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Title: Buck & Boost Transformers
Post by: Mike Sokol on June 11, 2014, 05:14:53 pm
I just came back from a church sound consult where the monitor console and its rack was being fed with very low AC voltage, starting at maybe 114 volts max with no load, but dipping down below 108 volts when the HVAC on the roof kicked in all the compressors. It appears that something in the rack (perhaps the console PS itself) ain't happy at 108 volts and begins doing a big buzz reset noise which ends up in all the floor wedges. I proposed adding a Buck-Boost transformer in Boost mode feeding the surge/conditioner that will add at around 6 volts to the incoming power for the rack, so now the voltage would swing between 114 volts and 120 volts rather than 108 to 114 volts.

So here's my question. The electrician doing the wiring thought I was a little nuts describing how to a Buck & Boost Transformer works, and how to hook it up. How many of you know what I'm talking about and have you ever used one to correct chronically high or low voltage powering a sound system or whatever.

BTW: I do know how they work, having installed dozens of them during my IE/EE past life. But I want to know if this is a subject worthy of discussion here. I'm sure that at least of few of you guys know what I'm talking about, but perhaps not a lot.

What your your thoughts on this?   
Title: Re: Buck & Boost Transformers
Post by: Frank DeWitt on June 11, 2014, 05:29:37 pm
Basically a auto transformer.

I have used them more then a few times.  I have one permanently installed it the voltage regulator of a generator of mine that was built for 50 hz.  I have it adjusted for 60 hz but the voltage went high so I fool the feed to the voltage regulator to get it back down.

I also used one to run 5 preamps that ran very hot.  They worked very nicely on 96 volts. 

In both cases I made the transformer from a step down transformer. Make sure the primary winding can handle the current it will see. The coils on the low voltage side are always higher current so as long as the insulation can take the higher voltage, you can series them.  I do wire them so that one side of the output winding is connected to neutral just to be sure.  In the case of the preamps I used a 24 volt transformer with the output winding bucking the input winding. 
Title: Re: Buck & Boost Transformers
Post by: Cailen Waddell on June 11, 2014, 06:21:44 pm

I just came back from a church sound consult where the monitor console and its rack was being fed with very low AC voltage, starting at maybe 114 volts max with no load, but dipping down below 108 volts when the HVAC on the roof kicked in all the compressors. It appears that something in the rack (perhaps the console PS itself) ain't happy at 108 volts and begins doing a big buzz reset noise which ends up in all the floor wedges. I proposed adding a Buck-Boost transformer in Boost mode feeding the surge/conditioner that will add at around 6 volts to the incoming power for the rack, so now the voltage would swing between 114 volts and 120 volts rather than 108 to 114 volts.

So here's my question. The electrician doing the wiring thought I was a little nuts describing how to a Buck & Boost Transformer works, and how to hook it up. How many of you know what I'm talking about and have you ever used one to correct chronically high or low voltage powering a sound system or whatever.

BTW: I do know how they work, having installed dozens of them during my IE/EE past life. But I want to know if this is a subject worthy of discussion here. I'm sure that at least of few of you guys know what I'm talking about, but perhaps not a lot.

What your your thoughts on this?

The only application that I have used buck boost is 208v to 240v buck/boost.   I've never thought of them for the application you describe but it is intriguing.   My question would be - are you solving a problem or hiding it?  If the voltage drop is so severe I would think there would be a utility problem or undersized feeder on the building or something else that should be addressed. 


Sent from my iPhone using Tapatalk
Title: Re: Buck & Boost Transformers
Post by: Mike Sokol on June 11, 2014, 06:31:13 pm
The only application that I have used buck boost is 208v to 240v buck/boost.   I've never thought of them for the application you describe but it is intriguing.   My question would be - are you solving a problem or hiding it?  If the voltage drop is so severe I would think there would be a utility problem or undersized feeder on the building or something else that should be addressed. 


Sent from my iPhone using Tapatalk

Their plant guys knows the street power transformers are undersized, but PoCo wants a bucket of money to fix it. They claim that 108 volts is fine and won't replace the street transformers on their dime. I'm looking for a $100 fix rather than a $100,000 one.
Title: Re: Buck & Boost Transformers
Post by: Cailen Waddell on June 11, 2014, 06:34:12 pm

Their plant guys knows the street power transformers are undersized, but PoCo wants a bucket of money to fix it. They claim that 108 volts is fine and won't replace the street transformers on their dime. I'm looking for a $100 fix rather than a $100,000 one.

Makes sense to me.


