PV2600 + DDT

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Dayleclarke
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PV2600 + DDT

Post by Dayleclarke » Sat Apr 16, 2016 7:22 am

Hi all,

I have a query about my PV2600 amp and DDT.

Basically my PV2600 has always ran 2x Peavey Pro Subs in the pub where I Dj every Saturday. The gain is never above halfway and have always noticed the DDT function start to operate when the master output on my mixer is between 1/2 and 3/4, which has always been fine.

I've just taken delivery of a Cerwin Vaga AB-36CX to replace the Pro Subs. The Cerwin Vega bin is a folded horn with a 8ohm, 18inch driver, 4"magnet rated at 800watts RMS, 1600watt peak. So naturally I though my PV2600 would power it fine in bridge mode without pushing too hard.

So I've simply enabled bridge mode and connected the new bin in place of the old Pro Subs, however the DDT function seems to engage when ran at the exact same levels as the Pro Subs which I didn't expect. So I dissengaged bridge mode and returned to stereo mode and again, DDT engages when master output on the mixer is around 3/4 up, the amp gain is half way and my new bin connected to channel A

The PV2600 is rated at 2x550w RMS at 8ohm or 1x1800w RMS at 8ohm bridged. So why is the DDT engaging in both modes at the same input levels? Surely the DDT should engage a lot earlier in bridge mode for the same given Input levels? And surely the bassbin is capable of handling pretty much anything the amp can supply in stereo mode?

Is it safe to push well into DDT if the speaker isn't distorting? Or is it reccomended to disable DDT and buy a half decent limiter?

Other equipment include:
Behringer mixer (with gains never in the red)
Pioneer XDJ-1000 x2
KRK Rokit monitor
JBL MPX1200 and unbranded speakers for mids/highs

The PV2600 is always ran with crossovers and low cut filters engaged as the crossovers in the Pro Subs have up years ago.

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Wooferhound
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Re: PV2600 + DDT

Post by Wooferhound » Sat Apr 16, 2016 8:23 am

Switching to bridge mode requires you to rewire the speaker wires to the amp outputs.
in stereo mode the speakers connect normally to the output terminals on the amp, red to red, black to black
in bridge mode there will be only 2 speaker wires and they both connect to the Red Terminals on the amp, or if you have a newer model of the amp the wire needs to replug into the Bridge Speakon connector.
Bridge mode of 1800 watts into a speaker rated at 800 watts is asking for a toasted speaker.

DDT is a limiter, but a compressor limiter will help you control and protect the whole system better.
Running with the DDT lights on the majority of the time compresses the signal and increases Program power to the speakers, plus compressed music has no life to it.

And Doubling the wattage of an amp does not get you double the volume, in order to double the volume you will need 4 to 10 times the watts.

To get loud like you want will require a bigger Amp and speaker system . . .
----- W o o f e r h o u n d -----

Dayleclarke
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Re: PV2600 + DDT

Post by Dayleclarke » Sat Apr 16, 2016 8:57 am

Sorry I should've specified, the speakon connectors are connected into the correct ports on the amp according to which mode the amp was in. I.e stereo mode=channel a and bridge mode=bridge channel.

I understand 1800 watts into a 800 watt rated speaker is not a good idea, but the gain on the amp is never more than 1/2. I read somewhere when I was buying the amp that pa amplifiers should be more powerful than the speakers they push to prevent the amps overheating/failing.

I was simply curious as to why the DDT function activates at the same input levels, regardless of the power handling of any connected speaker. In stereo mode the DDT lights flash with the same input level as bridge mode. Stereo mode is rated at 550watts RMS but the speaker is rated at 800watts RMS, so why does the amp think the speaker will distort when the amp in not capable of providing power in stereo mode close to what the speaker can handle?

Even without any speaker/load connected the DDT lights will still flash on loud bass frequencies. How can the amp detect possible distortion if there's no speaker connected?

Excuse my ignorance, I'm no sound engineer, I'm fairly new to all this.

The Cerwin Vega AB-36 is one of the most powerful single 18 inch subwoofers I could find. I plan to add at least one more when I can afford it.

The manufactur's specs can be found here...
http://www.cerwinvega.com/pro-audio/fol ... b-36c.html

They suggest power to between 1200-1600watts. I'm not sure if they mean peak or RMS?

Josjor
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Re: PV2600 + DDT

Post by Josjor » Sat Apr 16, 2016 11:28 am

Dayleclarke wrote:

Even without any speaker/load connected the DDT lights will still flash on loud bass frequencies. How can the amp detect possible distortion if there's no speaker connected?
Because distortion/clipping doesn't just happen at the speaker. It can also happen in the signal path.

You didn't mention what Behringer mixer you have, but does it have the following features:
1. Channel input gain
2. Channel clip light
3. A solo/PFL function

If the answer is "yes" then do this simple demonstration to hear distortion/clipping in the signal path so you will understand that it can happen without speakers attached.
NOTE: DO THIS WITHOUT THE POWER AMPLIFIER. We don't want to fry anything. :D

Plug an input source into a channel on your mixer and select a good thumpin' bass track.
Crank up the input gain on that channel until the clip light is either flashing a lot or even fairly steady.
Select the SOLO/PFL button on that channel and listen to it through your headphones.

That nasty-ass sound you're hearing is distortion/clipping and it's happening there at the channel in this case.

Have you tried it with the inputs on the PV2600 all the way clockwise?
www.yandasmusic.com
Don't believe me. I'm just guessing.
Neutiquam Erro

Dayleclarke
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Re: PV2600 + DDT

Post by Dayleclarke » Sat Apr 16, 2016 11:42 am

The mixer is a DDM4000.

