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Why are all mic power supplies designed for inefficience?
Old 5 days ago
  #1
Why are all mic power supplies designed for inefficience?

My tube/valve mic power supplies are lined up in one row on my rack. Regardless of the brand, the power cords all connect on the side with the on/off switch and LED indicator. The mic cables and pattern knob connect to the other side. This is inefficient and looks sloppy. Either way I turn them, dumb-looking cables are sticking out of the front of my rack. And they're ALL made this way. Why? Turning them sideways makes it too hard to reach the switch and see the LED. Besides the appearance, the problem is that no matter which way I turn it, I have to reach behind my rack to use it. Anybody know why PSs aren't designed to have all of the cords connect to the rear of the PS, with the LED, pattern knob and the on/off switch visible in the front?
Old 5 days ago
  #2
The idea is to keep the noisy AC line stuff as far away from the low-level audio circuitry as possible.
Old 5 days ago
  #3
Quote:
Originally Posted by David Rick View Post
The idea is to keep the noisy AC line stuff as far away from the low-level audio circuitry as possible.
Thanks, David. That is doubtless a technical concern, but it makes no sense to put the on/off switch and LED on one side of the PS and the pattern selector on the other. I accidentally left a mic on for two days once before I realized that I had forgotten to turn off the PS. That's when I realized that I needed to turn it around so that the LED faced me and reminded me to hit the off switch before leaving. Now I can see the LEDs, but the pattern selectors face the rear. It's inconvenient. All functions and controls should be located on one side; all cables should be on the other. I'm not an electrical engineer, but if proximity is really the issue, it seems this could be resolved by making the PS a little wider. I would rather have a PS three times as wide as the typical box if that's what it took.

BTW, I have audio cables that lie directly on top of AC lines in the cable spaghetti behind my rack. If there's any interference, I don't hear it.
Old 5 days ago
  #4
Lives for gear
Why not use an master power switch for the whole rack?
Old 4 days ago
  #5
Quote:
Originally Posted by BT64 View Post
Why not use an master power switch for the whole rack?
That's an interesting idea, BT. Might work. I think my concern would be that hitting the on switch on the master would engage every power supply, whether I needed every mic or not. Tubes and valves may last for years, but they all fail sooner or later. I hate to run tube-based gear if I'm not using it.

This came to light because I'm looking to add to my tube mic inventory. I know that I'm just grousing about what is either design laziness on the part of manufacturers ("That's just how they're made, man"), or a failure to see that a problem even exists. Audio engineers and studio owners may have noticed the problem, but have quietly accepted it as too minor of an issue to grouse about or to raise it with manufacturers.

Because of the way that power supplies are designed, what it comes down to is:
  1. Either the on/off switch and LED are visible and accessible from the front, or the pattern selector is visible and accessible from the front, but not both;
  2. Either the on/off switch and LED are in the rear and are neither visible nor readily accessible from my workspace, or the pattern selector is in the rear and is neither visible nor readily accessible from my workspace;
  3. Either the AC line sticks out of the front of my rack and has to be looped back or the audio cables must connect from the front, which would be even worse. The best I can achieve is to loop the AC line back, which looks dumb.

I've attached a couple of photos for illustration but I give up trying to make the pics appear with the correct rotation. Even rotating them to the right and resaving the rotated images doesn't work.
Attached Thumbnails
Why are all mic power supplies designed for inefficience?-ps-front-view.jpg   Why are all mic power supplies designed for inefficience?-ps-rear-view.jpg  
Old 4 days ago
  #6
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Well not all.
Old 4 days ago
  #7
It's not an oversight

Quote:
Originally Posted by 9xSound View Post
I know that I'm just grousing about what is either design laziness on the part of manufacturers ("That's just how they're made, man"), or a failure to see that a problem even exists.
It's not laziness; it's best practice. The vast majority of tube mics, being older designs, use linear power supplies. (Neumann built a newer one with a switch-mode supply, and there was no end of people grousing about it.) That means they all have a big-assed power transformer, and several secondary rectifier stages, all radiating magnetic fields that are very, very difficult to shield against.

Here's a picture showing the insides of one of my favorites, a Josephson C725. On the left edge you see an AC input board that holds the IEC power connector, line voltage selector switch, and power switch. Mic manufacturers buy this as a complete assembly from a company like Schurter, who certify it for safety in dozens of countries. Next to it is a large board containing the actual power supply. This board is a potential source of noise. It can have hundreds of volts on it, compared to millivolt or lower signals in the audio path.