Sent from my iPhone using Tapatalk
Title: Re: Buck & Boost Transformers
Post by: Mike Sokol on June 11, 2014, 06:38:06 pm
Makes sense to me.

We'll see if this fixes the buzz problem. I've asked their electrician to take pictures of the B&B installation and report back to me next week. I'll post them here.
Title: Re: Buck & Boost Transformers
Post by: John Roberts {JR} on June 11, 2014, 06:39:59 pm
It does not have to be an auto-former but since the secondary is literally connected to the primary there is no benefit from isolating the secondary, so auto-former can be a little more efficient.

I can imagine people getting in trouble from too much no-load high line voltage, and you do not get something for nothing so current draw will increase proportionately.

=====

I've told this story several times, but there is a step-up winding with automatic changing taps at my power sub-station to tweak voltage for changing load. One night I noticed that my lights were too bright and my mains voltage was measuring too high. Turns out the step-up was stuck in bump-up mode. As the neighborhood load started dropping off at night, my lights got brighter and brighter.  ::)  The guy at the power company didn't believe me when I called and told him I had too much voltage, but it was a slow night so he drove out and discovered I was not wrong.  8)

JR
Title: Re: Buck & Boost Transformers
Post by: Steve Kennedy-Williams on June 11, 2014, 06:57:26 pm
I just came back from a church sound consult where the monitor console and its rack was being fed with very low AC voltage, starting at maybe 114 volts max with no load, but dipping down below 108 volts when the HVAC on the roof kicked in all the compressors. It appears that something in the rack (perhaps the console PS itself) ain't happy at 108 volts and begins doing a big buzz reset noise which ends up in all the floor wedges. I proposed adding a Buck-Boost transformer in Boost mode feeding the surge/conditioner that will add at around 6 volts to the incoming power for the rack, so now the voltage would swing between 114 volts and 120 volts rather than 108 to 114 volts.

So here's my question. The electrician doing the wiring thought I was a little nuts describing how to a Buck & Boost Transformer works, and how to hook it up. How many of you know what I'm talking about and have you ever used one to correct chronically high or low voltage powering a sound system or whatever.

BTW: I do know how they work, having installed dozens of them during my IE/EE past life. But I want to know if this is a subject worthy of discussion here. I'm sure that at least of few of you guys know what I'm talking about, but perhaps not a lot.

What your your thoughts on this?

We use Buck Boosters for this purpose with projectors, especially when we aren't using our own distro.
Title: Re: Buck & Boost Transformers
Post by: Mike Sokol on June 11, 2014, 09:09:14 pm
For those of you who don't already know how these work, here's a basic schematic of one in "boost" hookup. To make it "buck" you just have to flip the polarity of the secondary so it subtracts rather than adds to the incoming voltage.
Title: Re: Buck & Boost Transformers
Post by: Stephen Swaffer on June 11, 2014, 11:01:57 pm
Their plant guys knows the street power transformers are undersized, but PoCo wants a bucket of money to fix it. They claim that 108 volts is fine and won't replace the street transformers on their dime. I'm looking for a $100 fix rather than a $100,000 one.

Makes me appreciate the local PoCo.  Last time I even mentioned a voltage problem to a lineman it got fixed quickly at no cost to my customer. 

108 volts might be marginally OK, but the NEC recommends no more than a 5% voltage drop at full load.  The HVAC alone is dropping it 5.25%.  Then again the PoCo will go by the NESC not the NEC and I am not sure what it says about voltage drop.  If you can't approach the right person in the right way and get it fixed that is pretty poor customer service-might even be a candidate for the state utilities board gripe line.

I have used them before in industry.  Voltages from the US, Japan, and Europe are just enough different that some equipment can be pretty touchy, so they are not uncommon.  A lot of Japanese stuff likes 200 volts-and 230-240 is a bit high.  Although it seems the newer stuff is a lot more tolerant on voltages.

Perhaps the biggest thing to consider in this situation is that likely no one will remember the boost transformer when the PoCO does fix the problem-after the transformer lets the smoke out or whatever-so you don't want it to boost high enough to create a problem at that time.
Title: Re: Buck & Boost Transformers
Post by: Barry Singleton on June 12, 2014, 12:50:52 am
Perhaps the biggest thing to consider in this situation is that likely no one will remember the boost transformer when the PoCO does fix the problem-after the transformer lets the smoke out or whatever-so you don't want it to boost high enough to create a problem at that time.