Ah I didn't know distortion can happen in the signal path. I'll try it tonight at work.

And no haven't tried it with the gain fully clockwise, I didn't want to work the amp that hard. I will try that too.

Thanks for the advice, it's much appreciated.

Josjor
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Re: PV2600 + DDT

Post by Josjor » Sat Apr 16, 2016 12:33 pm

The input knob on the front doesn't make the amp work more or less. In fact, it doesn't change how much power the amplifier is capable of putting out. What it does is adjust how much input voltage is needed before the amp will put out it's max power.
Turn the knob down = more input needed from the mixer to get full power.
Turn the knob clockwise = less input needed from the mixer to get full power.
www.yandasmusic.com
Don't believe me. I'm just guessing.
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Dookie
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Re: PV2600 + DDT

Post by Dookie » Sat Apr 16, 2016 7:40 pm

There is a lot going on here. Your PV Pro Sub's are 4 ohms each.

http://www.thomann.de/gb/peavey_prosub_ ... _serie.htm


Part of the input voltage needed for the amp to reach full output is the load the amp sees. The amp will need less input voltage with an 8 ohm load to reach full output and more input with a 4 or 2 ohm load. Also note a amp "sees" a load different when in bridge mode. A single 8 ohm speaker looks like a 4 ohm load per channel when your amp is bridged. Your amp gives 900 watts per channel at 4 ohms or 1800 watts 8 ohms bridged. The 2 , 4 ohm loads combined.

Knowing this its easy to see how the input is close to the same for your 2 sub setups. Also the impedance is rated as "nominal" or average. There could be peaks and dips in these sub's impedance that the amp sees.
I'm betting your starting to give 1800 watts peak to you CV sub when the DDT starts to hit.

Doug

Marty McCann
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Re: PV2600 + DDT

Post by Marty McCann » Tue Apr 19, 2016 2:48 pm

Visit the Tech Notes section and read. Search for my name and articles I have written.

Although this forum is intended to respond to questions, it is in no way intended to be a complete tutorial on pro audio.

audiophiliac
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Re: PV2600 + DDT

Post by audiophiliac » Sun May 07, 2017 12:11 am

I would look at the problem this way:

The posts above tell me the amplifier load has been changed from 4 ohms to 8 ohms per channel

The Peavey PV2600 specs tell me the power output will reduce from 900 watts to 550 watts

This means you cannot achieve the same volume level (SPL) as previously

To offset the reduction in power you have selected bridge mode

This then presents a load of 4 ohms per channel section = as previously

The PV2600 specs say power output in bridge mode is 1800 watts into 8 ohms, so there is no loss of power

Of course you will need two amplifiers - one for the subs and one for the remainder of the system

BUT

You have changed two critical elements in your system

You have changed to bridge mode, which places the amplifier filter capacitors in series, effectively halving their value and thereby reducing LF response in the lower range below 100 Hz where you want your subs to perform compared to the rest of your system

You have changed the speakers to folded horns, which will have a reduced LF response in that same critical range as to your Peavey subs

So by changing subs you have reduced the LF response of your whole system

Then there is the question of speaker SPL. The Cerwin Vega AB-236 C specs say the speaker system delivers an SPL of 108 db but is - 3db at 40 Hz and -10 db at 33 Hz

The bottom E on a bass guitar is at approx 40 Hz so if that is your signal then you need twice the power at 40 Hz as at say 100 Hz

This linked report shows a 10 db difference between 40 and 60 Hz despite the useable range being relatively flat response - which is very good overall

http://www.djchat.com/showthread.php/14 ... ve-(Fixed)

Then there is the question of the ACTUAL load impedance presented to the amplifier

This can be anywhere between 6 ohms and 100 ohms, depending upon the speaker type and construction and signal frequency - despite the label saying 8 ohms. In the case of program signals the actual load is complex and continuously changing

This can be seen at http://audioroundtable.com/forum/index. ... goto=28193

This page also shows the Cerwin Vega L36 enclosure response - assumed to be similar to yours

You mentioned you always use low cut filters engaged

This will of course reduce the bass from 150 Hz and above as described in the PV2600 user manual

One other possibility in performance is that the Cerwin Vega bins will deliver negligible harmonics, because the sound is reflected from the rear of the cabinet. This will very likely cause the bass signal to be undefined and softer sounding than a direct radiating speaker

Hence if your primary system speakers do not cover the range down to 150 Hz there will be a gap in the response in the critical range for music signals and voice, which has the effect of the system sounding less loud. That issue cannot be fixed by an EQ or by cranking up the power

In the issue of master volume control levels and DDT, much depends upon where in the system the master control is located

If the amp control is set too low the preamp may overload so its compression light (if it has one) will light up

If the preamp signal output is set too high the amplifier DDT light will light up when the input signal level reaches the automatic preset internal DDT activation level

1800 watts rms into 8 ohms delivers a current into the speaker line of 15 amperes rms. Peak currents are higher. Adequate cable cross section is essential to prevent power losses in the cables, which can be as high as 50% of amplifier output. At that power level there will be 120 volts rms across the output terminals

1800 watts into 4 ohms is worse, delivering 21 amperes rms through the cables.

Total cable DC resistance - both halves added together. One ohm of total cable resistance - there and back - results in a power loss of 225 watts rms at 8 ohms or 441 watts rms at 4 ohms

So it may be that your new system is less efficient overall than before, requiring more power from the amplifier

Need more information to unravel your system

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