19kHz FM Tone and my Tape Decks!

[Rob Savage]

Hi All, what I am looking for is for someone who could either post a schematic or point me in the direction of a audio device that could remove this pilot tone from the audio that comes out of my AM/FM Tuner. I do not have a tuner (Pioneer TX 5500II) that has a MPX Filter, and I would like to add one. The reason is that this 19kHz tone damages the Dolby circut in the tape deck. I am in the process of getting ($70 dollars CDN!):banana::banana: a second R2R (Sony TC-355) next week, and this machine has a noise reduction circut (unknown at this point what type ~ any comments??) My Pioneer CTF-4242's dolby circutry was destroyed (and it has caused other problems with the deck too :tears::tears:!) I have two AKAI decks that have it, but all of the other ones (11 other decks total ~ this includes my other R2R, a TEAC A6010 that is down for the want of a repairman that KNOWS WHAT HE/SHE IS DOING((sorely lacking here in LONDON ONT.,) do not), and I want to start recording FM broadcasts again. IF anyone reading can point me to a ready made device or to a schematic that I could put together, could you post a link?

Much appreciated!!

Rob Savage

[pioneernut]

I'm no tuner expert, but your problem intrigues me from my engineering days. I did some searching and found a post where a guy has both an active and passive designed filter. So the passive might be a good homemade solution to put on the audio output of your tuner or before your tape deck.

You'll see it about half way down on the link here.
http://www.prodigy-pro.com/forum/viewtopic.php?t=8107&start=15

Good luck

[mhardy6647]

yeah, adding an in-line, low-pass filter shouldn't be too difficult.

[grateful]

With a modern tuner like the Pioneer, the pilot tone will not be present in the output. You do not need a filter. It will only reduce the high frequency capability of a very good tape deck. The presence of the tone will not destroy the dolby circuits. It will just cause encoding errors that will effect the freq response of your recordings. The Sony has a high filter but nothing else that I am aware of.

[pioneernut]

Personally, I thought all tuners had MPX filters built in, but maybe his tuner has something wrong with it causing the 19khz tone. By chance Rob, did you have a way to confirm of the 19khz signal with an Oscilloscope?

[Fisherdude]

Contact AK'er PunkerX (see his "RadioX" ad at the bottom of the page).

He is an FM tuner expert, and would be able to give you the most accurate input/suggestions for your problem.

[jimj_wpg]

The 19 Khz tone is the stereo pilot, which controls the stereo light and activates the stereo decoder in the tuner.

This might help:

http://en.wikipedia.org/wiki/FM_broadcasting#FM_stereo

[EchoWars]

Every tape deck with Dolby that I've seen, which was capable of response beyond 19KHz, had a Multiplex filter switch. Are you sure that the deck does not?

[gkimeng]

The reason is that this 19kHz tone damages the Dolby circut in the tape deck.

Sounds like there's something seriously wrong with either your tuner or your deck/s. The 19khz pilot tone can cause problems with Dolby recordings even at levels too low to be heard because the Dolby tracking interprets it as high signal and incorrectly adjusts the tracking in response, but 19khz is well within the range of frequencies that Dolby equipped tape recorder is designed to record. A tone with the amplitude required to drive the circuits in your deck to potentially damaging levels would probably take your amplifier and speakers out along with your deck, as well as give you a nasty ringing in your ears.

[Punker X]

Most tuners. but not all have a low pass filter to filter out the 19Khz residual. Most people can't hear this high. Some MPX schemes do a better job at canceling it out. Alignment can help, but won't totally remove it. Even some LPF's are better than others.

FM Dolby broadcast shifted Deemphisis to 25usec to increase the 19Khz level. The higher level enabled better cancellation.

I would either get a better tuner, and/or tape deck with an MPX filter.

[vinyldavid]

I have noticed that when either of my ears are facing my JBL 4311's, I can sometimes hear a VERY high tone.....now I understand what it is......

[goldear]

All cassette decks with Dolby NR have a multiplex filter on the Dolby Circuit. It is only the better ones which have a defeat switch for the MPX filter. So if your cassette machine does not have a filter switch, then this is a non-issue because the MPX filter will always be in circuit when you record with Dolby.

[EchoWars]

Your decks maybe, but since you'd only need a MPX filter if you recorded off of FM, a switch makes sense...to be used only when needed, and every cassette I've ever used had one (except my first, who's response couldn't make it to 19KHz). Else, how you gonna get that 20-22KHz signal on your Nak? ;)

[grateful]

Gold ear is correct that is part of the original Dolby system license reqirements. Very high end decks have a switch to defeat the filter. Also all pll tuners have a lpf after the mpx circuits to filter the pilot tone. Old tube tuners and early transistor often have high levels of pilot leakage in their outputs. It really is a non issue.

[EchoWars]

Part of the spec? Interesting...

Nothing like boning up on dead technology to brighten a Fri morn. :thmbsp:

[grateful]

I am old, I remember when Dolby B was new. It all still seems cool to me. You and I Echo make our living dealing with obsolete technology.