  That would be my worry. How much current are you talking about? Could you use a real computer grade AVR?  We have some in our server rack that are 6000 watt and they surely do make smaller ones.
Title: Re: Buck & Boost Transformers
Post by: Mike Sokol on June 12, 2014, 07:00:38 am
  That would be my worry. How much current are you talking about? Could you use a real computer grade AVR?  We have some in our server rack that are 6000 watt and they surely do make smaller ones.
That doesn't worry me in this particular situation. They've got a Monster power conditioner as the distro in the rack, and it's got a BIG voltage display they watch all the time. But even if somehow the incoming voltage goes up to 120, then my 6 volt boost would only take it 126 which should be perfectly safe for everything. Hey, the line voltage at my school is 130, which made me a little worried the first time we measured it in sound practicum class, but the school plant guys insists it's been like that for a decade. What is it with these plant guys?  >:(

Right now, the church sound tech manually cycles the HVAC units off when the voltage gets below 110 and the preacher is doing his message. Then they'll turn the HVAC compressors back on when the choir and band is singing and let the voltage drop below 110 since the congregation can't hear the buzz from the monitors. Now these are BIG compressors since the room seats at least 2,000, but they have a wall mounted control next to the monitor console so at least he doesn't have to run into an equipment closest to tweak the HVAC. 

If this cheap fix works, then I've suggested they use it as a pitch to PoCo to fix the incoming voltage sag, but their plant guy insists the PoCo says they're not responsible for fixing the street transformers since the church is in an industrial park. Don't know what that has to do with it, but sounds to me like PoCo is just knitting A$$hole covers. 
Title: Re: Buck & Boost Transformers
Post by: Keith Broughton on June 12, 2014, 08:00:36 am
Mike, you could use a varac to power the console (HVAC off) and drop the voltage to see if it's actually a low AC supply that is causing the hum.
It may be something else rather than low AC.
However, if I had to bet, I would say it is the low supply voltage. :)
Title: Re: Buck & Boost Transformers
Post by: TJ (Tom) Cornish on June 12, 2014, 08:05:23 am

If this cheap fix works, then I've suggested they use it as a pitch to PoCo to fix the incoming voltage sag, but their plant guy insists the PoCo says they're not responsible for fixing the street transformers since the church is in an industrial park. Don't know what that has to do with it, but sounds to me like PoCo is just knitting A$$hole covers.
I think a device like this has a place, however on the continuum of cheap/low function -> expensive/high function, this is on the bottom end, as I assume it's a hardwired device.  A more end-user friendly version would be an automatic voltage regulator like this: http://www.sweetwater.com/store/detail/AR1215/, albeit at a higher cost.  The next step up the curve is a double-conversion UPS: http://www.tripplite.com/sku/SU1500RTXLCD2U.



Title: Re: Buck & Boost Transformers
Post by: Mike Sokol on June 12, 2014, 09:55:25 am
A more end-user friendly version would be an automatic voltage regulator like this: http://www.sweetwater.com/store/detail/AR1215/, albeit at a higher cost. 

That's a good idea. I'm sending it up the food chain.
Title: Re: Buck & Boost Transformers
Post by: Kevin Graf on June 12, 2014, 10:15:20 am
The Rod Elliott page on buck/boost transformers.

'Bucking Transformers'
Rod Elliott (ESP)
Contents
    Introduction
    1   Step Down Transformer
    2   Autotransformer
    3   Bucking Transformer
    4   Boosting Transformer
    Conclusion
    References

http://sound.westhost.com/articles/buck-xfmr.htm
Title: Re: Buck & Boost Transformers
Post by: Barry Singleton on June 12, 2014, 11:07:39 am
The Tripp Lite unit is exactly what I was referring to.

Our building has terrible power quality, so much so that the UPS's placed at PC work stations cycle so often that the batteries are exhausted by mid day and they shut off. After monitoring /data logging the voltage for eight days it was decided that retapping the transformers in the building would create an also unacceptable high voltage condition at night and weekends. Like you, our issue is inadequate supply on the PoCo side compounded by severely noisy, power unfriendly machinery on our floor.

  A fairly large AVR up stream of the offices was a complete fix. The UPS's in the server rack which are logged are not activated even once a month now, only on real power outages.

Our church seats 250 and likely has a similarly scaled budget, and while I would accept a small hand made / modified boost transformer in line to a peice of our equient as a proof test for a permanent fix, I would not allow it to be left in.  Why would you want that liability anyway?

  This is not a rebuke so please don't take it as such.

