1. Register NOW and become part of this fantastic knowledge base forum! This message will go away once you have registered.

Mystery of the Tube Mic

Discussion in 'Vocals' started by fjell_strom, Jun 4, 2005.

  1. fjell_strom

    fjell_strom Guest

    First of all: Recording.org rocks the nation.

    Now, Secondly: I want to kill my new mic! I received it four days ago. Have a look.


    This baby comes, as said, with its own power unit. A seven pin XLR connects the mic to the power unit. A three pin XLR connects the power unit to your input device (in my case an M-Audio Solo).

    What's my problem. It goes like this...I turn on the mic, allowing it to "warm up". The web page says it needs an hour. The instruction sheet provided with the mic says ten minutes. After about fifteen minutes, actually, some real life comes into the mic - I can hear it because I've got the headphones strapped on with the monitoring button on in Cubase. I can suddenly hear the whole room.

    I step up to the mic to give it a test run - fantastic. All is gravy. I proceed to work whatever song I'm fiddling with. Ten minutes pass. I step up to the mic again. The life has left the mic. Not all of it. About seventy percent. I can still hear myself. But all the lovely clarity is gone and my voice is very quiet and extremely boomy. I record another vocal take - the signal coming from the mic shows a stark decrease in strength on screen.

    At this point I thought - "well, the webpage must be right and not the paper insert. The mic needs an hour to warm up and not ten minutes." Only, an hour later, the mic is still dull and low and sending a very weak signal. Half an hour later it is the same. Two hours later it is the same. Three hours later it is the same.

    That sparkling life which occurs at around fifteen minutes after turning her on is sadly never to return. This morning, after having the whole rig off for the night, I repeated this puzzling affair nearly to the T.

    All right, boys. Give me your best guesses and tell me what key information I forgot to provide. I'm standing by, eagerly. All help appreciated as I dearly want this mic to sound the business.

    For what it's worth, my only suspscion is that it perhaps cannot get enough power. There is a switch on the power box which can read either 230 or 115. Is this to indicate it runs at 230 or 115 Volts? It arrived already set to 230. I tried switching it today to 115 and blew a fuse inside the box. I replaced it and am back to where I began at 230.

    Cheers, Dustin

    sorry fo the novel. Wish you fellas were here to mess with the mic yourselves. I've had it. :wink:
  2. Big_D

    Big_D Well-Known Member

    You do have it mounted upside down don't you? If not that could very well be your problem. The heat produced from the the tube and rising to the capsule can cause the issues you mentioned. If you mount it upside down heat wil travel away from the capsule not toward it. Besides the heat can damage the capsule permanently Since the sound degrades after it's been on for a while I would guess this is the culprit.

    BTW, the voltage should always be set the same as the A/C in your country, never change this unless it's set wrong from the factory. You can damage some very expensive gear with an incorrect setting.
  3. fjell_strom

    fjell_strom Guest

    Big D, your advice is muchly appreciated. I didn't have it upside down at all. I'm going to give it a try.

    I find it very troublesome that if this indeed is the problem, why they wouldn't have mentioned it in the long DO's and DON'Ts in the included instructions. Sounds like a good way to ruin a 300 Euro investment.
  4. Kurt Foster

    Kurt Foster Distinguished Member

    It's S.O.P. to "hang" tube mics. The manufacturers of tube mics (especially "budget" offerings) should mention this.

    That may not be the problem though ... you might try replacing the tube. Just because it's new, doesn't mean it's running up to spec ... tubes can be funny like that ... especially cheap tubes made in China.

    When a manufacture charges $4000 retail for a mic, they can afford to QC them, allowing every unit to run for hours and then checking to make sure they are up to snuff. But when you pay $300 for a mic, you can be assured that if your lucky, a short cursory QC was performed. In some cases they will spot check them, one out of ten or one out of hundred. So some mics with problems may slip through the cracks. Contact your retailer or the manufacturer immediately and tell them your problems so you have recourse later, if needed.
  5. Big_D

    Big_D Well-Known Member

    I agree and as Kurt said it should be mentioned in the instructions. Especially with budget mic's as these are more than likely in the hands of novices who may not already know this. I wouldn't have known had it not been for an engineer explaining it to me many years ago. Of course after hearing the reasoning it makes perfect sense.

