Nude Turntable Project

Hi Lew,
I agree.....speakers are normally the first thing to 'blow' with a sudden violent volume? I've had it happen to me and lost not only the tweeters....but also the midrange drivers!
Because of the shock factor.....I'm a little confused about the exact sequence of events but because I was testing this 'feedback' loop with various different turntable supports (including rubber sponge etc)....I will describe the methods I followed:-
1. Turntable motor is not switched on
2. Preamp volume control is turned down
3. Mute button is 'on'
4. Acutex 420STR cartridge is placed on the record
5. Mute button is switched 'off'
6. Volume control is gently turned up until low volume of 'feedback' just begins
7. Without touching the volume again....the feedback increases itself until I hastily turn it down and engage 'mute'

Now I had the MM gain input selected....not MC....and had the volume turned down as I described. Then I supported the copper Cu180 'plate' on spikes on the shelf and placed the Victor directly on the Cu180.
I placed the 420STR on the record and hit the 'mute' and that's when an almighty noise erupted.
It was a couple of seconds before I could hit the 'mute' to stop the noise.

Now here's where my memory seems confused?
I thought I repeated the testing of this feedback with the Victor on the Cu180 and the feedback loop at a lower volume whereupon I then returned the Victor to its original spiked support and then switched phono inputs to the Raven AC.
It was then that I had no sound from the phono stage. I reconnected a tonearm from the Victor and confirmed no sound and tried it with my headphones as well. All other preamp inputs (tuner, CD, tape, AUX) were fine.

Perhaps the fact that the 420STR is like a giant antenna (according to Chris and the Professor Timeltel).......the hunk of copper under the Victor, induced the feedback at a much lower volume level than otherwise?

Question: "I placed the 420STR on the record and hit the 'mute' and that's when an almighty noise erupted." Is this step #5? You just placed the 420STR on the LP and then un-muted?

I presume the tt was activated, platter was turning. Yes?

Can you characterize the crescendo of "noise"? Was it low frequency, high frequency, etc? Was it like what one hears at, say, a rock concert where the sound man is trying to adjust the mike and one can get that obvious microphone feedback between the bass player's speaker and the microphone, a "screech"?

Since your unit is already being repaired, I suppose all this is moot, but it might be a good idea to try to hash it out so the problem does not repeat itself, I guess.

Henry, I see that you already started a separate thread to discuss the problem. Sorry for asking you to repeat yourself here. I will read what has already been asked and answered on the other thread. Almarg is a very knowledgeable and thoughtful guy, as are others who have responded on the other thread.

The 'nacked truth' seems to be that there is no such a thing as a 'nacked TT'. The most of those we are talking about are made in Japan, while J.Carr explained that there
is no equivalent in Japanese for 'our' expression 'plinth'.
They use the expression 'base' instead so whatever one put
under his 'nacked TT' is obviously a 'base'. Raul's claim
to be the first who discovered the 'nacked truth' mentioned even 3 of those 'pneumatic' AT footers with obvious convinction that the expression 'plinth' has a
very clear denotation while those huge pneumatic footers
on which both his Denon's were 'footed' should be seen as a
totally different animal. I am known as very fond of semantics but this 'subject' is actually about the relation between the language and the so called 'reality'.
Besides without the notion of an 'base' one get confused
regarding what is 'above' and what 'below' so some of us
even used the copper mat to put not 'obove' the platter but
under the 'nacked TT' with some strange results.

Regards,

Dear Nicola, I do think there is a qualitative difference between a real plinth (including the 3-legged skeletal one described by Henry) and using just footers of one kind or another under the bottom of the chassis proper (which by the way was never intended to support the weight of the entire object). I guess you know as well that "base" is a synonym for "plinth" in English.