Choose an amplifier for me

[mtrycrafts]

Since this is a hot one let me add some fuel to the fire here as I have just started to do some research into this. I talked with Dave Moulton who is a recording engineer who does surround, and consults with firms doing the megabuck surround installations in this area. For more info try www.moultonlabs.com

In any case we were talking about this general subject very recently. Typically peaks for HT or Multi Channel are 20 mS to 25 mS in duration and most of this is bass. Typical spl peaks are 110db/spl at the loudspeaker and Dave tells me that practically no one can stand peaks any higher than this, because this starts to get well......uncomfortable. These peaks can happen in two to three channels simultaneously. Usually the sub, and right and left front. It is extremely rare (when the movie goes into an end of the galaxy routine) that peaks occur in all 5 channels, and if they do the spl peaks at the speaker are down to 100 db/spl.( approximately 10 watts peak?) Think about 5 or 6 speakers coming at you with those levels!
Now if we are using an HT set up with a powered sub, then the duration of the peaks go down for the receiver, probably in the range of 10mS at most. If we are using a 90db/spl speaker (typical for HT) than 100 watts peak (110db/spl at the speaker), and the speaker is the typical 8 ohms nominal with an absolute minimum of 4 ohms, then as far as I can tell the receiver is not asked to do a heckuva lot.
If the system has no powered sub, then the demands come up to 25 mS for two to three channels. It appears at this point, unless your running some of the heftier receivers, you may have issues.
Hope this helps;
d.b.

If you are peaking two of the main channels, excluding the sub as they are mostly powered, receivers are rated for two channels driven conditions as is the dynamic headroom as well which is tested at 20 ms. Now the issue is how fast do caps recharge.

 

[PENG]

Now the issue is how fast do caps recharge.

You can calculate it if you know the applied voltage, capacitance, dielectric permittivity (depends on the type of capacitors) and the resistance (however small) of the capacitor charging circuit.

 

[Dan Banquer]

It is not only how fast caps recharge, it's how well the transformer stays in regulation. If the transformer goes out of regulation and goes into saturation then you have have added issues. This is one of the main reasons why I and a number of other engineers strongly advocate watts rms power as opposed to burst power, becasue if you are monitoring the AC line for voltage, current, and Power Factor then you have a real good idea on what exactly the power supply is capable of, and where it is in regulation and where it goes out or regulation.
Just out of curiosity, I noted that no one commented on my earlier post. I was expecting someone to say,"that's not a heckuva lot of power your talking about Dan".
Oh Well,
d.b.

 

[rollinrocker]

Watts

Marshall

I currently (no pun intended) run a rotel rmb-1095 amp in my system.

It is 200 watts per channel (5 channel) and i love the way it sounds. I

read several reviews on this amp before i decided to audition and eventually

buy. It replaced a carver amp rated at 380 watts per channel (2 channel)

and another amp at 250 watts(3 channel). The rotel, imo, is a better

sounding , more "musical" amp. That said, i've also heard a proceed amp

rated at 125 watts per channel. It was a fantastic amp, more depth and

"air" around instruments. I would prefer to own the proceed, but it was

$5000.00. The rotel was $2000.00. I believe the rotel to get you 80%

of the proceed sound for 40% of the price. To me, that makes the rotel a

better value. I guess the point i'm trying to make is take some of these

recommendations and go LISTEN if you can. I wouldnt put a lot of stock in

watts per channel only.

 

[mtrycrafts]

You can calculate it if you know the applied voltage, capacitance, dielectric permittivity (depends on the type of capacitors) and the resistance (however small) of the capacitor charging circuit.

Hence, line frequency, what Mac is implying, is irrelevant. After all, the line frequency is rectified to DC, most likely by full wave, so frequency is irrelevant. Besides, AC cannot charge a cap. It must be rectified to DC.??

