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Post by emotifan on Jan 13, 2012 14:22:44 GMT -5
This is just a question of curiosity. Hopefully someone from Emotiva will jump in here.
Why does Emotiva use an architecture where the XPA-2 ends up with only 45,000 uF of secondary capacitance using twelve 10,000 uF capacitors? I read somewhere that it has to do with reaching their power output goal but I don't understand it.
The XPA-1 uses what looks like the same number and type and has 120,000 uF. And yes I know it's a mono amp.
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Post by Deleted on Jan 13, 2012 14:45:56 GMT -5
It's just the way they are laid out.
The XPA-2 has 12 output transistors per channel with a secondary capacitance of 45,000 uF
The XPA-1 has 24 output transistors per channel with a secondary capacitance of 120,000 uF.
Remember that the XPA-1 has two amps in the chassis. One is in phase and the other is 180 degree out of phase. It makes the Differential (balanced/XLR) design possible.
Just the way it was down. The extra capacitors store energy for those big booms, bass notes and dynamic scenes in movies/music.
On another note ASR amps can have over 1,500,000uF in capacitors in the secondary. Does this make for a better amp than the XPA-1 or -2? I do not believe so.....
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Post by House on Jan 13, 2012 14:57:09 GMT -5
On another note ASR amps can have over 1,500,000uF in capacitors in the secondary. Does this make for a better amp than the XPA-1 or -2? I do not believe so..... if one needed much more than that then i say its about time they just went to the movie theater  |
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Post by jackfish on Jan 13, 2012 15:12:49 GMT -5
The XPA-2 has twelve 50V 15,000uF capacitors for 180,000uF of capacitance, of which effective capacitance provided by a serial-parallel configuration is 45,000uF. However, this configuration is sufficient to provide a potential 100V of storage to drive the rail voltage up to supply rated power.
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Post by House on Jan 13, 2012 15:50:56 GMT -5
The XPA-2 has twelve 50V 15,000uF capacitors for 180,000uF of capacitance, of which effective capacitance provided by a serial-parallel configuration is 45,000uF. However, this configuration is sufficient to provide a potential 100V of storage to drive the rail voltage up to supply rated power. so what your saying is dont stick your tongue on the terminals while its plugged in? |
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Post by tchaik on Jan 13, 2012 17:29:45 GMT -5
The XPA-2 has twelve 50V 15,000uF capacitors for 180,000uF of capacitance, of which effective capacitance provided by a serial-parallel configuration is 45,000uF. However, this configuration is sufficient to provide a potential 100V of storage to drive the rail voltage up to supply rated power. so what your saying is dont stick your tongue on the terminals while its plugged in? probably would hurt a little. make sure your insurance is up to date before you try it. actually, i asked lonnie that very question about the xpa-2's secondary capacitance and his answer was complete, thorough and totally non-understandable by me. so.........i suggest you call and ask him to explain it again. what i do know, is that the amp remains completely unfazed by anything i throw at it, no matter what the material or volume. the only other amp i have owned that worked as well was a krell ksa-100 that i owned in the 80's. but this was at a much much higher price. tchaik............. |
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Post by emotifan on Jan 13, 2012 22:41:11 GMT -5
How or why does the serial-parallel configuration make for less capacitance than the sum total of the capacitors rated storage capacity? I'm not questioning the design, just trying to understand it. It's probably just over my head. The XPA-2 has twelve 50V 15,000uF capacitors for 180,000uF of capacitance, of which effective capacitance provided by a serial-parallel configuration is 45,000uF. However, this configuration is sufficient to provide a potential 100V of storage to drive the rail voltage up to supply rated power. |
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Post by knucklehead on Jan 13, 2012 23:54:25 GMT -5
Been a long time since I was in electronics school in the USN - 1965 in fact - but here goes a stab at answering that.
The principle is similar to how resistance works - if you wire 2 resistors in parallel the total resistance is half the total of the resistive values of both resistors. Put them in series and the sum of the value of resistor becomes the total resistance.
As to why Emotiva designed their amps in this manner - well - I'm no electronics expert so I can't answer that but I can guess that the XPA-2 would seldom run out of reserve energy and capacitance is nothing more than energy in reserve just waiting for a drop in voltage.
