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sk1939
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Mclean, VA
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Isolation Transformer

Simple question, I have an isolation transformer rated for 2.0 Amps, and I want to connect speakers rated 150W @125V Max Input (300W Max total). These speakers have a fixed volume control that does not go past 1/8 min due to the volume level. I know that 125V at 150W is 2.5A (roughly), but I am assuming that is under the literal max. Is this going to be an issue? I do not have access to a Kill-a-Watt at the moment.


leibold
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said by sk1939:

I know that 125V at 150W is 2.5A (roughly)

You probably meant the current for both speakers (300W).

The power consumption of the speakers is indeed related to the volume but setting the volume controls on the amplified speakers to 1/8th doesn't by itself indicate whether or not it is a safe setting (total volume also depends on the source signal).

Most likely you will be fine since the speakers won't operate at maximum input power continuously. The risk in using a transformer in excess of its current rating is the heat in the coils damaging the insulation of the wire which may lead to a short circuit. However as long as those periods are brief (and you are only talking about 25% excess) you should be ok.

Is that transformer a plain transformer you are wiring up for this purpose or is it a finished device (an enclosure with power cord and outlets) ? If this is something you are building yourself include a 2A fuse to protect the transformer (a finished device is likely to contain a fuse already).
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sk1939
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said by leibold:

said by sk1939:

I know that 125V at 150W is 2.5A (roughly)

You probably meant the current for both speakers (300W).

The power consumption of the speakers is indeed related to the volume but setting the volume controls on the amplified speakers to 1/8th doesn't by itself indicate whether or not it is a safe setting (total volume also depends on the source signal).

Most likely you will be fine since the speakers won't operate at maximum input power continuously. The risk in using a transformer in excess of its current rating is the heat in the coils damaging the insulation of the wire which may lead to a short circuit. However as long as those periods are brief (and you are only talking about 25% excess) you should be ok.

Is that transformer a plain transformer you are wiring up for this purpose or is it a finished device (an enclosure with power cord and outlets) ? If this is something you are building yourself include a 2A fuse to protect the transformer (a finished device is likely to contain a fuse already).

I did indeed mean both.

These are studio monitors, so they generally run at a rather low volume, at least low enough that they generally don't trigger the "Signal" light on the Equalizer infront of them in the signal chain.

It is a finished device (Powervar 2.0), and from peering inside the case it does have fuses, but the case is riveted shut sadly which would make replacement of the fuses a PITA.


cowboyro
Premium
join:2000-10-11
Shelton, CT
reply to sk1939
So those are 100 ohm speakers???
Are you planning on running the audio signal through a transformer intended for AC? It will sound crappy, the high frequency range will be drastically cut. Low frequencies may saturate the core at a high-enough volume.


sk1939
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said by cowboyro:

So those are 100 ohm speakers???
Are you planning on running the audio signal through a transformer intended for AC? It will sound crappy, the high frequency range will be drastically cut. Low frequencies may saturate the core at a high-enough volume.

No, they are self-powered speakers (JBL LSR2325P).


ArthurS
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reply to sk1939
What are you trying to accomplish putting powered speakers on an isolation transformer???


sk1939
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Eliminating the noise from the fluorescent lights on the same circuit.


ArthurS
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Put it on a different circuit!!


sk1939
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Would love to, but the way they wired the building means each room is it's own 20A circuit, everything included. I would pull a circuit from the next room with a drop cord, but that has a dimmer for the halogen lights which would be worse I think, and since it's rented space I can't run a new circuit.


cowboyro
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Shelton, CT
reply to sk1939
said by sk1939:

Eliminating the noise from the fluorescent lights on the same circuit.

They already have a transformer. If there is noise, there will be noise with another transformer too...
Better off use some decent filters, while at it cut the CM noise too.


ArthurS
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reply to sk1939
Hmmm, if you're getting noise coming into the speakers due to fluorescent lights, then the problem is:
1. Bad ballast on the lights
2. Faulty power supply in the powered loudspeaker.

Does the noise go away when you turn off the fluorescent lights? If not, then the problem is further up the signal chain, maybe a ground loop.


SmokChsr
Who let the magic smoke out?
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reply to sk1939
It will likely work just fine, but it could overload the transformer should someone decide to "crank it".

Might I suggest another simple option might be to use an Isobar to feed power to the speakers.

Also you may want to verify that the noise is getting into the speakers via the power side and not getting in via the audio path.
Are you running balanced or unbalanced audio?

