Measuring Amplifiers - Page 16 - AVS Forum
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post #451 of 1918 Old 11-21-2007, 09:50 AM
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Whoareu99: a PLX 3402 should be a pretty good amp for most purposes. 20 Hz-20 kHz 0.05% THD 1100W into 4 ohms stereo. Not too shabby! If I already had one of those, I probably wouldn't have bothered to go for the CE4000.

For sub CE4000 > PLX

For mains, the PLX is probably a better amp as it was
burst tested at 5kw by someone on the prosound forum.
I use four PLX3402 for mains in bridged mode, it's amazing.



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post #452 of 1918 Old 11-21-2007, 10:05 AM
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[quote=btp;12275615]
OK, so looks like I am going to wind up with two CE4000's now. If anyone reading this thread wants one RIGHT NOW, send me a PM and maybe I can have it shipped directly to you.

So you were one of the guys outbidding me!. You won both of the amps?
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post #453 of 1918 Old 11-21-2007, 10:38 AM
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If "both" means the two CE4000s that were from the Las Vegas seller and ended about the same time, then no. I only got one of them. The first CE4000 was a Buy It Now auction I grabbed over the weekend. Both amps should be on their way to me shortly.

By the way, you see that last CE4000 auction that ended? Went for $655 plus $50 shipping!

Back on the low-power, low-dollar track... I'm half tempted to pick up a Behringer A500 just to toy around with it, maybe upgrading the power supply caps and rectifier diodes. But it seems silly to do that without testing the results before and after, so that means I'll have to get semi-serious about the tools and methodology to test power amps.

Another amp that's interesting is the American VLP-600, rated at 200W into 8 ohms stereo. It sells for around $200 and might be worth fiddling around with if the power supply has more capacity than the A500 and others in the $200 range.

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post #454 of 1918 Old 11-21-2007, 11:59 AM
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Question... looking at the Bink test results, I am wondering why the PLX 1602 did so poorly at 20 Hz. 357 watts compared to 553 at 1 kHz. Is this a limitation of the power supply? If that's the case, I'm a little puzzled as to why QSC's "Powerlight" SMPS would not be up to the task.

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post #455 of 1918 Old 11-21-2007, 12:29 PM
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Quote:
Originally Posted by btp View Post

Question... looking at the Bink test results, I am wondering why the PLX 1602 did so poorly at 20 Hz. 357 watts compared to 553 at 1 kHz. Is this a limitation of the power supply? If that's the case, I'm a little puzzled as to why QSC's "Powerlight" SMPS would not be up to the task.

Random babble.

1. There is no amps on Binks test where the 20hz
power was equal to or greater in power
than the 1khz test @ 1% THD reference. So, QSC is not
alone, everyone seems to suffer. lol

2. The problem is magnified when you do a 96VAC line
sag test and you can now see that the PFC based
amplifiers did much better than non-PFC, those PFC
amps are; CE4000, 8002, PL6.0 PFC, PL9.0PFC, I don't
think there is anymore PFC amps on the binks list.

3. Traditionally, a standard power supply [60hz transformer] needs a big capacitor array to store
energy for better low frequency performance, that's
why those big and expensive home amps have big
cap arrays - but those amps are usually rated for less
power @ 8 ohms, hence it's easier to design a low
powered amp that 'doubles down' vs. a high powered amp
that 'doubles down' in power.

4. The QSC Powerlight is a marketing name for their
switch mode power supply design [SMPS]. SMPS allows
you to make a power supply using a smaller transformer,
and less power supply capacitors because the switching
frequency is much higher than 60hz, it can be anywhere
from 50,000hz to lets say 300,000hz. I think QSC's operates in the 200khz range. Now your capacitor bank is
being refreshed sooner than the 60hz design, so you don't
need alot of capacitance to do the same job.
... it's smaller
... it weighs less
... it's cheaper as you don't need big azz 60hz transformers
... it's more efficient
... it's more complicated to design, you need a few
IC's and some form of power transistor(s) to switch the
transformer.
... and it should cost alot less right? nope, the marketing
people charge more for SMPS amplifiers ... ROFL ....

[think computer power supply and how cheap they are,
yet powerful]

5. QSC amps have a lower power rating at 20hz than
the 1khz, so you have to look at the specs closely.

6. QSC's SMPS is nice, but the source of power still comes from the
AC wall outlet which is 60hz.

This is the block diagram for a conventional power
supply design.