    Good Luck
  6. fjell_strom

    fjell_strom Guest

    You fellas are superb. :D

    I turned off the mic for a while to let it "cool". Then I turned it upside down and after a half an hour or so, flipped the 'on' switch. Fifteen minutes later, the mic hit the good point where it really warmed up. I started singing a little, monitoring from Cubase. Sounded good.

    And it stayed! Still going strong, sounding beautiful. I wager to say, this might have fixed the problem. I hope so.

    But I still have an uneasy feeling about it. If it uniformly displays this problem when turned right side up but not when upside down, would you consider this perfectly normal and let it slide, given that there were no other apparent issues with the mic? I'm quite satisfied with its sound.

    Cheers, Dustin
  7. Big_D

    Big_D Well-Known Member

    It sounds like you solved the problem but just to be sure let it run for a few hours and test it once in a while. If the problem doesn't return I'd say your safe. If however you notice any issues do as Kurt said and contact the manufactuer right away.
  8. fjell_strom

    fjell_strom Guest

    I've been using the mic now for a few hours and it continues to sound just fantastic. Nothing like before at all. :D

    Last Q for you: How much of a distance should I keep from the mic when singing? And where should the pop filter be placed between myself and the mic - at what distance?
  9. Big_D

    Big_D Well-Known Member

    There are no hard and fast rules on this. I vary it with the mic I'm using and how much room I want to pick up. Sometimes I'm 12" to 18" away others times it may be 3' or more. The key is to pay attention to the sound, when it sounds good your in the right place.
  10. fjell_strom

    fjell_strom Guest

    Wow, those are massive distances compared to what I've been using and what I was expecting. But the advice is appreciated and I'm going to make some tests - back up a little bit.

    Thanks for all the help and your time, Big D. I wish you and your own projects heaps of success.

  11. Big_D

    Big_D Well-Known Member

    Not necessarily, if being right on top of the mic works for you and gets the sound you want then it's right. I had a guy in my home studio this past winter (solo act/accoustic guitar/vocals) and we had to angle my M9 up at his mouth to avoid bleed from the guitar. His bottom lip was practically touching the screen but it sounded great. He's a real pro who knows how to avoid plosives and work the mic. It's probably the best recording I've ever done.

    The point is experiment, move closer, further, left, right, up, down. Each song is different and could require a different approach. Find a good starting point and work it till you get the sound you want. The payoff is knowledge and a sound your proud of.

    I wish you the same Dustin.
  12. fjell_strom

    fjell_strom Guest

    Thought you might like to take a peek what road this same topic "Mystery of the Tube Mic" took on another forum (KVR). If you're interested:
  13. chriscavell

    chriscavell Guest

    The ONLY microphones that should ALWAYS be mounted upside down are vintage mics utilizing the Neumann M7 capsule due to the fact it's made of PVC (Namely early U47's).

    All other tube mics should not behave differently in the manner suggested here unless there is a problem with the microphone itself. AAMOF, most modern tube mics benefit slightly from being mounted right side up as the minimal amount of additional ambient heat helps to keep the capsule completely moisture free. The heat does not in any way damage the capsule, and I repeat, in most cases will improve the characteristics of the capsule if it contains any moisture.

    The only difference regarding the sound of a modern tube microphone regarding the angle of mounting should come from changes in the reflections b/w the face and body of the microphone. Any differences that are larger in scope than this means there is something fundamentally wrong with the mic, and you should have it serviced. It could be as simple as a poor connection at the tube socket.

  14. fjell_strom

    fjell_strom Guest

    Thanks for posting, Chris. :D I enjoyed the sound of the demos available on your studio website.

    I can see that this faulty mic's future is back at the manufacturer. I was wondering, however: If it's replacement is up to snuff, would there be an advantage in swapping it's tube with a "better" brand (I have no clue concerning the world of tubes, but I can only guess the one they'd ship in such a cheap mic would be something 'generic'). And would a quality external preamp be a sensible addition to a tube mic? To any mic?
  15. chriscavell

    chriscavell Guest


    If I'm not mistaken, I believe that is the same Shanghai tube mic so many are taling about lately (identical to the APEX 460 and Telefunken/RFT M-16). Finding a suitable replacement tube should be relatively easy and fairly affordable; but if the mic is under warranty, I'd just return/replace it altogether.

    As for a good pre: all sources tend to benefit sonically from picking the right gainstaging solution for the job.

