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Topic: Amp power and current (Read 51196 times) previous topic - next topic
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Amp power and current

Reply #50 –
Quote from: xnor on
No, both attenuation by the volume control and amplification (gain) by the amp are linear effects. Neither discriminate between, for example, 0.01V and 10V.
Only when you hit the limits of the amplifier, the peaks of the waveform will start getting compressed/clipped.


What I found with one of the expensive amps I had on demo, it had a lower claimed wattage, but on the volume knob, a small increase resulted in a big difference in loudness. On the more powerful amp, the same relative increases on the volume knob resulted in a much smoother delivery of volume, so it wasn't so peaky.

As I said before, I've experienced big jumps in volume with a slight turn of the knob ( often too loud by the 9 o'clock position). Others will give small gains per rotation. So if this isn't the gain, strictly speaking, then is it the design of the volume pot?

Amp power and current

Reply #51 –
Quote from: Rich B on
Seriously speaking, how can one identify an amp with high current? I have two stereo amps: one is rated 75 wpc (budget amp around 5k new), another 60wpc (about 14k new). The more expensive amp has more control on loudspeakers, plays cleaner at any volume. Actually, it plays louder than the 75 wpc, but cheaper amp. Is all this mainly due to current or there is more to it?  Funny enough, both have torodial transformers of similar size. But sound quality is night and day! Also, some amps give big jumps in volume with a slight turn of the knob ( often too loud by the 9 o'clock position). Others will give small gains per rotation ( and listenable up to around the 2 o'clock knob position).


Are you aware of TOS #8?

How did you measure "control on loudspeaker"?

Again: the calibration and law of the volume potentiometer has absolutely nothing to do with power.

An amp doesn't "have" current - some amps can source more current than others. But unless your speaker has a low enough impedance that your amp hits the current limit, it doesn't matter.

Amp power and current

Reply #53 –
Quote from: julf on
Quote from: Rich B on
Seriously speaking, how can one identify an amp with high current? I have two stereo amps: one is rated 75 wpc (budget amp around 5k new), another 60wpc (about 14k new). The more expensive amp has more control on loudspeakers, plays cleaner at any volume. Actually, it plays louder than the 75 wpc, but cheaper amp. Is all this mainly due to current or there is more to it?  Funny enough, both have torodial transformers of similar size. But sound quality is night and day! Also, some amps give big jumps in volume with a slight turn of the knob ( often too loud by the 9 o'clock position). Others will give small gains per rotation ( and listenable up to around the 2 o'clock knob position).


Are you aware of TOS #8?

How did you measure "control on loudspeaker"?

Again: the calibration and law of the volume potentiometer has absolutely nothing to do with power.

An amp doesn't "have" current - some amps can source more current than others. But unless your speaker has a low enough impedance that your amp hits the current limit, it doesn't matter.


So then it is not possible for a weaker amp to have a higher gain than a stronger amp, but with a stronger volume control (I'm not sure what to call this) so that the power delivery is more abrupt, rather than a gradual progression if the volume control was designed differently?

I'm just trying to explain my own experiences and asking questions that might answer this for me. Sorry if I'm being tedious about this.

Amp power and current

Reply #54 –
Quote
How did you measure "control on loudspeaker"?

Again: the calibration and law of the volume potentiometer has absolutely nothing to do with power.


I didn't measure control. I just heard what I heard. I don't claim for it to be absolute or perfectly reliable, but that's all that I can go on, based on what I experienced.

Amp power and current

Reply #55 –


Maybe I wasn't clear enough. The attenuation/amplification itself is a linear process, but a volume control usually does not have a linear relationship between position and attenuation. Our hearing is logarithmic so most audio volume pots approximate such a logarithmic curve. (15A or A is often used.)

You can also implement a volume control using a rotary encoder, so that you can do several complete turns until you reach full volume.
"I hear it when I see it."

Amp power and current

Reply #56 –
Quote from: Rich B on
I didn't measure control. I just heard what I heard.


Could you please re-read ToS#8? You agreed to those terms when joining.

