Re current capabilities, is there a measurement, or some type of spec number? I would imagine that the µ/m-Farad value of the caps would be an indicator, but then there is also the maximum discharge speed F/s (= slew rate???) playing a role.
Capacitor values are not frequently given in specs. Tried to find it for my Pass XA25; there was a bulletin board mention of 18x 10K µF caps = 180 mF. If correct, is that a lot or not? Not the foggiest. How is discharge rate affected by cap size? I would imagine that many small caps discharge faster than one large one (assuming same total F value).
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Would like to try a really accomplished class A someday but don't want to deal with heat. Same with tubes I suppose. Purportedly, some class D can sound very class A like and that could be the best option.
But if space suffers, instrument sep. and stage depth isn't there, I wouldn't like it overall regardless if how smooth it sounded.
If you have 10 watts of class A, it should perform well at both low to moderate SPLs including dynamic swings. The occasion peaks into class AB, etc probably wouldn't be audible until you turn it up to louder levels and at that point, its hard to listen too for longer periods of time and without risk to hearing.
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@invalid
True. Even the electron has its spin!
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Most solid state amplifiers can double the output power when impedance is halved if well under the max power spec. Not one amplifier I have seen measured by a third party has the ability to double max power when impedance is halved (not even the big Krell amps) the 8ohm spec is usually underrated to give this illusion.
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@richardbrand
There is only one number given for Class A watts that I’ve seen, which is why it stuck with me when the guy said they dropped into 4 ohms. It’s nothing to spend your time on, If someone who knows for sure comes across this thread maybe we’ll find out, but until then, forget I mentioned it.
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@tomcy6
I've been trying to think of the physics that may be responsible. When an AB amplifier is in Class A. the bias voltage is sufficient to accommodate the signal swings. If the impedance of the speaker drops, more current is needed to keep the output voltage at the right level, but the current also tends to make the voltage drop. I'll surmise that if the amplifier cannot keep up with the current demand, the bias voltage could drop sufficiently to actually reduce the Class A power.
According to Stereophile, the OP's Vincent Audio SV236MK measured 150-Watts into 8-Ohms and 231 in 4-Ohms. It is specified at 10-Watts Class A into 8-Ohms but not specified into 4-Ohms. Pity!
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@richardbrand
Yes it would be interesting to hear from some high bias Class A/B amp builders whether their amps switch over to Class B power sooner as speaker impedance drops. Maybe I just misunderstood.
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@tomcy6
Not my understanding at all! The relationship that requires double the power when impedance is halved applies to all amplifiers of all classes.
Solid state amplifiers exhibit an anomaly at the crossover point from +ve to -ve output voltage. Class A amplifiers avoid this anomaly by keeping entirely on one side of it, let’s say the +ve side. To do this, the input voltage is DC offset (biased) to ensure the output never goes -ve.
There are a couple of consequences - a lot of output power is wasted as heat, and the input power consumed is constant whatever the audio output power. My Krell consumes about 700-Watts all the time and has huge fins to get rid of the excess heat.
A class AB amplifier on the other hand does allow the output to go -ve, at a point determined by the bias voltage applied. The idea is that the cross-over anomaly occurs when there is some musical content, and won’t be as obvious as when playing near silence.
Your amplifier manufacturer may be saying that his class AB amplifiers go into the crossover zone at much lower power when feeding 4-Ohms, compared with 8-Ohms. In this case, class A power would be defined as the most power the amplifier can deliver before reaching the crossover zone.
Seems to me that his AB amplifiers do not really have enough current delivery capacity in reserve, at least on paper! It would be interesting to ask what AB power they can deliver into 8-Ohms, and into 4-Ohms. Ideally it would be double, even if the pure class A numbers take a nosedive
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@richardbrand
Yes, I agree with what you’re saying. I was trying to address a different matter.
I was told by an amp manufacturer whom I called (don’t remember which one) that the class A watts are specified at 8 ohms and would approximately halve into 4 ohms. In my case it was 25 watts in class A into 8 ohms, but that dropped to 15 watts in class A into 4 ohms. I assumed other amps operated the same in that matter. Is that your understanding?
