About 25 feet. Some Neumann and AKGs could be run longer not sure about the current crop of tube microphones.

The cables of the Neumann M149/M150 rentals that I use sometimes is 33 feet, I do scorn the quality of their Tuschel plugs but alas, they seem to work most of the time.
I've run a pair of Brauner Valvets on twice that length (66') a few times without any discenable degredation (a venue where I have to fly them). Generally, I do not belive that any modern tube (or SS) mike should have any problems with longer cable runs!

/ptr

I would think that the high-DCvoltage and high impedance nature of a tube microphone would pose problems beyond 50 feet? None of my Neumann tubes ever had more than 25 foot cables. I'm sure those Germans thought about that a long time ago and probably why we don't see longer cables for tube microphone's. But since I've never tried? Who knows? Maybe Eddie Ciletti knows? I sure don't. But then, I'm an idiot.

Boasting again
Ms. Remy Ann David

Cucco wrote: Anybody have any information or thoughts on the longest run of cable between a tube mic and the power supply?

With the exception of one or two models from Gefell (UM900) and Audio-Technica (AT3060), tube mics are not phantom powered and therefore require an external PSU. This frees them from the relatively low power constraints of phantom powering, and gives them the potential (sic) to have greater output power; therefore lower output impedance, higher output current and less susceptibility to cables. Not only that, it's a 'closed system' because the microphone itself will always be connected to the same input (the PSU/preamp unit) using the same cable (assumedly the one provided), and so the manufacturer has the ability to optimise things very nicely. Whether they take advantage of these benefits is another question, of course! (This also depends on where the audio circuitry exists - either all contained within the microphone body, or split between the microphone body and the PSU...)

In other words, the maximum cable figure will vary from model to model, and the only way to know for sure would be to either consult the user manual or contact the manufacturer.

I doubt that you can make a generalisation on such a figure without being quite conservative. The figure of 25 feet or so mentioned here is probably the safest you could rely on. Most tube microphones are designed for studio use, with the PSU in the floorspace with the microphone. With that in mind, there'd be no point in making the drive capability more than about 25 feet. Any more than that would be nice, but it may also push the price of the system up due to requiring higher powered components throughout, and the majority of purchasers are not going to appreciate that - all they'll see is that it costs more. Then there's the practical issue of cable length: for studio use, a 'dedicated' cable (as required to go between a tube mic and PSU) that's longer than about 25 feet is going to be a right royal PITA to deal with all the time!

This is only thinking about the audio aspect of the cable - there's also the matter of getting the power from the PSU to the microphone, but I would imagine that is less of a problem.

An engineer I know hangs C12's over orchestras. The cables like a 100-125' run.

Thanks for all the info guys.

The idea here is that I'm looking at using a few tubes on location in the near future where the nearest power would be about 100' from the mics. I can make the cable myself for the extra distance, I just want to make sure it's not going to be a problem.

Cucco wrote: The idea here is that I'm looking at using a few tubes on location in the near future where the nearest power would be about 100' from the mics.

Do you mean power source (i.e. mains power) or the PSU for the microphone. If the former, a long extension lead might be the go! ;-)

Cucco wrote: I can make the cable myself for the extra distance, I just want to make sure it's not going to be a problem.

You have the luxury of being able to experiment with the actual mics you intend to use, and therefore find out for certain whether it's going to be a problem or not... Start by making a cable of the length you think you'll need, and AB the performance against the supplied cable. (I guess that's obvious, but this is not the kind of thing I'd be relying on generalisations for.)

Unfortunately, extension cords wouldn't be permitted both for aesthetic reasons as well as fire code (our fire marshall is a jacka$$ who won't allow extension cords to run across any egress. He doesn't care about mic cables though.)

I've thought about just making the cable and seeing, but if it doesn't work, I'm out about $100. I've spent more money and gotten less on other things, but I still hate the idea of doing it.

I guess, if worse comes to worse, I could always cut it into smaller cables and use/sell the others.

Cucco wrote: (our fire marshall is a jacka$$ who won't allow extension cords to run across any egress. He doesn't care about mic cables though.)

Ah yes, that guy - I think you've mentioned him before...

Cucco wrote: I guess, if worse comes to worse, I could always cut it into smaller cables and use/sell the others.

How friendly are you with your local cable supplier? Or, more to the point, the supplier of the cable you intend to use?

