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Old 12th May 2009, 09:52 AM   #81
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Quote:
Originally posted by powerflux
hi, could i also have the EP2500 schematic? i'm about to recieve one with a dead channel

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Did someone send you a schem or do you still need one?
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Old 27th May 2009, 04:44 PM   #82
Dr_EM is offline Dr_EM  United Kingdom
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Quote:
Originally posted by Telstar
Hmm... between the Behringer A500 and the Alesis RA300 which would be the better amp to drive the Low-frequencies?
I'd also like to know this! The Behringer has a little more power it appears, but then some are saying it's capacitor coupled via the supply caps, which arn't that big. Mabye the Alesis is too though?
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Old 27th May 2009, 06:28 PM   #83
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Quote:
Originally posted by Dr.EM


I'd also like to know this! The Behringer has a little more power it appears, but then some are saying it's capacitor coupled via the supply caps, which arn't that big. Mabye the Alesis is too though?
In independent tests the A500 measures about 120/8 and 180/4.

What do you mean by "capacitor coupled via the supply caps"?
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Old 27th May 2009, 08:17 PM   #84
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It seems to me, an input limiter-compressor shown on the schematic was designed by Peavey engineer (Michael, AFAIR) for a bass guitar amp, and may be patented...
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Old 27th May 2009, 08:25 PM   #85
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Quote:
Originally posted by Brett

Did someone send you a schem or do you still need one?

i've got one, but i can confirm that it is exactly the same as the QSC RMX 2450. ok, some components are different, but that does not affect the functioning of the device, only the cost :P

the QSC schematic set is complete, the behringer contains only one channel. so use the behringer for the correct numbering and the QSC for everything else.
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Old 27th May 2009, 08:57 PM   #86
Dr_EM is offline Dr_EM  United Kingdom
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Quote:
Originally posted by Brett
What do you mean by "capacitor coupled via the supply caps"?
From audio asylum link posted earlier:

"maybe it sounds the way it dose because it’s a cap coupled bridge amp…let’s just add up the clues…no center tap off the toroid (single 52 volt rail), the big caps +/- connect to the positive output post, and there is no signal path for bridge mode (in mono channel 2 runs as a current mirror), four power devices."

I can't quite remember how the topology works but it uses a single polarity supply and somehow utilises the storage caps as coupling also. Most modern amps are dual polarity, DC coupled, which I assume is preferable? That said, it measured very flat down to infrasonic frequencies so perhaps it isn't a big problem. I'd only be using it for subs, a good damping factor is nice though!
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Old 27th May 2009, 10:15 PM   #87
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If you actually look at the A500 schematic you'll see it is the same topology used in the EP1500/2500, QSC RMX, and Alesis amps with + and - voltage rails. The output is AC coupled through the power supply caps, but it is not a single rail design.
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Old 29th May 2009, 04:59 PM   #88
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Hi,

Not to be picky but the EP2500 (and QSC RMX 2450) has the transformer center tap connected to speaker output. These amps are consequently DC coupled just as much as a 'normal' topology without output cap.
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Old 29th May 2009, 05:12 PM   #89
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The 2500 does have a center tap. Because the rail voltages are switched on demand, symmetry of the rails cannot be guaranteed without it. With a normal class AB output stage, like the 500 or 1500, a center tap is NOT needed. One could be used if you like.

Without the center tap, the caps do provide AC coupling. But the coupling is inside the feedback loop so it doesn't cause a roll-off in the bass. The input coupling cap actually does this. If the output caps are small, it does affect the clipping behavior at low frequency. And it would do that center tap or no center tap.
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Old 29th May 2009, 05:44 PM   #90
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Hi,

Yes, and you can run a 'normal' output stage without connected centertap as well by the very same reasons as you mention for the flying rail topology.

There is no argue but EP1500 has AC coupled output stage and EP2500 has not. And as you say it does not matter as it is inside the feedback loop. In this case, available power in lower frequencies will depend on power supply capacitance regardless AC coupling or not.
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