Please explain. Im all ears.
Actually Roger, I did that earlier. You must not have read the post?
The loading is for the benefit of the preamp, if its sensitive to RFI. If not, no loading is needed. IOW if you need loading to deal with brightness, the preamp has a problem with RFI. The loading resistor detunes the tank circuit caused by the cartridge and tone arm cable and thus knocks out the RFI caused by the tank circuit when driven into excitation by the energy of the cartridge. Here’s a couple of links that address this in greater detail; the link to the What’s Best forum includes posts by Jonathan Carr, a noted designer of LOMC cartridges. The one to Jim Hagerman’s website has some of the math and some charts that show whats going on:
http://www.hagtech.com/loading.htmlhttps://www.whatsbestforum.com/threads/cartridge-loading-a-misnomer.15077/Why, because it was made for audio, not B&W television.
There are some great books on the history of Heath written my people who were there.
This other stuff about sawing tubes in half make no sense. Ive taked to tube designers and they dont talk that way... at all.
With regards to the 6SN7:
From the RCA Receiving tube manual, RC-19, published 1959, page 229:
2nd sentence (after the part about being used in television circuits):
"Each unit may also be used in multivibrator or resistance-coupled amplifier circuits in radio equipment"
The same phrase about ’resistance-coupled amplifier’ is used to describe the 6SL7, 12AX7, 12AT7 and so on.
Roger, when you say that you don’t know of anyone that used the 6SN7 in audio applications, as in this post:
The 6SN7 was made for black and white TV and was never, to my knowledge, used in the audio chain.
And then turn around and say this:
My dad built the WM-2 in 1956 so I am very aware of 6SN7, as was Heathikit who used them everywhere they could. Are you aware that most of their early products were built largely from WWII surplus of which there was tons. They would buy tons of surpus and then figure out what to do with it. 6SN7 were in great abundance.
--- Could you clarify what you meant here? These statements appear contradictory.
Regarding the sawed in half comment, sure, tube manufacturers don’t talk that way and for the record, I don’t manufacture tubes. But I do use them. Look at a 12AU7 and compare it to a 6SN7 (GE 6SN7s are the best example for this) or a 6CG7; the 12AU7 plate structure is half the height. And when you look at the specs, extremely similar to the 6CG7/6SN7; the geometry and spacing was maintained. So ’sawed in half’ is a good layman’s description. It makes plenty of sense.
To those who write up pages of pseudo science and create paradigms to make excuse for bad specs I no longer care to see here. Skilled people in this industry have come up with some minumum standards for noise, distortion and output impedance.
"Skilled people"? Do you mean marketing?
Uh, Roger, in a way this seems aimed at me (the use of the word ’paradigm’; I’ve not seen anyone else here use that word). If so, you’re way off base (and I regard the attack as un-called for). Don’t think for a minute that we built our amps without feedback because we couldn’t apply it! In case you don’t know what is meant by the Power Paradigm, as opposed to the Voltage Paradigm, I did explain it at this link:
http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.phpIt is in no way an excuse for bad specs- and in fact our amps have some pretty good specs (if proper measurement technique is used, which means **don’t ground a speaker terminal during testing**, which is the mistake that almost everyone except Charles Hanson made/makes). I suspect you didn’t read the paper at the link very carefully, since you claimed that you read it, yet still with the remonstrations!
Briefly:The Power Paradigm is what was around prior to the Voltage Paradigm; the ground work for the latter being laid down by MacIntosh and EV in the late 1950s (it was not until the early 1970s that it had fully taken root). At the time, the only way to build an amplifier that acted as a voltage source was to use enough negative feedback to get proper output regulation. But it was well known at the time that this didn’t work for all speakers made- the speakers had to be built to work with the concept as well. That is why I use the term ’Paradigm’ (and I *also* use it because any thought outside of that platform is often regarded as heresy).
Here is an interesting example that at which you should take a look so you know I’m not making this up:
https://www.google.com/search?client=ubuntu&channel=fs&q=fisher+a-55&ie=utf-8&oe=utf...The first hit of this Google search for a Fisher A-55 is an image from a YouTube video. In the image we see the damping control of the amplifier. It is labeled at full counterclockwise " Constant Voltage", at noon "Constant Power" and fully clockwise "Constant Current". And yes, we’ve had this conversation before.
Speakers built in the old days that were under the Power Paradigm were usually equipped with midrange and tweeter level controls. These controls were not there to adjust the speaker to the room, they were there to adjust the speaker to the voltage response of the amplifier, which was an unknown (examples: vintage horn systems, Acoustic Research AR-1, 1960s KLH loudspeakers, the large Advent...). The Voltage Paradigm was an attempt to get away from having to do that- more ’plug and play’ so to speak.
Like any problem, the solution introduced its own problem- that of brightness as a coloration. This is a problem in every amplifier that employs loop feedback. How bad the problem is depends on the skill of the designer. The brightness is not caused by a frequency response error of course, it is due to residual levels of higher ordered harmonic distortion caused by the feedback application itself. See Norman Crowhurst.
The traditional argument is that the residual distortion is negligible. It is not!! The ear *uses* higher ordered harmonics to sense sound pressure; adding them in even trace amounts results in brightness that does not show up as a FR error because the ear converts the distortion into tonality.
(In their book "Control Design And Simulation", Jack Golten and Andy Verwer discuss (in chapter two) with regard to applying mathematical models to the real world: "...mathematical models invariably involve simplification. Assumptions concerning operation are made, small effects are neglected and idealized relationships are assumed."
It is the mark of a good engineer to know when and which things should be assumed, neglected or idealized. I maintain that violating one of the human ear/brain most fundamental perceptual rules is not good engineering.)
That the ear converts distortion into tonality is well-known. That the ear uses higher ordered harmonics to sense sound pressure is also well understood and non-controversial. It can be demonstrated by a test using simple test equipment.
Many high end designers recognize the brightness-as-coloration problem; the issue is what to do about it? That is why you see so many zero feedback amps that have "bad specs" but for some reason sound quite good. As I’ve pointed out many times, the "specs" don’t recognize the human hearing perceptual rules so what looks good on paper does not always translate to what sounds good as well. This fact is also non-controversial- we see it all the time in the pages of Stereophile, where a reviewer liked an amplifier quite a lot, and yet John Aitkinson is perplexed because the equipment measured poorly. The simple explanation, offered by HH Scott’s head engineer, is that the wrong thing is being measured.
BTW, these comments are not to be construed that every amp that measures poorly must sound better than it measures! There are some bad products out there and you and I are likely in agreement on many of them.
