recording and type "S" when I use the Sony and neither cuts highs when properly done.

By the way, the HK decks not being easily available where I was in the early 70s (ASIA), Teac was the big daddy cassette and reel-to-reel brand available to us. If you wanted a great reel-to-reel you bought a 2300 or 3300. If you wanted a great cassette deck, the 450 was the one. Even when the first NAK came out, the better Teacs were still the one's to buy. Only officers could afford a NAK 1000, even at PX prices.

 

[MCS Guy]

Does anyone here repair cassette decks?

I believe the head is wore out. I can feel a small groove in the head.

 

[ModernClassic]

A small groove in the head means it has stared the wearing out process, but does not mean it has reached the end of life.
Normally, a used set of heads have the following characteristics:
1. rolling off high trequencies getting more and more severe.
2. playback vs recording level much decreased.
3. hiss of the tape is getting more pronouced
4. heads getting misaligned.
So in your case, excessive tape hiss can be due to 2,3,4.
I use the word excessive because tape itself is a hissing recording media anyway. Use good quality tapes will have less hiss. Good ones are usually type II biased tapes such as TDK SA, SAX etc.

What machine are you having trouble with? High end machines uses header wearing heads, so they will wear less.

 

[MCS Guy]

I am using an MCS 3551 cassette deck, which I have no idea who built it.

I have another deck, and MCS 3570, which is one of the high end ones with the memory programable counter. The problem with that one is the take up reel is bent and wobbles causeing an "in and out" of the playback/Recording sound. Last time I used it, the recording had no real hiss to it.

 

[THOR]

Using a TT or tape player :

 

[MCS Guy]

I manage to find a pic of it, My father bought it in 1977

 

[msjanket]

hiss from audio player

Listening to a CD made by a Puff Adder usually causes a pretty nasty hiss.

 

[ModernClassic]

I still remember that my first cassette deck was the TEAC 350 of 1971, sounded rather good. I was told that the mechanism ( heads too ) was NAK. I used low noise Hitachi C90 tapes and found those tapes were reliable, except that the felt pad dropped out after several years and had to glue them back again.
The 350 uses a lovely looking ferrite head, dark and shinny, believe to be the same as the one of the head used in 450. The trouble with this head is, it also worn after a year of use.
The TDK SA tape came along ( 1974? ), so I modify the bias to take this new tape, but the head was rather worn and hissy too.
I sold it to my friend in 1981.
Now I own a NAK CR-5 and just acquired a non functional Akai GX F-90 and got it to working 2 days ago. Very nice decks, both of them.
I never uses Dolby BTY because it adds distortion to the signal. I would only use type ll tapes and record them at higher level ( +2 dB peaking) to minimize hiss.
Cassette technology is just for copying fun, there is no match for original materials!

 

[danj]

Judging from the pic you posted, your MCS was made by Sanyo. It's a decent piece but not worth putting much money into fixing up as the market value is less than the cost of repair.