  All the best,
                     Barry.
Title: Re: Buck & Boost Transformers
Post by: Frank DeWitt on June 12, 2014, 11:52:45 am
The real thing, Not hand made, start at $53 for 50 VA  1000 KVA is still only $124
http://www.automationdirect.com/adc/Shopping/Catalog/Power_Products_%28Electrical%29/Power_Transformers/Buck-Boost_Transformers_%28NEMA_Rated%29/240x120_VAC_to_24x12_VAC
Title: Re: Buck & Boost Transformers
Post by: Mike Sokol on June 12, 2014, 12:37:25 pm

Our church seats 250 and likely has a similarly scaled budget, and while I would accept a small hand made / modified boost transformer in line to a piece of our equipment as a proof test for a permanent fix, I would not allow it to be left in.  Why would you want that liability anyway?

Actually, Buck-Boost transformers are not hand made. They're standard in industrial power and have both Code on UL approval. When the PoCo adjusts the power coming into your building, that's essentially what they're doing, adjusting taps on a buck-boost transformer. We're just doing it on a small mixer rack that seems to be overly sensitive to low voltage (below 110 volts) instead of adjusting the entire building which is cost prohibitive. Plus I really can't be sure the noise is coming from this one rack due to voltage below 110. I only heard it once for a few seconds, and the rest of my troubleshooting matrix is from hearsay evidence provided by the sound team. So I'm looking for simple and cheap first, then more expensive and permanent later.

If the noise goes away by keeping this rack voltage between 114 and 120 volts, then I'm going to recommend a more permanent automatic solution like you mention. But right now this is basic troubleshooting 101 and figuring out intermittent noises is one of the hardest things to do. If I had a large Variac transformer for testing with at least 10 amps output, I would put it on the rack and keep reducing voltage until something made noise. But all my variable AC supplies are low power, maxing out at 3 amps which is too low to power the rack. Still, I think this is a reasonable try which would pass a code inspection.

I only brought this subject up because it's something unusual in commercial power, but used all the time in industrial power. I'll report back here in a week or so to see if my guess was correct.
Title: Re: Buck & Boost Transformers
Post by: Josh Millward on June 12, 2014, 12:41:51 pm
That's a good idea. I'm sending it up the food chain.

I agree completely with TJ on using the Furman AR-1215 (http://www.furmansound.com/product.php?id=AR-1215).

It is essentially an automated buck/boost transformer that is already set up for you. You just need to plug it in, turn it on, and you are ready to go. They offer a surprisingly wide range of correction. That way, when/if the PoCo does correct their problem, it doesn't create a bigger problem in your facility.

RE: PoCo knitting asshole covers...
I'm going to have to remember that one, I like it.
Title: Re: Buck & Boost Transformers
Post by: Mike Sokol on June 12, 2014, 02:07:00 pm
RE: PoCo knitting asshole covers...
I'm going to have to remember that one, I like it.

I did a Google search for them, and this is a close as I could find. Would make good presents for some management types I know.
Title: Re: Buck & Boost Transformers
Post by: Stephen Swaffer on June 12, 2014, 03:11:50 pm

 but the school plant guys insists it's been like that for a decade. What is it with these plant guys?  >:(


Had plenty of experience in maintenance.  If its been like that and still works, then its not broke so I don't need to fix it.

Breakdown maintenance vs preventative.

To me it is the equivalent of saying "There aren't any idiot lights on. So why should I check the oil in my car?"
Title: Re: Buck & Boost Transformers
Post by: Jonathan Johnson on June 13, 2014, 02:23:52 pm
Had plenty of experience in maintenance.  If its been like that and still works, then its not broke so I don't need to fix it.

But in this case, it IS broke. Because of the low voltage, critical systems are not working properly.

The way to fix this is to overload the PoCo's transformer 'til it melts down. Then they have to replace it. 8)

My church (seats 120) recently replaced an old oil-eating, fire-breathing dragon of a furnace with an electric resistance heat furnace (why resistance? Because at 4.75 cents/kWh, and the church occupied <10 hours/week, a heat pump would be dead of old age before the cost would be recouped through savings). That increased our electrical load dramatically, which overwhelmed the wimpy PoCo transformer out on the pole. We had expressed concern about it when we put the furnace in, but they brushed it off, saying if there was a problem they'd deal with it then. To their credit, they dealt with it, putting in a larger replacement transformer at no cost to us.
Title: Re: Buck & Boost Transformers
Post by: Mike Sokol on June 13, 2014, 02:39:42 pm
Buck-Boost update: I just got a call from the electrician doing the wiring who reported that with the "Boost" transformer in place they're now getting a solid 121 volts with no load that dropped to 119 volts with several of the HVAC units on. They're predicting another 2 volt drop on Sunday when ALL the HVAC units are running, so maybe this gets down to 117 volts worse case.

