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Post by monkumonku on Jul 17, 2018 23:15:49 GMT -5
What do you mean by "stabilize?" If you mean to deliver a constant voltage, a Variac doesn't do that. It only proportionately increases or decreases the incoming voltage and if that voltage varies, so does the output of the Variac. EVERY Variac I've ever used has a knob which allows you to up or down the output voltage. As load increases and line voltage drops, you can 'up' the Variac output and continue your test w/'perfect' line voltage. Others persons will 'Wake Up' long dormant gear by giving them maybe 50vac to 60vac for a while to allow Capacitors to reform, than slowly increase the voltage to the rated quantity. Do this over a period of maybe a couple days. By Stabilize? When you take a PAIR of XPA-1 and crank-em-up you will eventually SAG the AC line voltage. Lonnie mentions doing this when driving a 2-ohm load to the limit. The idea is to turn UP the line voltage BACK to 120 or whatever (118 would work, too, right?) but be sure your Variac is rated to that extreme load. I don't know the limits, but I'd suspect that any voltage under 105 could be harmful to the amp under high-load conditions. And the amp simply WON'T put out max rated under those conditions even IF it holds together. www.variac.comCheck the website, please. The highest capacity models are NOT cheap and usually won't be found in someones home, but those few who benchtest gear for a living SHOULD have one. I understand and agree with what you are saying but I think you misunderstood me. What I was trying to say was that a Variac does not make an varying voltage constant. If the input voltage varies from say 110 to 125 then the output voltage will vary proportionately depending on how you have the output level knob set. So if by "stabilize" you meant to make a varying voltage constant, a Variac doesn't do that. But yes, I know it can raise or lower the incoming voltage based on how you have the knob set. |
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Post by leonski on Jul 17, 2018 23:36:30 GMT -5
Right you are. It is under manual control by YOU and limited by your speed with the knob. But under test conditions? Usuallly done with a resistor and tone generator along with measureing stuff to get the power, you want a constant line voltage.
Not so good under dynamic consitions. I see you are using the more rigid definition of 'stabailize'. Not a problem.
Monster made an automatic version years ago and we had an X-Ray machine at work which had an automatic line voltage adjustment sytem which we could NEVER get to work properly.
On the last? When it came time to fix it, I was Up To The Store which had a TUBE CHECKER with a couple shopping bags of tubes. What a PIA That was!@ Good Times.
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Post by DavidR on Jul 20, 2018 8:45:16 GMT -5
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Post by leonski on Jul 20, 2018 16:17:28 GMT -5
Please PM me with some elaboration. It appears the CVT does not produce a sine wave output without some additional windings. Current capacity of a CVT? Enough to run a big power amp wide open? Link to stereophile review of the AVS by MONSTER. www.stereophile.com/powerlineaccessories/864/index.htmlWill This device have the current capacity to run such a large amp under test conditions? The variac provides high capacity and though it IS user variable, under most constant test conditions, this isn't much of an issue. |
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Post by counterpoint on Jul 22, 2018 15:48:27 GMT -5
Ok. I just got a Kill A Watt meter and played chapter 2 of the Transformers Blu-ray @ -10dB (which is about all I can stand really of that nonsense anymore lol). I kept my eye on the Amperage readout and saw a maximum of roughly 4 amps on the XPA-5 (all speakers set to LARGE). I read a maximum of about 6 amps on the HSU VTF-15H MK2. And I read a maximum of about 7 amps for everything else (MFW-15, plasma tv, receiver, bluray player, htpc that might have been on).
So, just to repeat, 3 outlets are on a single 20A breaker with 12ga wiring. 17 amps maximum draw (though probably not at the same instant in time) on that test (@ -10dB).
If I get another HSU to replace the MFW15 (which is likely) let's tack on another 3 amps. I'm maxing out my circuit at that point. The XPA-1s are going to draw more amps but the XPA-5 will draw less since I don't plan on going to 7 speakers in this room.
So, I think running some dedicated outlets is definitely in store just to be on the safe side.
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Post by leonski on Jul 22, 2018 16:51:16 GMT -5
Yes, you are nearing redliine. Sorry to ask for further data, since I know what a torture session Transformers must be, but how much of a hit did the VOLTAGE take?
