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[Stephen Kirby]

I'm having a "speak of the devil" moment watching a video posted in the Basement about the AC/DC back line.  Apparently they use a Kikusui PCR4000M AC Power Supply / Frequency Converter to supply their Marshall amps with exactly 236 VAC @60Hz, no matter where they are in the world.  According to their guitar tech it's a "very expensive" (I found a -LA model for $10,000 used) and since the weight of the 2000VA model is "1000 lbs." it must be a bear to move around.  But apparently well-heeled musicians who need precise power for their gear really use these things.

Ask a silly question and get a serious answer...by sheer coincidence. 

They also mentioned reserve current, which is been a great white whale for my home stereo.  But I don't want to threadjack any more than I already have.

One rig was at 60Hz and the other which used older UK amps was set to 50Hz.  That video led me to one of Brian May's rig where he also uses a Kikusui supply for his Vox AC30 amps which are notorious for going up in flames.  I'm wondering now how common these things are in varsity tours.

I do remember Robben Ford touring with a Variac which his tech would set in each venue so that his prized Dumble amp got the same line voltage.

[Speed Daemon]

One rig was at 60Hz and the other which used older UK amps was set to 50Hz.  That video led me to one of Brian May's rig where he also uses a Kikusui supply for his Vox AC30 amps which are notorious for going up in flames.  I'm wondering now how common these things are in varsity tours.

I do remember Robben Ford touring with a Variac which his tech would set in each venue so that his prized Dumble amp got the same line voltage.

I've seen the variac trick before for guitar amps, and thought it was pretty clever.  I've used them for smoke tests, and occasionally to fix bad AC voltages before inexpensive AVRs became commonplace.  I suppose that the fancy ones that AC/DC use pay for themselves, but put two roadies who used to watch the meters and tweak the variacs out of work.

I missed the part about using 50Hz on the older amps.  Did they say why?  At first I thought it odd to use the 230V taps with the 60Hz frequency as I'd expect the transformer to compensate for hysteresis loss at 50Hz.  I guess they like the sound when it's set that way.

One person who might know about who uses what for voltage control is Pete Cornish, who has made all sorts of things for top guitar players around the world.  He also rebuilt those AC30 amps, so that makes him an expert twice over at least.  It's no longer mentioned on his website, but there used to be a Cornish AC voltage regulator.  There's a photo of one with Lou Reed's rig:



Looks like he has email now: [email protected]  Anyone thinking of using it, please be respectful!

I once rang up his number expecting to talk to a receptionist or answering machine, and it was him!  He was very kind, considering that it was more of a fan call than a business call.  (I ordered a few cables just to save face.) You don't get that much any more, especially from someone who's a rock star of his own accord.  Don't want to lose that kind of accessibility.

[Jeff Lelko]

Thanks for the reminder! I'm shopping for a FOH UPS to keep my digital mixer from rebooting in the middle of a gig.

That's what I'm using mine for, along with legit battery backup purposes (don't want to lose my FOH in the middle of a show because someone decided that the coffee urn had seniority over the sound system).  I'm actually quite happy with this unit and the price isn't bad as far as UPS of this type go.  The size and weight is manageable and the smaller models will fit in a standard-depth rack.  I just wanted to be sure there wasn't something wrong with it after doing the clock test!  Quite an interesting discussion as well.  I'll look through the manual a bit more.  There are a number of somewhat advanced features on this unit and maybe frequency matching is one of them (doubt it, but it's worth a look).  Thanks for the input!

[David Buckley]

I did a quick Google search and the below schematic represents my recollection of the device.  This is a 400hz aircraft inverter but the principal remains the same.

Yeah Scott, I've seen this type of circuit before.



Essentially, the way it works is the capacitor provides the energy store that gives the swing back against the supply, so the thyristor is reverse biased and thus turns off.  But I wouldn't have thought this would be used for anything needing a lot of power, as half the power is stored in the inductance of the transformer and the cap.  On the bell ringer, the output is, shall we say,  less than a perfect sine

Threaded things with pigtails certainly sounds like a thryristor.  And there would be thyristors present for the static switch element, and the static switch is bigger than the actual inverting elements, as the static switch needs to deal with fault current.   And they have been known to blow up.  The Cyberex stand-alone static switches (of which I am a very big fan) were available in three "classes", the most expensive of which had no fuses in the thyristors, but used thyristors sufficiently overrated that they (in theory) could never be destroyed, Nevertheless, perhaps there is/was a way to use thyristors to make a UPS, just I'm not aware of it.  But... I cant have seen every possible UPS config, so perhaps I am very wrong.  It does happen  

[Speed Daemon]

That's what I'm using mine for, along with legit battery backup purposes (don't want to lose my FOH in the middle of a show because someone decided that the coffee urn had seniority over the sound system).  I'm actually quite happy with this unit and the price isn't bad as far as UPS of this type go.  The size and weight is manageable and the smaller models will fit in a standard-depth rack.  I just wanted to be sure there wasn't something wrong with it after doing the clock test!  Quite an interesting discussion as well.  I'll look through the manual a bit more.  There are a number of somewhat advanced features on this unit and maybe frequency matching is one of them (doubt it, but it's worth a look).  Thanks for the input!

Looks like we may have had some similar past experiences!

I have to admit that I didn't think of getting a UPS until someone else pointed it out.  Ironically I took the plunge with a digital mixer because at least in theory it eliminated the need for an effects rack at the FOH position.  I'd rather have a UPS bolted into a rack than find out the hard way that a UPS made to sit quietly under a desk doesn't travel well.  It seems silly to have a custom case made for a $500 UPS, and I do have a shock mount rack case handy, so...

