Effect of Weak Mains Power

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I recently had a blind opportunity to hear the effect of poor mains power. My NCore 400 had started sounding harsh in the mids and brittle in the hi end over the last month. My class A/B mosfet amp started suffering harsh mids. My Stereomour single ended triode showed no performance change in this period. Last weekend cf bulbs started flickering out and on. My power provider came yesterday and found bad supply to the house (buried cables failing at splice points). Immediately all amps were back to sweetness! I believe this may show that mains power will have very different effects on the different amp designs.
 
I'll go with that from Norway. I'm not trained in this stuff but the things I build work so that makes it fun. I'm a musician. I can say positively that the different amps acted (sounded) different before the situation was rectified. I'll be going back to my hometown in Wisconsin to celebrate Syttende Mai.
 
Some amplifiers cope with reduced (and possibly wildly varying) supply voltage better than others. Not very surprising. The behaviour depends on how well the PSU DC output voltage holds up when the AC input falls, and how well the amplifier circuit maintains correct device bias, voltage headroom etc.

Very rough generalisations:
1. an amp with an SMPS supply will cope well, as the DC should hold up
2. a valve amp may cope well, as most valve amps will be relatively unfussy about DC supply voltage
 
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