And what was the Power Factor? This will indicate how 'reactive' a load your gear is. Your gear Uses VA but you are billed for Watts. The more reactive your load, the higher the VA number in relation to watts.
Another circuit? Good idea. Amps go into THAT one and everything else stays where it is. That'll help. A 3rd circuit? Icing on the cake and you can put the subs on their OWN circuit with amps on a dedicated line as well.
Several ways, but in general keep low power and digital stuff away from the huge power draws like amps.
And not that it matters, but house wiring has a 20% 'derate' for longer time periods. So it's gonna be fine for 'bursts' to the limit but won't do that for long time periods. The -20% works out to 2400 watts - 240 = 2160 on a 20 amp service.
Than factor in Power Factor. A power factor of 1 represents a pure resistive load.
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Post by craigl59 on Jul 22, 2018 19:10:51 GMT -5
leonski, counterpoint:
Have been experimenting with the three circuits available to my XPA-1 system -- two 15 amp and one (30 foot away) 20 amp circuits.
Running the two XPA-1s off of a single 15 amp circuit works fine but can sound slightly harsh in crescendos and strings do not always have that "sweet" sound prized in class A.
Running one XPA-1 off of the long distance 20 amp by extension cord and the other by the nearby 15 amp circuit produces effortless volume and timbre BUT the XPA-1 attached to the longer extension cord has a very slight time lag that makes the 2 mono blocks together sound reverberant and slightly unclear. Instruments such as horns tend to get washed out in the texture and the muddiness is strong.
Running each of the XPA-1s off its own 15 amp circuit provides the most uniform result and the two monoblocks sound locked together AS LONG AS the power cords are of equal length. So one amp requires a 9 foot extension cord AND THE OTHER AMP benefits from having an equally long 9 foot extension cord added to it -- so that each monoblock has the exact same 13 foot power cord length. The improvement from this uniformity is clearly audible -- especially in orchestral textures and soundstage.
So my final result to is run each XPA-1 off its own discrete 15 amp circuit and all other electronics (Plasma TV, computer, DAC, Oppo 105, Cooling fans, and cable box) off of the long distance 20 amp outlet.
Have not gotten a Kill A Watt meter yet but still have the Radio Shack multimeter from my youth (now 50 years old and working as good as when new) and have been measuring voltages off of extension cords to check on voltage loss. Unlike the figures provided from Internet voltage calculators, see very little voltage loss on cables up to 25 feet in length (14 and 12 gauges). But this result might vary depending upon amperage load -- you folks tell me.
And am hoping that the amps do not draw full class A amperage when placed in standby mode (=yellow light). Do not have the manual and am assuming that in standby, no operating power is active.
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Post by leonski on Jul 22, 2018 21:09:50 GMT -5
At the highest levels you SHOULD see a voltage drop from 'baseline' and down anywhere from 2vac to 5vac. This depending on average current flow. Try BOTH XPA's on ONE 15 amp circuit at high levels. Another factor is the 'speed' of the meter. Most DVMs are not the most......dynamic......and lag behind fast changing conditions. If the amp IS true class 'A', it SHOULD draw a lot of power when doing nothing. This is the BIAS to the output devices. And not a trivial amount of power. That HEAT you note (or should) when at idle is simply electricity turning into HEAT. At maybe 30% efficiency when actually being used as an amplifier. www.electronics-tutorials.ws/amplifier/amp_5.htmlScan down to the section on Class 'A' for some further information. NOTE that EMO might improve the situation somewhat thru the use of what's called a 'Darlington Pair'. If the amp is WARM with the 'yellow' light on, it's drawing a lot of current. As for different power cable length producing an 'out of phase' or whatever effect you note, I think that's NUTS. All the power to the speakers comes from the PS of the amp, and only indirectly from the wall plug. You'd have more of a chance hearing such differences using short V Very Long SPEAKER cables. At the very highest levels, I'm NOT, however, surprised at the better results with the amps on seperate circuits, even 15 amp. |
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Post by counterpoint on Jul 23, 2018 11:43:36 GMT -5
