If his deemphasis fix for the 1000 is the same as he does with the 500/800 receivers don't do it, there is a resistor change that corrects the curve, Al's fix was to remove a coil, the coil was the 38K filter, without it, yes the curve comes out better, but so does the 19K and 38K bleed that causes noise when a station is. running HD or subcarriers.
I don't remember the exact fix but it is around here someplace, must search.....
The Fisherdoc's position on this: (A bit long-winded...)
The instructions and parts in my work and Resto-Pak Restoration Kits dedicated to the FM De-Emphasis "problem" is one of the least known and even LESS UNDERSTOOD aspects of the restoration process.
While I can appreciate the faith placed in the Fisher "engineers", by no means should anyone speculate that just because they are engineers that everything is "perfect". In fact, it is precisely due to the fact that they knew EXACTLY what they were doing that the FM De-Emphasis in NOT correct in ALL FISHER TUBE MULTIPLEX TUNERS OF ANY KIND issued by Fisher in the 1960's. You will be interested to note that this "problem" did not exist BEFORE MPX Stereo was introduced, and disappeared with the advent of Solid State tuners. I reiterate that it is EXCLUSIVELY PREVALENT in ALL TRUE MULTIPLEX VACUUM TUBE TUNERS AND RECEIVERS made by Fisher.
This aspect of these Fisher tuners was uncovered by a radio engineer that has been working with me for years. We have worked together in analyzing Fisher tuner circuits and uncovering ANYTHING that can be improved. The attained improvements that are the result of this research is provable with a schematic and a calculator and verifiable with the proper test equipment.
There are reasons for this problem, and unless these reasons are understood, you will see ignorant and thoughtless comments concerning this change to the circuit. I will now elaborate.
Let us first learn what exactly FM De-Emphasis is, what it does, and why it is necessary.
Random noise has a 'triangular' spectral distribution in an FM system, with the effect that noise occurs predominantly at the highest frequencies within the baseband. This can be offset, to a limited extent, by boosting the high frequencies before transmission and reducing them by a corresponding amount in the receiver. Reducing the high frequencies in the receiver also reduces the high-frequency noise. These processes of boosting and then reducing certain frequencies are known as pre-emphasis and de-emphasis, respectively.
The amount of pre-emphasis and de-emphasis used is defined by the time constant of a simple RC filter circuit. In most of the world a 50 µs time constant is used. In North America, 75 µs is used. This applies to both mono and stereo transmissions and to baseband audio.
This is very similar to how the Dolby system worked in reducing noise on recording tape.
Now as long as the receiver properly de-emphasizes, or reduces, the high frequency boost, the broadcast material will be heard as it was intended along with reduced noise. However, if too much de-emphasis is applied, the high frequencies will be attenuated, and the result is an inaccurate reproduction of the transmitted audio. The high frequencies will be slightly muted.
In the Fisher FM-1000 or FM-200-B (nearly identical tuners) as an example, not only is the FM de-emphasis NOT correct, it is substantially worse in mono as opposed to stereo. If one would take an original Fisher FM-1000, and while listening to a stereo broadcast switch from stereo to mono, you will immediately hear a loss of high frequencies in mono. The mind will make you think that this is because stereo inherently sounds "better", and this is PRECISELY what the Fisher engineers wanted you to think at a time when stereo was new and they were pushing stereo equipment.
The FM De-emphasis is not correct in stereo either, however, the difference is not nearly as bad as it is in mono. The reason it is not correct in stereo is due to the fact that the Fisher engineers wanted to reduce FM Stereo noise as much as possible, without "noticeably" affecting the quality of the audio.
As an example, in an original Fisher FM-1000 tuner, the FM Stereo De-Emphasis is set to 88us (microseconds de-emphasis) while in mono it is set to 108.9us. Remember that the correct setting is 75us. For this reason, reception in mono mode will sound muffled when compared to the stereo mode. Additionally, when comparing the stereo mode to another brand of stereo tuner that has the PROPER degree of FM de-emphasis, i.e., 75us, the FM-1000 will sound less "noisy" since it is in effect muting the high frequencies (and the stereo noise) slightly.
