Limiter Settings - Advanced

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geoffwarner1
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Limiter Settings - Advanced

#1 Post by geoffwarner1 »

Hey Guys,

Ive been reluctant to turn up my T48 until I got my limiter set correctly, so anyway, I just got my QSC GX5 amp and DCX2496 and Greenlee CM-450 TrueRMS voltmeter.

Ive been testing the voltage at the back of the amp (banana plugs, since I cant get my prongs into the speakons). Ive been able to get the voltage to 57 using a 100hz sine wave (Any louder and my ears would explode. However, my clip light comes on at around 28 volts, which is odd because it shouldnt be clipping at that low of voltage. Whats going on here? Is it really clipping or not?

According to the calculations on http://www.poulpetersen.dk/gblimthc.html, I should be at 450watts @ 67volts with a 10ohm load such as the Titan. (I know the driver is 8ohms, but everyone says use 10 because of the horn..is that right?)

That website is telling me to set the limiter threshold to 2.55 dBu, but with the DCX2496 I can only set to "negative" dBu. I must be confusing myself?

Any help you can provide me to answer these questions and help me figure out my Threshold setting on my DCX would be greatly appreciated!

-Geoff
(2) Titan 48s / 3015LF / 24"
(2) DR200s / Crossfired

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LelandCrooks
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Re: Limiter Settings - Advanced

#2 Post by LelandCrooks »

geoffwarner1 wrote:Ive been testing the voltage at the back of the amp (banana plugs, since I cant get my prongs into the speakons). Ive been able to get the voltage to 57 using a 100hz sine wave (Any louder and my ears would explode. However, my clip light comes on at around 28 volts, which is odd because it shouldnt be clipping at that low of voltage. Whats going on here? Is it really clipping or not?

-Geoff
The amp wattage is rated at 1k tone. Test with no speaker connected. Solid state amps don't need a load connected to set like an old tube amp does.
If it's too loud, you're even older than me! Like me.
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bgavin
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Re: Limiter Settings - Advanced

#3 Post by bgavin »

The GX5 has a gain of 34.4 dB for an input sensitivity of 1.2v. This should yield about 63v maximum output voltage from a 1.2v input signal.

When driven to clipping, this amp reduces the rail voltage to curtail power output. This probably accounts for the reason you are not seeing full output voltage.
My biggest worry is that when I'm dead and gone, my wife will sell my toys for what I said I paid for them.

geoffwarner1
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Re: Limiter Settings - Advanced

#4 Post by geoffwarner1 »

bgavin wrote:When driven to clipping, this amp reduces the rail voltage to curtail power output. This probably accounts for the reason you are not seeing full output voltage.
Which Means?
(2) Titan 48s / 3015LF / 24"
(2) DR200s / Crossfired

Sydney

Re: Limiter Settings - Advanced

#5 Post by Sydney »

There is basically an electronic governor that cause the Power Supply to drop the voltage to drop power to protect the amp.

geoffwarner1
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Re: Limiter Settings - Advanced

#6 Post by geoffwarner1 »

So, Im quite sure I have my DCX2496 Limiter setup perfect, Id just like to verify with everyone before proceed:

Limiting the BFM Titan 48 Subs to 60v (450w@ 8 ohms):
1. Turn amp gains all the way up.
2. Attach a TrueRMS voltmeter to the banana outputs (red/black) on the back of the amp (QSC GX5) with no speaker or load attached.
3. Start playing a 100hz sine wave sound source from a sound/freq generator.
4. Observe voltage, then raise the volume and/or gains until the voltage reads a steady bit over 60v, I used 65v.
5. Bring Limiter Threshold value down until the voltage stays constant at 60v.
6. Store the changes on your DCX and your done.

The Limiter Threshold that I got was -18.5dB for subs

Limiting the Yamaha S112IV Tops to 34v (150w @ 8 ohms):
1. Turn amp gains all the way up.
2. Attach a TrueRMS voltmeter to the banana outputs (red/black) on the back of the amp (AB International 600A) with no speaker or load attached.
3. Start playing a 1000hz sine wave sound source from a sound/freq generator.
4. Observe voltage, then raise the volume and/or gains until the voltage reads a steady bit over 34v, I used 40v.
5. Bring Limiter Threshold value down until the voltage stays constant at 34v.
6. Store the changes, apply to both channels on your DCX and your done.

