[Vintage-Audio] Stylus Feedback? Why?

Thu Jun 25 13:37:19 EDT 2009

Hello Sheldon,

The James B. Lansing Century L-100 mains are ceiling mounted. The B&W 630 
bi-wired monitors flank the seventy-two inch White Birch console on each 
end! This puts one of them along side the end of the console where the 
Sony/Marantz turntable is located. Since the B&W 630's are rear ported - you 
can change the port length + diameter + percentage of bass phase 
enhancement - and this sound bounces off a wall eight inches behind the 
speaker cabinet, you may be right on the mark!

The low frequencies from the B&W 630 monitors could very easily cause the 
stereo console itself to vibrate slightly and said motion could be 
transfered to the stylus. Bingo! There is the feedback loop.

I remember forty years ago when I had my first stereo amplifier, an EICO kit 
built for me just after I had been blinded. No cabinet, about 12-15 watts 
RMS I recon and the second love of my life! My custom car was the first, 
Andrea was third ... Wrong priorities! At least she and I are still good 
friends!

The EICO had a tube go microphonic.  I finally figured out which one by 
gently, very gently, tapping each tube with the eraser end of a wooden 
pencil! When I tapped the right one, "BOING! TWANG!" Odd sound!

Those were fun days Sheldon! Now we just put the amp in a foam padded box 
and either bury it or send it off to somebody to be repaired, hopefully.

----- Original Message ----- 
From: "Sheldon Daitch" <sdaitch at kuw.ibb.gov>
To: "Vintage home and professional audio equipment from 1975 back" 
<vintage-audio at mailman.qth.net>
Sent: Thursday, June 25, 2009 1:46 AM
Subject: Re: [Vintage-Audio] Stylus Feedback? Why?

