ok... here's my question: If I have a millivolt range audio signal and I add a dc offset to it, and then I take my new signal and send it to a speaker with a built in amplifer, will this be the same as sending the audio signal alone to the amplifier?
What I think: I think yes... because the way speakers work is by vibrating along with the fluctuations of the audio signal, and since a dc signal is flat, this wont affect the output of the audio amplifer....
thanks
How much DC are you sending and is it deliberate or a side effect of an amplifier stage? Sending DC to a speaker is not a really a good thing I would think as it will push the cone out of its centre range. But I would guess that the built-in amplifier is AC-coupled so the DC might never make it to the speaker as the first stage of the amp blocks it.
tre
s 2.5V, delibrate2.5V, delibrate
Why?
Tom
he
cks
. t aBecause I'm passing an audio signal through a 4066 analog switch which can not handle the negative swing from an audio signal, so I'd like to include a DC offset of 1/2 the Vcc of the chip in order to avoid this.
Because I'm passing an audio signal through a 4066 analog switch which can not handle the negative swing from an audio signal, so I'd like to include a DC offset of 1/2 the Vcc of the chip in order to avoid this.
Well you could always pass the signal through a capacitor before subjecting the amplifier to it. Kinda obvious (you can work out the value for yourself), and cheap!
Chris
Usually you'll want to AC-couple the output, although there is doubtless some AC coupling in an external amplfier.
You might get a wee bit of an audible click* at turn-on (and turn-off).
Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
-- Why not use a 4051 instead? Just set Vee to a voltage enough more negative than your input signal in order to provide the needed footroom and you should be OK. JF
If it results in a switching transient when you turn on or select the source, it will be annoying and possibly harmful. For example I have an iPod docking station connected to my powerful Denon stereo amplifier. When turning on the iPod, there is an annoying pop. If the amplifier gain was set for high level, the speakers could be damaged and/or the protection circuit will fire. Despite my misgivings, I had to install an isolation transformer to eliminate the transient.
-- Joe Leikhim K4SAT "The RFI-EMI-GUY"© "Treason doth never prosper: what\'s the reason? For if it prosper, none dare call it treason." "Follow The Money" ;-P
a s
o the
blocks
m...
d it
ce a
The 4051 looks pretty good, except its got a fairly high Ron resistance that might throw me off.... so.... there's not much of a difference between a MUX and an analog switch is there?
blocks
-- Actually, there is. An analog switch is a bidirectional contrivance which can transfer analog (or digital) signals back and forth, while a conventional multiplexer is unidirectional. JF
Or a 74HC4316, which is like a 4066 but has level translation like the
4051. You can make -V from +V with a capacitor charge pump such as a 7660 or an inductor-based switching supply.Best regards, Spehro Pefhany
-- "it\'s the network..." "The Journey is the reward" speff@interlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com
A DC offset will affect a speaker, if it is direct coupled.
Speakers use a standing magnetic field so ANY voltage on the coil will affect its position. That coil is suspended in the speaker assembly at a specific central (to its motion) rest point. A DC offset will change that "rest point", which will subsequently affect the speaker's operation. It will be compressed response for half the wave for every cycle it carries. For signals less than the offset voltage, the signal would "disappear" for that half of each cycle.
Hmm..., I must comment, since this vaguely implies that a speaker will "auto-AC-couple itself" in presence of signal with DC offset. It won't. Without a blocking capacitor, DC-component will choke the speaker, since, after all, a speaker is little more than a solenoid with membrane attached to the dynamic part.
An analogy would be getting a neck massage from a masseuse who applies, in addition the nice, gentle, AC undulating motion, a potentially suffocating DC grip that is always present.
-Le Chaud Lapin-
Almost all audio amps have capacitive coupling at / near the input stage, so all stages afterwards will not be affected. Usually evev the input stage is protected that way.
ot a
its
d so the
mp blocks
.com...
nal
send it
ysince a
h o .in
Correct, but only if you are talking about a digital multiplexer, which panfilero obviously isn't.
TheCD4051 (like the 4052 and 4053) are all analog multiplexers and perfectly bi-directional.
-- Bill Sloman, Nijmegen
As has been pointed out repeatedly in this thread, this is wrong. The DC signal will move the speaker coil away from it normal resting position. A small DC offset may not matter too much, but 2.5V is a lot.
One complicating factor, not mentioned in the thread so far, is that the stiffness/spring constant of many speakers is mostly determined by the compressibility of the air in the cabinet. The cabinet is never completely sealed - because if it were changes in atmospheric pressure would move the coil off-centre - so the stiffness of the speaker is much lower at DC than at music frequencies, and even a small DC offset can jam the speaker at one or other end of its travel, giving very nasty distortion if you try and get music out if it.
-- Bill Sloman, Nijmegen
the
blocks
it
since a
-- Regardless, his use of the non-qualified "MUX" leads to the possibility of digital multiplexers being considered bidirectional, which they usually aren\'t. My use of "conventional multiplexer" was intended to refer to digital multiplexers since analog multiplexers are more properly called "multiplexer/demultiplexer": http://focus-webapps.ti.com/general/docs/sitesearch/searchdevice.tsp;jsessionid=QD2JJG50OXSZVQC1JAVRNWQ?partNumber=CD4051 and, I believe, are used less frequently than digital multiplexers and demultiplexers, making them, in my view, less conventional.
Indeed. I have heard speakers with DC jamming the voice coil against the stop. If it's a hard stop, at low volume levels there is no sound and at high volume levels it shows asymmetrical revers clipping; instead of the peaks being removed, everything other than the positive peaks is removed. It sound remarkably like a Kazoo...
Anyone trying this should also be aware that many audio amplifiers have protection circuits that shut them down if there is DC at the output, so simply bypassing the capacitors won't always get you a DC amplifier. With capacitive coupling in place at an earlier stage, DC is a fairly good indicator of a shorted output transistor.
-- Guy Macon
So what you are saying is that DC causes sidebands? :)
-- John Devereux
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.