Very basic amplifier volts question

[Markgm]

Hi,
I hope you find this to be a very simple general (newbie) concept question. I'm reading and learning, and hope to be making psu circuits as my first personal dabbling.

If I make a psu, and it is putting out DC power at 30 volts, various current, and an amp hooked to that with a DC power cable (decoupled units)... What are the voltages in the amp? Are they starting low and getting higher through amp stages, until they get to 30 (and then clip)? Is it not 30 to start with, and by what mechanism is it lower than that?

TIA, and cheers -
Mark

[Markgm]

I'll put what I'm trying to understand a different way. If the voltage goes up in stages, how did it get to zero to start with?

TIA - mark

[DF96]

I don't understand your question. Are you talking about supply voltage or signal voltage?

[Mooly]

Originally Posted by Markgm

Hi,
If I make a psu, and it is putting out DC power at 30 volts, various current, and an amp hooked to that with a DC power cable (decoupled units)... Mark

If the PSU puts out 30v dc then the "power" is a function of the load. No load means no current drawn and hence no "power".

Power (Watts) is equal to amps * volts.
So a 30 volt supply with a 30 ohm resistor across it would draw 1 amp and dissipate 30 watts in the load.

Originally Posted by Markgm

Hi,
What are the voltages in the amp? Are they starting low and getting higher through amp stages, until they get to 30 (and then clip)? Is it not 30 to start with, and by what mechanism is it lower than that?

TIA, and cheers -
Mark

The amplifier is like a tap that can allow more volts (up to the limit of the supply) to flow to the load.
The gain of the amplifier is fixed. For example a voltage of 30
This means the output depends on what is fed into it... and that usually comes from a variable resistor, the volume control.
So 1 volt in would give 30 out (talking theoretically on a 30 volt supply)
0.1 volt in would give 3 volts out etc.
10 volts in would "clip" at 30 volts out.

And the "power" in each case would depend on the load resistance (speaker) connected to the amp.

[wakibaki]

Originally Posted by Markgm

Hi,
Is it not 30 to start with, and by what mechanism is it lower than that?

No the signal is not 30 to start with, it's fractions of a volt or at most 2 volts when it comes out of the source.

Originally Posted by Markgm

Are they starting low and getting higher through amp stages, until they get to 30 (and then clip)?

Yes they start low and get higher as they are amplified by the various amp stages, until they get to 30. In a well designed system they shouldn't clip, or, the operator shouldn't feed in a signal large enough to cause clipping.

In fact in passing from one stage to the next there may be no increase in voltage, but an increase in power due to current amplification, but this is a detail only.

Originally Posted by Markgm

If I make a psu, and it is putting out DC power at 30 volts, various current, and an amp hooked to that with a DC power cable (decoupled units)...

No, not various current. Just one current. The current may vary with time.

Originally Posted by Markgm

and an amp hooked to that with a DC power cable (decoupled units)... What are the voltages in the amp?

The amp has a feature called the power rail. The power supply output is connected to the power rail. Both are at 30 volts. All the stages draw their power from the rail. The amp may be arranged so that the voltage on the power rail drops as the rail approaches the input stages, but it can be that there is no drop. Each stage takes some power from the rail and shapes it into a higher power copy of its input at its output. No stage can output a voltage higher than its supply voltage.

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[Markgm]

Originally Posted by Mooly

The amplifier is like a tap that can allow more volts (up to the limit of the supply) to flow to the load.
The gain of the amplifier is fixed. For example a voltage of 30
This means the output depends on what is fed into it... and that usually comes from a variable resistor, the volume control.

So 1 volt in would give 30 out (talking theoretically on a 30 volt supply)
0.1 volt in would give 3 volts out etc.
10 volts in would "clip" at 30 volts out.

And the "power" in each case would depend on the load resistance (speaker) connected to the amp.

Hi,
I'd like to thank each person for help with this. The transistor is something I haven't gotten to, but I have a quick idea of it (and starting to think). So, building on what you said above, if there is a power supply (guaranteeing up to such-n-such requested voltage/current), then a transistor could take power into it from that and combine it with the input signal, making an amplified output signal, at any moment with its own voltage and amperage?

My first psu project is an unregulated supply, so I haven't looked at transistors yet. I was wondering what was going on there. I will also be wanting the power consumption on no-load conditions to be low, but I don't know how to do that, yet.

The other thing I want is to be able to put a knob on the psu to set the maximum voltage from 0 to 30. I think it would be nice to be able to hook it up to a little 12-volt amp as well. Any pointers as to what I would have to do (keeping the power clean), to have such a feature?

TIA, and Cheers,
Mark

[Markgm]

Originally Posted by Markgm

The other thing I want is to be able to put a knob on the psu to set the maximum voltage from 0 to 30. I think it would be nice to be able to hook it up to a little 12-volt amp as well. Any pointers as to what I would have to do (keeping the power clean), to have such a feature?

I'm moving this to another thread (it should have its own).

[AndrewT]

Download a few of the ESP articles that attract your attention.
Have a look at the decibel dungeon site.
Pass diy has a few articles detailing how transistors work.

[Markgm]

Originally Posted by AndrewT

Download a few of the ESP articles that attract your attention.
Have a look at the decibel dungeon site.
Pass diy has a few articles detailing how transistors work.

Andrew, Thanks for the pointers. I've started a new thread with the idea of a PSU - with all of its little ideas. It was unregulated, but now its got the voltage control (and maybe a nice ground connection) My reading will continue - in fact, right now I am still very much in reading mode.