[gkimeng]

I am old, I remember when Dolby B was new. It all still seems cool to me. You and I Echo make our living dealing with obsolete technology.

I can recall sitting in a studio (an older friend had PT job there when I was in school) looking at a Dolby A console when the "upcoming" Dolby B for home decks was announced and thinking, "how are they going to get THAT into a deck that I could afford?" The answer was, they didn't. The first Dolby B equipped deck was way out of my price range, and since I had a R-R deck and a cassette deck, my solution for the next few years turned out to be an outboard unit and a lot of cable swapping...

[grateful]

When I was in High School I Bought an Advent 201. It was the AR Turntable of cassette decks. (had one of those too) I was amazed at how good a cassette could sound. I still have that machine. Ah the good old dayz.

[goldear]

Your decks maybe, but since you'd only need a MPX filter if you recorded off of FM, a switch makes sense...to be used only when needed, and every cassette I've ever used had one (except my first, who's response couldn't make it to 19KHz). Else, how you gonna get that 20-22KHz signal on your Nak? ;)
The answer is that you don't get extended frequency response on decks without a defeat switch when running Dolby B/C. Manufacturers only started adding the MPX (defeat) switches when the frequency response of cassette decks started getting wide enough that the MPX filter started to negatively impact their specs.

Even on a deck without extended response these filters were necessary becuase the Dolby encoder would still "see" this pilot tone, but on playback it would be absent, thus causing mistracking.

I am old, I remember when Dolby B was new. It all still seems cool to me. You and I Echo make our living dealing with obsolete technology.
I'm not as old as you, but when I was a kid, I was so passionate about audio that I read every Audio Magazine, and electronics catalog cover to cover multiple times. Consequently I now know a whole lot of useless info about (now obsolete) audio technologies that interested me at the time.

[EchoWars]

No...I learned something. AAMOF, one of my old Signetics data books (who were apparently licensed to make Dolby chips) has a whole write-up on a Dolby B enc-dec, and I hadn't looked at it for years. The default is to include a MUX filter, which slipped by me back in the day (when it mattered ;) ).

[grateful]

That is one of the good things about going round and round on the planet.

[Rob Savage]

Hi all, sorry for the delay in responding to your welcome answers to my question. I have not had internet access for the last few days unfortunately! The CTF 4242 does not have a MPX switch, and YES it did damage the Dolby Chip/circut. I'm not sure how, at this point, but I remember reading about this very thing, here on AK, when I first joined, back in 2006 time period. My understanding from doing reading on this is that the 19 kHz tone, (R+L-R-L), is part of the radio signal, that is sent along with the music etc, of the signal, when first entering the Dolby chip, is expanded with the signal. It then goes through the circutry of the deck, then to the Dolby Chip, is then biased for the tape, then is recorded. The deck, when in Record mode, emits a loud tone, that peggs the VU meters right over at +5. This tone is heard through both speakers (or headphones) and is present on the recording. I have found that IF I (with my hands!!) push in the tabs on the top, and the indexing tab next to the supply spool, this tone disapears. Lately, it does not, and that the machine has started to run fast, like it is in FF all the time. I have not used this deck in about 7-10 months for this reason. I have purchsed a number of new Pioneer decks, and other makes also, and only the AKAI's have the MPX filter. This is why I asked this question now, is that all these decks, (the CTF 4242, CTF 900, CTF 500 {two decks} and my Kenwood KX-77CW, and my TEAC A6010) are going to be repaired as now I have finished furnishing my home (thats were my money went for the last 1 1/2 years) I don't want to have any other decks go down for the same reason.

Again, thanks for the responses to my question, and sorry for the no-show for the last few days!

Rob Savage!

Edit #1 To answer question #8... no it does not. EW, please see the Pioneer Manuals on the Pioneer section. To answer #9 gkimeng, the carier tone is included WITHIN the total signal. This is the problem. I have read the Dolby specs, on thier website, and it is include within the total spectrum that is companded (before expanded at the output end of the chip). To punker X, the reason I want to use the deck is that it is a Pioneer, and it is a great deck, with little time on the heads. Thanks RJS!

[grateful]

The presense of the tone will not hurt anything except possibly the high freq response of your recordings. That is a fact. It has nothing to do with the bias of the deck. Your deck has a dirty record / play switch that is causing the oscillation and meter pegging. It need to be serviced.

[goldear]

The presense of the tone will not hurt anything except possibly the high freq response of your recordings. That is a fact. It has nothing to do with the bias of the deck. Your deck has a dirty record / play switch that is causing the oscillation and meter pegging. It need to be serviced.
After reading your much more detailed description, I agree that this sounds much more like oscillation from the record-pay switch. Get some deoxit out and clean that switch, and your HF ocillation will probably go away.

[Rob Savage]

Edit #2 To grateful and goldear, responses # 23 and 24. I have used about three cans of cleaner on the deck. All of the switches and controls, over and over again! But, this points to something that I didn't think about. Would this switch, the piano record and play switches, if the surface of the contact of the switch, is damaged in some way, would this cause these above described problems?

Rob Savage!