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@tomcy6
I’ll tell you what I think I know and someone can correct me. Class A watts approximately halve from 8 ohms into 4 ohms, so you have between 5 and 10 watts of class A power.
You invited a correction, so here goes. (If you were talking about the point where a class AB amplifier starts to move from class A to class B and starts to exhibit cross-over distortion, forgive me!)
Most amplifiers provide voltage gain - the output voltage should be a multiple of the input voltage. When the amplifier is connected to a speaker, current flows which makes the amplifier work harder to keep the voltage the right multiple.
The amount of current flow depends on the impedance of the speaker. It turns out that the amount of power required doubles every time the impedance is halved. For example, my venerable Class A Krell KSA-80 is rated at 80-Watts into 8-Ohms, 160-Watts into 4-Ohms and 320-Watts into 2-Ohms.
Marketers sometimes use this to misinform, by publishing an amplifier’s power into 6-Ohms, or even 4-Ohms. The latter doubles the boast!
Almost all speakers have different impendences at different frequencies, and many have big dips at crossover frequencies where two drivers have to work in parallel. That’s where an amplifier with big current reserves scores. A quick way to check an amplifier’s current reserves is to compare its power into 8- and 4-Ohms. Ideally it will double, but rarely does
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It’s really easy for me to figure. My amps put out about 10 watts class A into 4 ohms. My speakers are rated at 91db at one meter and my listening position is 2.5 meters from my speakers and seeing as I rarely go past 75-80 dbs, I’m I’m class A most of the time.
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Yeah, you are still in class A. Unless you have really inefficiant speakers, or a very big room, most of us are only using a couple watts for normal listening.
Around 80db at my listening spot is also around a watt. 10w is vibrating the house, 100+w is vibrating pictures off walls.
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If your amplifier had VU meters your question would have been easily answered.
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Yes; for.a small office you've got probably 10x the power you need for those listening levels. A, A/B or other, watts is watts.
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Shengya is the designer/manufacturer, a home grown Chinese brand that’s been around a while and their amps are quite good for the price. I’ve tinkered with their products in the past.They make other amps on contract for brands like Vincent in other continents that don’t have manufacturing prowess.
Many ’ultra high end’ amps sold to you as European/North American brands are actually designed/manufactured by Chinese engineering. When it gets to European/North American shores, it gets an astronomical markup and a brand name so the buyer can feel like he is in the "ultra high end" club.
Don’t worry too much if you couldn’t spend big bucks.
Thank you all for the replies and insights. The question was more of a curiosity than anything. I’ve been into music since the late 60’s and audio gear since the mid 70’s. Regardless of operation, through a slew of solid state and tube gear, this amp is the best I’ve had and considering I can’t afford to spend big bucks, the system on the whole is very satisfying.
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Thank you all for the replies and insights. The question was more of a curiosity than anything. I've been into music since the late 60's and audio gear since the mid 70's. Regardless of operation, through a slew of solid state and tube gear, this amp is the best I've had and considering I can't afford to spend big bucks, the system on the whole is very satisfying.
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@OP Re Boomerbillone's post. It is a little misleading to tie references to distortion to the output devices. Class A operation avoids crossover distortion. However, amplifier distortion is influenced by a whole host of factors so you can still have a Class A amplifier that distorts. There is also the fact that because true Class A amps are inefficient, they may need to be driven harder to achieve high SPLs and thus increasing distortion. That is not to dismiss the benefits of Class A operation - it has a lot going for it when it comes to reproducing music.
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Just music. "Turn turn the volume up slowly until you measure 2.83 V AC at the speaker input" as in the speaker terminals on the speaker? Or should it be at the speaker tap on the amp?
Measuring true RMS voltage with musical signal is generally beyond the ability of a multimeter. That's why @erik_squires was recommending a 60 Hz test tone.
The difference between voltage at the speaker terminal and the speaker tap on the amp is whatever loss is incurred on the speaker cable, which should be small if you are using anything like a normal cable section and length. In any case, considering what you are trying to do, I would measure at the speaker.
