Nude Turntable Project

"It is now possible for me to design a circular aluminium frame cut and welded out of 10mm thick flats into which I can just 'drop' the Victor."

Be careful, Henry, that's what some of us call "a plinth".

If you want to take the time to describe in greater detail the events surrounding your disaster, perhaps I can help. I have quite a bit of DIY experience. From what you wrote, I don't have a clear idea. Was the Cu180 placed UNDER the TT101 prior to the event? And what exactly was the "event"? A burst of very high level signal is a danger to speakers primarily; I would not expect it to damage a phono stage or other electronic devices. An alternative hypothesis is that something blew in the phono stage, which is what you heard as a burst of loud noise. Nothing to do with acoustic feedback. But I don't know all the facts.

I was also thinking shouldn't the speakers been damaged and not the phono stage. You may be right Lew that something was going array in the FF line stage.

Lewm,
My take from his description is that he unmuted the preamp when MC was selected with the volume up and a MM installed - hence this probably blew the phono stage.
Now the feedback he referred to in the other thread could be any of physical, acoustic or electrical. We dont have enough info as you say.
Physical - just put the TT on a rubber sponge and see if it changes the level of feedback, if so this suggests physical. Swap the TT's around and recheck.
Electrical - could be earthing related or could be adverse reaction from combo of cartridge & 2.5 metres of Cardas litz, ie tuned circuit from those cartridges and cabling is upsetting the phono stage.

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.