Posts tagged amplifier
Posts tagged amplifier
So we’ve written a few posts on analyzing preamplifiers and amplifiers but whenever I hear someone saying that they’re setting up a preamplifier and amplifier, it makes me wonder what the difference is between them. Couldn’t you put two preamps together to equal a preamp + amp? Or are they fundamentally different?
So I’m going to browse through my old posts to pull up a preamp vs amp schematic. Preamplifier first!:
So on a very basic level:
What is mic level/line level/speaker level?
However, instruments and microphones can have a very wide range of output levels in reality, so it is most practical to think of instrument-level and mic-level in/outputs as just “a lot lower than line level”, rather than calculating specific dB amounts.
So in terms of my questions, I guess while both preamps and amps amplify a signal from a lower to a higher level, it depends on which levels we’re going from and to.
The second stage of a simple transmitter includes an amplifier circuit called a driver. Essentially, the output signal from the oscillator isn’t strong enough for communication over long distances. So the driver makes the signal stronger while allowing the oscillator to operate continuously at low power so that its frequency remains stable.
If you remember what we talked about transistors using smaller currents to push larger ones, that’s essentially what an amplifier circuit does. It takes its catalyst from the tank to fuel a larger current.
Once this signal is slightly stronger, it’s put through the power amplifier whose output is strong enough to provide a useful signal for communication with other stations.
I think this’d be like an amplifier for the amplifier.
So this portion of the manual focuses on radio equipment.
3 Elements of a radio station!
Connecting the Antenna to the XMTR and RCVR are feed lines/transmission lines.
And the XMTR + RCVR = Transceiver (XCVR). This makes sense cuz transceivers share one antenna by using a transmit-receive (TR) switch. Efficiency!
The antenna’s sitting on top of the TR switch there. And say 1 wants to transmit, bloop bleep bloop, the message goes from 1 —> 2 —> antenna. And say 3 wants to receive, the message goes from antenna —> 2 —> 3!
In order to get a signal from the antenna of a super lower power station (like the one I’ll be building eventually) to say Timbuktu, I’d need to utilize repeaters. These are stations that receive signals only to transmit them out immediately, kind of a simultaneous receive/transmit thing. “The job of the repeater is to provide a strong, low-noise signal that everyone can hear and understand well, especially in emergencies.”
The received signal is retransmitted to different channels/multiple channels even. And these use a duplexer instead of a TR switch so that it can do both receiving and transmission at the same time, instead of waiting for one to be done before being able to do the other.
Accessories, Accessories, Accessories!
Other stuff that may be needed obviously: Power supply, mic (transmitters add vocal data to signals), speaker, headphones.
They also mention amplifiers which I’ve talked about before:
Yay! ghetto picture! From what I read, this is what I gather can be hooked up and how signals flow to/from each component. A morse code beepbeep thing can also be hooked to the transceiver, but I just left it out for space sake
How does the quality of the amp affect the current going through it?
This was the question I ended on and it seems like this would include information on other things besides current. So I decided to put this in another post!
I’m going to start from looking at how amplifiers are classified. I’m doing this because the main difference between amplifiers besides their price are usually their specs.
AND in order to determine why these specs are important, we need to know what happens when an amplifier is working ideally or not:
“The ideal amplifier will do nothing to the input signal other than make it stronger. In a real world amplifier, the signal does get stronger (amplified) but because no amplifier is perfect there are other undesired characteristics that appear in the output signal (noise and distortion). In the very best amplifiers these undesired characteristics are quite small (but they are not zero). Also, all amplifiers have limitations as to how much power they can put out. If you try to get more power out of an amplifier than it was designed to provide, the output will rapidly become very distorted because the amplifier will go into a condition commonly referred to as “clipping”.” (http://www.rocketroberts.com/techart/powerart_a.htm)
Okay so let’s take the specs from….an Emotiva XPA-2. I’ve only heard of the brand name but don’t actually know the system. And it is a two channel audio power amplifier:
300 watts RMS x 2 into 8 ohms, 500 watts RMS x 2 into 4 ohms
And for reference, the specs from the Magnepan MMGs:
Sensitivity: 86dB / 500Hz / 2.83v Impedance: 4 Ohm
“An amplifier amplifies the electrical signal, causing the speaker to vibrate with greater force, otherwise the impulse would be barely audible (think of the size of a microphone vs. the size of a speaker). How much the amp drives the speaker is measured in watts. When an amp manufacturer gives it’s wattage rating, it’s always at a specific Ohm resistance. “100 watts @ 4 ohms,” for example. When the resistance is 4 ohms, this amp will produce 100 watts. If that resistance changes, the amp will produce a different amount of watts.” http://www.marktaw.com/recording/Electronics/OhmsAmpsandSpeakers.html
500 watts RMS @ 4Ohm: So this amplifier would translate to 500 watts @ 4 ohms. So when the resistance/impedance is four ohms, this amp will produce 500 watts.