Sorry to ask for further data, since I know what a torture session Transformers must be, but how much of a hit did the VOLTAGE take? And what was the Power Factor? This will indicate how 'reactive' a load your gear is. Your gear Uses VA but you are billed for Watts. The more reactive your load, the higher the VA number in relation to watts. With the receiver set to -10dB, the lowest the voltage got was 117.7V roughly, and the PF ranged between 0.63 and 0.68, spending the most amount of time by far around 0.66 roughly. I'm not sure what that shows exactly without doing my own research. With the receiver set to 0dB, the lowest the voltage dropped to was 115.7V I believe. With the subs OFF and the receiver set to 0dB, the maximum current draw on the XPA-5 was 7.8 Amps. I don't know what decibel level I hit. I didn't have my meter out. I'd have to look for it. |
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Post by leonski on Jul 23, 2018 13:04:44 GMT -5
When measureing your amp, click between 'Watts' and 'VA'. Watts is straight volts X amps and is considered the 'real' power. VA / Watts = Power Factor, which in your case is ABOUT .66 VA is always either the SAME as Watts (for PF = 1) or higher. NEVER lower. For a regular incandascent light bulb, it maybe very close to 1, indicating a nearly purely RESISTIVE load. VA would generally be used to size the cricuit to the load, in terms of capacity and wire size. blog.schneider-electric.com/it-management/2015/02/20/watts-vs-va-whats-difference-anyway/This will give you the general idea. In the case of Large factories which have a low Power Factor, they may even be charged a small premium on TOP of their existing electric bill. VA is a measure of how much the Voltage waveform is out of sync with the Current waveform. With your measure of PF=.66, I go backwards with my calcuator to find -COS which in this case is about 48 degrees. (COS 48 = .67) And from the extreme end of things, NO power is delivered when voltage and current are 90 degrees out of sync. And a PF = near Zero. |
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Post by Ex_Vintage on Jul 23, 2018 13:06:36 GMT -5
A 15 Amp circuit can deliver 1400 Watts to your speakers (assuming a 80% amp efficiency). Max current draw will only be present for low frequencies (high frequency is delivered by the support capacitance). Unless you are taking a function generator and running somewhere between 30 and 100 Hz constant input to the amps at full volume, you will never see rated watts output. For music and HT there will be some transients at those frequencies, but that is considered peak not RMS (Root Mean Square). Your 15 amp outlet is 15 amps RMS and the peak could be as high as 50-100 amps. Unless you are tripping a breaker, your power source is adequate.
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Post by leonski on Jul 23, 2018 16:08:56 GMT -5
The 50:50 power point for 'normal' music is about 350hz. This means that about 1/2 the power is used above and below that frequency. And while HF might be delivered 'by the support capacitance',(??) they must be 'recharged' at some point.
Which will be only when the cap voltage is BELOW the PS supply voltage. And THAN only for that brief part of the waveform in which the PS is above that voltage. And at line freuqncy of 60hz, unless a Switcher is used. (SMPS)
A few builders have made advertising 'hay' from having Power Factor Correction on the power supplies of their amps. If counterpoint is correct with a .66PF for his XPA-5, than that will be another limit on deliverable power.
Besides 'D' amp, I can't think of ANY amp which is 80% efficient from plug to speaker. In all fairness? Some 'D' amps can be higher than that. 1400 watts? I doubt Magnepan speakers could withstand that. I've heard of people using insane amounts of real power
on such speakers, but no reports of 'limits'. Mids and highs (of 3ways) are 'fused' with fast blow fuses on Magnepans. If you think your speaker can really 'handle' 1400 watts, plug it directly into the wall.
An A/B amp would be closer to 50% and would drop the 1400 watt number to maybe 900 to 1000 watts, Of which 97% would be HEAT, anyway, since speakers seldom exceed maybe 2% to 3% 'efficiency'. Running at 90 watts continuous and 900 watts peak,
as a 10db crest factor, would nearly certainly damage almost any speaker ever made. And WOW, would that be LOUD! 90 watts / 1 watt is nearly 20db
And while because of time constraints, you COULD theoretically get 50 amps from your circuit, I wonder at what VOLTAGE? Besides, most amps using a Silicon Bridge Rectifier won't be over a 30 amp rating. This would generally be considered enough of a safety
margin to make the part 100% reliable for a lifetime in service. Lightning strikes Not Included!