The Limiter Threshold that I got was -20.3dB for tops

Experts...Please let me know if this is the correct way to do it and it will work well!
(2) Titan 48s / 3015LF / 24"
(2) DR200s / Crossfired

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thijs666
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Re: Limiter Settings - Advanced

#7 Post by thijs666 »

The Limiter Threshold that I got was -18.5dB for subs...
...The Limiter Threshold that I got was -20.3dB for tops.
Yeah, they do that... The DCX can put out about +22dBU, which is far too much for most amps in my belief. If you set the limiter to 0dB it means the DCX will limit it's output at about +22dBU, so there you go. Substract 18.5 for the subs and you get about +3.5dBU when limited. Idem for the tops.

I thought this didn't help getting a better S/N-ratio, so I cranked open my DCX and altered it's output stages. I 'improved' my S/N-ratio by about 10dB this way. The limiter for my subs is now at -5.6dB (for 60V with a Peavey PV-2600) and for the tops at -9.9dB to get about 40V for my DR200's (with BP4078 amp modules from Coldamp), so I guess you're quite right with your settings.

Just to be sure: you set the gain on your amps to max when you dialed in the limiter? That way your system's safe even when some dickhead turns the gain on the amps to their max 'just for fun' :x
BF cabs built to date:
2x T48 21" 3015LF; 1x T48 24" 2xBP102; 1x DR250 2510 loaded, cross firing; 4x DR200 Beta 8, melded array; 1x TT HL-10c; 2x WH Beta 8, melded 'array'; 3x AT 15" Tang Band W8-740P; 1x AT 15" JBL GTO1014

geoffwarner1
Posts: 92
Joined: Fri Sep 05, 2008 4:56 am

Re: Limiter Settings - Advanced

#8 Post by geoffwarner1 »

thijs666 wrote:
Just to be sure: you set the gain on your amps to max when you dialed in the limiter? That way your system's safe even when some dickhead turns the gain on the amps to their max 'just for fun' :x
I sure did :) Thanks!
(2) Titan 48s / 3015LF / 24"
(2) DR200s / Crossfired

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AntonZ
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Re: Limiter Settings - Advanced

#9 Post by AntonZ »

thijs666 wrote:I cranked open my DCX and altered it's output stages
Did you take notes of what you changed Thijs? I may purchase a DCX at some point and would like to apply that modification when time (and budget :oops: ) comes.

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thijs666
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Re: Limiter Settings - Advanced

#10 Post by thijs666 »

AntonZ wrote:
thijs666 wrote:I cranked open my DCX and altered it's output stages
Did you take notes of what you changed Thijs? I may purchase a DCX at some point and would like to apply that modification when time (and budget :oops: ) comes.
Eh, no, I didn't take notes, but it's very easy and will cost you only 0.30 eurocents or so (.10 for each resistor :wink: , I changed only 3 outputs and left the other 3 alone). But I can open up the DCX at anytime and make pics if you like. But that needs to be on another thread, I suppose :lol:.
BF cabs built to date:
2x T48 21" 3015LF; 1x T48 24" 2xBP102; 1x DR250 2510 loaded, cross firing; 4x DR200 Beta 8, melded array; 1x TT HL-10c; 2x WH Beta 8, melded 'array'; 3x AT 15" Tang Band W8-740P; 1x AT 15" JBL GTO1014

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thijs666
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Re: Limiter Settings - Advanced

#11 Post by thijs666 »

thijs666 wrote:
AntonZ wrote:
thijs666 wrote:I cranked open my DCX and altered it's output stages
Did you take notes of what you changed Thijs? I may purchase a DCX at some point and would like to apply that modification when time (and budget :oops: ) comes.
Eh, no, I didn't take notes, but it's very easy and will cost you only 0.30 eurocents or so (.10 for each resistor :wink: , I changed only 3 outputs and left the other 3 alone). But I can open up the DCX at anytime and make pics if you like. But that needs to be on another thread, I suppose :lol:.
Click here for that 'other thread'.

Regards,
Thijs
BF cabs built to date:
2x T48 21" 3015LF; 1x T48 24" 2xBP102; 1x DR250 2510 loaded, cross firing; 4x DR200 Beta 8, melded array; 1x TT HL-10c; 2x WH Beta 8, melded 'array'; 3x AT 15" Tang Band W8-740P; 1x AT 15" JBL GTO1014

gdougherty
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Re: Limiter Settings - Advanced

#12 Post by gdougherty »

Okay, so I now have a TrueRMS limiter and finally got around to pulling the amp rack and hooking it up to reset my limiters.
I did exactly the same thing as described here except I left the amp gains down a bit where I've found that the "quiet" noise out of my EQ's isn't annoying in a quiet room. For the subs I passed a 60Hz sine wave and for tops and monitors I used a 100Hz sine. My limiter values as I'd expect were higher than noted and I saved everything as good. I limited to 60V on the subs, 38V on the tops and 28V on the monitors.