86dB/500Hz/2.83v: This is a measurement of just what volume a driver or speaker will produce with a particular input power. Usually, this is given as a volume with 1watt of input power from 1m away. For example, with these speakers, if you use a 1watt input signal and measure at a distance of 1M away, you’d hear a 86dB SPL (sound pressure level) IF they were 8Ohm Impedance. The 1W/1m ratio is represented by the 2.83v portion of this spec assuming 8Ohm impedance. With 4 Ohm impedance factored in, putting 2.83V into the 4 ohm rating of the MMGs requires 2W of power, so the rating is more like 83dB/1W/1m.
It would seem from my reading that the main variable is the wattage portion of the specifications (I’m scared of going into the other specs) as many people have 50w/channel amps. So Maggies, in other words, will take a ton of wattage before clipping or saying, wait, that’s too much.
The other aspect is that they present a nearly constant 4-ohm load (amount of work) over their operating range, which I am guessing means that because the amount of resistance is constant - instead of a up-down fluctuation - it takes more power to maintain that amt of current to continuously press through that resistance. Maybe?
@atdiy / @tymkrs
So in the last post I wrote about MMGs I wondered why they were so power hungry if according to their Ohm levels (or whatever), they seemed to have less resistance to the power…I think I’m confusing myself…
But! Then I came across what seems to be some sort of blog post that stated that it is true that you cannot have too much power for the maggies, however the power is not required for volume, but rather “the resolution of micro detail at any volume setting.”
It seems that most people refer to the amplifier when talking about the dealing of power. This person wrote “The fact is any amp will drive a maggie, even an old junky receiver. On the other hand, the better the quality and especially the more good current (not watts) behind it, the better it will sound at all volumes.”
So there seems to be something about how it’s not the power per se, but the current (if those can be construed as the same thing), and that the increase in power helps to increase accuracy of detail rather than volume or anything on that macro of a level.
So I thought I’d take a little time to look up what an amplifier does, what current does in the amplifier, and how the quality of an amp relates to the current that goes through it. (And that may not be the right order, but I will find out!)
What does an amplifier do?
So…an amplifier simply increases, or amplifies, the power of a signal. And it would seem that the type of amplifier I should be focusing on is an audio amplifier. To break this down further however, what power does an audio amplifier use and what kind of signal is it increasing?
Power: Energy from a power supply such as a battery
Signal: Low power audio signals (signals composed primarily of 20-20,000Hz)
—> This requires me to backtrack to how sound is created. And from the previous MMG post, I mentioned that in normal cone speakers, electricity is what causes the cones to move back and forth creating the sound waves we hear. Specifically, when sound waves are recorded, they move a microphone diaphragm back and forth causing a fluctuating electrical signal to be recorded on some sort of medium. When you listen to a recording, you’re hearing a more powerful version of those same fluctuating signals that are moving a speaker membrane.
So it isn’t required to have a powerful audio signal while recording or while processing, but rather while “playing” it. I suppose it’s for volume, and in the case of MMGs, for clarity.
I found a very easy-to-understand explanation for what amps do on http://www.howstuffworks.com/amplifier.htm/printable:
“In actuality, the amplifier generates a completely new output signal based on the input signal. You can understand these signals as two separate circuits. The output circuit is generated by the amplifier’s power supply, which draws energy from a battery or power outlet. If the amplifier is powered by household alternating current, where the flow of charge changes directions, the power supply will convert it into direct current, where the charge always flows in the same direction. The power supply also smooths out the current to generate an absolutely even, uninterrupted signal. The output circuit’s load (the work it does) is moving the speaker cone.
The input circuit is the electrical audio signal recorded on tape or running in from a microphone. Its load is modifying the output circuit. It applies a varying resistance to the output circuit to re-create the voltage fluctuations of the original audio signal. “
What does current do in the amplifier?
I’ll again refer to this page: http://www.howstuffworks.com/amplifier.htm/printable
as I think it could explain it better than I.
How does the quality of the amp affect the current going through it?
I think I’ll put this in another post…