Need understanding on amperage

Hi Phil, if by momentarily, you mean only at one frequency, then things can be a lot different, depending on the frequency. For example, a lot of ESLs have impedances like that at high frequencies where no power is required. Despite that, many tube amps can often drive that just fine.

Thanks for the question. The Caddock volume control makes the MP-1 a little more transparent. Of all the options we offer, it is both most expensive and the least sonic effect. FWIW the new volume control on the Mk3.2 preamps in stock form is more transparent than Caddock controls of the older versions.

hi Ralph,
Thanks for responding about my query. i'm not sure what if the load should dip to 1 ohm MOMENTARILY for certain high freq. and playing at whisper quiet level, does this mean the amp should still be capable of handling such load (theoretically speaking)
BTW, i'm interest in your preamp, can i know what benefit by changing to Caddock volume control? is it more steps than original of 24? and about the damping package? my dealer said something about anti-resonant feet for the pre, is it?
regards -phil

Philipwu, to drive a 1 ohm load is a difficult task for any amplifier.

You might want to consider that if the load is difficult to drive, the amp will not sound its best! This is true of all amplifiers.

For tube amps this requires a special transformer to allow it to happen and you will find such a transformer to be very rare. While some transistor amps can actually drive a one ohm load, in general they would be better off using some sort of matching transformer as well.

IOW, a one-ohm speaker is impractical and should be avoided, as there are no amplifiers that can really sound like music playing such a load. As the saying goes, why go where angels fear to tread?

Can anyone help to illustrate how and what components in the amp (eg. transformer VA, capacitance, transistor rating, etc) that are crucial in delivery into difficult loads e.g. lower than 1ohm in peak situations? thanks.
If the listening level is very low (whisper low) does this mean ALL amp can drive the load well even 1 ohm? Thanks again.

Yes, of course. Murphy's Law is a humorous outlook on everyday troubles. It is based on the premise that, "If something can go wrong, it will." One corollary is, "When left to themselves, things go from bad to worse." And another is, "Nature always sides with the hidden flaw." 8>)

Tonyw:

Murphy's law should have nothing to do with it. But the amp designer should by specing the right power transistors. Safe operating area data are provided by all the power transistor manufacturers.

So Murphy's Law in the World of HiFi: 24, $20 transistors will blow to protect a $0.05 fuse.

Yes, I have often wondered whether this claim for 60 amps by Parasound was an actual measured performance spec or strictly hypothetical "potential" capability. I guess only John Curl can answer this question.

If the current limiters kick in long before the 60 amps, then its hypothetical. Something I did not consider in my analysis.

Tony,

It is possible that the entire output stage could fail if the safe operating area of those transistors is not broad enough to allow the fuse to burn before the transistors fail. This is the potential weakness of having a plurality of power transistors in parallel in the output stage. The weakest one fails first, then the others have to carry the remaining current and they start failing in a cascade phenomena.

Atmasphere:
You are correct re the re-charge. 1/2 sine at 60 Hz is about 8 milliseconds, so it would depend on where in time the transient occured. Nevertheless, I doubt of the power transformer could supply anything near 60 amps. Bombay also seems to assume the 8 amp fuse is in the AC input side but it is actually on the DC power busses supplying the output stages.

You know, Murphy's Law says that a $20 transistor will blow to protect a $0.05 fuse. I wonder how Murphy's Law applies in the world of HiFi where fuses cost $80.

Right! Now this is just my feeling about the matter, but I don't think the 60 amp rating is realistic if it means that the amplifier could be damaged or the like in the process. At that point we are clearly operating outside of the linear region of the amp- and such an amp is intended for music not square waves.

Bombaywalla, its not a given that the caps would be charging if the window is 10mS. A lot would have to do with where the AC waveform was at the time of the 'event' :)

BTW thanks to all that have contributed here.

agree, Dhl93449 calculations showed the delta-V (or droop) across the power supply cap to be 24V meaning that the final voltage after 10mS would be 80V-24V=56V but at this point in time the fuse would have blown (per the Littlefuse data sheet) as the current draw from the wall would have peaked at 8A in a valliant effort to re-charge the drooping power supply caps. Thus, the output protection ckt should have kicked in ASAP to cut off the output signal from reaching the speaker binding posts & there should be pin-drop silence from the speakers! ;-) And, as Dhl93449 noted, the output stage is hopefully intact & there is no smoke curling out of the amp......

Atmasphere/Tonywise

Yes, the remaining voltage would be 56 volts, and the average power delivered would be between 3600 and 3136 Wts. And it may be somewhat less because we are not accounting for the voltage drop across the output stage transistors (it won't be zero, and will be dependant whether the transistors are being driven into saturation or not).

Guys, it was just a ballpark analysis. It also did not include the re-charge of the capacitor by the transformer or that perhaps both the V+ and V- capacitors might be discharged partially.

