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

[Nevada Pete]

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.

Thanks! It always made more sense to me to use pin 2 hot. I looked up the impedance balancing. That's really interesting. Thanks for putting that up there. Yet another technique I didn't think of, and never heard of. I know your busy, but one more question please. Do manufacturers spec this as 'single ended impedance balanced', or do they just do it and not mention it in the specs? In other words, is it commonplace now?

 

[byacey]

Some manufacturers would "cheap out" and make a pseudo balanced output like this. However, to an end user, it's difficult to implement properly because you need to know the exact output impedance of the signal output to select an appropriate resistor. Any mismatch reduces the common mode rejection, especially for high frequency noise.

 

[okcrum]

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.

Even line level runs are not safe in an RF saturated environment like Manhattan. Using star power distribution topology:

As you say, in this case the short run should be fine.

 

[agedhorse]

Thanks! It always made more sense to me to use pin 2 hot. I looked up the impedance balancing. That's really interesting. Thanks for putting that up there. Yet another technique I didn't think of, and never heard of. I know your busy, but one more question please. Do manufacturers spec this as 'single ended impedance balanced', or do they just do it and not mention it in the specs? In other words, is it commonplace now?

Generally it's specified as impedance balanced, or impedance compensated.

 

[okcrum]

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.

Was that an East Coast/West Coast thing? We built everything in NYC 2-3-1 red(+)-black(-)-gnd back then. So did all the networks and cable joints. Maybe the radio guys were the weirdos?

 

[agedhorse]

I think it was more a Japanese-Europe-North America thing.

 

[okcrum]

That I remember! Sony, no, baloney...

EDIT: That brought up an old UN-fond memory chasing phase reversals. The guys we'd hire to make cables got to make extra $$$ rewiring those import machines - everybody we knew in the biz was pretty OCD about keeping stuff in phase throughout the plant.

 

[byacey]

I think it was more a Japanese-Europe-North America thing.

A lot of older British and Australian gear was pin 3 hot, Soundcraft, Soundtracs, Klark Teknik and a myriad of American companies too. There really wasn't any rhyme or reason for or against pin 2 hot. I think pin 2 hot became the adopted standard by the early 1990s. On most gear with a balanced in and balanced out, it didn't really matter, but if an unbalanced out was required, absolute phase became very important. Many older microphones were wired pin 3 hot and were a source of concern when used in multiple microphone situations where they would be out of phase with each other.

 

[BassYerFaceoff]

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?

103db 1w/1m
I do have earplugs. lol

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.

I was thinking of limiting it to 1000w actually.
I'm particularly confused as to why QSC recommends using an amp that is TWICE the wattage of the RMS of the speaker as per their amplifier calculator...?

 

[agedhorse]

103db 1w/1m
I do have earplugs. lol



I was thinking of limiting it to 1000w actually.
I'm particularly confused as to why QSC recommends using an amp that is TWICE the wattage of the RMS of the speaker as per their amplifier calculator...?

103dB/1W/1M average sensitivity in any bass reflex cabinet? Or is the spec. based on voltage which would equate to 100dB/1W1M into a 4 ohm load. Details and accuracy matter.

QSC's recommdation is based on ideal PA applications where there is no compression, no distortion, no overdrive and optimum HPF setting. For MI applications I recommend powering at no more than the RMS or continuous rating of the speaker.

 

[BassYerFaceoff]

103dB/1W/1M average sensitivity in any bass reflex cabinet? Or is the spec. based on voltage which would equate to 100dB/1W1M into a 4 ohm load. Details and accuracy matter.

QSC's recommdation is based on ideal PA applications where there is no compression, no distortion, no overdrive and optimum HPF setting. For MI applications I recommend powering at no more than the RMS or continuous rating of the speaker.

Unfortunately that's all I have to go on...
I think I'll just keep the Amp wattage around 900 to 1000w and take it from there using the earballs and sniffer. lol

 

[byacey]

103dB/1W/1M average sensitivity in any bass reflex cabinet? Or is the spec. based on voltage which would equate to 100dB/1W1M into a 4 ohm load. Details and accuracy matter.

QSC's recommdation is based on ideal PA applications where there is no compression, no distortion, no overdrive and optimum HPF setting. For MI applications I recommend powering at no more than the RMS or continuous rating of the speaker.

I don't think I've ever seen a bass reflex do 103db @ 1W/1m, this is more horn loaded territory.

 

[BassYerFaceoff]

I don't think I've ever seen a bass reflex do 103db @ 1W/1m, this is more horn loaded territory.

