QSC MX3000a question

[AngrySailor]

Just to add, if your not familiar with “active” crossovers, they’re signal level and generally have a slope of 24-32dB per octave.

 

[AngrySailor]

I think the reason your coil burned is because of the gauge of the coil. They are too small for that kind of power. My crossovers have 16g coils in them. And I'm running a wimpy 509wpc

They’re “rated” for 400w... I think driving one amp hard (clipping) was probably the cause? I’d like opinions on this as it seems better with more power. I think it’s a case of more clean power is easier on stuff than lots of dirty signal? Anyways it sounds good and that’s why I’m in the shop at 5:20 am making sure “my speakers are lubricated” (enjoying a beer)

 

[WOPL Sniffer]

There’s an active crossover sending 120hz and below to the big amps, 120hz and up to the stereo cabinets. I’m using a Rotel RA-1412 for its preamp section only.

I think you got your scheme mixed up. What you are sayin is impossible.

You said the signal to your amps are split before the amplifier, then you said the crossover (before the amp send the 120Hz and up straight to the speaker cabinet which would make it UNAMPLIFIED. Do you really know how this works.? Remember, yo had it hooked up wrong (your first post) which is why you came here.

Splain this again to me Lucy....

 

[WOPL Sniffer]

You've had more than one if you are trying to pass this off on me.... bye

 

[laatsch55]

AS, coils burn because of too much current. Be that AC or DC it does not matter. Wire gets hot, burns insulation, wire shorts out....

 

[BlazeES]

Sniff, wtf ... why so grumpy in the morning ?

 

[BlazeES]

Inductor coils windings behave just like transformer windings, just like voice coil windings, just like motor windings.

A common failure mechanism is by way of thermal degradation due to excessive or frequent fault current, or by dielectric breakdown due to high voltage stress.

And age is big underpinning factor. Insulating material is no exception to property changes with age.

 

[fitz43]

Just to add, if your not familiar with “active” crossovers, they’re signal level and generally have a slope of 24-32dB per octave.

I learned something today.
I always thought "active" meant not just L- C - R components. Active xovers had real electronics in them. I used to think they were behind the power amp. Today I learned that isn't always the case.

https://www.genelec.com/key-technologies/active-crossovers

From Wiki
Active crossovers are distinguished from passive crossovers in that whereas passive crossovers split up an amplified signal coming from one power amplifier so that it can be sent to two or more drivers (e.g., a woofer and a very low frequency subwoofer, or a woofer and a tweeter), an active crossover splits up audio signal prior to amplification, so that it can be sent to two or more power amplifiers, each of which is connected to a separate driver type.

How are the Eminance crossovers (pictured) wired inside the speaker cabinet? input, W, M, T to corresponding speakers?

 

[VSAT88]

Damn, I thought I knew how this active/passive crossover thing worked and now I am questioning myself !!

 

[AngrySailor]

I was looking at your burned crossover, that's a regular crossover Not for splitting the signal from the preamp...... c'mon man, do you have enough ventilation in their shop or are you sniffin the oil can.

Lol. Those are in the three way cabinets being fed by the high frequency amp. The active crossover is in the blue rack mount unit above the amplifiers.

 

[AngrySailor]

How are the Eminance crossovers (pictured) wired inside the speaker cabinet? input, W, M, T to corresponding speakers?

Yes, they receive power from one of the high frequency amps. Signal rage is 120hz and up. They then split the signal to the three speakers in those cabinets. It’s a standard 3 way passive crossover except the lows were separated in the rack and sent to the sub amps.

 

[laatsch55]

We need Joe to chime in here,but if you are running stick crossovers in a 3 way cabinet with an active crossover cutting out everything from 120 down, to me , it would seem there is a lot of extra energy going to or available to the mids and tweets of the 3 way cabinet.

What cool is burnt in the 3 way passives?

 

[AngrySailor]

Here’s a signal path overview
Red is full range from the pre amp
Blue is summed mono lows, 120hz & down
Green is stereo high 120hz & up

The green left and right amps then send this amplified signal to the respective 3 way cabinets where it passes through the passive crossover and is sent to the w, m and tweeter.

It’s a 4 way system, sub 120 down, woofer 120-500, mid 500-3.5k, tweeter 3.5k and up.
Mono subs, stereo 3 way.

Edit: I should have drawn the high signal to show that it is separate left and right but I’m doing this on my phone. THERE IS a separate left and right line to the high frequency amps to maintain stereo output.

 

[AngrySailor]

We need Joe to chime in here,but if you are running stick crossovers in a 3 way cabinet with an active crossover cutting out everything from 120 down, to me , it would seem there is a lot of extra energy going to or available to the mids and tweets of the 3 way cabinet.
What cool is burnt in the 3 way passives?

That is somewhat the point of splitting frequency at signal level in that you’re not wasting power amplifying signals you don’t want to use. It does free up ALOT of extra power. The sub amps don’t amplify highs that won’t be used and the high amps aren’t amplifying lows which would then have to be filtered out with a passive.