Amp power and current

Reply #57 –
Quote from: Rich B on
So then it is not possible for a weaker amp to have a higher gain than a stronger amp, but with a stronger volume control (I'm not sure what to call this) so that the power delivery is more abrupt, rather than a gradual progression if the volume control was designed differently?



Quote from: julf on
Again: the calibration and law of the volume potentiometer has absolutely nothing to do with power.


Quote
I'm just trying to explain my own experiences and asking questions that might answer this for me. Sorry if I'm being tedious about this.


But you don't seem to understand (or refuse to understand) the answers.

Don't take this the wrong way, but I really suggest you read an introduction to basic electronics (high scool physics level is good enough), after that I am sure we are more than happy to try to answer your questions.

Amp power and current

Reply #58 –
Quote from: julf on
Quote from: Rich B on
So then it is not possible for a weaker amp to have a higher gain than a stronger amp, but with a stronger volume control (I'm not sure what to call this) so that the power delivery is more abrupt, rather than a gradual progression if the volume control was designed differently?



Quote from: julf on
Again: the calibration and law of the volume potentiometer has absolutely nothing to do with power.


Quote
I'm just trying to explain my own experiences and asking questions that might answer this for me. Sorry if I'm being tedious about this.


But you don't seem to understand (or refuse to understand) the answers.

Don't take this the wrong way, but I really suggest you read an introduction to basic electronics (high scool physics level is good enough), after that I am sure we are more than happy to try to answer your questions.


I asked in plain English :

"So then it is not possible for a weaker amp to have a higher gain than a stronger amp, but with a stronger volume control (I'm not sure what to call this) so that the power delivery is more aggressively put down, rather than a gradual progression if the volume control was designed differently?

I'm just trying to explain my own experiences and asking questions that might answer this for me. Sorry if I'm being tedious about this."

You say I don't accept the answer. But I believe that I need to ask the right questions in order to know if I'm on the right path. So I've asked the questions as best I can, and I need to know if what *I'm* thinking is more or less correct. Otherwise it's going to drive me crazy.

Amp power and current

Reply #59 –
Quote from: julf on
Quote from: Rich B on
I didn't measure control. I just heard what I heard.


Could you please re-read ToS#8? You agreed to those terms when joining.


I must have skipped over the ToS#8 when I joined. I joined for casual reasons, to discuss AV topics. Perhaps I joined for the wrong reasons, but I can say that the input I've been given on other topics have been invaluable, so I'm glad I joined.

Am I going to be banned because I did not adhere to the ToS#8?

Amp power and current

Reply #60 –
Quote from: Rich B on
I asked in plain English :

"So then it is not possible for a weaker amp to have a higher gain than a stronger amp, but with a stronger volume control (I'm not sure what to call this) so that the power delivery is more aggressively put down, rather than a gradual progression if the volume control was designed differently?


And I answered:

Quote from: julf on
Again: the calibration and law of the volume potentiometer has absolutely nothing to do with power.


Quote
So I've asked the questions as best I can, and I need to know if what *I'm* thinking is more or less correct. Otherwise it's going to drive me crazy.


But you tend to pose your questions in the form "but isn't true that X?". That only shows us that your thinking still isn't correct, but doesn't help us understadn *why* you are thinking X might be true.

Amp power and current

Reply #61 –
Quote from: Rich B on
Am I going to be banned because I did not adhere to the ToS#8?


As the moderators haven't stepped in, it seems you got away with it this time

Amp power and current

Reply #62 –
FWIW I'm working on an amp design that has a gain of over 1000 but only 20W output.  Part of my labor included trying to spec controls with the best taper to suit my needs.

As far as the rules go, it is expected that all members read, understand and follow them. Leeway is often granted in many situations. Generally speaking, very little leeway is given for TOS #9 and #12. TOS #8 can often be member-policed. In this case I doubt it will cause any perpetuation of misinformation, which is a common metric that I use in deciding whether to enforce this rule. Future posts breaking this rule will be binned, however. We are not interested in the communication of perceived sounds as a statement of fact by a member unless he is prepared to provide evidence as it is required by our rules.  This is merely an FYI and is not open for discussion here.