The above fact can be proven by those who are knowledgeable in FM circuitry with a calculator and the FM-1000 schematic. This is NOT a matter of opinion, it is a FACT of mathematics. I have no intentions of attempting to educate the masses on this, because as evidence and experience has proven, a little knowledge can cause LOT of damage.
As any experienced true audiophile knows, the human audible "memory" is quite short. Therefore, switching between mono and stereo on an original FM-1000 tuner will clearly reveal this difference, and will make one assume that stereo sounds "better" while in reality is should sound the SAME, albeit, without left and right separation. However, if someone thinks they are going to be able to "remember" precisely what their unit sounded like before they did the work to it, this is a big mistake as it is simply not possible. The difference is slight and only noticeable upon immediate A B comparison which is how Fisher got away with it in the first place.
But if you were pushing stereo equipment in an era where audiophiles were using mono tuners exclusively, what better way to market your wares but to show how much better stereo sounds! These kinds of marketing ploys have been going on for years, and not just with audio equipment, and it is exactly these kinds of marketing ploys that prey on human gullibility.
As far as the comments posted concerning my "modifications" , it is clear these unfair comments are made out of pure ignorance. The moment the resident purist hears the word "modification" he shudders at the thought, and immediately draws the self-induced conclusion that ANY modification is bad, without having the slightest understanding or knowledge of what he is talking about.
This change which brings about correct and accurate FM reproduction is the ONLY "modification" my work provides. NOTHING else is "modified". There are also two filters in the Multiplex decoder that I recommend removing. They were put there to attenuate the 19kc Multiplex Pilot Signal since this MAY interfere with the bias applied to tape by certain tape recorders. The problem here is the filters are a bit "sloppy" and can interfere with the audio. Since tape is rarely used, removal is recommended but not necessary.
Now if it is your desire to have a tuner or receiver that does not faithfully reproduce radio broadcasts as they were intended to be heard by the radio stations, well, that's your business. It is a self defeating desire, since we seem to migrate towards tube equipment for its quality of sound.
Lastly, it is totally unfair to grade equipment I worked on after it has changed hands, perhaps many times. I have seen some of the worst butchery imaginable in the Fisher equipment I have restored. The world and especially the Internet is full of "experts" who in reality should be banned from even OWNING a soldering iron, never mind USING one and actually putting their hands inside something as complex as a tube tuner!
The individual who posted the comment about their FM-1000 sounding "tinny" is an example of this - NO knowledge whatsoever about such things and NO knowledge about what was done and why OR who messed it up after I worked on it if indeed I worked on it at all. All you hear are things like "my tech" did this and "my tech" did that. They place faith in those who are NOT experts in this field and believe anything they are told.
My specialty is Fisher equipment dating from 1937 through 1972. I am not a jack of all trades who likes to play with a soldering iron. My work is based on over 30 years of intense SPECIALIZED study, using a calculator and knowledge, not Internet hearsay. I have met and have had technical discussions with Fisher engineers. I have Fisher records and files that exist no where else. NO ONE has even a FRACTION of the knowledge contained in my mind and files.
I have exhausted much time composing this note. This will hopefully place light on this darkened topic. I have no intentions of generating argument or debate over something that is not debatable, and therefore will NOT entertain hate mail on this topic.
I hope I have made my position clear.
"The Fisher Doctor"
He made a few posts to the group in 2004, one in 2005, one in 2007, and several between February and June of this year. So, he basically disappeared for five years. He usually resurfaces when there are a growing number of customers who have been ripped off, and they start getting vocal. He then blames all his problems on his special-needs children, asks for patience, and then disappears again.
All of his public posts, whether in various Fisher groups or in his ads on eBay, are full of upper-case rants and make it clear that he considers himself the number one Fisher expert on the planet and everyone else is an idiot.