The cab has a tweeter but no horn. That was what I was told the sensitivity of that particular cab was though.
P.S. I mostly keep the tweeter off.
*edit* They ARE highly efficient and a custom built drivers from B&C so I'm not sure that these drivers would even be listed on the B&C website. Someday I'll open it up and read whats written on the drivers.

 

[okcrum]

A lot of older British and Australian gear was pin 3 hot, Soundcraft, Soundtracs, Klark Teknik and a myriad of American companies too. There really wasn't any rhyme or reason for or against pin 2 hot. I think pin 2 hot became the adopted standard by the early 1990s. On most gear with a balanced in and balanced out, it didn't really matter, but if an unbalanced out was required, absolute phase became very important. Many older microphones were wired pin 3 hot and were a source of concern when used in multiple microphone situations where they would be out of phase with each other.

Phase (actually the correct term in this context is polarity) reversal was/is kind of important in mixing, especially when trying to resync audio to video, or when you use the scratch track(s) from the video recording to fill in a missing or corrupted bit from the audio master when editing. I guess in the first case you could just tune for the null, but that was never considered good practice. One channel out of polarity in a stereo mix or 1 or 2 out in a 5.1 mix does not sound good.

Modern mix boards and digital signal processing take away many of those old headaches, thankfully.

Given the 30 or so years it took to come up with workable digital video broadcast standards, it's kind of encouraging it only took about 10 years for cable polarity to settle down.

 

[agedhorse]

Unfortunately that's all I have to go on...
I think I'll just keep the Amp wattage around 900 to 1000w and take it from there using the earballs and sniffer. lol

Good choice. I see the results of too much power enough that the warning is not without reason.

I don't think I've ever seen a bass reflex do 103db @ 1W/1m, this is more horn loaded territory.

Agreed.

The cab has a tweeter but no horn. That was what I was told the sensitivity of that particular cab was though.
P.S. I mostly keep the tweeter off.
*edit* They ARE highly efficient and a custom built drivers from B&C so I'm not sure that these drivers would even be listed on the B&C website. Someday I'll open it up and read whats written on the drivers.

That's not what byacey is talking about, horn loaded cabinets are an entirely different TYPE of cabinet.

 

[Nevada Pete]

Even line level runs are not safe in an RF saturated environment like Manhattan. Using star power distribution topology:

As you say, in this case the short run should be fine.

One electrician said wire the transformer delta / star. The other said, why?

 

[BassYerFaceoff]

Ok... So this sort of applies to this thread but not really...
I decided to go with the QSC PLD4.2 with which I can do ALL kinds of stuff with... MOST importantly ADJUSTING that wattage to my cab... (Spoke to QSC reps to confirm and it will do what I need). Also thanks @agedhorse.

Now to the OFF topic part which I didn't want to create another thread for and I couldn't really find an answer for on other threads...(I looked but maybe not hard enough) Unless one of you long time members know where to EXACTLY point me.

The QSC PLD4.2 has a DEPTH of 9" and my AMPEG SVT3PRO has a DEPTH of 15"... (*edit* BOTH are 2u and 19" wide I believe).

I have NEVER owned a rack case. I WANT to make sure that the front and rear of BOTH are firmly secure. The QSC has both front and rear (although the rear looks like it connects to the "side" or laterally although this could become a sematics battle lol BUT the Ampeg has no REAR connection except for one weird little hole directly in the middle of the back pretty much labeled MUST USE FOR RACK MOUNT... which makes sense because it a heavy amp (The SVT... and yeah I wouldn't expect it could hold on firmly without bending something only by front end support... physics n' such).

What can I buy as a rack (hardshell) that can be breathable, tough, ACTUALLY FITS BOTH SECURELY, ATA compliant AND has shock absorbsion (rubber washers?) in the event of a hard knock?

PLEASE HELP SOMEHOW!

 

[agedhorse]

Generally the rear mounts are not necessary on the short chassis QSC amps. They are for extreme handling, something your SVT3 isn't going to be happy with under any conditions.

 

[BassYerFaceoff]

Generally the rear mounts are not necessary on the short chassis QSC amps. They are for extreme handling, something your SVT3 isn't going to be happy with under any conditions.

I agree! So I'm trying to find something that has that weird mount for the little hole in the rear of the SVT but can also accomodate the QSC with 9" depth on the rear as well for the best support. I also like my gear to be as safe as possible so I am looking to support ALL secure points. How or where can I find this case?

 

[agedhorse]

I don't think you are going to find it.

I toured with dozens of QSC amps doing thousands of gigs without a single amp failure. I think you are worrying about nothing.

If you handle your gear rough enough to damage the QSC amp without the rear bracket, you will have already damaged your SVT-3 with the brackets installed.

It's your choice, good luck.