My point being is that the delivery of 60 amps to the load will be limited by the fuse characterisitcs primarily. Whether it is 10 milliseconds or 15 milliseconds is not that important.

BTW, I would hope that the fuse was sized to prevent the bipolar output transistors from going into secondary breakdown. If this happens, the power transistors fail and the entire output stage is toast before the fuse can protect them.

I think the change is voltage (dV) is 24V. So starting from 80V in DHl's equation means that the ending voltage after 10ms is 56V which is still 3136 Watts, right?

Dhl93449, your math looks right but your conclusion doesn't. At the end of 10mS the supply voltage is only 24V so the current would be 24 amps- only 576 watts. The fuse would go a little longer and the 3600 watt figure would go much shorter or am I missing something?

From the A21 schematic published by Parasound, each power buss to the output stage is fused to 8 amps. No amplifier fused for 8 amps will run 60 amps very long before vaporizing the fuse link.

From the Littlefuse data sheets for an 8 amp fast blow fuse, 60 amps blows the fuse in about 10 milliseconds. Each channel has 50,000 mfds of capacitance, and left and right channels have separate power supplies (so the full 100,000 mfds is not applied to a single 60 amp transient, only 50,000 mfds is, and those are further divided to a V+ cap at 25,000 and a V- cap at 25,000 mfd).

If you calculate the drop in voltage of the 25,000 mfd capacitor, I=C*dV/dt, so I=60 amps, C=25,000 mfd, and dt = 10 milliseconds (the time to blow the fuse), we find dV = 24 volts, or about 1/3 of the 80V supply voltage.

So if you shorted this amp, it would deliver 60 amps for the 10 milliseconds needed to burn the fuse, and have plenty of power supply voltage left in the capacitor.

It could potentially drive a 1 ohm load to 60V (or 3600 W) for 10 milliseconds. That's it, and it's limited by the fusing.

Agreed. I know nothing of his specific amp other than they rated the transistors at 60 amps. No speaker could handle that level of amperage without blowing fuses, crossovers or drivers.
That is cool about your tube amps. I agree, there is no substitute for iron and copper. One nice feature about tube amps with transformer outputs- you can't blow them by shorting the outputs. Transistor amps are not so robust regardless of their current rating. I don't know how much protection today's SS amps, or my SS amp for that matter, have built in to guard against shorting. I'm certainly not willing to test my amp. But I know a few decades ago that one of our LVDT suppliers used to use audio tube amps for testing them and never had issues. When they updated to SS amps, even the briefest shorting of the output leads would pop the transistors. They had to redesign their test stations so the production operators couldn't short the amps.

Tonywinsc, that music has such transients and that a stereo needs either very high power and/or efficient speakers to reproduce those transients is not a matter of debate.

What is a matter of debate is the math. Its more than just the current rating of the output devices; if you are really drawing 60 amps from the output section its pretty safe to say that the power supply voltage will be near zero as the amplifier is not capable of 14,000 watts (4 ohms) or 3600 into one ohm. In fact in this case the specs show that from 8 ohms to 4 this amp does not double its power, so we can see that there is a current limit somewhere (likely the power transformer). So the 60 amps will not be coming through the speaker terminals. Its a measure of the storage in the supply and when you look at the brochures this is confirmed. Its got a lot of storage, 100,000 uf. That is all the 60 amp figure is stating.

We make a tube amp that can do the same thing. In fact its rated at 80 amps because it has more storage than this transistor amp does! But in both cases all that current is not available to the speaker, if it were such amps would have a bad reputation with speaker manufacturers :)

The extra energy storage does however help with authority and smoother delivery at high power levels as there is less noise in the power supplies and so less intermodulation distortion. But it has no bearing at all on the amp's ability to drive 'difficult' loads. If you look at inexpensive SS amps of similar power, they have similar specs and ability to drive difficult loads; the difference is they likely don't sound as good doing it. **That** is the difference between the men and the boys, and why we pay the extra dollars.

Seriously? You better believe it. Real life sounds have sharp, high transient peaks that seem like no big deal but require massive power to faithfully duplicate in a sound reproduction system. The amplifier has to generate sufficient power to overcome the mechanical and electrical inertia of the speaker drivers to make the slap of a drum or pluck of a string sound real. The more power on tap in the amp, the more realistic the sound. That's why amplifiers have big transformers and capacitors, so they can hit those momentary high Wattage peaks if just for 10 ms or so. Not 14,000 Watts probably, but 3000 Watts is possible for a very short time. That power is needed to make the fast rise times so the music doesn't sound blurred or distorted. That's the difference between listening to a hifi system and a clock radio. For sure, the transistors will pop like fuses if they have high current levels for too long. It is all about heat buildup inside the semi-conductors. His amp manufacturer rates the transistors for 60 amps, but no idea if that is for 1ms or 1 hour. The circuits may be capable of those power levels, as I am thinking for robustness, but agreed the amp could never generate those power levels for more than milliseconds (and likely not 60 amps) being supplied by a standard 120VAC wall plug.
One example that comes to mind is the 1812 Overture. I have never heard the cannons faithfully reproduced by a stereo system. The power to do it would be at the industrial level, as well as the speakers to handle that sound pressure level. I mean you know they are cannons that are being fired, but not even close to the impact and shear power of the real cannon shot. I think it would be fun to play the record and have someone fire real cannons at the appropriate moments, but the neighbors might not think it so much fun.