Does your Eaton unit come with a 4 post mounting kit?  I'm thinking that's a must have for anything with lead batteries.

I wouldn't worry too much about the frequency drift as cheap alarm clocks may be the last thing to use line frequency as a time base.  My bedside clock sets itself from a local FM station.  The pure sine wave thing may only benefit your USB hub, or maybe an electric fan if you used one to keep cool at outdoor gigs.  Some USB chargers are known to overheat and fail with square wave inverters, and AC motors don't like the low crest factor.  My old square wave standby models actually work quite well, but prices of double conversion models have gotten so affordable it's worth spending an extra $100 to have.

One more thing that I don't think anyone has covered:  If you're using a digital snake, chances are that your stage box will also be susceptible to power interruptions, and need a UPS there too.  I didn't think about that until my stage box arrived and I saw the free software license booklet that's a dead giveaway that there's a little Linux computer in there somewhere.  So much for saving weight...

[Scott Holtzman]

Does your Eaton unit come with a 4 post mounting kit?  I'm thinking that's a must have for anything with lead batteries.

The Eaton is a standalone system that has battery cabinets and either integrated or discrete rectifer inverter modules that are added to backplane frames.  I have not taken the training yet.  The APC it is replacing is 4 cabinets takes about 100 square feet of floor space.    I will post pictures of the old and new.

[Scott Holtzman]

Yeah Scott, I've seen this type of circuit before.



Essentially, the way it works is the capacitor provides the energy store that gives the swing back against the supply, so the thyristor is reverse biased and thus turns off.  But I wouldn't have thought this would be used for anything needing a lot of power, as half the power is stored in the inductance of the transformer and the cap.  On the bell ringer, the output is, shall we say,  less than a perfect sine

Threaded things with pigtails certainly sounds like a thryristor.  And there would be thyristors present for the static switch element, and the static switch is bigger than the actual inverting elements, as the static switch needs to deal with fault current.   And they have been known to blow up.  The Cyberex stand-alone static switches (of which I am a very big fan) were available in three "classes", the most expensive of which had no fuses in the thyristors, but used thyristors sufficiently overrated that they (in theory) could never be destroyed, Nevertheless, perhaps there is/was a way to use thyristors to make a UPS, just I'm not aware of it.  But... I cant have seen every possible UPS config, so perhaps I am very wrong.  It does happen  

I searched for quote awhile to find any data on the Lorain Power Systems ConstAC.  We are talking about something that is almost 40 years old.  I think it was a 10Kva unit if I recall. Relatively speaking it was a very small part of the power plant.  95% of the gear ran off the 48V DC power system.  For the few things that needed 110V, like the ROP printer a small inverter was usually installed in the frame.

The Lorain unit used a 48V input and had a built in rectifier, it was a full time device and you could either use it as just an inverter or a stand alone UPS.  The batteries were about 4 feet tall and clear plastic so you could read the hydrometer and see plate damage.  The copper bus bars were a work of art.

Again IIRC there was no static switch.  THe maintenance bypass was an external mechanical switch.  If the thing failed the output went out. 

 

[Speed Daemon]

The Eaton is a standalone system that has battery cabinets and either integrated or discrete rectifer inverter modules that are added to backplane frames.  I have not taken the training yet.  The APC it is replacing is 4 cabinets takes about 100 square feet of floor space.    I will post pictures of the old and new.

I'm not following you, Scott.  The Eaton PW9130L1000R-XL2U that I'm looking at has a 2RU form factor, but no rack ears.  I've had the dubious honor of helping install a few APC 2RU SmartUPS units, and they can't be supported by the front ears alone; you must use the 4 post kit or put them on a very sturdy shelf.  They're built like tanks, and with the weight to match.  And that's just for fixed installation!  I don't want to have a rackmount UPS torque itself off its rack ears after falling off the top of a stack of cases.  These things happen at the most inopportune times.  In that respect it sorta makes sense to order a $1000 custom road case for a $500 regular style UPS--at least the foam would support it in all directions.

[Scott Holtzman]

I'm not following you, Scott.  The Eaton PW9130L1000R-XL2U that I'm looking at has a 2RU form factor, but no rack ears.  I've had the dubious honor of helping install a few APC 2RU SmartUPS units, and they can't be supported by the front ears alone; you must use the 4 post kit or put them on a very sturdy shelf.  They're built like tanks, and with the weight to match.  And that's just for fixed installation!  I don't want to have a rackmount UPS torque itself off its rack ears after falling off the top of a stack of cases.  These things happen at the most inopportune times.  In that respect it sorta makes sense to order a $1000 custom road case for a $500 regular style UPS--at least the foam would support it in all directions.

That's because I am not making sense Bill.

I need to be very careful posting from my phone.  We had a side discussion going about full time UPS's, switching times and such in this thread.  I had mentioned that we are upgrading the UPS in our datacenter to a new Eaton not remembering that the original UPS mentioned was an Eaton.

So I butted in and hijacked, with no malice intended so please accept my apologies and carry on.

[Speed Daemon]

That's because I am not making sense Bill.

I need to be very careful posting from my phone.  We had a side discussion going about full time UPS's, switching times and such in this thread.  I had mentioned that we are upgrading the UPS in our datacenter to a new Eaton not remembering that the original UPS mentioned was an Eaton.

So I butted in and hijacked, with no malice intended so please accept my apologies and carry on.

No worries.  I too had been crossing topics, and thought that I had missed something.  My vague thought was "I don't want to buy a road case for that!"

[ProSoundWeb Community]