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Ampeg SVT3 Pro PREAMP OUT Balanced or Unbalanced? NEED A DEFINITETIVE ANSWER QUICK!!!

#122
Wasnex said:
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It's all fun & games until a trucker drives by the venue and keys up the 500 watt lin-yar amp on his CB. The show producer will not be amused when "Breaker, breaker one nine" comes out of the mains at full levels. Then you'll wish you'd done it right. You don't need common mode rejection until you do. :roflmao:
 
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#124
ctmullins said:
So, @BassYerFaceoff - How was the gig last night, and how did your new rig do?
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Ended up just sticking with the Ampeg alone and running the Mic line DI into FOH and only pushed the Shroeder with the Ampeg... Yeah it was loud!

Also I ordered today the QSC PLD4.2 so I can A/B these things. I think the QSC PLD4.2 will be able to be dialed in better / fully programmable to match Speaker wattage, ohms and spl. Plus I can run all kinds of configurations with it.
 
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#125
okcrum said:
It's all fun & games until a trucker drives by the venue and keys up the 500 watt lin-yar amp on his CB. The show producer will not be amused when "Breaker, breaker one nine" comes out of the mains at full levels. Then you'll wish you'd done it right. You don't need common mode rejection until you do. :roflmao:
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I totally agree its wise to use balanced lines. Sometimes you need more pares, though, and its nice to know how to get them. We did literally hundreds upon hundreds of shows going unbalanced from a line driver FOH to the PA amps through a 250' snake (Belden) and never had one issue with it. Would not dare do something like that at mic level for any length of cable. At mic level common mode rejection is mandatory or you might very well get some guy in the parking lot or nearby truck stop paging a lot lizard through the PA mains! But your up at line level on returns which makes a big difference. Our cannon plugs were always pin one to ground on both ends. It may be helpful to note that we found the bigger problem (using an analog snake, anyway) is ground loops. You can solve most of that by running 16-3 from the stage where your powering your amps down your snake for AC power to your board. For a bass amp rig with a short little jumper from a preamp to a power amp balanced or unbalanced shouldn't be a problem, I don't think, provided your using top grade cable (Belden) and connectors (switchcraft). But in that case, why not go balanced? No reason not to.

I used to hate those guys with the big linears! On 11 meters (CB band) when the band is open 500 watts will reliably get you all the way across the country. It totally clogs up the band and sometimes makes it unusable. A lot of the guys would cuss them out on the air! I don't know if they still do this or not but Cobra made a sweet little CB rig that was actually a 25 watt radio dialed back to 5 watts to comply with the FCC rules. You could "tune it down" as we used to say up to 25 watts by removing a few diodes and such in the power supply. With co-phased antennas on SSB, 25 watts is all you need on the highways. It gets you right out there. And your headlights don't go dim when you key the microphone.

Glad everything worked out well at your gig.
 
#127
A MUCH better way to integrate an unbalanced signal into a balanced input without the use of a transformer is via impedance balancing. This greatly improves the rejection capabilities over directly connecting pin 3 (or pin 2 for you old guys) to the unbalanced ground. If the impedance balancing is tight, the CMRR will be pretty decent.
 
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#128
@agedhorse How do you feel about the QSC PLD4.2 since it can be completely programmed for the Cab ohms and wattage rms? *edit* Also has some nice 4th order HPFs (which to me is also very attractive... although so does the Crown Xti 1002)... I honestly haven't even hooked up the Crown yet to test it.
 
#130
agedhorse said:
As long as you limit it back to a safe value it's fine. Your definition of what's safe is likely different than mine however.

Both amps have enough power to damage your speakers imo.
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Ok what wattage for a 1200W 4ohm cab with 2 12" and an attenuable tweeter 3" voice coil and Neo Magnets would you recommend.

PS.. I was told straight from the horse's mouth that they ran an 1100w amp into it and knew it could take more.
 
#131
What’s the sensitivity rating on your 12” drivers? 1200 watts into any of the 12s that I would use results in far too much sound for the stages I play. Do you have a good set of earplugs?
 
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#132
BassYerFaceoff said:
Ok what wattage for a 1200W 4ohm cab with 2 12" and an attenuable tweeter 3" voice coil and Neo Magnets would you recommend.

