a technical question

but i suspect i havent understood your question. can you provide some context? i.e. why are you asking?

enjoy

ken

If it is not true, and the amp deals with many signals at the same time, there is another question:
The signals are "running" in the amp at a light speed, sure the speaker doesn't react so fast,
so how does it work ?
I hope I'm clear, if not, can I ask it in Hebrew ?

Arye

It's like having a big brother sitting at the supper table, and he's always eating faster than you. As a result, you sometimes walk away from the table hungry.

That's why it's good to have separate supplies for each component, so that the demands of one doesn't affect the supply of the other.

-=> Mike Hanson <=-

this is not my understanding, but i dont claim to know it all. the pre-amp is not a high current device -- the power amps HAVE to be to drive the speakers.

i am sure someone in the know will provide a more detailed explanation to satisfy arye's curiosity.

arye, yes, signals travel at the speed of light along conductors, but changes in the signal (i.e the music) do not happen at the speed of light. if they did, i doubt if our brains would be able to resolve them.

enjoy

ken

Mike,
At a giving time, is there only one signal in the amp (one channel, of course) or more than one, let's say a signal in the power and another signal in the pre ?

arye

wait a minute. i dont think current changes at the speed of light for the reason that i have given above. it need not.

if you take the view that the signal travels from source to speakers -- at the speed of light, then, pedantically, at any given time, the signal in the power amp is further along the music waveform than the one in the pre-amp. i say pedantically as the time between these two points on the waveform is so small that to all intents and purposes its practically zero. which is lucky really, otherwise, you would observe your cd player having stopped playing, but the last part of the song's waveform still yet to arrive at the speakers.

enjoy

ken

quote:

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the pre-amp is not a high current device

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Correct. However, if the power amp is demanding too much current, then the shared power supply may not be able to supply a steady voltage (and the requested current) to the pre-amp. Therefore, both pre-amp and power-amp can falter. If each has its own supply, then this interdependance will not occur.

quote:

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At a giving time, is there only one signal in the amp (one channel, of course) or more than one, let's say a signal in the power and another signal in the pre ?

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In a word, YES. There should be only one signal, although there may be an ***extremely*** short lag from the front of the chain to the end. However, you can consider it to be a single signal.

-=> Mike Hanson <=-

Arye

Don't think of it like a truck that's lumbering from station to station. Instead, think of the music like wave/swell in the ocean, and your stereo is a boat. When the wave wants to go up, the entire boat goes up as a single unit. Perhaps the bow of the boat goes up a little sooner than the stern, but the boat generally stays horizontal.

In the same way, when the music signal says "go up", your entire amplification system (from the audio circuits in the CD player, all the way to the speakers) needs to respond as one synchronized unit. Therefore, the pre-amp and power-amp are asking for power at the same time.

If the power amp asks for lots of current, there's a chance that the power supply will falter, and the voltage will drop. If this same supply is shared by the pre-amp, then it will not have a consistent voltage, which will cause distortion.

-=> Mike Hanson <=-

Arye

quote:

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I ashamed to say that I was an electrician in the army and I dealed with amplifiers and transmiters/recievers, but had nver thought of these things...

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I've always sided with the engineer's approach, versus the technician's: Don't tell me "what" to do. Just tell me "why" it needs to be done, and I'll probably figure out the rest. I have a very strong abstract schema, so I need to understand the "why's" before I'm willing to accept and learn the "how's".

In contrast, people with a concrete schema like to be shown "how" to do it. After they've seen enough examples and done it enough times, they'll start to deduce "why" those steps were necessary in the first place. Sometimes their deductions are right, and sometimes they aren't.

It takes all kinds.

-=> Mike Hanson <=-

-=> Mike Hanson <=-

In contrast, things like capacitors and inductors respond differently to different frequencies. Therefore, they need respond the the waveform over a period of time before passing on the goods to the other side. This is why we can have problems with phase coherency and such things, which is something that Naim pre-amps handle very well (at least from the 72 on up)

BTW, it's been a very long time since I've done anything "practical" with electronics. However, I remember much of the basic theory that I learned back in my engineering days. (It's that old abstract schema thing cropping up again. )

-=> Mike Hanson <=-

Arye

quote:

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Only when they are very (to about a power of 9) tired!

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I'm talking about the absolute speed of a given electron. A electron gets bumped "from behind", causing it to bump one "in front" of it. This bumping motion causes the wave the propagate at close to the speed of light.

However, if you were to map the speed of an individual electron, it's moving only a few inches per second.

This description was given to me in my engineering physics classes in the mid-80's. Perhaps our view of the world has changed since then, but I hadn't heard anything different.

-=> Mike Hanson <=-

I thought this was due to the multiple circulations of the same waveform through the amp caused by the high-feedback design.

I believe this is why a Naim pre-amp is required to enable safe operation of a power-amp - they set the 'operating conditions'.

However, Arye, within these safe limits I would guess that the signal appears out of the power amp only microseconds after being fed into the preamp.

Interesting question, and I'd be fascinated to hear any definitive answer. Anyone have an osciloscope (sp?) and can measure the delay in a signal passing through a pre/power system (or a NAIT which should give almost identical results).

cheers, Martin

I liked Mike H's boat analogy - in one physics lab we played a single note on a violin with a microphone connected to an oscilloscope and observed the microphone voltage waveform (prior to digitizing it!). Pre-amps and power amps basically exist to take that waveform and make it bigger so that our speakers can replicate the violin string sound only LOUDER.

Vague college memories also prompt me to say that the slew rate is the fastest 'ramp rate' of an amplifier and is required to be limited in amplifier circuits to prevent 'ringing' - insufficient damping causing constant overshoots of the target output. Too slow a slew rate will cause loss of high-frequencies by over-damping. High-feedback design is usually negative feedback to reduce the gain and increase bandwidth and/or input impedance.

Now back to Mike H to explain Laplace transforms and why square waves aren't.

Cheers

The speed of a signal in a cable is dependant on the dielectric used in the cable, in thin Ethernet cable the velocity of propagation is usually quoted as 80% of the speed of light, this figure is used in cable testers to determine the distance to a fault, a narrow pulse it sent down the cable and the time taken for it to return and whether it is inverted or not tells the distance to the fault and whether its a short (inverted pulse) or open circuit. With a good TDR (Time Domain Reflectometer)which cable meters are based upon, the change in impedance change of some one standing on the cable and be measured to with in inches.

The fastest cable would use air as an insulator some thing would have to used to keep the cables apart like thin insulating disks for a coax cable I have thought of making one but life is to short ;-)

pete