This allows NO passive crossover in the subs speaker line. There is a 35hz high pass in the signal line to the low amps. The speakers are wired directly to the amp which only amplifies 35-120hz

I’ll check what coil is burned when I get back to the shop.

 

[oldphaser]

That is somewhat the point of splitting frequency at signal level in that you’re not wasting power amplifying signals you don’t want to use. It does free up ALOT of extra power.

Correct.



If my memory serves me correct..........

With passive crossovers there can be an "insertion loss" of anywhere from 1 to 3 db.

In order to get 3dB louder you have to double the output power of an amplifier. (i.e. 100 watts to 200 watts only gains you 3dB). Likewise to go from 1000 watts to 2000 watts only gains you 3dB as well.

Additionally, there are other ways to gain 3dB. Double the number of drivers. (i.e. from (1) 12" driver to (2) 12 inch drivers).

With regards to loudspeakers; there is an inverse square. You will lose 6dB every time you double the distance away from the speaker. Apparently line-arrays don't follow this inverse square law. If you have a line array (of like drivers) of say 10 feet tall, you square the height (of 10 feet) and come up with 100. In this case, you don't lose 6dB per doubling of distance but 3dB instead out to 100 feet. After 100 feet it then loses 6dB per doubling of distance thereafter. In the case of P.A. systems this can be quite significant difference out at 100 feet.

 

[oldphaser]

Here’s a signal path overview
Red is full range from the pre amp
Blue is summed mono lows, 120hz & down
Green is stereo high 120hz & up

The green left and right amps then send this amplified signal to the respective 3 way cabinets where it passes through the passive crossover and is sent to the w, m and tweeter.

It’s a 4 way system, sub 120 down, woofer 120-500, mid 500-3.5k, tweeter 3.5k and up.
Mono subs, stereo 3 way.

Edit: I should have drawn the high signal to show that it is separate left and right but I’m doing this on my phone. THERE IS a separate left and right line to the high frequency amps to maintain stereo output.

Somewhere in my collection of stuff is a "Interphase Acoustics" 4 way active (requiring external power) distribution box that was used in the Heart P.A. system many years ago. It was designed to go after a 4-way active crossover and before the amplifiers. In turn the distribution box provided outputs for (4) amplifiers each for lows, low mids, high mids, and highs for a total of (16) amplifiers.

If my memory serves me correct, one the Audio Analysts Phase Linear 700 series II amp racks that Darrel F. has some sort of passive distribution system (Audio Analysts S-4 Power System) at the top of the rack (that holds (4) amplifiers each). Somewhere in my collection is a schematic Darrel provided me with. Darrel has also used Crest and QSC amplifiers in his PA system over the years and he has told me he prefers the Phase Linear amps.

 

[AngrySailor]

Somewhere in my collection of stuff is a "Interphase Acoustics" 4 way active (requiring external power) distribution box that was used in the Heart P.A. system many years ago. It was designed to go after a 4-way active crossover and before the amplifiers. In turn the distribution box provided outputs for (4) amplifiers each for lows, low mids, high mids, and highs for a total of (16) amplifiers.

If my memory serves me correct, the Audio Analysts Phase Linear 700 series II amps that Darrel F. has have some sort of passive distribution system (Audio Analysts S-4 Power System) at the top of each rack (that holds (4) amplifiers each). Somewhere in my collection is a schematic Darrel provided me with. Darrel has also used Crest and QSC amplifiers in his PA system over the years and he has told me he prefers the Phase Linear amps.

That’s cool! I’d love to have a rack of big PL amps, they’re just hard to come by as compared to the QSC stuff, way more pricey too! These amps all come from clubs or bars that shut down. I only got one from Craigslist and didn’t pay a whole lot for it.

I’ve got a PL 400 I’m going to set up in my living room when I get a chance. Simple system, one amp, two way speakers. Old school.

Just thinking about band equipment... my uncle owned one of only two alesis ADAT recorders in North America at that time. He was contacted by RUSH as they required it to record “Presto”. He got the next one available, I would have asked for THAT one back just for the cool factor.

 

[BlazeES]

Just thinking about band equipment... my uncle owned one of only two alesis ADAT recorders in North America at that time. He was contacted by RUSH as they required it to record “Presto”. He got the next one available, I would have asked for THAT one back just for the cool factor.

Now that IS totally cool ! I'll never listen to 'Presto' the same way again.

 

[oldphaser]

Here is a link to Darrel F's comments about Phase Linear amps.
NOTE: Darrel is also owner of the purple Phase Linear 700.

Scroll about one-half way down on the page and look for "Purple Phase Linear 700"
http://www.audioreview.com/product/amplification/amplifiers/phase-linear/400.html?p=2#reviews

 

[AngrySailor]

Examined the crossover. Seems that the 40mfd on the mid range and the 4mfd on the tweeter circuits have failed. The coils all show resistance and not a short. I’m just testing the caps with the “cap” function on my cheap meter. None of them seem to read what they should though. Most are close but not in tolerance. For example the 26mfd caps read 18 and change on my meter? Maybe I’ll swap some caps out and see if I can get one board working.