AC input {50/60hz} -> big transformer -> rectifier -> cap -> smoothed DC voltage.

For SMPS, you delete the big transformer so it's like so;

AC input {50/60hz} -> rectifier -> cap -> smoothed DC voltage.

You take that smoothed DC and now you connect it
to the power transistors that drive the new smaller
transformer.

As you can see, in both designs, they both suffer with
the fact that the smoothed DC voltage is not regulated,
and the capacitors on that input side 'should be' oversized
to get better low end performance.

That's why the PFC design is just so superior to both
the methods above, but it's more complicated.



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post #456 of 1918 Old 11-21-2007, 12:37 PM
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I'm half tempted to pick up a Behringer A500 just to toy around with it, maybe upgrading the power supply caps and rectifier diodes.

I started a thread a long time ago on another forum as
I saw that there was alot of extra room inside that amp
for cap upgrades. I would look into surplus electronics and
try to find some deals as you don't want to spend alot of
money upgrading the amp, for instance, if the amp cost $200
and the caps ended up costing you $100, it's not worth it.
I had some sources for cheap caps, but the supply is variable.
You need to find out what the unloaded DC voltage is and size
up some caps. It would be a nice project but the A500 is still
limited by the transformer, output stage, etc.



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post #457 of 1918 Old 11-21-2007, 01:49 PM
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Good points, most of which I have considered. If I buy a A500, it would be for $150, and I wouldn't want to spend more than $50 or so modding it. I was also going to check on capacitor prices before making any purchases.

Curiosity is getting the best of me: do you think that PLX 1602 could benefit from larger caps and/or other tweaks to the SMPS?

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post #458 of 1918 Old 11-21-2007, 02:18 PM
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Quote:
Originally Posted by btp View Post

Good points, most of which I have considered. If I buy a A500, it would be for $150, and I wouldn't want to spend more than $50 or so modding it. I was also going to check on capacitor prices before making any purchases.

Curiosity is getting the best of me: do you think that PLX 1602 could benefit from larger caps and/or other tweaks to the SMPS?

I've done PLX3402 capacitor experiments using capacitors that are huge and would never fit inside the chassis.

There is two places to upgrade the caps, the input side
and the SMPS output side. I've done both and
I was able to measure a more stable v-rail voltage under
transients, but hearing voltage rail sag isn't so easy,
I don't think I would pass the ABX test with a stock PLX
vs. heavily modded one. I did start to design a PCB with
connector to add more power supply capacitors to the
output SMPS of the PLX amps, there is a nice location for
this upgrade inside, but these mods cost money, take time,
and in the end will it be audible? While it's a nice electronics
project to try out and do, in the end that project is on hold
because I have better things to do with cash. lol ......

You can read about the PLX cap quest here;
You will find broken links as that is an old post.
http://www.caraudioforum.com/vbb3/sh...hlight=PLX3402

Keep in mind that QSC PLX series and PL2 series seem
to share a common circuit board, perhaps this is true
for certain older models as well. It makes sense to reduce
costs - one PCB -- does all .. hehe

What you can do that is sweeter is snag the PLX2402
amp vs. PLX1602 amp -- because --

1. PLX2402, PLX3002, PLX3402 are class H, so you
have the dual +V and dual -V rails inside, the only
difference *per QSC schematics* is ;

a. I don't see anything obviously different from PLX3002
vs. PLX3402, but armyguy had a problem running a PLX3002 into an abormal load like I run my PLX3402's, so
we haven't figured out that mystery.. Maybe the 3002
are calibrated different?

b. PLX2402 schematic shows they removed 2 power supply
input caps [total of 6 in the design, 2200uF each].

Typically, the rail voltage is the big player in power output
and I've noticed that the PLX3402 schematic shows
+/-117v but my amps measure +/-130v.... So, they also
show 117v for all those three models which is weird, maybe the schematic is in error, I'd expect the lesser models to have reduce rails as they are rated for less power.

PLX1202 and PLX1602 per schematic and published spec is where they
removed the class H power supply, there is only a single
+V and single -V rail, plus they further reduce the input
and SMPS output caps.