The right-most side of this board has the DC output connections, and that's the only part of the board it's safe to be close to. No surprise, then, that that where the third board containing the audio connectors and pattern switch is located. Anywhere else would be noisy, and also risk running afoul of regulations on minimum safety spacing. One thing about this particular mic will warm your heart, however: The audio board also contains a green power-present LED. David Josephson could get away with putting it there because LED's run from low-voltage DC. But most tube mics use an AC-powered incandescent lamp, which needs to be on the left side for reasons already stated. Why did they do that? Because, when most of them were designed, LED's did not exist.

Tube mic supplies are arranged in this way because nobody wants to drop $6,000 to $12,000 on a mic with audible 120 Hz hum.


David L. Rick
Seventh String Recording
Old 4 days ago
  #8
Quote:
Originally Posted by BT64 View Post
Well not all.
Ha! Now we're cooking with fire. That's what I'm talking about. Thank you, BT.
Old 4 days ago
  #9
Quote:
Originally Posted by David Rick View Post
It's not laziness; it's best practice. The vast majority of tube mics, being older designs, use linear power supplies. (Neumann built a newer one with a switch-mode supply, and there was no end of people grousing about it.) That means they all have a big-assed power transformer, and several secondary rectifier stages, all radiating magnetic fields that are very, very difficult to shield against.

Here's a picture showing the insides of one of my favorites, a Josephson C725. On the left edge you see an AC input board that holds the IEC power connector, line voltage selector switch, and power switch. Mic manufacturers buy this as a complete assembly from a company like Schurter, who certify it for safety in dozens of countries. Next to it is a large board containing the actual power supply. This board is a potential source of noise. It can have hundreds of volts on it, compared to millivolt or lower signals in the audio path.



The right-most side of this board has the DC output connections, and that's the only part of the board it's safe to be close to. No surprise, then, that that where the third board containing the audio connectors and pattern switch is located. Anywhere else would be noisy, and also risk running afoul of regulations on minimum safety spacing. One thing about this particular mic will warm your heart, however: The audio board also contains a green power-present LED. David Josephson could get away with putting it there because LED's run from low-voltage DC. But most tube mics use an AC-powered incandescent lamp, which needs to be on the left side for reasons already stated. Why did they do that? Because, when most of them were designed, LED's did not exist.

Tube mic supplies are arranged in this way because nobody wants to drop $6,000 to $12,000 on a mic with audible 120 Hz hum.


David L. Rick
Seventh String Recording
Thank you for the really informative post, David. Interesting read. I totally get the need to avoid hum. And best practice is best practice. Every industry finds its own particular sea level. I guess where I'm coming from, as an end user and not an expert in electronics, is that the front-to-back distance on my power supplies (which are for new mics, I should add — not talking vintage) isn't much greater than the width left-to-right. Seems like it should be possible to design a PS that is perhaps housed in a wider chassis to provide the necessary separation to avoid hum, and puts the switches and LED on the front.

I don't know. Like I said, I'm mostly just grousing.
Old 4 days ago
  #10
Lives for gear
It wouldn't be a big problem placing the power switch on front.
I'm guessing most power units are in general not placed in a rack and so in most casus it's no problem.
Old 4 days ago
  #11
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avare's Avatar
 

Quote:
Originally Posted by BT64 View Post
It wouldn't be a big problem placing the power switch on front.
I'm guessing most power units are in general not placed in a rack and so in most casus it's no problem.
The reasons have been told.

Why don't you make power supplies as you like?
Old 3 days ago
  #12
Quote:
Originally Posted by BT64 View Post
It wouldn't be a big problem placing the power switch on front.
I'm guessing most power units are in general not placed in a rack and so in most casus it's no problem.
Yes, agreed. I'm not sure what most people do with their tube mic power supplies vis-a-vis placing them in a rack or not. (Interesting question. Any pix out there?) I never liked having them sit on my desktop because of the cables, so when some rack space became available, that's where I moved them. But I should mention that they were on my desk when I accidentally left a mic on for two or three days before realizing it. (I had it turned so as to see and use the pattern switch, which was the only practical way to position it while searching for the sweet spot. So the on/off light wasn't visible and I overlooked it when shutting down. I didn't discover it until the next time I tried to turn it on.)

