Fuse for McIntosh
September 22, 2008
I just received a McIntosh amp: model MC2105, 110V from the
USA. I live in the UK (220V). This morning I plugged in the amp via a transformer. The amp
did not turn on. After inspecting the fuse I have noticed that the fuse is gone and also
is a 5A 250V! I just don’t know if this the right fuse and should it not be 110V?
Could you please advise me what the right fuse is for this amp? Many thanks.
Hamid
Send an email to the McIntosh Labs service department
at sbutt@mcintoshlabs.com and I’m sure they will be able to advise you on what you
need. There is also a toll-free phone number, which is (800) 538-6576. I’m sure there
is a McIntosh dealer network in the UK that can probably also help you, and establishing a
relationship with a good service department might not be a bad idea. Vintage equipment
like you have will from time to time need attention to keep it up and running for many
more years. Good luck.
"Understanding Decibels" error?
September 18, 2008
Thanks for your excellent site. It's a refreshing change to
see such a constructive meeting of solid facts and the audiophile view of the subject, as
there's so much junk info and messed-up ideas around these days.
Your "Understanding Decibels" feature is extremely well presented
and very clear -- congratulations on that!
One small bone of contention though -- in the section on
voltage gain. You say that you might see these specifications written as simply
"dB," but it’s more precise to indicate them as "dBV." Now, while
some manufacturers might use dBV, it isn't actually correct. The reason that you more
often see these specifications written as simply "dB" is that (in this, perhaps
rare, case) it's actually right!
That's because, although the decibel is "by
default" a relative unit; it can be "converted" into an absolute unit by
specifying an absolute reference. This is usually done by adding a suffix to
"dB," and dBV is an example of that. Other examples would be dBm (dB relative to
1 milliwatt), dBu (dB relative to 0.775 volts, "unterminated") and dB SPL (dB
relative to 20 micropascals). dBV is just another one of these -- dB relative to one volt.
So a value in dBV is not a measure of relative voltage
level, such as between the input and output of an amplifier (i.e., the voltage
gain), but rather is an actual voltage level -- an absolute quantity. That is an
inappropriate way to specify gain, because clearly the output voltage level varies with
the input voltage level and in general the input is not going to be consistently exactly
one volt -- the level that would be required to produce the gain figure in dBV at the
output.
Put another way: For a given setting of the amplifier
controls (if it has any!), the voltage gain of the amplifier is a fixed value. As the
output level of the amplifier is not a fixed value (as it depends on the input level),
quoting a specific value of absolute output level is not a sensible way to specify the
gain.
OK, I know that for an audio power amplifier, an input of
"exactly" 1 volt could be applied in the lab, in a steady-state sine-wave test,
but not using a real program signal such as music, although such a source may have a
quoted "nominal" level, its actual level is constantly changing. Perhaps more
importantly, so that gain can be specified in a consistent way for all types of amplifiers
(including preamps that are capable of accepting only very low input levels), it would be
unhelpful to specify the gain as an absolute output level value that was unachievable in
practice due to the design of the output stage and the fact an input level of 1 volt would
drive the input stage of such a preamp into severe clipping.
Since voltage gain is a relative thing (the output voltage
relative to the input voltage required to produce it), the units used for it should always
be just "dB," and this is indeed normal practice in all properly written
amplifier specifications.
Thanks again for your site, and I hope you find this
comment useful. Any further discussion welcome.
Mark Phillips
Thank you for your very clear comment. To put it
simply, I was incorrect. I wrote dBV to specify voltage gain as amplifier specifications
often say simply "Gain: ##dB," which is ambiguous. Furthermore, since no
amplifier exhibits the same gain at all input voltages, specifying gain as dB is somewhat
misleading. The example I went on to explain uses a 1V reference, as is quite common. Such
a measurement could be written "Voltage Gain (at 1V input): ##dB," which, you're
right, is not the same as ##dBV. On www.amplifiermeasurements.com, where we collect measurements of the
amplifiers that we review on SoundStage!
and SoundStage! A/V,
voltage gain is also specified as a multiplier -- e.g., 31.62 x input. To an
engineer, that is the same as saying 30dB, and it does assist in explaining what gain
really means.
Above all, we strive for accuracy, and we thank you for
bringing this error to our attention....S. Andrea Sundaram
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