Some years ago, when we were designing the custom preamp to allow the Royer SF12 to drive very long cables (300m or so), we needed to test it on a very long length of cable. I contacted a local cable supplier that I had a good customer relationship with, and he leant me a couple of 100m rolls of balanced cable - brand new. Even though the cable was on the roll, both ends could be accessed - the start of the roll protruded through a hole in the cable drum, which is how they held it in place before rolling. There was enough protruding to solder a male XLR to (just the pins, not the shell or anything else like that). By doing that I was able to turn each roll into a massive 100m long microphone cable, and joined them together for 200m. Of course, the cable was still rolled and there might have been inductance issues, but a) this was shielded cable so I wasn't expecting any inductance between the inner conductors of different windings, and b) we were running at very low levels. It worked a treat. And when we were finished, I simply snipped the XLRs off the ends. Those cables probably became 5cm shorter at the most, and were returned to the supplier in brand new and saleable condition.

I know a tube mic cable is a different beast - it has power supply conductors as well as signal conductors, but they're all DC and shouldn't cause much problem on coil. It might be worth a try...

Thanks - I'll give it a whirl...

Jeremy just WTF?

I'm really not quite sure why, with all of the marvelous & quiet solid-state microphones available on the market today, why anybody needs to run a tube microphone with a cable with more than six wires in it, over 100 feet? Surely, most microphones, within 25 feet, should be near an electrical outlet in a theater and/or church. After all, this was the industry-standard ever since the 1930s. Since the power supply also contains the microphones output, one can send that output, from the power supply unit, upwards of 1000 feet, without problems. THAT'S NOT A PROBLEM. So I really don't buy that blah blah about not being able to run a standard 110 volt, insulated & double jacketed (i.e. orange extension cord) across any egress with proper taping and/or mats in place. That's BULL CRAP! I'd go over their 4 foot 2 inch head if I had to as before 1968, this was the standard. Why don't you just hang them from the ceiling? Like I have?

You might also want to tell the moron, that the electrical extension cord is only 110 volts, designed for abuse and trampling upon, while the tube microphone carries a 12 volt, high current DC supply, alone, sufficient enough to kill someone, along with a fairly high current 350 volt plate DC supply along with the healthy AC microphone signal. The jacket is much thinner on this cabling and more prone to damage that might expose wires with dangerous voltage on them if accidentally abraised by an exposed nail within a shoe heel, since this kind of cable is not meant to regularly be trampled across like a nice heavy-duty orange extension cord is. College graduates....Idiots, all idiots! Fire marshals understand high-voltage supplied tube microphones? I DON'T THINK SO!

So I assume that Bruce & I have lost George Etheridge's Wind Symphony, to you, since your lip is still screwed up? As it sounds like you're describing the problems over at Schlesinger Hall? Stupid beyond comprehension. Nowhere near as bad as those bigger idiots at DAR Constitutional Hall. I'll never take a gig there again. Rules are for when the brain's run out. You don't need no stupid tube microphones, so why bother? They're not consistent enough these days anyhow in stereo pairs.

You can't fix stupid
Ms. Remy Ann David

Cucco wrote: Unfortunately, extension cords wouldn't be permitted both for aesthetic reasons as well as fire code (our fire marshall is a jacka$$ who won't allow extension cords to run across any egress. He doesn't care about mic cables though.)

I've thought about just making the cable and seeing, but if it doesn't work, I'm out about $100. I've spent more money and gotten less on other things, but I still hate the idea of doing it.

I guess, if worse comes to worse, I could always cut it into smaller cables and use/sell the others.

OK, J, here's what you do.

You take a cardboard box with a lid and fill it with house bricks, but leaving enough room inside for a socket board. You cut a hole in one face through which you pass a bright orange cord for the socket board. On the opposite face you make another hole and wire your 100 ft of BLACK mains cable which you plug into the internal socket board. You tape the box shut, cover it with brown paper and write POWER SUPPLY. WARNING: HEAVY with a fat felt pen on the top. Position the box near your only mains outlet, plug the bright orange cord into the outlet and run the black cable to power your tube preamps 100 feet away. This should pass the Fire Marshall's inspection as orange mains comes in to the box and gets transformed to much safer black mains, which can be sent anywhere.

Good luck!

When I worked at the local college we had two SM-69 microphones and one AKG C-24. The AKG C-24 was in the smallest of the three halls and the power supply was tucked away on the top of the wooden surround of the hall and was turned on remotely with a simple 24 vdc stepping relay. Pulse it once it turns on pulse it again and it turns off. The microphone cables went into a snake and from there to the control room. In the larger of the two halls the microphone power supply was originally in a large box suspended over the audience's head and was a bitch to work on it was turned on and off through a remote switching supply. The microphone in the medium sized hall was mounted out in the open and there was a cable that ran from the microphone a very long way to a room with the power supply it it. The run was way over 50 feet. When the concert hall was renovated the microphone power supply was relocated to a space above the auditorium and microphone lines run from there. I never had any problems with any of the microphones even the one that ran over 50 feet. Neumann and AKG both had extension cables that they sold for the purpose of extending the lines and the power supply had to me slightly modified for the extended length. Suggest you talk to your microphone's manufacturer.