I'm not really worried about having cables protrude from both ends. That issue merely disturbs my studio aesthetic. The main thing for me is that I would like all of the controls to be located on a single side. But until then, I'll deal with it.
Old 3 days ago
  #13
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avare's Avatar
 

Why do you not place what you want on the front panel or wherever you want them? This is not a complex undertaking electronically.

When originally designed, the power supply was in the studio. There was tens of feet of hidden cable going to the control room.
Old 3 days ago
  #14
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There are a lot of options like this:


You can have one power supply per outlet and switch it from the front (with a led light up on the switch)
Your problem is solved.
Old 3 days ago
  #15
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Quote:
Originally Posted by 9xSound View Post
Tubes and valves may last for years.
Don’t the valves last longer because of the mild English climate?
Generally boots seem to outlast trunks, and chips survive longer than fries, reportedly for that reason.

How ‘bout you don’t rack your mic power supplies? How many do you have? I only have three right now, and I store the power supplies as they came, in cases with the mics.
Old 3 days ago
  #16
Thanks for all the replies!

I'm actually rather surprised to find myself alone in seeing this as an issue at all, if only a minor one. If I want to use the pattern switch, I need to be able to see and access it. Yes, I can put down my guitar and headphones and go around behind my rack, reach in through the cables and change the pattern, then go back to my workspace, get my guitar back into position, put my headphones back on and test whether I like the sound. Then repeat. And repeat.

Or, I can turn the PS around so the pattern switch faces my workspace. Now life's good. Except that now the on/off switch and LED are only visible from behind the rack. This creates a risk of an inadvertent hot connect/disconnect, which could harm the mic. And it again becomes an annoyance to get totally settled in with your guitar in position, headphones on, ready to roll and: Damn! The mic isn't on.

David Rick did a nice job of explaining my initial technical question regarding why power supplies are designed the way they are. To resolve my immediate issue, I'm sure I could rig up some sort of master power strip to position all the on/off switches in a more visible location, but that just seems like overkill. I don't have spare rack space to sacrifice just to solve what amounts to an inconvenience and the burden of remembering.

But the theoretical issue goes to something Avare alluded to: this cannot possibly be that complex electronically. All amplification must deal with the issue of potential hum. Where's that dual channel universal PS that will operate any tube mic safely, which fits into a single rack space, with voltage selectors, pattern selectors, LEDs and on/off all facing the front, while the AC line and audio cables are in the rear at a sufficient distance to dodge the hum?

I know, I know! I don't know WTH I'm talking about. Rock and roll.
Attached Thumbnails
Why are all mic power supplies designed for inefficience?-ps-rear-view-l.jpg  
Old 3 days ago
  #17
I posted that photo to show that I accidentally figured out how to make images appear in correct rotation. Now if I can just remember how the hell I did it.
Old 3 days ago
  #18
Quote:
Originally Posted by Bushman View Post
Don’t the valves last longer because of the mild English climate?
Generally boots seem to outlast trunks, and chips survive longer than fries, reportedly for that reason.

How ‘bout you don’t rack your mic power supplies? How many do you have? I only have three right now, and I store the power supplies as they came, in cases with the mics.
We're both in California, so I'm stuck with trunks, fries and tubes, too. I store my mics in their cases when not in use. Pretty meticulous about that. But the power supplies are in a permanent position. Each PS is connected to a dedicated signal path of outboard gear. I absolutely hated keeping them on my desktop. Man, it just was troublesome, and having cables littering the desktop drove me nuts. I only have two tube mics at the moment, but I'm in the market for a third, probably an M149. Undecided. So I started looking at power supplies to see whether there were any options. Nope. Not really. Looks like Rode has the right idea with the K2, if I wanted another Rode. All power supplies should be designed like that. Functions this side: cables that side. All I'm saying.
Old 3 days ago
  #19
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nosebleedaudio's Avatar
 

One thing for sure is the transformer generates FAR stronger magnetic field than the power cable does..
It only takes a few inches to make a difference, distance between audio & AC..Most of the time..
I will say for a supply (Small non rack mount) expected to be on the floor OR bottom of rack the power switch ect is usually AC rear, DC front..Including most that I build.