Amp power and current

Reply #63 –
Quote from: greynol on
FWIW I'm working on an amp design that has a gain of over 1000 but only 20W output.  Part of my labor included trying to spec controls with the best taper to suit my needs.

Seems to be too low for phono-, too high for line-level. What's the source?
"I hear it when I see it."

Amp power and current

Reply #64 –
Quote from: Rich B on
How would I reach full power from the amp?


Provide an input signal to the amp that drives is to just below clipping.

The actual voltage of this signal depends on the amp's maximum gain and any attenuation that is built into the amp.

Most stand-alone power amps have an input attenuator.

Most AVRs have both a volume control and a channel trim that act together.  The channel trims help balance the loudness of the speakers even if they have dissimilar efficiencies. They also strongly affects the effect of the main volume control knob.  A channel trim can be used to set up the gain structure of an AVR so that it is impossible for it to clip when driven by a digital signal. Alternatively, it can be used with a microphone to calibrate the front panel volume control knob in dB SPL for an input signal with a specified amplitude in the digital domain.

In modern AVRs the channel trims are often implemented in the digital domain, but the main volume control is usually implemented in the analog domain by solid state devices that are digitally controlled. The main benefits of these analog volume control are that they allow the AVR to have a "pure analog mode" where the AVR has reduced function but analog input signals never enter the digital domain. They also provide an easy means for implementing remote control. Their channel balance and stepwise linearity that is generally better than can achieved with traditional variable resistor type volume controls, especially when cost is considered.

Some DAC chips have a digital volume control feature that is usually fully implemented in the digital domain. It makes sense - most of the parts required are already there to make up the DAC, and the gain control function is often needed.

There are concerns with digital volume controls that are based on the idea that they are always implemented in a naive fashion. Since a digital volume control necessarily reduces resolution, they effectively requantize the digital signal and therefore must re-randomize the quantization error that results. IOW they need dither or something like it. A properly designed digital volume control does not increase the distortion of the signal as the attenuation increases, but rather like analog volume controls simply reduces the amplitude and SNR of the signal.  It may surprise some to hear that analog volume controls decrease the resolution of the signals they attenuate, but since there is noise generated by the amplifier that follows them, the SNR and therefore the resolution of the signals they attenuate decreases.

As others have ably pointed out, the attenuation versus rotation of an analog volume control can and often does vary. Ideally, this part would have a logarithmic curve so that the perceived effect of the volume control would relate to how the human ear responds.  An amp whose volume control progresses to a low attenuation state with very little rotation of its knob can make the amp seem more powerful. This is one of the oldest tricks in the book going back to the beginnings of mass market radio in the 1920s and 1930s.

Amp power and current

Reply #65 –
Quote
An amp whose volume control progresses to a low attenuation state with very little rotation of its knob can make the amp seem more powerful. This is one of the oldest tricks in the book going back to the beginnings of mass market radio in the 1920s and 1930s.


Perhaps I'm misunderstanding what you mean by attenuation in the above context. Based on what you're saying there is more signal with less rotation of the knob, but it sounds like the opposite. Apologies if I misunderstood your meaning.

But if the volume knobs of amps are different, and the gain, that also means that different preamps can sound different just because of the implementation of the volume controls and the gain of the preamp? Correct?

So if someone does claim adding a preamp made an audible change, then it isn't really so far-fetched given the variables above. But not because of any inherent secret sauce, but more because of changes in loudness from preamp to preamp.

Amp power and current

Reply #66 –
All it means is that if you fail to level match the amplifiers then of course they will sound different.

To properly match levels you must measure their outputs with a decent voltmeter, not by turning their knobs to the same setting, or by  listening by ear.

Amp power and current

Reply #67 –
Quote from: Rich B on
But if the volume knobs of amps are different, and the gain, that also means that different preamps can sound different just because of the implementation of the volume controls and the gain of the preamp? Correct?


I would say its a safe bet that different volumes will sound different.  Specifically some may be louder than others !

Amp power and current

Reply #68 –
Amplification and attenuation, if done properly, do not color the sound, except for the possibity of added noise depending on where and in what order they are placed.