If they get through a few Sundays with no buzzing noise, then they can demonstrate to POCO that the low voltage is actually causing a problem and maybe get something changed for free. But in the meantime if this Buck-Boost fix works the pastor will be most happy. Now I'm crossing my fingers that I guessed correctly about the low voltage causing the power supply buzzing noise in the rack. I'll update this thread on Monday once I get feedback from the church but I'm optimistic. 
Title: Re: Buck & Boost Transformers
Post by: John Roberts {JR} on June 13, 2014, 02:55:04 pm
Have you tried putting individual gear on VARIAC to see what acceptable low line voltage is for them?

Good luck, sometimes it isn't simple.

JR
Title: Re: Buck & Boost Transformers
Post by: Mike Sokol on June 13, 2014, 02:56:47 pm
So here's a good question on the automatic voltage adjuster alluded to earlier in the thread: http://www.sweetwater.com/store/detail/AR1215/

If you have it inline and very slowly adjust the incoming voltage down so that it begins to add "boost" taps, what exactly happens to the output waveform at the instant of switching. Do the have a bunch of zero-crossover Triacs doing the switching, or something as barbarian as relays? If it's relays I wouldn't trust it not to do something bad during the Boost switch point. However, I myself could easily design a Triac circuit to do this electronically with no dropouts, so I've got to assume their own engineers did the same thing.

Have any of you actually looked the output of one of these things with a storage scope while it's switching the voltage? Got a schematic of how they do the switching under load? I want to see this for myself before I recommend the technology to anyone else.
Title: Re: Buck & Boost Transformers
Post by: Mike Sokol on June 13, 2014, 03:02:34 pm
Have you tried putting individual gear on VARIAC to see what acceptable low line voltage is for them?

Good luck, sometimes it isn't simple.

JR

Not yet, and they're a two hour trip each way from me. But if this "shotgun" approach fixes the buzz problem, I'm still going to recommend some future testing. Right now they're ready to shoot the monitor guy every time this happen during a worship service.  But that's probably a bad thing to do in church. :-\  At a rave, maybe... :o

But seriously, a lot of times the apparently complicated problems are really simple once you figure them out. And the intermittent fails are the worst ones of all to troubleshoot. I'm crossing my fingers this is it, but I've been fooled before.
Title: Re: Buck & Boost Transformers
Post by: John Roberts {JR} on June 13, 2014, 03:13:16 pm
Not yet, and they're a two hour trip each way from me. But if this "shotgun" approach fixes the buzz problem, I'm still going to recommend some future testing. Right now they're ready to shoot the monitor guy every time this happen during a worship service.  :-\ But that's probably a bad thing to do in church. At a rave, maybe... :o

But seriously, a lot of times the apparently complicated problems are really simple once you figure them out. And the intermittent fails are the worst ones of all to troubleshoot. I'm crossing my fingers this is it, but I've been fooled before.

They are often simple after you determine exactly what is going on...  8)

Yes voltage sag sounds logical, if it sags enough, but larger professional equipment designers accommodate operation around the world where voltage stability is far worse than we generally see here in the US..  Back when euro gear shipped with 220/240V switches some customers used them for some extra help... and would blow up marginal circuitry with over voltage on good days.  :-[  (I recall re-engineering one powered mixer amp module to survive such customer misuse (high line in wrong voltage position.)

Modern universal power supplies generally work down to pretty low line. While it just takes one marginal unit design in the entire path to corrupt the audio. 

JR

Title: Re: Buck & Boost Transformers
Post by: Mike Sokol on June 13, 2014, 03:39:20 pm
Yes voltage sag sounds logical...

Modern universal power supplies generally work down to pretty low line. While it just takes one marginal unit design in the entire path to corrupt the audio. 

Yup, and I think that whatever is buzzing right now at 108 volts is probably going to hard fail at some point in the future. But if this wide spectrum cure corrects the problem for now, at least we have a little breathing room and have isolated the problem to a single rack of gear. Then we can experiment with each piece of gear until we find the culprit. Divide and conquer is my motto.  ;D

BTW: I really suspect the old Allen & Heath power supply in the bottom of the rack. Just a gut feel, but that's the first thing I'll put on a big variac to try to force a failure. Of course, if my voltage correction doesn't correct the "buzz" then it's back to square one. We shall see...  8)
Title: Re: Buck & Boost Transformers
Post by: Jonathan Johnson on June 13, 2014, 04:06:31 pm
But seriously, a lot of times the apparently complicated problems are really simple once you figure them out. And the intermittent fails are the worst ones of all to troubleshoot. I'm crossing my fingers this is it, but I've been fooled before.