 

[mtrycrafts]

It is not only how fast caps recharge, it's how well the transformer stays in regulation. If the transformer goes out of regulation and goes into saturation then you have have added issues. This is one of the main reasons why I and a number of other engineers strongly advocate watts rms power as opposed to burst power, becasue if you are monitoring the AC line for voltage, current, and Power Factor then you have a real good idea on what exactly the power supply is capable of, and where it is in regulation and where it goes out or regulation.

OK, I'll buy this. But Mac was implying that line frequency is the limiting factor, 16ms, this being the time for 1 cycle of 60 Hz, and 20ms in Europe. He is mistaken.




Just out of curiosity, I noted that no one commented on my earlier post. I was expecting someone to say,"that's not a heckuva lot of power your talking about Dan".
Oh Well,
d.b.


I read your posts but with so many now, which one ?

By the way, I get picked on for my typing and spelling errors, but when others have such errors, no comments form the peanut gallery I guess they just like me more

 

[mtrycrafts]

That said, i've also heard a proceed amp

rated at 125 watts per channel. It was a fantastic amp, more depth and

"air" around instruments. .

I wonder how an amp does this magic?

Air can be had with lots of phase shift as would the depth be affected, or the recording and speakers or room acoustics. But an amp? Something funny is going on in there.

 

[PENG]

Hence, line frequency, what Mac is implying, is irrelevant. After all, the line frequency is rectified to DC, most likely by full wave, so frequency is irrelevant. Besides, AC cannot charge a cap. It must be rectified to DC.??

I could be wrong but I thought he meant how much louder 3, or 10 dB SPL is, depends on the frequency.

 

[PENG]

Hence, line frequency, what Mac is implying, is irrelevant. After all, the line frequency is rectified to DC, most likely by full wave, so frequency is irrelevant. Besides, AC cannot charge a cap. It must be rectified to DC.??

I could be wrong but I thought he meant how much louder 3, or 10 dB SPL is, depends on the frequency. He wasn't talking about capacitance.

 

[MacManNM]

What? Caps cannot recharg faster than this? Really?

They can if they aren't plugged into a 60Hz outlet.

 

[mtrycrafts]

They can if they aren't plugged into a 60Hz outlet.

So, you are implying that those caps cannot recharge faster than 16ms because they are plugged into a 60Hz power source?
I thought that is recitified and DC is fed to the caps, hence, the line frequency is irrelevant. But, since your past records of some claims, you won't mind if I consult with more knowledgeable folks, do you? Just in case you are wrong, again.
My sources so far has nothing about line frequency, only RC time constants. But, who knows, maybe you are right for once?

 

[mtrycrafts]

I could be wrong but I thought he meant how much louder 3, or 10 dB SPL is, depends on the frequency.

This is what he stated above, a few posts before yours above, where we have a serious issue:

You don't buy it because you don't understand it. The recovery time can't be any faster than 16ms (20 ms if you live across the big pond). Now, if your peak is 60 Hz or lower they won't recover in time.


16 ms is the period for 1 cycle of 60Hz, and 20ms for 50Hz in Europe.
It is clear to me that he is implying a limitation, excluding RC time constants for charging, due to line frequency. But, I am pretty sure he is wrong as that frequency is rectified to DC, hence, line frequency is not an issue, never is as caps charge on DC volts.

 

[PENG]

Well then, I am not going to guess what Mac meant and I am sure we'll hear from him soon.

One can argue that if the music signal peaks at 60 Hz or lower, it would probably deplete more stored energy in the caps than it would for much higher frequencies. The caps are on the d.c. side, but how long it takes to charge them up would still depend on how empty they were to start with.

 

[MacManNM]

It is not only how fast caps recharge, it's how well the transformer stays in regulation. If the transformer goes out of regulation and goes into saturation then you have have added issues. This is one of the main reasons why I and a number of other engineers strongly advocate watts rms power as opposed to burst power, becasue if you are monitoring the AC line for voltage, current, and Power Factor then you have a real good idea on what exactly the power supply is capable of, and where it is in regulation and where it goes out or regulation.

OK, I'll buy this. But Mac was implying that line frequency is the limiting factor, 16ms, this being the time for 1 cycle of 60 Hz, and 20ms in Europe. He is mistaken.




