What does DC coupled mean? (Kenwood)
gbf...@msu.oscs.montana.edu
a circa 1982 Kenwood reciever, model KR-7050, in MINT condition and I have been
using it ever since.
I'm a little confused about some of the buttons though... there's one labeled
"DC coupled" on/off and some others for the radio part labeled
FM 25 micro-seconds (on/off) , FM muting (on/off) , and IF band (narrow, wide)
I haven't done a lot of experimenting, but for the most part I can't tell much
difference in the sound when I switch them.
I called Kenwood but they wanted something like $18 for the origional owners
manual (NOT) And that was after a good 15 minutes of being put on hold and
transfered around.
Also, does anyone know how much power the thing has? the meters go up to 160
so I would guess it's something like 80 RMS/channel but I have no idea.
If anyone can help me out I'd appreciate it. I really like it and got it
practically for free at a garage sale.
-Brian
Doug Mauldin
gbf...@Msu.oscs.montana.edu writes:
[...]
> I'm a little confused about some of the buttons though... there's one labeled
> "DC coupled" on/off and some others for the radio part labeled
> FM 25 micro-seconds (on/off) , FM muting (on/off) , and IF band (narrow, wide)
The standard pre-emphasis curve for FM broadcasters in the US has
a time constant of 75 microseconds. The 25-microsecond option was
included in some receiver designs in anticipation of something that
never came about. Some kind of encoding/decoding scheme for Dolby
broadcasting or something like that. I'd leave it turned off.
Muting is supposed to squelch the normally-occuring thermal noise
an FM receiver makes when it's tuned to a spot with little or no signal.
IF (intermediate-frequency) bandwidth determines the selectivity and also
can affect signal-to-noise ratio and audio bandwidth. Not knowing what
"narrow" and "wide" meant to the Kenwood engineers in this case, I have
no advice except to use what sounds good.
Ah, yes, the DC coupling thing. Back in the '70s it became fashionable
to use DC-coupled amps, even though no one can hear DC. The thing was
to pull the grilles off the speakers and watch the woofer cones jumping
in and out in response to turntable rumble and record warp. ("Just LOOK
at that bass response!") Never mind that the speakers or the records
didn't have any audio response below 50 Hz or so. It took some time for
these guys to realize that they were (a) using up a lot of their available
amplifier voltage-swing to no purpose, and (b) contributing to Doppler-induced
intermodulation distortion. I'd leave the DC coupling turned off.
> Also, does anyone know how much power the thing has? the meters go up to 160
Get your multimeter (you DO have one, don't you?) and measure the
AC voltage across the speaker terminals as you crank up the volume listening
to your favorite music. (Don't use a steady-state tone or interstation
hiss for this, you'll blow something out.) Calculate power using
2
P = V / R
(that's voltage squared divided by resistance) where voltage is the highest
indicated RMS voltage from your meter at the amp's highest level without
distortion, and resistance is the nominal impedance of the speaker system.
Using voltage in volts and resistance in ohms gives power in watts.
Many years ago I was given a demonstration of this nifty little technique
in person by none other than Paul Klipsch.
Regards,
Doug
Jamie Hanrahan, Kernel Mode Systems
> a circa 1982 Kenwood reciever, model KR-7050, in MINT condition and I have been
> using it ever since.
>
> I'm a little confused about some of the buttons though... there's one labeled
> "DC coupled" on/off and some others for the radio part labeled
> FM 25 micro-seconds (on/off) , FM muting (on/off) , and IF band (narrow, wide)
"DC coupled": When enabled, disables a high-pass filter, generally set to cut
off the output below 10 Hz or so. In many amps this switch is labelled
"subsonic filter" - "subsonic filter on" corresponds to your "DC coupled off".
The subsonic filter is generally considered to be a good thing, unless you know
for absolutely certain that ALL of your source components have zero DC offset
in their output. With DC coupling, any DC offset in the input appears as DC
offset in the output to the speaker, which means a constant DC voltage through
the woofer coils (and corresponding cone offsets). The filter is also a good
thing if you're playing warped LPs (and all LPs are warped to some degree) --
without it you can watch your woofer cones move slowly in and out as the
cartridge rides over the bumps... again, large, nearly-DC currents through the
woofer coils. The subsonic filter blocks these very low freq, inaudible,
woofer-damaging signals.
"FM 25 usec": Changes the equalization (de-emphasis) in the FM tuner. I
believe the us standard is 75 usec. There was a movement for a while to go to
a different standard (I seem to remember that 25 usec went along with the use
of Dolby NR) so these switches appeared for a few model years.
"FM muting": When enabled, acts like a squelch control on a two-way radio or
scanner, killing FM interstation hiss when you aren't tuned to a strong
station. Normally leave this on. Disable it if you're searching for weak
signals.
