Resonance of case affected audio

[brucew268]

20 years ago I had a Theta transport which performed heads and tails above anything I could find in its price class... and then the laser went out and had sadly gone out of production, with lesser replacements on offer. Before the Theta betrayed me, whilst looking inside one day, I found something that caused the music to take on a much greater sense of natural, analog-like ease that I'd not heard out of a digital in the 90's, without giving up any detail or definition. The cause was removing the case top. I had previously applied bitumen damping to the cover, which reduced some ringing and increased the sound stage. But removing the cover altogether was a revelation. Unfortunately at the time I could not think of a good solution to keep dust et al away from the transport drive and electrics. And I was a little concerned about health and safety. So I reluctantly screwed the cover back on.

It could have been a resonant interaction with the mechanics of the transport, and/or it could have been an interaction with some of the components on the PCB.

Reminded of that today, I wonder if my preamp would also respond well to removing or isolating the cover from the rest of the case. So I may try putting a thin layer of rubber between the case top and the main structure, screwing down only lightly. Since the cover wraps around on the sides, that will mean the side screw holes will not likely line up and will need to leave those unfixed.

[walpurgis]

That's an odd story Bruce. I've never tried using gear with metal covers removed, but some manufacturers like NVA and DNM use non metal casings, so maybe there's something in it.

I wouldn't necessarily recommend completely isolating a metal cover. There may be an earthing issue and that could impact on safety.

[Jimbo]

20 years ago I had a Theta transport which performed heads and tails above anything I could find in its price class... and then the laser went out and had sadly gone out of production, with lesser replacements on offer. Before the Theta betrayed me, whilst looking inside one day, I found something that caused the music to take on a much greater sense of natural, analog-like ease that I'd not heard out of a digital in the 90's, without giving up any detail or definition. The cause was removing the case top. I had previously applied bitumen damping to the cover, which reduced some ringing and increased the sound stage. But removing the cover altogether was a revelation. Unfortunately at the time I could not think of a good solution to keep dust et al away from the transport drive and electrics. And I was a little concerned about health and safety. So I reluctantly screwed the cover back on.

It could have been a resonant interaction with the mechanics of the transport, and/or it could have been an interaction with some of the components on the PCB.

Reminded of that today, I wonder if my preamp would also respond well to removing or isolating the cover from the rest of the case. So I may try putting a thin layer of rubber between the case top and the main structure, screwing down only lightly. Since the cover wraps around on the sides, that will mean the side screw holes will not likely line up and will need to leave those unfixed.

Hi Bruce, I have heard that valve pre amps in particular do benefit from being used without casing. Not tried it myself as I don't want to accidentally go up in puff of smoke.

[YNWaN]

I've just replaced the cases housing my phonostage with acrylic and their seems to be a sonuc advantage over the previous aluminium - this may be a resonance issue, an eddy current issue, or just my fancy (not decided yet).

[YNWaN]

I'm having a nice listen now and it definitely sounds better - which is odd as all I have done is replace the aluminium sleeves of the cases with acrylic and moved the two halves (it's mono in two cases) 40mm further apart. This is just the main circuit - all the power supply is in two more cases and they are a metre away already!

Edit: or, as ventilation is better, the DC thermal drift is better controlled - could be that.

[The Grand Wazoo]

Despite being held down against almost spring-like tension with about 12 screws, my pre sounds better without it's lid on. I never tried it without the identical bottom cover removing though. The Radford is also improved by the lack of it's box-like transformer cover, but I don't have the recklessness to try to risk the potential consequences of doing either long term.

[YNWaN]

Why is there 'spring like tension', is the lid bowed?

[Marco]

I'm having a nice listen now and it definitely sounds better - which is odd as all I have done is replace the aluminium sleeves of the cases with acrylic and moved the two halves (it's mono in two cases) 40mm further apart. This is just the main circuit - all the power supply is in two more cases and they are a metre away already!

Edit: or, as ventilation is better, the DC thermal drift is better controlled - could be that.

I believe that Anthony TD, in a discussion elsewhere about acrylic casing, said something along the lines of acrylic making an excellent insulator, or something like that. I can quiz him again on it, if you like? There were certainly sonic reasons why he built his Soul amplifiers with acrylic cases.

Btw, what's with this 'effected' pish (not just you, incidentally)? It's affected!! Honestly, wot skoolz did yooz lot go to?

Marco.

[The Grand Wazoo]

Why is there 'spring like tension', is the lid bowed?

Yes, it's a sheet of metal, perforated except for a solid border and with a very slight curve in it, only becoming apparent when you begin removing the fastening screws. The apex of the curve runs across the width of the unit and I fasten the front and back of it against the tension, rather than pulling the centre down, as it would be it it were flipped over (if you follow me).

[YNWaN]

It's because I'm typing on my phone and I can't properly see the predictive text doing it's annoying thing - happy?

I'm (well) aware of acrylics properties - it a reasonably good insulator (both of electricity and of heat) but that isn't the reason DNM used (may still use) it for their cases - I've already alluded to that - eddy currents - induced magnetic fields in non ferrous materials. This phenomena definitely exists but whether it is generated in an amplifier and whether it is relevant in this context are different issues.