I think COUNTERPOINT, above, is on to something, measuring a lower line voltage with amp under 'stress'. And shows the reason why testers under constant stress conditions of tone and tone burst testing will use a Variac to stabilize line voltage. Various automatic ways exist to make such adjustments, but this is not generally needed for 'constant' load testing.
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Post by Ex_Vintage on Jul 23, 2018 22:20:44 GMT -5
leonski -Lots of unsupported numbers. Put a power analyzer on the supply cord and record the peak and RMS voltage, current and resultant power. Yes the efficiency is between 50 to 80% based on the bias point, but neither of those would produce 97% HEAT. You would be enlightened by the facts.
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Post by leonski on Jul 23, 2018 23:51:28 GMT -5
It's easy. Speakers are typically no more than 3% efficient. Therefore the REST of the power going TO the speaker is either reflected back to the amp and subject to damping factor which heats the output devices OR as heat which heats the voice coils of the speaker. Output devices have very LOW on-resistence, but still it IS resistive and does end up as heat. Given that an A/B amp worst case is about 30% power and efficiency should RISE with power output, 50% is the highest number I've heard reliably quoted. Just a random article on amplifiers, this one calls A/B efficiency 50% to 60%. Can you document an amp with 80% efficiency, plug to speaker, that is NOT a 'd' amp with SMPS? www.electronics-tutorials.ws/amplifier/amplifier-classes.html'D' amps can run maybe 90% or a little higher. These numbers are from PLUG to SPEAKER, not just the output section which makes no sense, since you need it to actually be doing something. Let's say your amp is drawing 100 watts and the PS is a pure resistive load. (few are) You might get 60 watts out and at maximum output, of those 60 watts, you'll have about 3 watts being USED, by even fairly efficient speakers. There's your 97% going to heat. The 3 watts I mention would be for maybe 100db sensitive speakers playing fairly loudly (lets say you have 2 of 'em) 100 watts IN and 3 watts to acoustic output yields 97% waste energy. Unsupported numbers? Excuse me, but I could document every reference I made. For example? You may question a speaker being maybe 3% efficient. Here's a calculator for 'ya to convert back and forth. www.sengpielaudio.com/calculator-efficiency.htmI don't have access any more to sophisticated measureing equipment. But my Kill-a-Watt meter makes good sense and is consistent. Though no peak-hold feature and it isn't the 'fastest' meter. Just ONE question for 'ya? Where do the 'support capacitors' get their energy if not from the amps PS? I've been over many schematic and never have seen reference to 'support capacitors'. And 1 watt to 100 watts is 20db 10x (log100) |
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Post by garbulky on Jul 24, 2018 13:41:21 GMT -5
leonski, counterpoint: Have been experimenting with the three circuits available to my XPA-1 system -- two 15 amp and one (30 foot away) 20 amp circuits. Running the two XPA-1s off of a single 15 amp circuit works fine but can sound slightly harsh in crescendos and strings do not always have that "sweet" sound prized in class A. Running one XPA-1 off of the long distance 20 amp by extension cord and the other by the nearby 15 amp circuit produces effortless volume and timbre BUT the XPA-1 attached to the longer extension cord has a very slight time lag that makes the 2 mono blocks together sound reverberant and slightly unclear. Instruments such as horns tend to get washed out in the texture and the muddiness is strong. Running each of the XPA-1s off its own 15 amp circuit provides the most uniform result and the two monoblocks sound locked together AS LONG AS the power cords are of equal length. So one amp requires a 9 foot extension cord AND THE OTHER AMP benefits from having an equally long 9 foot extension cord added to it -- so that each monoblock has the exact same 13 foot power cord length. The improvement from this uniformity is clearly audible -- especially in orchestral textures and soundstage. So my final result to is run each XPA-1 off its own discrete 15 amp circuit and all other electronics (Plasma TV, computer, DAC, Oppo 105, Cooling fans, and cable box) off of the long distance 20 amp outlet. Have not gotten a Kill A Watt meter yet but still have the Radio Shack multimeter from my youth (now 50 years old and working as good as when new) and have been measuring voltages off of extension cords to check on voltage loss. Unlike the figures provided from Internet voltage calculators, see very little voltage loss on cables up to 25 feet in length (14 and 12 gauges). But this result might vary depending upon amperage load -- you folks tell me. And am hoping that the amps do not draw full class A amperage when placed in standby mode (=yellow light). Do not have the manual and am assuming that in standby, no operating power is active. In stand by they draw practically no power |
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Post by leonski on Jul 24, 2018 16:19:56 GMT -5
How can that be? A class 'A' amp is defined by bias current with no signal being HIGH. This puts the trsnsistor basically in the middle of its operation curve. And needing LOTS of heat-sink.