That's my general experience with computer networks. The bigger the problem, the easier the solution. Whole network down? Everyone twiddling their thumbs? It's probably something unplugged. We'll have the network up in 5 minutes.

It's those minor annoyances that can really take up your time and money. Back in the day, I probably spent days trying to figure out why Windows 98 wouldn't shut down properly. Finally I decided that's just the way it is, so that's what I told my customers. (I think I actually DID figure out why it wouldn't shut down. 98 would stop the networking drivers before it finished logging off from the network, so it would hang during log off waiting for the process to complete which it never could do because the network was turned off. Microsoft never issued a fix, so I just told people to hold the power button until it turned off. Thankfully Windows 98 is so far in the rearview mirror I can't see it anymore.)

Must be something about the law of diminishing returns in there.
Title: Re: Buck & Boost Transformers
Post by: Greg_Cameron on June 13, 2014, 04:53:32 pm
That's a good idea. I'm sending it up the food chain.

I hope Furman has improved the reliability of those smaller ARs. Back in the 90s we would installed those on portable Avid editing systems. I had several burn up in spectacular manner over the course of a few years and they weren't even regulating because the house power was plenty stable. One burned up the rack pretty well and could have burned down the building if someone wasn't present when the flames were present. I believe it was the toroid that cooked in all cases.
Title: Re: Buck & Boost Transformers
Post by: Mike Sokol on June 14, 2014, 09:08:38 am
I hope Furman has improved the reliability of those smaller ARs. Back in the 90s we would installed those on portable Avid editing systems. I had several burn up in spectacular manner over the course of a few years and they weren't even regulating because the house power was plenty stable. One burned up the rack pretty well and could have burned down the building if someone wasn't present when the flames were present. I believe it was the toroid that cooked in all cases.
Somewhere in the back of my memory bank I seem to remember hearing something about that type of failure with those Furman units. I'm going to ask them to send me one for review and experimentation. Guess I'll have to keep a fire extinguisher close by the test bench.  ;) 
Title: Re: Buck & Boost Transformers
Post by: Mike Sokol on June 15, 2014, 02:13:15 pm
Just got a report back from my B&B transformer installation, right during the middle of the Sunday service. The lead tech says the incoming voltage dropped to 110 volts, but the rack never dipped below 117 volts (they have digital meters on everything) and there was no buzzing noise from whatever doesn't like the low voltage. He says the pastor was REALLY HAPPY. He's going to send me a few pictures of the install this week which I'll post here. He knows we want to do additional troubleshooting to find out the exact piece of gear that's unhappy below 110 volts, but at least now he doesn't have to stop the entire service while the monitor system buzzed at 100 dB on the stage. Yikes...

And yes, this is a code compliant fix using UL listed components. Buck & Boost transformers just aren't used very much in Commercial or Residential installations. But we use them all over the place in Industrial wiring. That's where I learned how they work and began installing them 35+ year ago. Good heavens, has it been that long?  :o

As a side note, while I was crawling around in the back of the amp rack in their equipment room I also pulled the drain wire (pin-1 lift) from the Phoenix input connector on one of the amps since all the others had them cut and it looked like a good idea. I also threw in a Whirlwind ISO2 box on another monitor amp that had XLR inputs and a slight hum in the output. Doing those two things corrected a slight ground loop hum I heard on the pastor's monitor speakers. They said the monitors were now "quiet as a mouse and very clean". I really think that any hum in the floor monitors, no matter how little, gets inside your head and messes with your performance. I work hard to get the noise floor of the monitors way down both for my own playing as well as any gigs I'm engineering. I just hate hum...
Title: Re: Buck & Boost Transformers
Post by: Mike Sokol on June 15, 2014, 08:10:54 pm
So here's a good question on the automatic voltage adjuster alluded to earlier in the thread: http://www.sweetwater.com/store/detail/AR1215/

If you have it inline and very slowly adjust the incoming voltage down so that it begins to add "boost" taps, what exactly happens to the output waveform at the instant of switching....

Have any of you actually looked the output of one of these things with a storage scope while it's switching the voltage?

Found this in the AR1215 Manual. It is indeed a multi-tap buck-boost transformer with Triac switching to provide regulation. Looks good on paper, at least.

