Going Topless

When changing tubes on my ARC preamps, I noticed a substantial lift in performance when the top covers were left off the units. An increase in "Air", 3D and just plain "relaxed ease" was appearent when the covers were off.
Now my particular units have Litz signal wire running from input selector and PC board to the RCA I/O jacks in the back. These bundles of wire come close to the top chassis cover, without actually touching it.
Are we dealing with "Eddy Currents" here? I have come to the conclusion that all (music)signal carrying wires, must be isolated from close proximity to metal. I have heard the same effect on ICs and Speaker wire. All of these wires appear to be well shielded and use a stiff dielectric. There must be stray Magnetic Eddy Currents at work here.
Anyone else go through this? Better yet; Can anyone explain this?
The moral, Metal and wire don,t mix...........Frank
Frank, while I do not disagree with your experience, there can be an additional factor at work here. Is the ARC preamp tube type? If so, tubes seem to prefer having all metal removed from their proximity. My Wolcott amps are run with the covers off for this very reason. My experience with the performance gain this provides, pretty much mirrors the benefit you received with your ARC.
Removing the lids on components can have a DRASTIC effect sometimes. Besides tubes receiving more direct stimuli via vibration transmitted through the air with the covers removed, circuit stability may also be effected. While most of my experience in this area is with RF based products, i have watched some amplification circuits go from completely unstable and on the edge of oscillation ( covers on ) to running beautifully ( covers off ). While my situation probably pushes things a little more due to the nature of RF wanting to float, removing the lids may reduce the overload that a low level circuit was seeing due to being overpowered by a high level signal. Instead of the fields "jamming" up the guts internally, it is now "freewheeling" around in the room, producing less concentration inside of the component. The reverse is true of our audio based gear. With the lids off, RF can now enter the gear more easily although you may have also minimized the magnetic interaction between incorrectly routed wires or the field generated by a transformer. Either way, run it how you think it sounds best. I, for one, will not doubt that the unit IS performing differently. Just keep in mind that you may have to clean the internals out due to collecting dust and that there may be safety issues to deal with if you have pets or kids. Sean
I prefer topless:

In fact, I even took the metal cover off my breaker box because my system sounds more dynamic (less constricted). I replaced the cover once, but didn't like the resulting affect on my system, so I removed it again and have been enjoying it without the cover for the past few years. (Kids don't try this at home!)

I also had good results removing the top covers from some tube preamps and amps. I just cover the gear with plastic when not in use to keep the dust out. --Bruce
frap, which arc do you have? can removing the covers be cooling the tubes and causing this effect? do you have tube rings on?
just a thought.
Albert, I never suspected the tubes; that puts a new light on it. Sean is ,of course, correct about the safety and dust factors.
Bruce, I hope you live alone on that one!!!!
Kubla, I run 2 systems. One analog, One Digital
Analog ARC SP-10II, SP-8 Mk-1 preamps
Digital: ARC-SP-3A-1 & LS-2 MkII preamps
I do NOT like the sound with the rings on, It seems to dull the sound somewhat. Now if using the mostly "zippy" sounding Sovtek tube, the rings may help that bad situation.
Dennis, I'm quite certain its the effects of metal.
Shouldn't the metal cover protect against RF interference? I too have had similarly positive experience with a tube where the manufacturer advised naked if the room was "free of TV and radio interference", and covered otherwise. The sound was invariably better naked (with the occasional taxi CB adding lib to the odd concerto). The idea, as I probably don't remember it, was that the cover created a "farraday trap"(??).

Maybe Sean could throw light on my gibberish?
A variation on this scheme would be to try removal of the cover & using copper screen as an alternative cover/shield to attenuate incoming RFI (& fingers etc.). This reduces the deleterious effects of signal proxomity to ferrous steel (assuming the cover is steel?) while retaining RFI shielding properties. Or how about making an aluminum cover instead? It would provide less shielding than copper or steel, but would be more easily workable and functional
Bob, I agree that copper or aluminum would both be better alternatives than steel. Interestingly, I have heard from a couple of equipment manufacturers that they use steel in their DACs and preamps because the extra weight somehow equates to value in the mind of the consumer. One manufacturer admitted that he knew his aluminum-cased DAC sounded better than the steel-chassis version; even so, he was reluctant to continue the aluminum version because his customers perceived the lighter weight model as less desirable than the heavier steel version.
Bob & Plato bring up some interesting points. On top of what they stated about the weight of a steel chassis, one also has to think about rigidity and overall strength. When one looks at the amount of posts on the web about goods damaged in shipment, the thought of a transformer breaking free from a soft metal chassis (like aluminum) or the possibility of that same type of chassis twisting / denting far more easily from rough treatment starts to sink in. I do agree that this would act as a "reasonable" shield AND minimize reactance to the internal magnetic field though.

