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In Reply to: RE: But my expectation was that the first amp was going to sound great... posted by Paul Joppa on June 2, 2021 at 09:12:26:
These days supposedly a new car can be run as how you would normal drive right from the shop floor. In days past you had to carefully "run in" the engine for the first 1000 Km / Miles.
A few times I or members of my family have bought a new car and in spite of today's habits / advice we carefully ran in our cars as per old day instructions. The result was that we got a very long life out of our engines, at 200 000 Km timing belt replacements the mechanics would ask us what we had done, what we had used for oil because the tolerance were still like new.
In my younger days I had a vacuum coater for aluminizing (putting a reflective coat) on telescope mirrors. The heating element was tungsten. Heating the filament up in a hurry it would last two or three times. If done ever so slowly... twenty , thirty times.
Tube specifications often give live expectancy and / or how often a tube is expected to be switched on. Basically this has to do with the expansion / contraction of the filament - the more this happens the more likely it will be there is a break. Some studies have been made that instead of switching the filaments off reducing the filament voltage to half extends the life.
Whenever metal is machined / formed internal stresses appear. Slow heating and cooling will reduce stresses.
Conceivably this is what can happen inside parts too. Capacitors do warm up ever so lsightly depedning on its internal losses so conceivably there is some heating / cooling internally and together with electrical current there might be some alignment of the atoms. (just like a transformer has a magnetic field)
Until a year ago I thought tube rolling was a lot of { use your favourable derogative expression } but then I made an amplifier with very little feedback. And for the first time ever I noticed a difference in changing tubes. I now have an open mind on this subject.
At the moment I am working on a SE amplifier with only local feedback in the output stage and no feedback in the driver stage. Modelling shows 0.27% distortion at 1 Watt and it will be intersting to see what the results are once I get around to building it (other chores to do first but health issues have interfered). I wonder if tube rolling of the input stage may have a noticeable impact but as they say: proof is in the pudding.
I don't recall where I read it but it was a studdy about different speaker performane when the voicecoil was warm or not. Similarly a speaker with rubber surrounds had to be "run in" when new to get the surround to flex properly. And over time... the rubber surround hardens and the speaker response curve changes.
AM
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- RE: But my expectation was that the first amp was going to sound great... - AmadeusMozart 06/2/2115:52:13 06/2/21 (0)
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