I just purchased a brand new Rotel RB-1080 two channel amplifier. The amp
is rated at 200 watts per channel into 8 ohms. My question is this - one
side of the top of the amplifier is just a little bit warmer than the other
side (I used it for about an hour at a medium volume). If I was rating the
heat, one side would be a ten and the other side would be between 8 1/2 and
9. I probably wouldn't be asking this question, but somebody once told me
that if one side of the amp is hotter than the other side (in a two channel
amp), eventually the hotter side will not sound as clear as the cooler side.
Is this true when the difference in warmth is minimal as compared to a
greater difference in warmth (for instance one side is a 10, and the other
is a 4). Am I being too much of a perfectionist? Do all amps have
differences in warmth?

Thanks in advance,

Randy

Randy & Michelle wrote:

I just purchased a brand new Rotel RB-1080 two channel amplifier. The amp
is rated at 200 watts per channel into 8 ohms. My question is this - one
side of the top of the amplifier is just a little bit warmer than the other
side (I used it for about an hour at a medium volume). If I was rating the
heat, one side would be a ten and the other side would be between 8 1/2 and
9. I probably wouldn't be asking this question, but somebody once told me
that if one side of the amp is hotter than the other side (in a two channel
amp), eventually the hotter side will not sound as clear as the cooler side.
Is this true when the difference in warmth is minimal as compared to a
greater difference in warmth (for instance one side is a 10, and the other
is a 4). Am I being too much of a perfectionist? Do all amps have
differences in warmth?


Well, since it is still under warranty, you can have the dealer check it
out, if they have a competent service department.

One possible reason: Amplifiers are adjusted for a certain level of bias
on the output transistors, which affects quiescent current, and puts
them a specified amount into Class AB operation. More bias, more
quiescent current, farther into Class AB, theoretically less crossover
distortion, and more heat. Different amplifier channels, due to parts
variations, may take slightly more or less bias and quiescent current to
attain a given level of low level crossover distortion. Most
manufacturers adjust by the quiescent current in the output stage, which
normally will equalize heat generated by the amplifiers at idle, but
perhaps Rotel actually measures the distortion when setting up the amp,
and that could cause a difference.

Another possible reason could be asymmetric physical layout. Power
supply regulators often put out as much heat as an idling or
small-signal-driven amplifier channel. If the regulators are farther to
one side than the other, that side of the amp could get warmer. I am
not sure of the layout of the RB-1080, or of how that might affect that
particular amplifier.

Of course, something could actually be amiss, a good reason for having a
good technician check it out.

-GP