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Hello Craigvmn. All the numbers can be intimidating, especially when newer, younger writers, with no real knowledge and eager to please their bosses, write rubbish with is filled with pure rubbish and misuse of technical terms. For instance, many preamps are being advertised as Class A. All preamps are Class A. This means the output devices produce a faithful replica of the input, only larger in some way. Other classes of amplification produce altered, non accurate versions of the input. Class B uses two (or more - an even number) outpur devices one producing an enlarged version of the positive going part of the input. enlarged, and the othe the negative going portion of the input, suitably enlarged. These two get added together and fed to the output device, usually a speaker. The advantage is: less power gets wasted and two output devices can produce four times the output power compared to what one of the output devices could produce on its own, by itself. Class AB (there are several forms) is a combination which produces less inherent distortion than Class B. There is a Class C which is used in radio tranmitters. Class D is another animal entirely and not worth discussing here.
You have purchased very good merchndise and may be suprised to hear that sound is a very odd form of energy. We humans can hear a mosquito flying in a room several feet away, a very small amount of power. Standing at Niagra Falls, the falling wter creates a great deal of sound energy. It vibrates our clothes, but it doesn't kill us. We hear on a logrithmic scale (spelling may be off). Most people can barely detect an increase in loudness of 3 db. An increase of 6 db is not difficult to notice, but is small. That 6 db represents 4X the power of the sound. A 10 db increase requires 10 times increas of power, but it doesn't sound much louder. As a result, most people don't use much power. Only when the drums go BOOM does the amp need to do serious work. Engoy the music! You are not likely to heart any distortion in your listening situation. Relax, life is too short to waste on worrying.
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Yes, you will be operating in class A
Both speakers playing, distance is just shy of 2 meters
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I'll tell you what I think I know and someone can correct me. Class A watts approximately halve from 8 ohms into 4 ohms, so you have between 5 and 10 watts of class A power.
Accuphase does the calculation of watts being output at any given time, but they say the calculation is complex. Here is their explanation:
Indicates the True Power into the Speaker
The power into the speaker is the product of the amplifier’s output voltage (V) and the current (I); that is, W = V×I. While the voltage is easily measured with a voltmeter, the measurement of current is more complex. Typical power meters avoid this complexity by assuming that the load resistance is equivalent to the speaker's nominal impedance. For these meters, then, I = V/R, and therefore, W = V×V/R, and so W = V2 /R. But as Figure 1 clearly shows, the actual impedance of the speaker varies complexly according to the frequency. The load resistance changes considerably as the impedance moves from peaks to dips, causing the power to change as well. Because typical meters measure only the voltage, they are unable to calculate true power at any given time. The A-80 meter, in contrast. uses detection circuitry, installed at the outputs, to dynamically detect both the load voltage and the current. The meter converts these analog readings into digital values that are then used to calculate the power. It can therefore display the true power value even as the power fluctuates along with the impedance
They have a microprocessor in their amps do the calculation.
Just a guess, but I think that in a small office with 80 db peaks you would stay in class A watts most of the time and probably wouldn't notice if you went into class B watts.
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Just music. "Turn turn the volume up slowly until you measure 2.83 V AC at the speaker input" as in the speaker terminals on the speaker? Or should it be at the speaker tap on the amp?
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Take away another 6 dB for doubling the distance.
Were you doing the test with a pure tone input, or listening to music?
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Both speakers playing, distance is just shy of 2 meters
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Depends how far you are measuring at and whether your iPhone’s DB scale is reliable, but probably. Sensitivity is rated at 1 meter, so you should make sure to measure around that distance.
You’d be amazed how little power most of us actually use while listening.
If you want to be sure, get a 60 Hz test tone and an AC capable multimeter. Turn turn the volume up slowly until you measure 2.83 V AC at the speaker input. That’s 1 Watt at 8 or 2 Watts at 4 Ohms.
Also, if you are playing in stereo you'll get a 6 dB bump. That is, if you put out 2.83V into 2 speakers you'll measure 6dB more than into 1 speaker.
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