Even thought it's too late now, I don't like "powered" speakers I prefer an amp in the rack going to conventional speakers. It's always a PITA to have to bring power and audio to speakers that are mounted or suspended. Not to mention the problems that having long line level antennas tied into your system brings.


sk1939
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Mclean, VA
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1 edit
reply to ArthurS
It goes away when the lights are off. The light dosen't have a ballast for better or worse, it uses starters....


sk1939
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reply to SmokChsr
Not likely since I'm the only one with access to it.

There is an Isobar in place which elimates the noise, but it is currently full.

Balanced audio via quality XLR cables.

Perhaps, but I've found that they are easier to transport from place to place, and generally quieter than cheap rack mounted amps.

public

join:2002-01-19
Santa Clara, CA
reply to sk1939
said by sk1939:

Simple question, I have an isolation transformer rated for 2.0 Amps, and I want to connect speakers rated 150W @125V Max Input (300W Max total).

Isolation transformers are rated for line frequency operation. At audio frequencies core loss will be higher.


ArthurS
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said by public:

said by sk1939:

Simple question, I have an isolation transformer rated for 2.0 Amps, and I want to connect speakers rated 150W @125V Max Input (300W Max total).

Isolation transformers are rated for line frequency operation. At audio frequencies core loss will be higher.

However in this case the transformer will be used at line frequency only, since each monitor has it's own power amp built in.


ArthurS
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reply to SmokChsr
said by SmokChsr:

Even thought it's too late now, I don't like "powered" speakers I prefer an amp in the rack going to conventional speakers.

However the advantage of a built in amp and processing of a loudspeaker is that you're guaranteed better consistency speaker to speaker, processing optimized for that particular speaker (active crossover, equalization built in, even some with auto equalization), amplifiers sized correctly for the drivers so you don't blow them up. It's a growing trend with many studio monitors these days.

said by SmokChsr:

It's always a PITA to have to bring power and audio to speakers that are mounted or suspended.

It's just one more cable, and is the responsibility of the electrician, no big deal.

said by SmokChsr:

Not to mention the problems that having long line level antennas tied into your system brings.

If the input stage is designed correctly, you shouldn't have a problem with the line level feed behaving like an antenna. Unfortunately not all audio equipment is designed correctly in the first place. And in this case, I'm suspecting a poor power supply design that is letting the noise of the fluorescent into the powered speaker.


sk1939
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It could also be picking up noise from the mixer, as it also picks up radio stations from time to time. It's getting replaced shortly...


ArthurS
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said by sk1939:

It could also be picking up noise from the mixer, as it also picks up radio stations from time to time. It's getting replaced shortly...

Ah! More information to help us solve the puzzle!

If you disconnect the powered speaker from the mixer, does it still make a noise when the light is turned on? If not, then it's likely something further up the signal chain, and if it's a cheap mixer needing replacement (sounds like it is), there is your culprit. No need for an isolation transformer on the speakers.


sk1939
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Indeed, the speakers are near silent by themselves. The mixer isn't cheap per say (Mackie 1604-VLZ), but it hasn't been the same since someone spilled cola on it (which is why I'm the only one near the gear now).


IllIlIlllIll
EliteData
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said by sk1939:

Indeed, the speakers are near silent by themselves. The mixer isn't cheap per say (Mackie 1604-VLZ), but it hasn't been the same since someone spilled cola on it (which is why I'm the only one near the gear now).

i dont get what kind of person would have *any* liquids near the Mackie in the first place, especially the worst type, Cola.
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sk1939
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The kind that doesn't understand what "No Liquids in the Studio" signs mean.


SmokChsr
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2 edits
reply to ArthurS
said by ArthurS:

If the input stage is designed correctly, you shouldn't have a problem with the line level feed behaving like an antenna.

It act's like an antenna in both directions, back to the source, and out to the speaker.
Now I may be used to dealing with more RF than most would normally encounter. But when you have a AM broadcast transmitter sitting on the other side of the wall from the studio you learn to expect these sorts of troubles. I'm building 2 more studios this month, they will have non-powered speakers. Not to mention I've got 2 Alesis M1 Active MK II that a client bought, sitting in the shop, both crapped out, no support from Alesis, and those are supposed to be the good ones. Can't even get a schematic out of them yet.
EDIT: Have to take that back just found it on a .ru site..