[grateful]

The record play switch is inside the unit. It is mounted on the main pcb. It is activated by a lever linked to the record button on the front panel. It is long and has many contacts. Take the top cover off and press the record button observe the mechanism you will see the lever push it in and out.Spray inside that switch from each end and the middle. 3 or 4 squirts should be all you need. A can of contact cleaner should be good for dozens of repairs.

[mhardy6647]

He speaks the truth. Cured a lot of old decks of the "pegged VU meter syndrome" just like this.

[grateful]

Kind of wondering if the guy is pulling my leg here. Sprayed 3 cans into the unit?

[goldear]

Kind of wondering if the guy is pulling my leg here. Sprayed 3 cans into the unit?
No. I'm not pulling your leg. Now, that doesn't mean that I am necessicarily correct. But I am certainly sincere about this guess. And yes, as others have indicated, this swich is deep inside.

Perhaps Fred Longworth will chime in? I'd certainly trust his diagnosis over my own.

[grateful]

From what I am reading I think he sprayed 3 cans into the front of the unit not the record play switch. It kind of boggles the mind. I mean that is a lot of spray it must have been pouring out in rivers. FWIW I am also a pro in this business with 30 years of experience and make my living doing stereo repair.

[goldear]

FWIW I am also a pro in this business with 30 years of experience and make my living doing stereo repair.
Cool. I didn't know that. :thmbsp:

[grateful]

Sure thanks, I like it (most of the time)

[Rob Savage]

Yes I did use about 3 cans of spray cleaner. NOT the stuff from RS or in our area the "Source", but the pro 10oz cans from the defunct Audio parts store known "CounterParts". It would be the equ to the US stuff known as DeOxit. Yes all of the switches over and over again. I haven't taken the top off of the old girl in some time, but, I used the little red plastic attachment to the can, and squirted in ALL of anything that even LOOKED LIKE IT moved! Over and over again, as to some of the references above, I thought that this was the cause (dirty switches) but I don't think so. I used this deck to only record FM broadcasts, and somewhere, either on this board or the InterNet, I read that the carrier tone from FM attacks the Dolby chip. When I turn OFF the Dolby, 75% of the time the tone is not present. I also found that there was a small indexing pin on the face of the deck just below and to the left of the supply reel of the cassette, and when this switch is not pushed in, the deck will not operate. Remember, this is one of the decks that has NO CASSETTE DOOR, and this switch allows the deck to operate. 25% of the time, the tone is present even if this switch is pressed in, and then at the end of the time I used it, the speed of the deck totally went, meaning it sort of ran as if the FF forward switch was pressed, EVEN THOUGH I pressed the PLAY Switch. I also found that if I sprayed the Record Head, directly, this high pitched squeal would disapear. I thought at first it was a loose lead to the head, but I checked it and it was not so. The heads show NO WEAR marks at all, and the only problem was that the prevous owner got mad at the deck and hit it with something on the left side (Power Switch push button) as the switch was grounding out until I re-bent it back. It must have been operated WITHOUT the top on it. The PC Board is not cracked or damaged in any way, as I checked it with a 20.000' degree Kelvin light (bluish white light ~ very strong!) and it showed NO Damage.

So I'm open to any suggestion. Right now, this deck is not used by me, as it does not work. I was thinking that if I could find another deck of the same type, this would end up as parts. But I hate to do that as this thing works, and I'd like to suss out this problem instead.

Rob Savage!

[grateful]

You have to take the top off to do it correctly. You have to get the spray into, not on the switches. There are 2 sense switches in the well one of them is the record interlock the other the 70us equalization that automatically sets the playback of cr02 / metal tape. the lever is not the switch the switch is attached to the lever. The spray has to go into the body of the switch. The record /play is a long switch you must remove the cover to access it. spraying "everything that moves" will ruin the deck. It will wash away the lubrication and make an oily mess out of the chassis.

[Rob Savage]

Hi all again! To grateful, thanks for the posts .... yes I understand that. The deck came with the top off, (top separate) and I sprayed the switches that are connected to the metal arm that has the round alum SW cover. NO, I just don't spray willy nilly on anything. OK, maybe I wasn't clear (too much verbage I think ...) that I didn't just coat the whole circut board with spray. I sprayed in to each SW, past the metal arm, and worked it up and down. IF I could figure out how to post pic's, I would. I have a Digital Camera, and what I should do is post some pic's. But I think that it is either the Dolby Chip, or the contacts in the SW. Oh Well. What I was hoping was that if someone had the service manual or the schematic, could they post it at the Pioneer section? It would go along way to helping solve the problem.

Thanks again

Rob Savage!

[wiredbecker]

When I was in High School I Bought an Advent 201. It was the AR Turntable of cassette decks. (had one of those too) I was amazed at how good a cassette could sound. I still have that machine. Ah the good old dayz.

Hey Grateful, I think I know where I can get some of these 201s if you need parts. Just lemme know

[grateful]

Thanks I like them but have 2 already. The pinch roller is like gold. Most of them have turned to goo by now and are unavailable. They really sound nice especially with classical music. ( because of the very low wow and flutter and low noise) Are you interested in getting one going?