My Acurus A150 is an interesting amp. I don't know what the total capacitance is but when I turn it off and the source is still playing the speakers put out sound for about 20 seconds or so. I suspect if you could cause an XPA-1 to do the same it would play for much longer.
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Post by mj on Jan 17, 2012 15:57:48 GMT -5
Caps are different than resistors. Assume for simplicity that you have a bunch of capacitors that are all the same value. And still keeping it simple, let's assume that these capacitors are 1 Farad for each one. (1 F. is huge, but we'll assume these caps come from Texas.  ) A cap is very simple in concept - just two conductors separated by an insulator. For any cap you eventually reach a voltage where that insulator will fail, so each cap. has a maximum voltage associated with it. For our simple Texas sized caps, let's assume that they are rated to 100 volts. If you put two caps in parallel, then their effective capacitance is the sum of both. So with our example caps, if we put 2 in parallel we get effectively a 100 V rate 2f cap. If you put two caps in series (and the values are the same) then their effective capacitance is 1/2, but their voltage rating is 2x. So with our same caps. in series, we'd create what was effectively a .5F capacitor with a voltage rating of 200 V. It's slightly more complex if the caps. have different values, and you have to do a few simple things in the series situation to make sure that there aren't problems. But engineers have been doing this safely for a very long time. The caps in the XPA2 have been put in a series parallel combination to reach the desired working voltage and capacitance. I dont' have one to look at the individual cap. ratings so I can't speculate on the exact configuration. But as I noted earlier, this is well understood and perfectly fine to do. - mj |
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Post by bobbyt on Jan 17, 2012 18:53:29 GMT -5
For the same capacitance in series (like resistors in parallel), you halve them.
The general formula for two different capacitors Ca & Cb is:
1/C = 1/Ca + 1/Cb
So if Ca = Cb = 1 F, total C = 1/2
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Post by audiosanity on May 25, 2013 21:24:44 GMT -5
How or why does the serial-parallel configuration make for less capacitance than the sum total of the capacitors rated storage capacity? Note that capacitance and energy are not the same thing. The end result of series versus parallel is how much voltage versus current you want. The energy stored is the same. For instance, let's take 10mf capacitors of 50V. The energy U stored in a capacitor is U = 1/2 C V^2. For two in parallel, C = 10+10 = 20 mf, V = 50V. So U_par = 0.5*20*50^2 = 25,000 mJ For two in series, C = 1/(1/10 + 1/10) = 5mf, but V = 2*50 = 100V. So U_ser = 0.5*5*100^2 = 25,000 mJ But we got U_ser = U_par! So they store the same amount of energy! But the series configuration can drive 100V versus 50V for the parallel one, at the cost of reduced current capability. I suspect the triple Darlington devices used are the reason why higher voltage is required to drive them to full power. So the thing to remember is that no capacitance is getting "wasted." We still have the same amount of energy storage as we would have if all the capacitors were in parallel. It's just that with the series configuration we can drive the output devices with higher voltage (in exchange of less current, but same power). This amp is still a beast and has huge energy reserves that the effective capacitance figure does not reflect. Disclaimer: it's been ages since I have done anything of consequence with analogue circuits ;D |
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Post by audiosanity on May 25, 2013 21:31:12 GMT -5
The caps in the XPA2 have been put in a series parallel combination to reach the desired working voltage and capacitance. I dont' have one to look at the individual cap. ratings so I can't speculate on the exact configuration. But as I noted earlier, this is well understood and perfectly fine to do. Very nicely explained. I'll just add that the thing to remember is that in the end, the stored energy ends up being the same, but with different working voltage and current. |
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Post by repeetavx on May 26, 2013 10:53:34 GMT -5
emotifan,
The answers above are absolutely correct. But if I may, let me try to simplify it.
When two capacitors are "stacked on top of each other" (series) the energy that each one stores has to pass through the other to complete the circuit. This allows the voltage rating of the two capacitors to add together but restricts the current flow. So when you "stack" capacitors you can handle more voltage but it restricts the amount of current (capacitance) it can supply to the device.
When Lonnie and Dan designed the XPA-2 they found that this configuration did what they wanted it to do. Since the XPA-2 is a legendary amp, we can only "wonder" at how they got more from "less".
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