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Quote:
Originally Posted by btp /forum/post/12282162


Ack... those higher voltage, high capacitance caps cost an arm and leg.
And I'm sure the more affordable ones are larger in physical size. *sigh*


Interesting how the QSC RMX 1850 with the class H step driver can use 50V caps (18000 uF each), placed between the high rail, the low rail, and ground on both the + and - sides. So even with +/- 88 volt rails, they don't need physically larger and more expensive 100V caps. By contrast, the RMX 1450 uses twin 100V (3300 uF each) caps in parallel on each rail (+/- 78V).


Yeah, upgrading from a PLX 1202 to 1602 or from a 1602 to a 2402 sounds like a better idea than modding a Behringer A500.

RMX 1850

+88v high rail

50v 18000uF cap

+44v low rail

50v 18000uF cap

ground


When the high rail is off, the amplifer draws from

the 44v low rail supply with 18000uF cap.


When the high rail is on, the amplifier draws from

the 88v high rail but now you have two 18000uF caps

in series so total capacitance is really 9000uF.


High rail Joules = 35

Low rail Joules = 17


*******************


RMX 1450

+78v rail

dual 100V 3300uF caps [6,600uf]

ground


Joules = 20



So, the RMX1450 has more energy storage in the caps

than RMX1850's low rail design. /hehe/


P.S. This thread is messy, 16 pages of babble. Where's the mods to move the babble to

another thread ? lol .....................
 

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Good thing i check twice i was about to other 20 of them
 

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Joules... yes... appears your math is correct, Thy. I still can't really wrap my head around that whole grounded collector design QSC uses, though.
Kind of mystifies me, and makes me glad I switched careers and went into software development (instead of electronics).



I was also thinking I should apologize to Chuck for diluting and polluting his thread so badly.
 

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Quote:
Originally Posted by btp /forum/post/12283329


Joules... yes... appears your math is correct, Thy. I still can't really wrap my head around that whole grounded collector design QSC uses, though.
Kind of mystifies me, and makes me glad I switched careers and went into software development (instead of electronics).



I was also thinking I should apologize to Chuck for diluting and polluting his thread so badly.


Grounded collector is intersting so they can connect the transistors directly

to the metal heatsink without mica insulator - for best heat transfer... because

they have a design where the heatsink is touching the grounded chassis.


But PLX and who know what other series doesn't use grounded collector,

the PLX is a standard output stage and they also directly connect the

transistors to the heatsink, this time, the heatsinks are kept floating

with a warning label not to touch them as there is high voltage, hehe
 

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I wonder if the RMX 5050 and F2000TX amps could be tested. Hmm.
 

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I'm sure they could (be tested) if someone provides the samples...
 

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Quote:
Originally Posted by whoaru99 /forum/post/12289630


I'm sure they could (be tested) if someone provides the samples...

Yeah. We need some nice folks to provide some more amps for testing.
 

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qsc rmx 5050 put 93 volts across 2 buttkicker lfe parraleled on each channel before lighting clip light using sine wave of of test cd ... pulled 28 amps from 230 volt service .... my 5050's have their current limits modified from stock
 

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Sold...close to $650...pretty good for who ever got it (although seller had zero feedback)!
 

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Avus... AVS Forum has a filter that doesn't allow links to eBay (and some Amazon links) to be posted.


I was half tempted to snipe that CE4000, just because I was feeling evil.
I'm glad that poor guy finally won. He's bid on every CE4000 on eBay for the past week or so!


Anyway, let's try to get this thread back on track. I've got a new amp on the way now: a QSC CX404. I'm going to use it for my regular speakers. It's a 4 channel amp that is rated 250W into 8 ohms. It does have the PLX style switch mode power supply, but I believe it is a just a regular class AB amp.


Man, I'm so tempted to go buy a 5 gallon bucket and some water heater elements and see what some of these amps will do.
I just don't have anything to measure THD.



Bradley
 

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I took the cover off my XS900 and took some pics.






There is a total of four 4700uf 100V caps and six 1800uf 200V caps. Also, the fans are 70mm, which is a bit different.
 

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Nice pics, Will! Very interesting. The location of the fans is interesting, as well as the 70 mm size. Those 200V caps must be part of the switching power supply, filtering the straight rectified 120 VAC. Also interesting how it's one great big motherboard for power supply and amp. Looks like a clean design. Very nice.


What are you going to be using this amp for? Subwoofer? Bridged or stereo?


If anyone is interested, I can take pictures of the QSC PLX 1202 I have in addition to RMX 2450, RMX 1850, and soon to be in my possession: Crown CE4000 and QSC CX404 (4 channel) amps.
 

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Quote:
Originally Posted by armystud0911 /forum/post/12314290


I love that heatsinking, very nice, loads of caps is always sexy to see as well. How much did you snag that one for?

I like it too! I am very pleased. I got it for $400 new, off ebay. Then Chuck shipped it to me for $23. You can find them on ebay fairly regularly, there are also some in stock on Musicians Friend, new and blemished/b-stock. The PSW Sound Reinforcement classifieds is also one place to look. http://srforums.prosoundweb.com/

And the caps, if it matters at all, are Jamicons (Taiwanese). http://www.icd-sales.com/JamiconProducts.asp

Quote:
Nice pics, Will! Very interesting. The location of the fans is interesting, as well as the 70 mm size. Those 200V caps must be part of the switching power supply, filtering the straight rectified 120 VAC. Also interesting how it's one great big motherboard for power supply and amp. Looks like a clean design. Very nice.

I wish it used 80mm, because the selection of 24VDC 70mm fans is quite limited. But they're strapped down anyway, so if I did anything I'd probably grab a couple of 2pin extensions and do a resistor mod on them and then put the extensions in-line. But no worries, I actually disconnected the fans for now because they aren't particularly quiet. I figured with the house at ~66F and it being used for relatively light duty, I needn't worry. I have it at on top of an old rack so it can breath well. But yes, clean is one of the first things that popped into my head as soon as I took the cover off.

Quote:
What are you going to be using this amp for? Subwoofer? Bridged or stereo?

Subwoofer. It is in bridged mode as we speak, gain knobs full, hooked up to my 15" TC-2000. Using an RCA-XLR cable, Panasonic XR55 receiver LFE out set to 9 (on scale of 0-20). I had to run a ground wire from the chassis of the receiver to the XS900 because there was a ground hum but that cleared it right up. She sounds fantastic.
 

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Discussion Starter #477

Quote:
Originally Posted by Willd /forum/post/12314869


It is in bridged mode as we speak, gain knobs full, hooked up to my 15" TC-2000.

Will:

Read the owners manual. I am not sure that both gain controls are supposed to be wide open. I think I remember reading that only the left channel is supposed to be up. Glad you got rid of the hum! Great.


Chuck


Just checked and the manual it says "NOTE: In Bridge-Mono mode, only the

Channel 1 Level control is functional." So I don't know if having the Channel 2 level control up will affect S/N or not.
 

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Quote:
Originally Posted by chasw98 /forum/post/12327441


Will:

Read the owners manual. I am not sure that both gain controls are supposed to be wide open. I think I remember reading that only the left channel is supposed to be up. Glad you got rid of the hum! Great.


Chuck


Chuck, I think you are correct. I remember reading that same thing in manuals for other amps. I think I recall something along the lines of "to avoid noise being introduced" set the gain of the other channel at 0.
 

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Willd, come on man. One up one down. Get with it man, duh.



Just kidding.
 
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