It depends on the design and construction of the amp chassis (and the dust cover and base of the turntable). I imagine some amps are put together in such a way that their lid provides structural integrity to the complete chassis, the lid reinforcing the faceplate and rear and side panels by being screwed to them, thereby lessening chassis panel vibrations and the resulting resonances. A better tact is to build an amp without an enclosure containing loose panels to begin with, the way amps were made in the 1950’s and 60’s. Contemporary amps so built are those by EAR-Yoshino, Music Reference, McIntosh, Jadis, Air Tight, Primaluna, Lamm, Allnic, Conrad Johnson, and others. These are all tube amps, which are more commonly available as "open chassis" designs than are solid state ones.
Turntables with a solid plinth, almost(?) universally of non-suspended subchassis design, can be used with a dust cover in place without a sonic penalty IF one does what I have. I have a base that surrounds my table’s solid plinth on all four sides, but without a bottom panel that the plinth sits on. The base surrounds the plinth, but the two are connected only in that they both sit on the same surface, the shelf of a stand. In my case, that "shelf" is actually a Townshend Audio Seismic Sink, whose top plate is relatively dead/non-resonant (the bottom of it’s top panel is damped). Attached to the four-sided base via hinges is a dust cover, which I close after placing an LP on the table’s platter. The resonance of the dust cover is free to migrate down into the base, but is not transferred into the table's plinth, which is isolated from both the Seismic Sink and the base & dust cover by being placed on three roller bearings. True, the air "trapped" inside the dust cover may create a minor cavity resonance, but that is a price I am willing to pay to prevent dust from falling on my precious LP’s during play, far more important to me than any possible slight loss in sound quality!
Well, I have always run my tube amps without their metal lids/covers. The result is an opening up of the sound. Almost as if a metal veil has been lifted. Try it.
Could be your just exciting tube microphonics and adding false euphonics.
A simple good test to see if any tubes are microphonic in tube preamps or amps, is to turn the volume up to normal, have someone listen close at each speaker, and for you to gently flick each tube with your finger nail. The person listening at the speaker will tell you if they can hear that flick, bad ones will really stand out.
George. Agreed. Though my Teles pass the (OCD) fingernail test. ;-)
bdp24, Good stuff. Regarding the amps, perhaps the metal lid/cover affects the electromagnetic field around the tubes (and maybe the transformers). I even find removing screens for low signal stage tubes beneficial. On the turntables, it’s got to be acoustic feedback being amplified within the closed lid space.
Eyes can hear more than ear -- open sound/closed sound
Nobody that truelly loves vinyl would play a turntable with a dust over on.
...except owners of compact linear arm technics decks that must have dust cover closed during playback.
’George said’..."Could be your just exciting tube microphonics and adding false euphonics.
A simple good test to see if any tubes are microphonic in tube preamps or amps, is to turn the volume up to normal, have someone listen close at each speaker, and for you to gently flick each tube with your finger nail. The person listening at the speaker will tell you if they can hear that flick, bad ones will really stand out."
George. I would rather think Kevin Deal has the true skinny on tube microphony...
From Kevin’s website...
Microphony, tube dampers, and tapping on tubes -
Okay...listen closely class, because I will say this only once: DO NOT TAP ON TUBES! You can permanently damage them! Repeatedly tapping on a tube’s glass can cause a perfectly good tube to become too microphonic for use.
ALL tubes are microphonic to a greater or lesser degree. Whether or not that microphonics is audible will depend more on the tube’s function in the product, rather than the microphony of the tube itself. In some positions, you will never hear anything, even with the worst tube. In other positions you will hear something even with the best tubes. At that point you make a judgement call: does this level of microphony interfere with my listening enjoyment?
Tubes are supposed to make noise when tap you tap on them! If a tube is truly microphonic, and in a position where it is critical, you will know it. It will feedback as you play music and be so objectionable you’ll turn it off.
For those interested in a more in-depth discussion on microphony, click here.
not necessary to tap on tubes it’s enough to tap on amp/preamp chassis to hear tube microphony. also if you softly touch with palm of your finger you may hear either hum or noise.
My LP12 has a dust cover. I like it. Keeps platter and Tonearm cleaner than Kuzma Stabi even w/ a cloth cover on it. But I am a proponent of the long ICs / short speaker cables school. Only amps and speakers in the listening room! At low volume no problem with eguipment and TT in room; but at normal to Rock Out volumes IT IS a problem!! Even wth all the racks, spikes, footers, isolation platforms, that I have tried in last 28yrs out of 45yrs; I prefer the long IC/ short speaker cable and TTs and other eguipment OUT of the room!
Sure it is a compromise; but so is the short ICs and all equipment stacked between the speakers school.
Yes, I am one of the lucky guys. Dedicated Room, no kids, no pets, great WAF.
I bought better ICs than tons of $ on racks, platforms, spikes, you name it !!! It is easier to clean, change out a piece of eguipment for audition, more pleasing to the eyes, and sounds better to these ears.
Listen, Trust your Ears,
Best to all on this Journey!
I've been doing this with my Rogue Ares phono preamp. The lid+sides is one piece of sheet metal of relatively low gauge; any disturbance and it rings like a bell -- not a good thing for a tube phono stage. Plus the weird tube cage thingy is ugly. So, off with the lid.
Meanwhile my Rogue Hera preamp chassis is machined aluminum, and works quite well to isolate the components/tubes inside, so the thick/heavy lid stays on.
And as has been said before -- DON'T tap your running, hot tubes with a fingernail, etc. Tap around them, or at most use a light touch with the soft part of finger (depending on how hot).
Yes, I am one of the lucky guys. Dedicated Room, no kids, no pets, great WAF.
Is it definition of audiophile luck?
Is it no pets/kids or no wife with plenty of hi-end stuff?
I'm happy with my parrot, but had my luck much better when my kids lived with me though.
As just another audio nut with his own opinion and the related anatomy to go with it, here's my take...
Covers on a normal turntable playing vinyl causes an unacceptable sound quality. And sure, if you have the money for a big isolation platform and your cover fits over the entirety of the whole TT, then I can see where it would be workable.
As to amps, I had a fabricator make a Faraday cage just for the amp transformers, leaving the tubes open to the room. It greatly improved the sound, but the main power transformer, while working within its operating temperature range, got hot enough to degrade the sound after about an hour. So, then i installed a cooling fan within the cage. Problem solved.
After buying custom racks, all kinds of footers, including custom made pointy footers from solid brass, I went to mass loading. At the one large aluminum recycling place in north Denver, they have every size of solid blocks of this metal, including 2 by 4's. Placing these and moving them around to find the right spot on small & large components was beneficial and inexpensive.
A word about vinyl. I somewhat scientifically cleaned 1,000+ records with a Loricraft followed by critical listening. The most important things learned were that regardless of all the other variables, you MUST not use rubbing alcohol as it is to strong of a solvent (use denatured up to a maximum of 25% in solution) and you MUST re-lubricate every record post cleaning, even if the cleaning chemicals suggest they do so. The only product I found suitable was a tiny amount of Gruv-Glide applied per the directions. Otherwise the diamond will cut the crap out of a dry, clean record and ultimately degrade the sound. I estimated that 16 tiny pops were added each time a "dry" record was played. Lastly, always clean every record before play, new or used. New records are greasy and sound smeared and dull. Used records flip dirt into the cartridge wrecking the cart suspension.