DESIGN
The AR-Series uses a design based on an eight-tap
toroidal autoformer. The toroidal design assures
minimal leakage of stray magnetic fi elds, and, be-
cause of its high effi ciency, a very compact size for
its rating. The Voltage Regulator’s circuitry monitors
the incoming line voltage with each cycle, comparing
it to an extremely precise voltage reference, accurate
to ±0.15%. If a voltage fl uctuation requires that a
different tap be selected, the new tap is electronically
switched exactly at the zero-crossing, to avoid dis-
torting the AC waveform. If necessary, it can switch
taps as often as once each cycle. Most commercial
voltage regulators using multiple-tapped trans-
formers switch taps at uncontrolled times, thereby
creating voltage spikes and clicks that can leak into
the audio! Hysteresis in the switching circuits avoids
“chatter” or unnecessary switching back and forth be-
tween adjacent taps.
Title: Re: Buck & Boost Transformers
Post by: Jeff Bankston on June 16, 2014, 06:09:23 am
i'v never installed a buck-n-boost to correct for the problem you encountered. i have installed quite a few in wired for boost when the service is 120/208V and the machinery/equipment requires 240V. the last one i installed was for a very large 3 phase computerized HASS lathe that required 240V and the service was 120/208. the buck-n-boost trransformers work great. as for thr problem you encountered Mike thats a conditon of either the main service feeders being to small or the feeder wire coming from the weatherhead to the main panel being too small due to the main breakers on the panel being to small. i wpuld need to see the service but imo its too small for what they need. if you need a 225 amp service but only have 200 you will get vd. its also possible the receptical run is too long for the size wires and this is also contributing to the problem. i'v troubleshooted a lot of low voltage problems and its usually the service is too small. people trying to save money. the buck-n-boost will take care of it but if they add more stuff and draw more current the problem will probably return. i would be currious what the voltage is at the lugs/pigtails in the a/c unit is. if its too low those motors and compressors might nit last as long as they should. i'v seen motors and compressors burn up from low voltage. if the service is 277/480 you could also move the stepdown transformer coil taps to boost the voltage. Mike Sokol if you ever want to talk to me on the phone send me a pm and i'll give you my number.
Title: Re: Buck & Boost Transformers
Post by: Mike Sokol on June 16, 2014, 06:42:13 am
Thats a condition of either the main service feeders being to small or the feeder wire coming from the weatherhead to the main panel being too small due to the main breakers on the panel being to small. i

Yeah, you're right. If my B&B correction on the rack continues to work for the next month, we'll have solid proof that the voltage drop during HVAC current draw is causing the sound equipment to malfunction and can justify troubleshooting the entire electrical distribution system. I'm going to suggest a meeting with the plant maintenance guy (who knows where all the panels and breakers are), the lead sound tech (who's been living with this problem), the local electrician (who's been fighting this problem for over a year), the POCO (who can measure voltage and confirm the size of the street transformers), and me (who can make the sound system buzz and misbehave). Maybe we can then get everybody to stop pointing fingers at each other and fix the actual problem.
Title: Re: Buck & Boost Transformers
Post by: Mike Sokol on June 24, 2014, 12:42:49 pm
Buck & Boost Transformer Update: Just got an email from the electrician who reports that the sound system at the church worked perfectly again last weekend, even though all the HVAC units were running full-tilt-boogie. So it seems that if we can keep the processing rack above 110 volts then the system is quiet. They're reporting that the voltage on the rack with the transformer in boost mode didn't drop below 115 even with 108-109 volts incoming, and everything is working perfectly. I'm now recommending that we troubleshoot the rack to find exactly which piece of gear is acting sensitive to the low voltage, then backtrack and figure out if there's any taps on the incoming transformer that can be changed to get the nominal voltage up closer to 120 volts. But at least the preacher is happy and we now have intel about the actual failure mechanism. I'll post later once I learn more.
Title: Re: Buck & Boost Transformers
Post by: Mike Sokol on July 01, 2014, 08:12:04 pm
Buck & Boost fix worked perfectly for another very hot weekend. This is getting boring (not really).

I need to get a 10-amp Variac for this type of testing. No need for an isolated secondary like on my bench units.