Now as for the matching? that's never been an issue. A matched pair of good speakers and a decent amp, the sound will be right.


sk1939
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Also would cost a whole lot more; a decent amp would set me back more than what I paid for the speakers total. Most professional power amps are designed for power, not quality.


SmokChsr
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said by sk1939:

Also would cost a whole lot more; a decent amp would set me back more than what I paid for the speakers total. Most professional power amps are designed for power, not quality.

What ever makes you happy..


IllIlIlllIll
EliteData
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reply to sk1939
a "real" amplifier wont introduce noise generated from a "simulated" modified sine wave inverter being used as its input VAC power supply.
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ArthurS
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reply to SmokChsr
said by SmokChsr:

said by ArthurS:

If the input stage is designed correctly, you shouldn't have a problem with the line level feed behaving like an antenna.

It act's like an antenna in both directions, back to the source, and out to the speaker.
Now I may be used to dealing with more RF than most would normally encounter. But when you have a AM broadcast transmitter sitting on the other side of the wall from the studio you learn to expect these sorts of troubles.

Read the June 1995 Journal of the Audio Engineering Society. To this day, it's still one of the best works on the topic, and a treasure trove of information dealing with these kinds of problems. Every wire acts like an antenna, whether is 5 feet long or 50 feet long. How well a device fends of RF fields, even in extreme cases like yours has everything to do with how well the input stage of all your audio devices is designed. Your chain is as strong as the weakest link, it only take one device with a pin 1 issue to bring everything down to it's knees.

said by SmokChsr:

I'm building 2 more studios this month, they will have non-powered speakers. Not to mention I've got 2 Alesis M1 Active MK II that a client bought, sitting in the shop, both crapped out, no support from Alesis, and those are supposed to be the good ones.

Whoa! Stop right there. Any sentence that contains the words "Alesis" and "good" is an oxymoron. Cheap crap like that has no place in high RF environments like yours, and will be a pain to get working right. Be prepared to get some decent audio line transformers to make that work!

said by SmokChsr:

Now as for the matching? that's never been an issue. A matched pair of good speakers and a decent amp, the sound will be right.

Indeed if you size the amp correctly, there's no problem using an external amplifier. However the one size fits all mentality prevails and often the amp is either too big or too small, not to mention that the majority of engineers out there have no clue how to set gain structure correctly, process and eq the speakers properly, and set limiters so that the drivers are not destroyed by inadvertent misuse. It takes a special set of tools and knowledge to do this properly. Well beyond the average project studio operator. Don't forget we're dealing with a project studio here, not a dj setup in a radio station. Having a flat, neutral response in your studio monitors is critical to getting the mix right in a project studio (in addition to good acoustics). In a radio station, all that matters is that your monitors produce sound, you watch your meters, and no dead air occurs. So slap in a 1/3 octave eq, power amp, and a pair of decent speakers and you're good to go! Maybe dig out those old Sentry 100's or Yamaha NS-10's with the toilet paper taped on the tweeter!

My point being that decent self powered studio monitors are usually biamped or triamped internally, with the amplifiers sized correctly for the individual drivers, along with the necessary equalization and active crossovers to make the anechoic direct field response of the monitor as optimal as it can be out of the box using the built in DSP. Also, built in limiters are set by the manufacturer to prevent damage to the drivers. To the average project studio owner who does not have the tools, knowledge and resources to be able to do this, self powered monitors are a great solution to get the most accuracy from a speaker without the complexity.

Whether the line level signal goes to a power amp in a rack, or a few feet further directly to a powered monitor should make no difference in even harsh studio environments, provided you use equipment that has been designed right to begin with (obviously cheap self powered monitors excluded) and properly shielded wiring. Using an external power amplifier vs self powered monitors provides little benefit to the end user with regards to noise interference problems, even in your case.


SmokChsr
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Saint Augustine, FL
said by ArthurS:

Whoa! Stop right there. Any sentence that contains the words "Alesis" and "good" is an oxymoron.

I can't argue that.. I sure wasn't impressed when I opened it up. just going by what others had said.

said by ArthurS:

It takes a special set of tools and knowledge to do this properly. Well beyond the average project studio operator. Don't forget we're dealing with a project studio here, not a dj setup in a radio station. Having a flat, neutral response in your studio monitors is critical to getting the mix right in a project studio (in addition to good acoustics).

You mean like a calibrated microphone with a 1/3 octave spectrum analyzer, distortion analyzer, signal level meter, calibrating everything so the +4dbV = 0dbVU.. nahh wouldn't know anything about that..