As to Greg's comments, sorry if i was unclear. I have to remember that this is an audio forum and not an RF forum. As such, my explanation and experience has been with the low level circuitry in RF gear being overloaded by high level RF that was emanating from within the same chassis. By removing the cover(s) on some high power amplifiers and transmitters, the RF is allowed to "leak" into the atmosphere. The high level signal is therefore less concentrated near the low level circuitry that was being driven into oscillation and the problem was fixed ( kinda sorta ). Sorry for the confusion, as i was coming from an "i'm still at work" point of view.

This does bring up some valid points about how equipment is designed and tested though. Since engineers and technicians basically build and test everything with the lids removed for ease of access and being able to take test measurements, it is QUITE possible that equipment could measure differently with the lids on. Being able to get around this and take "accurate" measurements would take some real ingenuity on the part of manufacturers.

As i have stated before in other threads pertaining to similar matters, one manufacturer had a product that ran like gangbusters until the lid (which was metal) was slid into place. Once this was done, the amplifier would do some REALLY squirrelly things. Rather than go through, redesign the amp, change all of the parts in production, etc... they simply went from a metal plate to a hard plastic plate. Besides being cheaper for them to produce, it took care of the instability problems.

As such, Greg is correct in stating that the lid of your audio gear would normally act as a shield and keep rf out. Removing it would expose the internal circuitry to whatever interference happened to be floating in the air. This might or might not be a big deal, depending on where you live and how many "good buddies" you had driving around the area. Sean
sean that was just about the best damn reply i've ever seen on this site. congratulations.
I somehow missed Sean's name at the bottom of his entry and thought that Kublakhan had posted it. No offense Kubla, but I was thinking "What in the hell is going on here?". Nice post Sean.
Dekay, offense well-taken LMAO!
Thanks for your help, Sean!
What about using a sheet of kitchen aluminum foil for a top cover? I have been told that this blocks RFI and EMF (electro magnetic?) and at one time used it between an amps external power supply and my CD player which were cramped togther.
Your reference to eddy currents reminds me Frank of a traumatic event that I have not been able to explain. I had on loan an amplification chain -Spectral dmc12 and McCormack DNA1- and a pair of MIT330 interconnects. One of the MIT RCAs was defective and I could not use them so I placed them on top of the pre. One day as I was changing a CD I moved my hand over the interconnect. I did not touch it and it was not connected to the sysrem anyway. There was a loud brief ugly sound and two tweeters and a woofer died on the spot. I suspected some kind of magnetic field like when you change the reception of a radio by moving in the room. I have no idea what is inside the famous MIT boxes. Supposedly the dealer spoke with MIT and they repaired my speakers free of charge. However I was never given an explanation. Anyone knows what happened? Sorry for straying from the topic.
Pefstratiou it seems the you may have been the victim of a stray static electric charge induced from your body into the equipment as your hand passed over the cable's insulator? It may or may not have had anything to do with that cable, so I think you were incredibly lucky to have the damaged drivers repaired at no charge. But then again MIT is like that: very customer-supportive I've found. One day when I called them (& no one else was avaliable to answer a question) they actually put Mr. Bruce Brisson on the phone for me; I was impressed. MIT probably mistakenly thought that the defective connector caused your damaged equipment & absorbed liability as a courtesy issue - so I am even more impressed with them now then ever.
Those 'famous boxes' contain passive group-delay equalizers which control time alignment of various fequency ranges, such that they all arrive at the load end of the cable in-phase. While these components are a serious issue of debate between various detractors & proponents of the technology, I must confess that although I too laughed at the idea for years, I stopped laughing when I finally decided to try their cables for myself. What happened? I bought some more!