I then hooked up a wedgehorn to a monitor channel and played some music through them. The meter was reading as high as 13V, an SPL meter at ear level about two feet behind the monitor (~6ft on angle from the monitor) read peaks of 98db and the limiters were kicking in on the peaks.

I'm just running a little PLX1202 for monitors but it seems like I should be getting more out of these when I'm hitting the limiters. If they're really getting only ~13V then they should be perfectly safe but they're also only getting about 20W and could easily handle more for a little more headroom.

Greg Plouvier
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Re: Limiter Settings - Advanced

#13 Post by Greg Plouvier »

geoffwarner1 wrote:Hey Guys,

Ive been reluctant to turn up my T48 until I got my limiter set correctly, so anyway, I just got my QSC GX5 amp and DCX2496 and Greenlee CM-450 TrueRMS voltmeter.

Ive been testing the voltage at the back of the amp (banana plugs, since I cant get my prongs into the speakons). Ive been able to get the voltage to 57 using a 100hz sine wave (Any louder and my ears would explode. However, my clip light comes on at around 28 volts, which is odd because it shouldnt be clipping at that low of voltage. Whats going on here? Is it really clipping or not?

According to the calculations on http://www.poulpetersen.dk/gblimthc.html, I should be at 450watts @ 67volts with a 10ohm load such as the Titan. (I know the driver is 8ohms, but everyone says use 10 because of the horn..is that right?)

That website is telling me to set the limiter threshold to 2.55 dBu, but with the DCX2496 I can only set to "negative" dBu. I must be confusing myself?

Any help you can provide me to answer these questions and help me figure out my Threshold setting on my DCX would be greatly appreciated!

-Geoff
Set limiters without speakers connected
Greg Plouvier
http://www.magnumcaseworks.com
Protective casing, speaker cabinets, Colorado BF builder, A/V installation, sales, live sound

Greg Plouvier
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Re: Limiter Settings - Advanced

#14 Post by Greg Plouvier »

gdougherty wrote:Okay, so I now have a TrueRMS limiter and finally got around to pulling the amp rack and hooking it up to reset my limiters.
I did exactly the same thing as described here except I left the amp gains down a bit where I've found that the "quiet" noise out of my EQ's isn't annoying in a quiet room. For the subs I passed a 60Hz sine wave and for tops and monitors I used a 100Hz sine. My limiter values as I'd expect were higher than noted and I saved everything as good. I limited to 60V on the subs, 38V on the tops and 28V on the monitors.

I then hooked up a wedgehorn to a monitor channel and played some music through them. The meter was reading as high as 13V, an SPL meter at ear level about two feet behind the monitor (~6ft on angle from the monitor) read peaks of 98db and the limiters were kicking in on the peaks.

I'm just running a little PLX1202 for monitors but it seems like I should be getting more out of these when I'm hitting the limiters. If they're really getting only ~13V then they should be perfectly safe but they're also only getting about 20W and could easily handle more for a little more headroom.
I'm assuming you meant 1000Hz for the tops and mons?
Greg Plouvier
http://www.magnumcaseworks.com
Protective casing, speaker cabinets, Colorado BF builder, A/V installation, sales, live sound

gdougherty
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Re: Limiter Settings - Advanced

#15 Post by gdougherty »

Greg Plouvier wrote:
gdougherty wrote:Okay, so I now have a TrueRMS limiter and finally got around to pulling the amp rack and hooking it up to reset my limiters.
I did exactly the same thing as described here except I left the amp gains down a bit where I've found that the "quiet" noise out of my EQ's isn't annoying in a quiet room. For the subs I passed a 60Hz sine wave and for tops and monitors I used a 100Hz sine. My limiter values as I'd expect were higher than noted and I saved everything as good. I limited to 60V on the subs, 38V on the tops and 28V on the monitors.

I then hooked up a wedgehorn to a monitor channel and played some music through them. The meter was reading as high as 13V, an SPL meter at ear level about two feet behind the monitor (~6ft on angle from the monitor) read peaks of 98db and the limiters were kicking in on the peaks.

I'm just running a little PLX1202 for monitors but it seems like I should be getting more out of these when I'm hitting the limiters. If they're really getting only ~13V then they should be perfectly safe but they're also only getting about 20W and could easily handle more for a little more headroom.
I'm assuming you meant 1000Hz for the tops and mons?
Nope, 100Hz. The RMS multimeter is only good up to 500Hz for True RMS readings and I was more interested in limiting the destructive low frequencies. I probably should try it again with a higher frequency. In truth, I haven't been running them with a limiter since I typically run enough cabinets that I'm not pushing them too hard. The monitors are cut with a Linkwitz-Riley 48db/oct HP filter at 100Hz to match the tops and if there's any distortion from them it's time to back them down.

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