| captain |
I am new to all this. I am in the early stages of a LM4783 Gainclone project. I plan to use two 12-volt lead acid batteries connected in series giving +12/-12 rails. I want the Gainclone connected directly to a DVD (or CD) player using the "LINE OUT L/R" (line level) connectors on the back of the DVD.
Since "volume control" is not an option on most DVD remotes I need the volume to be handled somewhere between DVD and GainClone. I want to use a "LM1973 attenuator" tied to a "micro controller" to do volume control with a separate "universal IR remote".
However, this raises the following assumptions and questions:
Assumptions:
1. I assume that most CD recordings are laid down within certain "DB Levels" so that the listener is not having to constantly fiddle with volume from one CD to the next. (Although there seems to be exceptions.)
Questions:
1. Is there normally (or always) something that has to sit between the "LINE LEVEL SOURCE" and the "power amplifer"?
In other words, some "middle amplification stage" that needs to "boost" the signal before doing the "volume control"...and ultimately feeding the "power-amp stage"?
2. Since the LM1973 chip is strictly "an attenuator" (using gangs of resistors), that means that when it is set to "zero resistance" it will pass the FULL LINE LEVEL signal. Is that enough oomph? If not, I guess I can always increase the gain by increasing the amp chip's feedback resistor (say from 20K to 30K). I've also seen suggestions where the LM1973 can actually sit in the "feedback loop". I'm new to all this...but this design doesn't sound like a good idea.
3. Also, what the heck is a "buffer"? An what is a "preamplifier"? Does a "preamplifier" take an "extremely weak signal"...from say a microphone...and get it up to "LINE LEVEL"?
I've actually learned quite a lot...but some of these generic terms throw me. And they all seem to mean different things to different people. |
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| ofb |
| quote: | Originally posted by captain
1. I assume that most CD recordings are laid down within certain "DB Levels" so that the listener is not having to constantly fiddle with volume from one CD to the next. (Although there seems to be exceptions.) |
little bit about that:
http://www.prorec.com/prorec/articl...6256C2E005DAF1C |
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| sek |
Hi,
| quote: | Originally posted by captain
I assume that most CD recordings are laid down within certain "DB Levels" so that the listener is not having to constantly fiddle with volume from one CD to the next. (Although there seems to be exceptions.) |
Unfortunately, this is not so. If it were so, the average level of all recordings might be equal(ized). But as the dynamics of all recordings differ, a standard on average level would tell you nothing about a maximum level.
It is the maximum level that is set. Not by a CD standard, but by the maximum ouput voltage capability of the CD player in use. That means: your CD player has a limited output signal voltage which it won't ever increase (unless you modify it :cool: ).
When I listen to music, I catch myself fiddling with the volume control each and every time the next song brings me into a different mood. This makes me turn a little louder and smile, or maybe crank up and dance, or even reduce the volume and stand still in order to listen carefully.
You definitely want to have a volume control. ;)
| quote: | | 1. Is there normally [...] some "middle amplification stage" that needs to "boost" the signal before doing the "volume control"...and ultimately feeding the "power-amp stage"? |
Well. The level of the recording determines the CD player's dynamic output voltage level.
Now, the amplifier amplifies this particular voltage level by it's amplification factor, a.k.a. gain.
This creates a certain amplifier output voltage level to drive your speakers.
Your speakers have a certain (frequency- and room-dependent) efficiency that determines how much output voltage level (and thus power) is needed for a certain sound pressure level, a.k.a. S.P.L.. ;)
Now, if your CD player is able to deliver a voltage level that is high enough to get amplified to a high enough amplfier's output voltage (and thus power into the speaker) for the speaker to actually sound loud enough, ... , then you won't need any intermittent "boost" stage. ;)
| quote: | | 2. Since the LM1973 chip is strictly "an attenuator" (using gangs of resistors), that means that when it is set to "zero resistance" it will pass the FULL LINE LEVEL signal. Is that enough oomph? |
It is very likely that your CD player is capable of putting out enough peak signal level to actually overdrive an amplifier. So the question should actually be: "Isn't this too much oomph"? Another reason for having a volume control. ;)
If unsure, you can do some calculations by looking up your CD player's output voltage level in it's datasheet. Compare this to the recommended input level in the LM4783 datasheet.
| quote: | | If not, I guess I can always increase the gain by increasing the amp chip's feedback resistor (say from 20K to 30K). |
Increasing this resistor reduces the gain.
| quote: | | I've also seen suggestions where the LM1973 can actually sit in the "feedback loop". |
Not recommended. The feedback loop is no proper place to regulate the volume, because this loop circuit actually does more than just setting the gain.
It might work for buffer circuits in line stages, but not in power circuits.
Which leads us to your last question. ;)
| quote: | | 3. Also, what the heck is a "buffer"? |
Buffers isolate connected circuits in order to prevent influences from one circuit on the other.
| quote: | | An what is a "preamplifier"? |
The thing you don't need, as your CD player is loud enough. ;)
| quote: | | Does a "preamplifier" take an "extremely weak signal"...from say a microphone...and get it up to "LINE LEVEL"? |
Yes. The term 'preamplifier' is used universally where a signal source has to be 'preconditioned' before being usable, e.g. for recording or supplying to a power amplifier.
There are preamps for microphones, instruments, turntables, etc...
Sebastian. |
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| captain |
Thanks OFB!!!
What an excellent article on the technical side of CD recording!!!
Also, very insightful in regards to the current trends in the music industry.
Thanks Sebastian!!!
Very good information on all counts!!!
Thank you both for taking the time to respond.
Your posts have helped tremendously!!!...;) |
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