For driving 8 ohm HT speakers with high headroom,
the PLX2402 is probably the sweet spot as you probably
will have a hard time differentiating this amp from
the PLX3002 or PLX3402 if you have an easy loudspeaker to
drive. This is my guess.

What is the price difference between PLX1602 vs. PLX2402
on the used market? If the price isn't that much more,
then snag the 2402 to get the class H circuitry which is
alot more helpful than doing capacitor updrades.



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post #459 of 1918 Old 11-21-2007, 02:36 PM
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I bought my caps from surplussales

Example of costs.
http://www.surplusales.com/Capacitor...-300000uF.html

Lets assume that the capacitors will fit inside the small amplifier
chassis.

A 12,000uF 75V capacitor cost $17 and measures 3" x 4"

You need two of them, one for +V, one for -V. That probably
$50 with shipping, etc.

I'm going to take a wild guess and say the A500 has 3300uF
caps, see pic;
http://home.pacbell.net/lordpk/proam...ger_A500-2.jpg

Seems like 100V rating, but I highly doubt the A500 has
> 75V rails.

Adding 12kuF more is nice, that is 3.6x more capacitance than
stock.

What is a good number? I think 10,000uF per rail is nice for
an A500 caliber amp. I consider this the starting point. If the
chassis were bigger, I'd probably double it. If the output stage
was beefier and there is a bigger transformer, I would try to
get into the 40,000uF or greater capacitance range. That is
what they do in the higher priced home amps.

Tight fit?
http://home.pacbell.net/lordpk/proam...ger_A500-1.jpg

Or you can locate 3000uF caps and parallel the smaller ones
and cram them inside the chassis.

http://www.surplusales.com/Capacitor...F-99999uF.html



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post #460 of 1918 Old 11-21-2007, 03:15 PM
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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.

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post #461 of 1918 Old 11-21-2007, 04:18 PM
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Quote:
Originally Posted by btp View Post

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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post #462 of 1918 Old 11-21-2007, 04:25 PM
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Overstock.com has CE4000's on sale for $119

http://www.overstock.com/Home-Garden...cid=93896&fp=F


















// lol //
// hehe //



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post #463 of 1918 Old 11-21-2007, 04:59 PM
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Good thing i check twice i was about to other 20 of them

Warning to prevent risk of injuries, you should always be smarter than the equipment you are about to use.
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post #464 of 1918 Old 11-21-2007, 06:00 PM
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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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post #465 of 1918 Old 11-22-2007, 10:18 AM
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Quote:
Originally Posted by btp View Post

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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post #466 of 1918 Old 11-22-2007, 12:59 PM
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I wonder if the RMX 5050 and F2000TX amps could be tested. Hmm.

...
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post #467 of 1918 Old 11-22-2007, 04:42 PM
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I'm sure they could (be tested) if someone provides the samples...

Just because there is a knob doesn't mean you should turn it.
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post #468 of 1918 Old 11-22-2007, 06:32 PM
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Quote:
Originally Posted by whoaru99 View Post

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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post #469 of 1918 Old 11-25-2007, 01:33 AM
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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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post #470 of 1918 Old 11-25-2007, 02:59 PM
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There's a CE4000 on ebay right now about to end for only $600.

http://cgi.*********/ws/eBayISAPI.dl...MEWA:IT&ih=001

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

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post #472 of 1918 Old 11-25-2007, 09:29 PM
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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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post #473 of 1918 Old 11-25-2007, 10:29 PM
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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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post #474 of 1918 Old 11-25-2007, 10:49 PM
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I love that heatsinking, very nice, loads of caps is always sexy to see as well. How much did you snag that one for?
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post #475 of 1918 Old 11-25-2007, 10:50 PM
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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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post #476 of 1918 Old 11-26-2007, 02:10 AM
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Quote:
Originally Posted by armystud0911 View Post

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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post #477 of 1918 Old 11-27-2007, 09:13 AM - Thread Starter
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Quote:
Originally Posted by Willd View Post

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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post #478 of 1918 Old 11-27-2007, 09:15 AM
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Originally Posted by chasw98 View Post

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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post #479 of 1918 Old 11-27-2007, 09:18 AM - Thread Starter
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I just edited my post and quoted the manual.
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post #480 of 1918 Old 11-27-2007, 09:19 AM
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Willd, come on man. One up one down. Get with it man, duh.


Just kidding.
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