Just out of curiosity, I noted that no one commented on my earlier post. I was expecting someone to say,"that's not a heckuva lot of power your talking about Dan".
Oh Well,
d.b.


I read your posts but with so many now, which one ?

By the way, I get picked on for my typing and spelling errors, but when others have such errors, no comments form the peanut gallery I guess they just like me more

No, I am not mistaken, the limiting factor of a WELL designed amp is the input line current,frequency. The things that Dan are talking about happen well after the capacitave reserve runs out, so, the more capacitance you have, the better.

 

[MacManNM]

This is what he stated above, a few posts before yours above, where we have a serious issue:

You don't buy it because you don't understand it. The recovery time can't be any faster than 16ms (20 ms if you live across the big pond). Now, if your peak is 60 Hz or lower they won't recover in time.


16 ms is the period for 1 cycle of 60Hz, and 20ms for 50Hz in Europe.
It is clear to me that he is implying a limitation, excluding RC time constants for charging, due to line frequency. But, I am pretty sure he is wrong as that frequency is rectified to DC, hence, line frequency is not an issue, never is as caps charge on DC volts.

It is rectified but it is pulsed DC. The caps are what make it line level DC

 

[MDS]

I don't know the answer to this debate, so let me ask a question instead. When do the caps recharge? If Mac is right, then that would imply that they can only recharge after one full cycle; ie at the positive going zero crossing.

 

[mtrycrafts]

I don't know the answer to this debate, so let me ask a question instead. When do the caps recharge? If Mac is right, then that would imply that they can only recharge after one full cycle; ie at the positive going zero crossing.

The AC is rectified. Caps charge by DC so there is no crossing, just DC and the RC time constant is in play on charging time.

But, I will call the amp designer at Bryston, again, Chris Russell. He gave me the straight on amp clipping as well, not Mac.

 

[mtrycrafts]

Well then, I am not going to guess what Mac meant and I am sure we'll hear from him soon.

One can argue that if the music signal peaks at 60 Hz or lower, it would probably deplete more stored energy in the caps than it would for much higher frequencies. The caps are on the d.c. side, but how long it takes to charge them up would still depend on how empty they were to start with.

Well, you answered the question. It is on the DC side, so it is not limited by the line frequency as Mac is implying. The implication is clear, especially when he included the European line frequency.
We were not discussing how long it took due to the amount of discharge, nor did he even mention the RC time constants, just the limiting factor of the line frequency of 60 Hz, 16ms.

 

[mtrycrafts]

It is rectified but it is pulsed DC. The caps are what make it line level DC

Then, by your logic, if you played a 10kHz sine wave to check the RMS power output, those caps would never recharge and would be depleted in a hurry as you are discharging faster than you can recharge it? Or what are you really saying?

 

[Dan Banquer]

Choose an amp for me

When the rectifier diodes change the AC to DC they change it to a 120 Hz positive or negative going wave. The positive DC upply will look like the two halves of the sinusoidal wave only they are going from about zero volts to whatever the peak positive is, and the negative DC supply does just that but only going in the negative direction.
In any case I wish I could draw the wave forms, becasue a picture would explain a thousand words.
Now that we sort of have that explained, you must remember that recharging a cap is not only a function of current it is also a function of voltage. so not only does the cap have to refill it's resovoir of current it also must climb back to the nominal voltage. In essence John is right: it does take at least one full cycle to recharge, that's about 17 mS. He is also saying that if we had a higher line frequency the recharge time would be even less. Think of it this way: if we take the reciprocal of 60 hZ we get about 17mS. if the line frequency was at 120 Hz than we could be recharging those caps at about 8.5 mS. For those of you who are math challenged the reciprocal is 1 divided by a number, so when I say the reciprocal of 60 Hz it is 1 divided by 60 Hz which comes out to about 17 mS. So the reciprocal of a known frequency is also the duration in time it gets to do one full cycle.

Does everyone understand?
d,b,