> Duane,
>
> I think another possibility is feedback via the turntable and record
> because the lower frequency energy from the speaker system causes
> either the turntable platter itself and/or the record to vibrate and then
> that it picked up by the cartridge stylus mechanically, as if it were a
> legit groove vibration.
>
> One possibility with the single channel pickup could be the turntable
> is located is a point where the low frequency energy from only one
> speaker is high enough to send the system into a feedback mode.
>
> It was not unusual in the the broadcast industry to have this feedback
> occur, under certain conditions where there was no audio on the
> system ( I know, BAD) the turntable pot up a bit too high, the
> control room monitor up and then the audio AGC equipment would
> raise the gain.
>
> I seem to recall reading about TT cabinet stands specially designed to
> allow operators to place bags of weighting material, bagged sand
> generally, in those bases, to get the resonance frequency of the
> cabinet down low enough so the resonance frequency was below
> the frequency response of the station's audio system.  This was
> usually no issue with AM stations, but FM broadcast exciters tend
> to have excellent low frequency response.
>
> Oh, in typing this, I just remembered something about low end
> response.  Sometimes, we'd have records with a little warping
> of the surface, and that would show up at a very low frequency
> "sine" wave as the record played.  The AM transmitter never
> saw it, but the Harris TE-3 exciter would not only pass this
> audio, it would show up as very high level modulation on the
> FM mod monitor and under some cases, the AFC on the
> exciter would unlock momentarily.
>
> I also had one radio station where the tape cart machines for spot
> announcements stopped with a fairly heavy mechanical jolt and
> they were mounted on the same cabinet surface where the left turntable
> was located.  With heavy bass boost on a receiver and good low end
> response on the speakers, I could "hear," on the air, the cart machines
> stopping, if the left TT pot was up and there wasn't enough other
> program audio to cover up the stop jolt.
>
>
> 73
> Sheldon
>
> Duane Fischer, W8DBF wrote:
>> Hi All,
>>
>> Several days ago while I was experimenting with different bass, midrange 
>> and
>> treble settings for my B&W 630 three way monitor speakers, that I 
>> sometimes
>> blend in with my James B. Lansing Century L-100 ceiling mounted mains, I
>> thought that I heard a rumble coming from a source other then my stomach!
>>
>> Hark! Was that an electronic Harpsacord or just another harmonic caused 
>> by a
>> Gamma Ray rebounding off that atom smashing thing in the Ann Arbor, MI 
>> home
>> of the University of Michigan Physics lab where someone got their 
>> doctorite
>> by discovering that "Wilson-Phillips" could not sing! No! It was coming 
>> from
>> the eight inch active poly ... some kind of thing woof woof wanna be cone
>> three feet to my right.
>>
>> I got up off the carpeted floor where I had been squatted down doing the 
>> IHF
>> +/-2 Db adjustment procedure and switched over to the ceiling mounted JBL
>> Century L-100's. No rumble, Rumba or other residual reverberations. So 
>> just
>> what was giving the B&W 630 high frequency bi-wired monitors that 
>> rhythmic
>> distress?
>>
>> The Shure diamond stylus was picking up a rumble from the Sony/Marantz 
>> 5520
>> turntable, amplifying it and causing audio distortion. Frankly, it 
>> sounded
>> to me as if I had somehow enhanced a turntable drive mechanism rumble
>> feedback loop, but only in the one set of speakers. It seemed to me that 
>> I
>> should have had the rhumba rumble in both sets of speakers.
>>
>> As Maxwell Smart used to say; "Missed it by that much!" Which explains 
>> why
>> Secret Agent #99 never became pregnant! (LOL!) It scares me to ponder 
>> what
>> might have happened if old Max might have hit the target!
>>
>> I did a little reading in my previously created audio research note file
>> circa 1999 and found out that the James B. Lansing Century L-100 speakers
>> were low efficiency and that the B&W 630 speakers were high efficiency. A
>> concept that I am still not sure I fully comprehend yet today! One of 
>> those
>> "low" is really high and "high" is actually low cosmic time space
>> dimensional shifting event horizon things where one is correct if the
>> velocity of light is positively accelerated by the density of a Black 
>> Hole
>> that is not a hole, but a round sphere that is invisible because of the
>> Black On Black optical principal or negatively accelerated if the 
>> universe
>> is truly infinite and time never ends! No wonder our children can not 
>> tell
>> what time it is on a watch or wrist watch having moving hands!
>>
>> So more continuous RMS (What the Hell is Root Mean Square all about 
>> anyhow?)
>> is going to the B&W 630 speakers and less to the JBL Century L-100's? But 
>> if
>> the volume control knob is in the same position for both speakers at the
>> same moment in time, how can that be? Maybe it has something to do with 
>> the
>> Metric System! I've always been suspicious about people who called money 
>> a
>> "pound", when a pound equals sixteen ounces, unless it is a prescious 
>> metal
>> pound and then is has only twelve ounces! Then they call a "meter" 39.2
>> inches and the car windshield a "windscreen"! Someday someone is going to
>> make a lot of Yen, Yuro's, Pesos or Ben Franklin's by announcing that the
>> real secret hidden in the King James Bible, U.S. Declaration Of
>> Independence, ceiling where that famous inventor - painter of nude 
>> women -
>> gear reduction thing with a big spring that kept time, the day of the 
>> week,
>> the month of whatever year system was then in use, predicted famines and
>> plagues and wars and plagues of Turtles with an image of Susan B. Ugly
>> Anthony on their backs ...Discover that it is really the Metric System 
>> that
>> killed off the Dinosaurs, wiped out the Inca's before the Spanish did and
>> tried to cheat the Mayan Indians out of leap year was not the Da Vinci 
>> Code,
>> but that damn Metric System!
>>
>> Sorry about that. I just hate it when the deserving person, be it for 
>> good
>> or evil, fails to get his or her dues because some so called Greek 
>> Scholar,
>> American archieologist, Soothsayer, cosmic visionary who causes Bald 
>> Eagles
>> to grow hair on the sixth Thursday of any month with three full Moons 
>> etc.
>> All because they can not spell on a stone tablet, parchment scroll, chalk
>> board, mechanical typewriter or word processing computer program where 
>> they
>> click the mouse and it fixes all of their flaws!
>>
>> So tell me, please! Why do I get a sixty cycle hum from the B&W 630 
>> speakers
>> when the Shure stylus tracking at 1.25 grams is playing what is hiding in
>> those deep dark vinyl grooves and only the sound of silence from the JBL
>> Century L-100's? Is it the Simon and Garfunkle effect?
>>
>>
>>
>>
>> Duane Fischer, W8DBF - WPE8CXO
>> E-Mail: dfischer at usol.com
>> Hallicrafters web site: www.w9wze.net
>> HHRP web site: hhrp.w9wze.net
>>
>> ______________________________________________________________
>> Vintage-Audio mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/vintage-audio
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:Vintage-Audio at mailman.qth.net
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
> ______________________________________________________________
> Vintage-Audio mailing list
> Home: http://mailman.qth.net/mailman/listinfo/vintage-audio
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Vintage-Audio at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>
>
> -- 
> Internal Virus Database is out-of-date.
> Checked by AVG.
> Version: 7.5.557 / Virus Database: 270.12.4/2081 - Release Date: 4/26/2009 
> 9:44 AM
> 