It could be noted that the EMO amps running in class 'A' would most correctly be called 'high bias'. This give the first amount of power biased heavily to 'A' but shifting more towards 'A/B' as demand increases.
This is NOT exactly a 'brick wall' condition but more of a slope.
Is standby to be considered different than 'on' but no signal draw? If the amps are hot / warm in standby, that means the DO draw power.
If the switch is in 'A' position and standby with near-zero power draw, it's going to take 30 minutes to 60 minutes, at least, to reach proper operating temp from actual 'on'.
I don't see any references to 'A' amps having more than about 25% efficiency, just sitting there. As power demand of the xpa-1 increases, efficiency should ALSO increase to 50% or greater, nearing full power.
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Post by garbulky on Jul 24, 2018 17:11:20 GMT -5
In standby when the power light is amber |
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Post by leonski on Jul 24, 2018 18:43:57 GMT -5
So at that point the amp is stone cold, or at least room temp?
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Post by craigl59 on Jul 24, 2018 20:59:01 GMT -5
Garbulky: thanks; feel comfortable that the amber state draws virtually no power
leonski: Am declaring you the winner in the XPA-1 sweepstakes although all of the posters have provided helpful information. Here's why.
After I finished the last post describing the various combinations tried I realized that there was one other not yet tried -- running both monoblocks off of the single 20 amp circuit (by extension cord). SO I rigged up a 12 gauge power cord and connected both monoblocks with their Pangea AC-9 cables to this single cord.
SURPRISE!
This was clearly the best power option -- including, by comparison, to the hooking up of each monoblock to its own separate 15 amp circuit (although the latter is also a very good option).
Here's why. The 20 amp option livens up the XPA-1s, makes them louder (by about 2db as measured in REW) and imparts added vitality to singers and soloists. The difference is significant in my system and home.
All five power options were carefully tuned with REW/JRiver using the impulse and frequency convolution filter so the comparison of these options is valid. Here is the order or success from worse (5) to best (1):
5. One monoblock powered by 20 amp circuit, another by a 15 amp one (reverberant and muddy)
4. Two blocks off of a single 15 amp circuit (harsh crescendos and lack of sweet class a strings)
3. Running both blocks off of a Furman Elite (not bad, but a little thin by comparison to the next two)
2. Each block connected to its own discrete 15 amp circuit -- nice and clean, plenty of definition
1. Both block powered by a single 20 amp circuit -- best feeling of live performance, volume/crescendo control, and markedly best soundstage
So all of this started with me questioning leonski's original suggestion that I run the blocks off of a 20 amp circuit and IT TURNS OUT HE IS RIGHT -- at least from my experience and system.
NOW, ON THE OTHER HAND, leonski is not right about differing power cord lengths causing objectionable results -- that he called "nuts." Suggest you try this before you leap to this conclusion. Got reverberant/muddied problems both times I had the two blocks on different length power cords.
And because of the above, spent today revising the 20 amp outlet in my adjoining dining room, confirming its 20 amp capability, and building a 20 amp power cord (with GFCI) that has all now singing particularly well.
And I am going to turn my attention to other projects; this is enough power cord education to hold me for a while.
OH, did I mention that the amps sound spectacular? Yes, they do and we've got to light a fire under Emotiva to bring back another class A amp.
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Post by rbk123 on Jul 24, 2018 21:02:10 GMT -5
So at that point the amp is stone cold, or at least room temp? The amp is probably off except for the trigger listening circuitry. Keith could confirm. |
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