I have to work with one of the most ANAL fire Marshall in the US of A. He has been known to "drop in" at recitals in the Conservatory and shut them down for the most trivial reasons. In one case because the performer had a smart card recorder on a seat and their was an untaped wire running from the first row to the stage for the power supply. There were about 10 people in the hall at that time and there a three very big doors leading outside. He said it was a matter of egress. EXCUSE ME...

I always have to be on my guard when I do recordings at the college and we are sticklers for taping and re-taping every cord and have gone to some ridiculous lengths to please this gentlemen but we have never had a concert shut down by him due to our "problems".

In this day and age there should be enough AC outlets for you to be within 15 feet at most of an AC socket. Why not do as someone else has suggested and simply plug the microphone power supply into a local AC outlet and run the microphone cords to your position?

Best of luck!

Used to record one of the local orchestra here in town with all tube mics. We placed a universal power supply at the edge of the stage and ran the cables to each mic from there. Some of the runs approached 100 feet and we never had a problem. The mics that were flown went into a second power supply that was upstairs in the catwalks, so those cables were shorter, but the runs were still at least 50 feet.

The mics used included Neumann 582's, Schoeps 221 A and 221B, Neumann UM57, Neumann 254 and 264, Neumann SM 69 and I'm sure a couple others that I'm not remembering right now.

--Ben

FifthCircle wrote: We placed a universal power supply at the edge of the stage and ran the cables to each mic from there.

It's probably a cliche by now, but Einstein once said, “If at first the idea is not absurd, then there is no hope for it”. When I first read Ben's post (above), I actually misread it and thought he had suggested an *uninterruptible power supply*.

That's absurd, I thought to myself. Then I realised that, in theory at least, the idea offers a lot of hope for dealing with a situation like yours. Imagine that you had a battery powered AC supply, as used in uninterruptible power supplies, that was powerful enough to drive your tube mics for the duration of the rehearsal and gig. You'd probably need one or two lead acid batteries (deep cycle type is preferred, although a car battery might get you by for occasional use) hooked up to a true sine wave inverter, with an appropriate ampere/hour capability and maximum current capability to power your tube mics for the day.

I think that would be a great solution; you can place the AC where you need it, and where the fire marshall's book doesn't need it. And apart from the fabulous autonomy, you can feel smug in the knowledge that the AC produced by your true sine wave inverter has (typically) 2% lower THD than the mains power - so maybe cleaner audio!

It's a very simple system. All it needs is a mains powered battery charger, the battery itself, and a pure sine wave inverter. The whole assembly could be mounted on a small trolley and wheeled to where you needed it - a bit like the lower half of a film sound recordist's rig. And, just to be on the safe side, between sound check and gig you could unplug it, wheel to a fire-marshall-approved-AC-powering-position, and top up the charge.

Okay, okay, I'm going back to my box in the patent office now. Sorry...

Interesting...that's not a bad idea, albeit a little on the Rube Goldberg side. :wink:

Okay, so I haven't really weighed in on the many replies thus far, so here goes:

Re: running extension cables -

One of the things I'm trying to avoid is having power supplies scattered all over the place. I'd like to have them in one convenient location (such as in the wings, etc) and have all the leads come from there. In some of the locations I deal with (200+ year old churches) there isn't grounded power or sometimes any power within 100 feet (approx 30 meters).

So, if I were to have say 6 tube mics in use, I'd have 6 extension cords running from a single point to tube power supplies scattered in a hall (and in many cases, no place to visually "hide" the power supply, so there'd be a big ol' box sitting in the floor next to the mic stand.)

I'm not worried about the voltage or current running across the lines (although the local fire marshall is). It's more of a convenience thing for me. (and a big factor that is!)

Re: the fire marshall:

Yes, he's a jerk and an idiot. However, there's no getting around him. Fortunately, the only FM I've ever had a problem with is the guy that does stuff here locally. Since that makes up less than 5% of my business, I can get over that. I've never had problems with FMs in any of the major cities in the US that I've travelled to.

Remy - it's actually not the guys at Schlesinger. Despite their relatively stringent rules about leads, etc., they're a breeze to work with (but you know that...) Yes, I did actually get the contract for George's ensemble and I do feel bad that I "took" it away from you and Bruce. Please understand that, while I did indeed thirst for their business, I was under the impression that it was their bass-clarinetist that was doing the recording and didn't know until 1 hour before we were both on site that it was otherwise. I will gladly make it up to you with free beers for life whenever we have the fortune of frequenting the same watering hole at the same time.

