It's been an annoyance since I developed this neurosis. Discussions among consonantly cursed comrades indicates this malady is wide spread in hi-fidom. What could possibly cause such an affliction? [Other than insanity and / or other neurosis?] As even today's mid-fi components are assembled from high tolerance components on sophisticated computer controlled assembly lines, the unit to unit variablilty of decades past should no longer be a problem. They maybe mediocre, but they will be consistently mediocre.

I've mentioned elsewhere that our Rotel RX-1050 took about 45 minutes playing for optimum sound. This interval was determined in the heat of the Los Angeles summer, with evening temperatures near 75°F. The ambient temperature during the day in our den could be as high as 85°F. Hence, when powered, the amp is somewhat warm. In November 2003, we had a cold snap with evening temperatures dropping below 40°F. With the den at 66°F, we found, dependant on program material, it could take as long 2 hours before acceptable sonics were achieved.

Most perplexing. Cleaning the connectors had no effect. Inspection of the loudspeaker drivers revealed nothing amiss. Line voltage was stable and no excessive noise detected.

Reasoning perhaps some local disturbance that ceased later in the evening, we commenced listening between 19.00 and 23.00. Regardless, about 2 hours hence, the sonics cohere. When 'right,' the sound stage is much more akin to that experienced in a good hall and it is well nigh impossible to localize the loudspeakers. Each instrument is bouyed on its cushion of air, decaying unhindered into the stygian void. [We should note that most listening was to 'small' ensembles at moderate levels.]

Recollecting similar defects [sound stage center too forward, delineated loudspeaker cones, scabrous harmonics and tattered decays] were noted while developing DSP products, I began to wonder...

We were able create these defects by adding the minutest smidgens of distortion, typically less than .003%. Realizing that disortion products are a function of several causes*, including temperature, were we hearing thermal effects?

During subsequent listening, noting the 'rightness' of the sound, I also noted the heatsink temperature of the amplifier. At 60°F, the sound is gritty and exhibits the triangular stage noted previously. The sound can be best described as agressive and 'transpistor zippy'. Things begin to improve when the heatsink rises into the mid 80's. With the heatsink at about 95°F the sound comes into its own. The zippiness is displaced by balanced harmonics and decays are silken. The stage perspective is as it should be. The effect is very similar to the image in a camera viewfinder snapping into focus. Often, while doing these listening tests, I'd test myself to see if I could estimate the heatsink temperature from the sound stage and found I could estimate the temperature within a 5°F range below the 95°F transparency threshold. Until the heatsink rises above 120°F, which takes quite agressive levels with substantial low end, things remain very musical. Interestingly, agressive levels with the likes of Led Zepplin is more thrilling above 120°F! The low end rocks! [And no, it's not my ears clamping! I toasted up the amp while out of the room!]

Before we 6.4*10^9 primates poisoned the atmosphere with our greenhouse gasses, we never turned the equipment off, so as to preclude these annoying thermal effects. Not desirous of exacerbating global warming, we cannot in good conscience leave the hi-fi powered when it is only enjoyed a few hours diurnally. [In an endeavor to leave a drop of petrol for the future, we only heat occupied rooms and the instant mother nature provides free heat or cooling, we open the windows.]

*distorion causes...
Transpistors, and tubes, are inherently non linear devices. They are superb switches, but less capable 'valves' to control the electron flow that consitutes an audio signal. ALL devices have a range where they are more linear, i.e. less distorted. Circuit designer chicanery ameliorates, but never removes, all distortion products. Verily, the chicanery is frequently at cross purposes with an audio signal. Test signals are steady and music ain't! It is possible to design circuits with exceedingly low distortion that are dreadful, not dulcet!