PS.. I was told straight from the horse's mouth that they ran an 1100w amp into it and knew it could take more.
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The cab's designer should be able to run a program to determine the mechanical power handling limit of the driver/cab combination. The results are based of the driver's T/S parameters and cabinets dimensions. It's impossible to know the mechanical power handling limits without having the data on the drivers or cabinet dimensions.

As an example take a look at the attached tunings for the Eminence 2512. Look for the cone displacement graphs. These graphs show the power level where the driver will meet its Xmax. This document contains several tunings for the driver so compare the different cone displacement graphs.

The designer of your cab needs to run a similar graph for your driver/cab combination. That will determine that amount of power you can use and where you should set your amp's HPF and limiter.
 

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#133
BassYerFaceoff said:
Ok what wattage for a 1200W 4ohm cab with 2 12" and an attenuable tweeter 3" voice coil and Neo Magnets would you recommend.

PS.. I was told straight from the horse's mouth that they ran an 1100w amp into it and knew it could take more.
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I ran some quick calcs based on what's available standard in the B&C line and pretty much every driver that was suitable for bass guitar exceeded Xmax in an optimized cabinet before 600 watts RMS (some well before). Increasing Xmax would almost 1 for 1 reduce the sensitivity due to losses outside the gap plus the increased moving mass. I would recommend between 800 and 1000 (RMS) maximum based on what I know.

BUT, I did not design your cabinets and I don't have to stand behind it in the event that you have a failure. Therefore, I would strongly suggest that you get a recommendation from the builder (don't recall who that was) a recommendation that they will stand behind for warranty purposes.
 
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#134
agedhorse said:
I ran some quick calcs based on what's available standard in the B&C line and pretty much every driver that was suitable for bass guitar exceeded Xmax in an optimized cabinet before 600 watts RMS (some well before). Increasing Xmax would almost 1 for 1 reduce the sensitivity due to losses outside the gap plus the increased moving mass. I would recommend between 800 and 1000 (RMS) maximum based on what I know.

BUT, I did not design your cabinets and I don't have to stand behind it in the event that you have a failure. Therefore, I would strongly suggest that you get a recommendation from the builder (don't recall who that was) a recommendation that they will stand behind for warranty purposes.
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Shroeder 212PL. The website lists two options Opt 1 800W RMS, Opt 2 1,000W RMS...but per post #97 and #100, the drivers are upgraded to 1,200W RMS.
 
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#135
agedhorse said:
A MUCH better way to integrate an unbalanced signal into a balanced input without the use of a transformer is via impedance balancing. This greatly improves the rejection capabilities over directly connecting pin 3 (or pin 2 for you old guys) to the unbalanced ground. If the impedance balancing is tight, the CMRR will be pretty decent.
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Pin 2 + / Pin 3 - / Pin 1 G? Perhaps not surprisingly, I'm totally mystified why pin 2 would go to ground for us old guys, actually. How old do you have to be? Was it ever different. Help! I'm drowning in a sea of confusion. Not the first time, but....
 
#136
Nevada Pete said:
Pin 2 + / Pin 3 - / Pin 1 G? Perhaps not surprisingly, I'm totally mystified why pin 2 would go to ground for us old guys, actually. How old do you have to be? Was it ever different. Help! I'm drowning in a sea of confusion. Not the first time, but....
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Because there was both a pin 3 hot and pin 2 hot standard back in the 70's and into the 80's. Not unlike the positive terminal of a speaker pushing forward or pulling back depending on which standard used when a positive voltage was applied back in the good 'ol days.
 
#137
agedhorse said:
Because there was both a pin 3 hot and pin 2 hot standard back in the 70's and into the 80's. Not unlike the positive terminal of a speaker pushing forward or pulling back depending on which standard used when a positive voltage was applied back in the good 'ol days.
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One step further. If the output is impedance balanced, you kill the signal if you apply ground to the wrong pin.

Here's a related article.

Invalid Link Removed
 
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#138
Wasnex said:
One step further. If the output is impedance balanced, you kill the signal if you apply ground to the wrong pin.

Here's a related article.

Invalid Link Removed
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Yup, joy-joy!
Some gear included switched pin 2/3 hot options (TOA and Yamaha did certainly).
 
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