Boz -
I love the idea of the AC box. It fits my sarcastic profile to a T. Of course, practicality goes out the window there, but hey, it's humerous none the less.

My whole reasoning behind all of this is that, for the longest time, I've been using Schoeps CMC 6 bodies and various caps for most of my recordings (along with some odd-ball Gefells and AKGs and of course various ribbon mics). However, in a move that I'm considering right now, I may be shifting to quite a few Schoeps, Neumann, and Mojave tube microphones to use along with some of my existing stuff.

That being said, I don't want to be leaving little droppings all over the various halls consisting of tube power supplies, extension cords and all the other lovely acoutrements.

Given that about 80% of my business is live-concert recording, this just simply isn't an option.

I do appreciate all of the advice and information that you have provided. Ben and Tom - your empirical evidence is enough to convince me that I shouldn't have a problem.

I will likely attempt to use 100' cables on the Mojaves when I have them here for review later this year and see how they work out.

Thanks-

Jeremy

If you were using the same mics, one could build a central HV+heater supply. This would be a practical and elegant solution. Clean on stage or in the cloud, easy set-up and low hump factor.

*****************************

The UPS idea is kind of neat. You need to figure out the power req's. Lets say the tubes are going to pull 12v @ 300mA for the heaters and 300V @ 3mA for the B+...

12*.3= 3.6W
300*.003= .9W
_____________
Total Power per mic = 4.5W

and for Six Mics = 27W

27W from 115V will pull 250mA. Assume you want this thing to supply for 6 hours to cover reh and perf.

6*.25=1.5Ah battery

Wow...that's even less power consumption than I originally thought.

The battery idea might not be a bad one! Considering that rate, I could get by with a relatively light battery.

Sorry, I had to pull away before I finished my last post.

That 1.5Ah figure is wrong. The 250mA is the A/C current draw. Likely the battery connected to the inverter will be 48V. 27/48=600mA. * 6hours = 3.4Ah from the battery. I always like to at least double my requirements to cover stray losses and for safety. So that leaves us with 7Ah minimum from the battery.

Zilla wrote: If you were using the same mics, one could build a central HV+heater supply. This would be a practical and elegant solution. Clean on stage or in the cloud, easy set-up and low hump factor.

It was awesome in the "hump factor." The way this system was designed (I didn't design it- rather my colleague who was somewhat of a tube design genius did) was that the power supply output whatever the top filament voltage required for any of our mics was. Then, each cable was modified (usually with a diode) to knock that voltage down for a given microphone to what it required. No changes were made to the actual signal path of the mics. For microphones that had variable patterns (say an SM-69 or a UM-57), a small adapter was made to adapt that single feed into what the microphone needed to operate with multiple patterns.

He made a variety of power supplies that all sounded pretty awesome that ranged from 2 channels all the way up to 8 channel supplies. Believe me, it saved a huge amount of effort in the setup and tear-down of gigs where multiple tube mics were used as the rig was really not much more difficult than placing a set of preamps on stage for the mics.

--Ben

Zilla wrote: Likely the battery connected to the inverter will be 48V. 27/48=600mA. * 6hours = 3.4Ah from the battery.

Right... but before going too far with that, we need to factor in the efficiency of the inverter, which is typically 90%. So to get 27W out of the inverter, we'll need to put 27/0.9 = 30W into it, from the battery.

If a standard 12V DC car battery was used (not the best choice for regular work if deep discharging is required, but okay for occasional use, and cheap and readily available), you would be drawing 30/12 = 2.5A.

If you wanted, say, 6 hours of autonomy the 12V battery would have to be rated at 6 x 2.5A = 15A/h.

Zilla wrote: I always like to at least double my requirements to cover stray losses and for safety. So that leaves us with 7Ah minimum from the battery.

Agreed. So for six hours autonomy with a 12V battery you'd want something around 2 x 15 = 30A/h capacity. Theoretically, you could run your microphones for six hours and the battery would only be 50% discharged - this is reassuing if things end up going a bit longer than six hours. It's also good for the battery life.

Then there's the 12V DC to 115V AC inverter to consider. The equipment requires 27W. A true sine wave inverter rated at 50W or more would do the job with ease.

Of course, all of this assumes that the total power drain from the system to power the tube mics is 27W. If you wanted to get serious about this idea, you'd need to go back and figure out how much power those mics are actually drawing. I reckon Zilla's earlier estimates would be pretty close, however...