dcx2496

[DJ Big Ronn]

Just checking a couple things on my limiter. One T-48 per channel, 10ohms, correct?. If so, then 10ohms times 60volts would be 600 watts?

[DJ Big Ronn]

DOH!, i mean 360 watts

[Tom Smit]

Yup, 360 watts.

[DJ Big Ronn]

When i set my limiter at full volume, everything is fine. When I hook the subs back up, the amp will start to clip at high volume. Is this normal?

[Radian]

When you're setting the limiter values and have a meter attached to the outputs of the amp, is the signal coming into the limiter as hot as you'll ever get? If it's not, then that's the most likely culprit. If it's clipping just at the utter peaks of the signal, then you're pretty darn close. Also, are you using pink noise while doing this?

[DJ Big Ronn]

That sounds about right, i just dont understand why it doesn't clip with the meter. I'm using a 60 hz sine wave

[Radian]

What amp are you using?

(edit) It's not clipping with the meter because the load is different. Are you sure that amp is rated for 60V?

[DJ Big Ronn]

oh ok. I didnt realize that it would be a different load with the speaker hooked up. Im using PV-2600's so I dont think theres a problem there. If it wont clip with the meter, but will with the speaker, does that mean that it's getting more power even tho the limiters are set?

[Radian]

Well, now I'm confused too. I wish I was there with ya, then we could hack this out over a couple beers. It just seems like the amp is at it's edge.

Checklist:
- 66V is the max for the amp at 8 ohms
- At 60 Hz, the T48's impedance is 32 ohms
- At anything to the side of that it's 10 ohms
- Is the input signal clipping at all?

I'd fire up one the K2's and my DCX right along with you, but I haven't got a dummy load to throw across the amp in place of a stack of subs to keep from getting visited by the fuzz.

Best Regards,
Radian

[bgavin]

The words aren't working right for me yet.

The amp puts out a given voltage, dependent on the input voltage.
This output voltage is the same, for both open circuit and a speaker load.
The difference is, the open circuit draw is zero watts. I think your 'clip' indicator is probably indicating over current.

Find the lowest impedance (not resistance) in your operating range.
This is the point of highest power draw, and should be used to calculate the limited voltage for your amp.
This is in the 40~50 and 80~90 Hz range for T48.

The amp is stated to be 66v into 8 ohms, or 544 watts capacity.
5.3 ohms is the worst possible case for impedance. This is DCR for the 3015LF driver.
This power limit is 53.7v at worst case impedance.
You can see that guessing incorrectly about the impedance has a huge consequence.

[Radian]

Per the Peavey PV-2600 manual:

"DDT™ ACTIVE LEDS
These indicators illuminate when DDT compression is taking place in the associated channel. With
the DDT ENABLE / DEFEAT switch on the back panel in the ENABLE position, these LEDs indicate
clipping is occurring in the corresponding channel."

"DDT™ (DISTORTION DETECTION TECHNIQUE) SWITCH
This switch is used to enable or defeat the DDT compressor circuitry. It is also a conventional pushpush
type, requiring a small “tool” to activate. The IN position is DEFEAT; the OUT position is
ENABLE. Normally, the DDT function should be enabled to minimize the possibility of either or both
channels going into clipping or overload. With this feature defeated, a severe overload could cause
the mains circuit breaker to trip."

"Peavey’s patented DDT (Distortion Detection Technique) compression circuit enables the sound
technician to maximize the performance of the amplifier/speaker combination by preventing the power
amplifier from running out of headroom (clipping). This compression system is activated by a unique
circuit that senses signal conditions that might overload the amplifier and activates compression
(reduces the channel gain) when clipping is imminent. The threshold of compression is clipping itself,
and no specific threshold control is used. This technique effectively utilizes every precious watt
available for the power amplifier to reproduce the signal, while at the same time minimizing clipping
and distortion. DDT significantly reduces the potential of loudspeaker degradation and damage, and is
the most effective, automatic, hands-off approach to the problem of power amplifier clipping.
Since PV series power amplifiers use a circuit breaker for overcurrent protection, the DDT
compression system plays an even more important role in continuous performance by preventing
each channel from clipping and overload. Continuous operation at clipping can cause the circuit
breaker to trip, but with the DDT activated, this problem is minimized. For this reason, the DDT
compression system should always be enabled."

Have you tried defeating this feature to see if the lights go out? Are you indeed getting 60V across the subs when they're hooked up? What is the wall power doing during this whole charade? Just brainstorming....

[DJ Big Ronn]

Thanks guys, I got to clipping and then backed it off another 10 volts. I'm playing on a Mardi gras float tom. and I'll see how it goes.

[DJ Big Ronn]

You might be on to something Radian. I didnt try to defeat the DDT, but I put it all in the trailer and I'll try next time. Now that you mention it, I was running off of a 50ft ext. cord to my shop and the lights were dimming a lot. I'll retry under better voltage conditions. Thanks !

[DJ Big Ronn]

so i should set limiter at 8 volts or 10 volts?

[Radian]

How was the parade?

I have a hunch. Try repeating your whole procedure using 85Hz and see if you get the same results. I believe what's happening at 60 Hz is that although the impedance of the box is at it's peak, it's most likely also in an area of maximum reactance (a polar impedance plot or oscilloscope would show us in plain sight). Therefore, the box is most likely storing all kinds of reactive power (VAR's) in addition to the real power expended and triggering the DDT. I think in this case, this is going to be your limiting factor, and you have your DCX set optimally.

As far as 8V or 10V, it would be whatever setting is just below that DDT light coming on as that's the amp's signal that you've lost appreciable headroom.