Please stop assuming basic components contribute to some signature sound and are part of some greater magic sauce. It's plainly wrong and this desire to cling to these woo-based misconceptions has gone well past annoying.

Amp power and current

Reply #69 –
Quote
...with less rotation of the knob, but it sounds like the opposite. Apologies if I misunderstood your meaning.
I guess it depends on the direction of rotation. 

The most common design uses the pot as an attenuator.  Fully-clockwise the pot has no effect and the signal passes-through as if the pot wasn't there.  Fully-counterclockwise the signal is fully attenuated to zero.    But, that's not important to the user...    To the user, the amplifier with a volume knob is just a "black box" that provides variable amplification.

Once, I tried to build a preamp with the pot in the feedback loop so the pot actually controlled the gain instead of simply attenuating the input.    But, it turned-out to be an oscillator instead of an amplifier...        That was in the early days of op-amps and many op-amps weren't stable at low gains...  I didn't know that and I fried my power amp with an RF signal that (of course) I couldn't hear.

Amp power and current

Reply #70 –
Quote from: greynol on
Amplification and attenuation, if done properly, do not color the sound, except for the possibity of added noise depending on where and in what order they are placed.

Please stop assuming basic components contribute to some signature sound and are part of some greater magic sauce. It's plainly wrong and this desire to cling to these woo-based misconceptions has gone well past annoying.


Please stop assuming things that I never said. I said that if the volumes are different because of different volume pots and gains, that it could sound different and that people who make the claim that various preamps sound different wouldn't be so far fetched. I also specifically said "But not because of any inherent secret sauce, but more because of changes in loudness from preamp to preamp". Clearly I was not implying any such "magic sauce". That is your strawman!

Why don't you read what I write instead of making assumptions about you think I wrote? It's also getting annoying! You just come crashing in and start stirring the pot. Why can't you stay away from my threads?

Amp power and current

Reply #71 –
Quote from: Rich B on
Why don't you read what I write instead of making assumptions about you think I wrote? It's also getting annoying! You just come crashing in and start stirring the pot. Why can't you stay away from my threads?


Because what you write tends to incomprehensible.  Your statement above about different volumes sounding different . . . are we supposed to assume that you didn't realize that volume control could make something sound more or less loud?

Amp power and current

Reply #73 –
Quote from: Rich B on
Perhaps I'm misunderstanding what you mean by attenuation in the above context. Based on what you're saying there is more signal with less rotation of the knob, but it sounds like the opposite. Apologies if I misunderstood your meaning.

Assume you have a volume control with a couple fixed positions. From the fully-turned-up position (no attenuation) to the next lower position it might only be a 1 dB difference, but from the 3rd to last to the 2nd to last position the difference could be 10 dB.
So you turn up from silence: wow, huge volume increase with each step. But these get smaller and smaller...


Quote from: Rich B on
But if the volume knobs of amps are different, and the gain, that also means that different preamps can sound different just because of the implementation of the volume controls and the gain of the preamp? Correct?

It would be perceived as differences in sound, yes, but these differences usually disappear once you properly match the levels.


Quote from: Rich B on
So if someone does claim adding a preamp made an audible change, then it isn't really so far-fetched given the variables above. But not because of any inherent secret sauce, but more because of changes in loudness from preamp to preamp.

Except that they ignore all the variables and bias and claim/conclude that the devices themselves have greatly different sound signatures, which they usually do NOT.
"I hear it when I see it."

Amp power and current

Reply #74 –
Quote from: saratoga on
Quote from: Rich B on
Why don't you read what I write instead of making assumptions about you think I wrote? It's also getting annoying! You just come crashing in and start stirring the pot. Why can't you stay away from my threads?


Because what you write tends to incomprehensible.  Your statement above about different volumes sounding different . . . are we supposed to assume that you didn't realize that volume control could make something sound more or less loud?


It was said earlier that different volume controls have different attenuation and different amps have different gains. So based on this I assume that comparing preamps at specific volumes will be invalidated based on the these two things.

I'm just trying to understand this. I don't appreciate the badgering.