  16. Big_D

    Big_D Well-Known Member

    In my experience every studio I have ever worked in has either hung tube mics or mounted them horizontally (OH's) never upright. Kurt has also stated that it is "standard operating procedure" to hang them. I have also been told this by other engineers. You are in fact the first I have heard say this is not the case. I don't doubt the validity of the M7 capsule being affected by heat as I have seen and heard of other capsules which are affected similarly.

    So you are suggesting that the heat is in fact good for the capsule. It will improve the sound by removing moisture huh. Silly me, and I thought a moisture problem is better dealt with through dehumidification and proper storage. Oh well live and learn.

    So tell me how do we deal with moisture on non tube condensors? Wait I know we hold them above the tube mic so they recieve some of that ambient heat right.

    Speaking of ambient heat Chris let's try something shall we. Turn on a tube mic for an hour or so, now remove the cover and grab hold of that glowing bottle of ambient heat. Did you get burned? Funny how that ambient heat can burn human flesh but does no damage to a delicate capsule.

    More on this issue comes from Kurt's review of the CAD-M9. The issue was reported in a post at RO and Kurt included it in his review.

    That kind of says it all doesn't it.

    It's funny how turning the mic upside down seemed to solve the problem. For all I know your suggestion that a connection could be loose may be correct. I hardly see how turning it upside down would correct that but funnier things have happened. There could very well be something wrong with this mic so for kicks let's try a little experiment.

    Fjell, Try reseating the tube in the socket, if the issue is a poor connection between the socket and pin this may correct it. If the issue is a loose wire on the tube socket it may come completely loose from the effort needed to reseat the tube.

    Now put the mic in it's holder right side up and run it for an hour or so and test it. Is the issue still there?

    Now let it cool turn it upside down and retest. Is the issue there now?

    Repeat the test 2 or 3 times. If the problem is always when it's upright then this particular capsule is affected by the heat.

    If the results have no correlation to the mics direction then the mic has issues that need to be addressed.

    If you do intend to replace the mic, test the new mic in both positions and post back so we can all see the results.

    Good Luck Fjell
  17. chriscavell

    chriscavell Guest


    I stand steadfast by my previous statements. Further research into empirical data on your part, rather than simply observing the practices of others, will yield you the same results as stated by yours truly.

    The M7 is a capsule made of PVC which is adversely affected by heat in a profound way. Very few of these capsules have survived to modern times. All other modern capsules are most often of a mylar material that can easily withstand the amount of heat reaching it from the tube with absolutely no change in their operating characteristics from those at room temperature. The ambient heat merely provides the added benefit of drying out the internal componentry if such dehumidification is necessary. If the mic is working properly, you should mount it at the angle that provides the most pleasing sound that results from the change in reflections b/w human face and microphone body.

    What I have stated may not be common knowledge to you, but it is definitely common knowledge to all the microphone repair and restoration experts in the business.

    The best way to prevent moisture issues is to work in an airconditioned environment (typically 70% humidity and lower) and store the microphones in a plastic bag (isolating it from a foam case, preventing contamination from the eventual deterioration of the foam) with a packet or two of silica gel inside the bag with the mic.

    When something becomes habit among many over the course of several years (i.e. standard operating procedure), often the full reasoning behind that s.o.p. is lost and forgotten by the very practitioners of that procedure. If you'd like some additional resources to educate yourself with regards to this s.o.p. and why it is for the most part obsolete in today's recording studio, I'd be more than happy to point you to them via private communication.

    My statements were without bias, accurate, and not directed toward anyone in an attempt to create conflict. If in reading my earliest post in this thread you read it to the contrary, I assure you it was not in any way intended to offend, but merely accurately educate.

  18. Big_D

    Big_D Well-Known Member

    No offense taken and none intended. I was merely cracking wise to make my point.

    If you say it is no longer SOP I believe you. I believe you when you say this is common knowledge amongst repair and restoration experts. But we are not talking about mics deserving of restoration or even serious repair, these are budget tube mics selling for a few hundred dollars at most. These mics are manufactured to a price point and design flaws do exist. The M9 is a perfect example (I own a pair) and the same heat buildup that Kurt speaks of in his article exists in mine with a deterioration in the sound if left uncorrected. When mounted upside down the this issue doesn't exist. Maybe it's design, manufacturing, tubes I don't know but the problem does exist and with more than one brand of budget tube mic. Some like the Rodes don't seem to be affected.