I use the Furman Rack mount surge protection for the Outlets & power switch mostly..One per bay..
Old 3 days ago
  #20
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9x,
From a user standpoint, yes, it makes perfect sense. But, logical as your thinking is, you are writing about mic power supplies, which are not usually designed to be racked.
It is even more mystifying to me to buy rack gear that has all the connections on the back and ALMOST all the user controls on the front, EXCEPT THE POWER SWITCH. It is not a rare thing. Once you rack that piece of equipment in a filled rack , the switch is not easily accessible or even visible. I sometimes don’t use a certain racked device for weeks at a time. I don’t want that piece to be powered up when I know I’m not going to use it.
Northern California... beautiful country for the most part. I’m in the Central Valley above Fresno (“above” on a map, not up in the mountains).
Old 3 days ago
  #21
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Quote:
Originally Posted by Bushman View Post
It is even more mystifying to me to buy rack gear that has all the connections on the back and ALMOST all the user controls on the front, EXCEPT THE POWER SWITCH. It is not a rare thing.
That is because the internal power supplies are bought from third parties who bear the expense of getting them qualified for different regional/regulatory markets. Switch, fuse, IEC inlet as one "cartridge"
Old 3 days ago
  #22
Wasn't the power supply on the floor or out in the room, back in the day? Some of the pics I see have the PS sitting at the bottom of the mic stand or lined up against a wall. If the PS isn't "racked"in the control room then these inconveniences might not matter.
Old 3 days ago
  #23
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avare's Avatar
 

Quote:
Originally Posted by Sombrerogrande View Post
Wasn't the power supply on the floor or out in the room, back in the day? Some of the pics I see have the PS sitting at the bottom of the mic stand or lined up against a wall. If the PS isn't "racked"in the control room then these inconveniences might not matter.
Agreed. I wrote about this earlier in the thread.

Quote:
When originally designed, the power supply was in the studio. There was tens of feet of hidden cable going to the control room.
Old 3 days ago
  #24
Gear Addict
 
audiospecific's Avatar
 

Quote:
Originally Posted by Sombrerogrande View Post
Wasn't the power supply on the floor or out in the room, back in the day? Some of the pics I see have the PS sitting at the bottom of the mic stand or lined up against a wall. If the PS isn't "racked"in the control room then these inconveniences might not matter.
Yes its common practice to have the power supply at the mic stand. Because there is high losses in DC power on long cord runs.
Old 2 days ago
  #25
Lives for gear
Hmm... yes, the power supply relatively near the musician was and is the usual practice in pro studios. In a traditional studio, with separated control and recording rooms, it wouldn’t even have been possible to keep the power supplies racked in the control room. Audiospecific mentions a reason to limit the cable length between a tube mic power supply and microphone. In addition, tube microphone cabling between the power supply and microphone isn’t standard 3-pin XLR cable, so it wouldn’t have been possible to connect a remote power supply to the microphone using the standard XLR plugs and wiring that is OK for passive and phantom-powered microphones.
Old 2 days ago
  #26
Quote:
Originally Posted by Bushman View Post
9x,
From a user standpoint, yes, it makes perfect sense. But, logical as your thinking is, you are writing about mic power supplies, which are not usually designed to be racked.
It is even more mystifying to me to buy rack gear that has all the connections on the back and ALMOST all the user controls on the front, EXCEPT THE POWER SWITCH. It is not a rare thing. Once you rack that piece of equipment in a filled rack , the switch is not easily accessible or even visible. I sometimes don’t use a certain racked device for weeks at a time. I don’t want that piece to be powered up when I know I’m not going to use it.
Northern California... beautiful country for the most part. I’m in the Central Valley above Fresno (“above” on a map, not up in the mountains).
I am much better informed today than I was last week about mic power supplies. Progress is good. No longer do I stare at them with a WTF look while muttering obscenities. We'll see where it leads... Hey, I have friends near you down in Clovis. I'm in the Sierra a short drive from South Lake Tahoe.
Old 2 days ago
  #27
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Quote:
Originally Posted by 9xSound View Post
I am much better informed today than I was last week about mic power supplies. Progress is good. No longer do I stare at them with a WTF look while muttering obscenities. We'll see where it leads... Hey, I have friends near you down in Clovis. I'm in the Sierra a short drive from South Lake Tahoe.
If you are near Lake Tahoe, you might be getting a lot more music business than do I.
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