Also, I've been reading all sorts of reports of strange buzzes that seem to randomly come and go on various church sound forums. I'm wondering just how often this sort of low-voltage induced buzz happens in other places. Have any of you guys ever seen or diagnosed it? Maybe I'll start a thread on the PSW church forum and pose the question.
Title: Re: Buck & Boost Transformers
Post by: frank kayser on July 02, 2014, 07:58:06 pm
IIRC, Dick Rees is a big Furman 1215 proponent.  I've used one at FOH where genny voltage hovered around 101.  No problems at FOH, but the Crown XTI 1000 amps were VERY UNHAPPY with the low voltage, running hot and prematurely hard clipping.  Since then, if there is even a hint of doubt about low or high voltage (within the limits of the 1215), it gets plugged in.


As far as the PoCo not wanting to replace the pole transformer... and rather than trying to load it to the point of meltdown...


A totally irresponsible individual (none on this board) might suggest just to place something about .308 diameter and 170 grains very close (maybe even touching) the windings in the can.


Call the PoCo and then them the pole transformer is shot.


frank





Title: Re: Buck & Boost Transformers
Post by: John Roberts {JR} on July 02, 2014, 08:37:14 pm
I'd be curious to dig a little deeper and ID the product, or products that are dropping out of regulation. I recall when designing for products to work around the world that low line and high line voltages were more extreme than typical data sheets suggest.

The old CS800 amp was nick named the "Burro" down in SA because it would work to silly low voltages... The Australian outback was notorious for silly high line voltages when they pumped up the distro voltage to send it too many miles down the feed lines.

My guess is some smaller domestic electronic company may have not been conservative enough about PS regulation, but somebody will be the weakest link in any chain and even old companies hire junior engineers.

JR
Title: Re: Buck & Boost Transformers
Post by: Peter Morris on July 03, 2014, 12:02:55 am
I'd be curious to dig a little deeper and ID the product, or products that are dropping out of regulation. I recall when designing for products to work around the world that low line and high line voltages were more extreme than typical data sheets suggest.

The old CS800 amp was nick named the "Burro" down in SA because it would work to silly low voltages... The Australian outback was notorious for silly high line voltages when they pumped up the distro voltage to send it too many miles down the feed lines.

My guess is some smaller domestic electronic company may have not been conservative enough about PS regulation, but somebody will be the weakest link in any chain and even old companies hire junior engineers.

JR

I’m from the Australian outback … and yes some places did have extremely high voltages, but most places were spot on 240V - 50Hz. The Australian Standard was +/- 6% at that time.  I lived on a mine site that had 40Hz power!  We ran most of our appliance through a “Buck & Boost” or auto transform   to reduce the voltage to 196V.  Mathematically that produces the same flux density in the iron circuit of the transformer.  Most things worked OK except record players – 20% de tune … no wonder as a musician my pitch and timing was never good :-\ but my CS800 was!

Another option in this case could be to use a Ferroresonant Transformer to mainatiain the correct voltage.

Title: Re: Buck & Boost Transformers
Post by: Steve M Smith on July 03, 2014, 02:41:20 am
I lived on a mine site that had 40Hz power!

I have a book at home with advertisements for Gibson guitar amplifiers which had a 25Hz option instead of the standard 60Hz.  They must have had some huge treansformers!


Steve.
Title: Re: Buck & Boost Transformers
Post by: Ron Hebbard on July 03, 2014, 03:04:24 am
I have a book at home with advertisements for Gibson guitar amplifiers which had a 25Hz option instead of the standard 60Hz.  They must have had some huge treansformers!


Steve.

Hi Steve;

When I was born, we had 25 Hz power in our homes, 120/240 volts but at 25 Hz, or CPS (Cycles Per Second) as we phrased it in those days.  The Sir Adam Beck hydro generating station at Niagara Falls, Ontario kept a 25 Hz generator up and running 24/7/365 to service the steel industry in Hamilton, Ontario for many years after the rest of us were forced to switch over to 60 Hz.  I can remember my Dad helping me carry four transformers that powered our 027 Lionel model railway to an exchange centre where they'd swap whatever you lugged in for 60 Hz equivalents.  People were lugging in anything and everything with motors, transformers, chokes, ballasts . . You've got the picture.
A quick Google tells me our province of Ontario took most of a decade to fully convert beginning in 1949.

Toodleoo!
Ron Hebbard
Title: Re: Buck & Boost Transformers
Post by: Peter Morris on July 03, 2014, 09:40:53 am
I have a book at home with advertisements for Gibson guitar amplifiers which had a 25Hz option instead of the standard 60Hz.  They must have had some huge treansformers!

Steve.

I believe that the lower frequencies were about minimizing the hysteresis losses in the transformers but it did make for bigger iron circuits...

Peter