Pay attention to what Ralph from Atmasphere is saying in this thread and you will be for the better.

Seriously, is anyone suggesting that the output section of this amplifier can deliver 3600 watts even briefly?? The output devices would be destroyed. Now if you assume a 4 ohm load rather than 1 ohm, the power is then 14,400 watts. Obviously this 60 amp figure has to do with something else- the math isn't lying...

This rating has nothing to do with the output power of the amp. It does get conflated that way quite often though and I think a lot of manufacturers like it that way.

Like a few have already stated, power is a better way to look at the system because power is constant even when current and voltage are changing. What that means is that the amplifier has transformers to reduce the voltage levels. So current out of your amp can be higher than the current at the wall since the voltage is lower. Your amplifier spec is stating 60 amps to either show a short term power storage peak output or else to say that the transisitors are robust enough to withstand that current draw for some period of time without popping.
A 120 VAC wall plug can safely handle about 1200 Watts. Looking at high power home appliances, I doubt you could find a microwave oven or toaster rated higher than that. I searched far and wide for a 2-slot toaster rated at 1200 Watts so I can have decent toast. Anyway, 1200 Watts is a 10 amp load and anyone with an older home will tell you, don't try to run a microwave oven and a toaster on the same circuit at the same time. So like someone already said, if you were to input 60 amps into a 1 ohm speaker load, that would be 3600 Watts. It may be possible for some milliseconds with the help of the energy storage capacity in your amp, but not continuously simply because a house circuit could not handle that load.
My amp pulls about 5 amps all the time out of the power conditioner. I have seen it peak at 5.7 amps if I have the music cranked. My voltage hangs in there at around 122 VAC because I have a dedicated circuit. So I am pulling up to 700 Watts total- but only for a second or two. The amp output would be something less than 350 Watts per channel. Then my wife tells me to turn it down and my current draw is back to 5 amps. If my speakers have say a 4 ohm average load, then the current draw into each speaker is no more than 9 amps. That is 18 amps total, even though the current draw at wall is only 5.7 amps. These are rough examples because the power output to the speakers will be a little less than the power into the amp due to losses through the amp (in the form of heat).

the 60 amps is stated under "current capacity" under the specifications section on their website.

Watts = Volts * Amps

Never heard of an amplifier rated in "amps per channel" before.

To further clarify.

When you look at a "current rating" spec you need to know at least two things:

(1) At what voltage is the current being specified.

(2) Is the rating CONTINUOUS or transient.

The ratings on wall power are usually continuous maximums (in root mean square or RMS) and are at your line voltage of 120 V AC.

The 60 amp rating for a power amp like the Parasound are TRANSIENT, good for only a very short time and at a voltage much lower than your line power levels.

Make no mistake, if that A21 tried to output 60 amps for more than a few milliseconds, fuses would blow.

In the old days, manufacturers were required to avoid transient power/voltage/current specs because they can be so misleading for consumers. Only RMS continuous specs were allowed to be published.

To clarify: The 60 amps figure of the amplifier is not how much current the amp can produce driving the speaker. If it were, we could apply the power formula, which is that Power equals the current squared times the resistance of the load.

So if we give the amp the benefit of the doubt and use a 1 ohm load, that means that the power output of the amp is 60 amps squared; 3600 watts! Obviously the amp can't do that, what this 60 amp number represents is how much current is produced when the power supplies are shorted out for 10 milliseconds, something that you would never, ever want to do!

So this has little to do with whether the amp can make a lot of 'current' when driving low impedance loads. I know of several tube amps that don't make nearly the same power than tout the same figure.

Thanks for your responses. Makes complete sense, thanks for using small words:)

LL

Your 20 amp circuit supplies continuous current to the receptacle. Your amp can output 60 amps "peak", very briefly. The duration of the "peak" 60 amps depends upon how much electricity is stored in the amplifiers power supply capacitors. Transformers unlike capacitors, do not store electricity.

The specs on your power conditioner state: Input - 15 Amp capacity required and Output - 11-15 Amps RMS (maximum, all outlets combined - continuous). The 45 amp rating is the peak current rating for the conditioner output which, just like your amplifier, depends on how much electricity is stored in its capacitors.

Adding the power conditioner will make peak current available to all of the components plugged into the conditioner. However, since your circuit is 20 amps and the conditioner input is rated for 15 amps, you are not getting the benefit of your 20 amp circuit.

You don't trip your 20 amp circuit breaker because the input of the both the amplifier and conditioner are designed to limit their current demand to 15 amps.

Greg