"IF band": "Wide" provides greater audio bandwidth on FM (though, with the
practices many FM broadcasters use, you may not notice), "narrow" allows
greater selectivity. Leave it set to "wide" unless you are going after
stations that are very near (one or two channels, 200 or 400 kHz away from)
other stations, esp. if the nearby, unwanted stations are markedly stronger.
> Also, does anyone know how much power the thing has? the meters go up to 160
> so I would guess it's something like 80 RMS/channel but I have no idea.
If the individual meters go up to 160 that's probably 160 peak per channel.
You're probably in the ballpark re RMS ratings. If you have a used stereo
dealer near you you can ask them to check the Orion Blue Book -- it will give
RMS power ratings.
btw, $18 for the owner's manual isn't that outrageous -- at that price they're
practically giving it away, as it probably costs them nearly that much to
handle the order. Whether it's worth that to *you* is of course another
question!
--- Jamie Hanrahan, Kernel Mode Systems, San Diego CA
Internet: j...@cmkrnl.com (JH645) Uucp: uunet!cmkrnl!jeh CompuServe: 74140,2055
Michael Cowart
: I wonder if anyone out there knows anything about this.. A while back I bought
: -Brian
Hi Brian,
I have the 7050. DC stands for Direct Coupled (not direct current) in this
case. With it on, you bypass the output capacitor, which allows the amp to
output all frequencies down to dc (direct current). I advise you not to use
this feature. You will waste a lot of power on extraneous signals (turntable
rumble, etc.) The unit is spec'd at 80 watts RMS into 8 ohms per channel at
.009 THD, I think (may have to look that one up). It listed for around $800
back in the early 80's. I think I paid $500 for mine. It is a good receiver
and the amp section is very good, IMHO.
I have the manual and will send you a copy if you haven't got it already.
cheers,
Mike
Jamie Hanrahan, Kernel Mode Systems
> In article <00982451...@Msu.oscs.montana.edu>, gbf...@Msu.oscs.montana.edu writes:
>> I wonder if anyone out there knows anything about this.. A while back I bought
>> a circa 1982 Kenwood reciever, model KR-7050, in MINT condition and I have been
>> using it ever since.
>>
>> I'm a little confused about some of the buttons though... there's one labeled
>> "DC coupled" on/off and some others for the radio part labeled
>> FM 25 micro-seconds (on/off) , FM muting (on/off) , and IF band (narrow, wide)
>
> "DC coupled": When enabled, disables a high-pass filter, generally set to cut
> off the output below 10 Hz or so. In many amps this switch is labelled
> "subsonic filter" - "subsonic filter on" corresponds to your "DC coupled off".
In a private e-mail message, WIT...@aed.dsto.gov.au (Witold Waldman) pointed
out to me that the terminology here is incorrect: The term "subsonic" properly
refers to a speed less than the speed of sound (contrast with "supersonic").
The correct name for these filters is "infrasonic filter".
Now, almost every amp or preamp I've seen with these filters labels the switch
"subsonic filter", so my statement above ("In many amps...") stands, but that
doesn't mean they're correct to do so.
Lon Stowell
>
>In a private e-mail message, WIT...@aed.dsto.gov.au (Witold Waldman) pointed
>out to me that the terminology here is incorrect: The term "subsonic" properly
>refers to a speed less than the speed of sound (contrast with "supersonic").
>The correct name for these filters is "infrasonic filter".
>
>Now, almost every amp or preamp I've seen with these filters labels the switch
>"subsonic filter", so my statement above ("In many amps...") stands, but that
>doesn't mean they're correct to do so.
>
Consider this public notice that Cal Lott is hereby notified that
the bass junkie mailing list must from this point on, refer to their
favorite toys as "infrawoofers".
In all seriousness, might not be a bad term for the true
plaster-crackers as opposed to those junky bass modules coming out
of the woodwork.
Jamie Hanrahan, Kernel Mode Systems
> In article <1994Aug4.001151.4351@cmkrnl> j...@cmkrnl.com (Jamie Hanrahan, Kernel Mode Systems) writes:
>>
>>In a private e-mail message, WIT...@aed.dsto.gov.au (Witold Waldman) pointed
>>out to me that the terminology here is incorrect: The term "subsonic" properly
>>refers to a speed less than the speed of sound (contrast with "supersonic").
>>The correct name for these filters is "infrasonic filter".
>>
>>Now, almost every amp or preamp I've seen with these filters labels the switch
>>"subsonic filter", so my statement above ("In many amps...") stands, but that
>>doesn't mean they're correct to do so.
>>
>
> Consider this public notice that Cal Lott is hereby notified that
> the bass junkie mailing list must from this point on, refer to their
> favorite toys as "infrawoofers".
*grin*
> In all seriousness, might not be a bad term for the true
> plaster-crackers as opposed to those junky bass modules coming out
> of the woodwork.
The latter are more properly called "woofers". (Unless they're better-suited
as midrange units.) :-)