    Now you still haven't addressed the issue of why his mic is fine in when suspended but the sound quickly deteriorates when placed upright. Do you have an answer for this?

    I don't know about you but if conventional wisdom says it can't be affected by heat and then I observe something different I go with my observation. Remember conventional wisdom once said the earth was flat.

    I've spent most of my adult life trouble shooting everything from tiny components to massive networks and the process is always the same. Reasoning skills are the key to troubleshooting. In this case heat appears to be the issue. If it weren't I doubt that turning the mic upside down would correct it. Maybe it isn't the capsule. Maybe heat is affecting the electronics. I can't say for sure as I don't have the mic in my hands to test. But I can say it most certainly is not a loose connection.

    The goal here is to solve Fjell's problem and give him a working microphone. Regardless of our difference of opinion I think we have done that.

    Best of luck to you
  19. chriscavell

    chriscavell Guest

    The difference in sound is not due to the effect of heat on the capsule. Again, the amount of heat that actually reaches the capsule is far below the level required to change it's operating characteristics given the material from which it is made. There are only two PVC capsule still made, one is a single order custom manufactured replacement to the M7 hand made by Gunter Wagner, and the other is the actual M7 still made by Gefell and only used within a few Gefell mics (they don't have an OEM side to their business, and actually won't even sell you the replacement part unless you are a registered owner of a Gefell mic that contains the M7). No other mic capsules made today are ill affected by the amount of heat reaching it from a tube circuit. No asian mics, including the shanghai mic at question within this thread, use PVC capsules. They ALL use polyethelene/mylar membranes.

    If, with a tube mic that does not use an M7 capsule, any timbral changes beyond those that occur from changes of the reflection b/w the face and mic body are observed, those changes are due to a fault within the microphone body.

    This can range anywhere from a capacitor operating out of spec, a cold colder joint, or the affects of oxidation+heat on the connections between tube and socket (which is the most common culprit). Power leaves a tube in a few ways: radiated heat, light, work performed electronically, and conducted heat through the pins to the socket. A small amount of oxidation causing a poor connection can eaily create a capacitor at one or more of the pins whose capacitive properties change drastically with small changes in temperature. The amount of energy leaving a tube in the form of conducted heat through the pins can very greatly depending upon whether the tube is upside down or right side up, hence the change in characteristics b/w mounting methods of the microphone itself.

    However, given this particular microphone, and the knowledge of how other OEM rebranders of this microphone opt to use very specific components installed not in Shanghai, but at their own facilities without altering the values or circuit, I would hypothesize the issue is most likely due to one or more of 4 capacitors within this mic that are not functioning properly. (Case in point, the Tele RFT M-16.) The problem may also be one of a few high value resistors within this mic functioning not as resistors, but as thermistors...but that is far less likely.

    Honestly, I didn't realize I'd have to delve into this so deeply, as this (a problem with the internal componentry) is precisely what I proposed as being the most likely cause of problems back in my first post in a far less verbose manner.

  20. fjell_strom

    fjell_strom Guest

    Well, boys, I certainly didn't hope or expect the t.bone sct800 to fuel debate but here we are. I thank both of you, Big D and Chris, for your help thus far and for what it's worth I find the issue of rightsideup vs. upside down quite interesting.

    Yet a new curve has been thrown into the picture - the mic doesn't seem to respond hardly at all, now. I haven't changed or touched it since turning it upside down a few days back whereupon it seemed to be working fine. But now, suddenly, the mic is simply 90% unresponsive. I can hear my voice through it, but only very faintly, although the mic had been on for more than two hours before use.

    I got up the nerve to unscrew it and try and remove and inspect the tube which I did successfully. Since I am a tube mic novice, I had no idea what to look for, but I thought it worth a try. With shaking fingers (I had nightmare visions of breaking the thing) I got the tube out, gave it once over, and popped it back in. Once the mic was back in one piece and back on the stand (upside down) I gave it power and tested after letting the mic warm up. Still nothing. I'm afriad this mic is out of commission as far as I'm concerned and without any further testing or trials, I'm going to send it back and ask for a replacement. You probably know how it is to get a new piece of equipment and really want to be able to actually use the thing. :wink: That's how I feel now.

    But as soon as the replacement arrives, I will certainly post back and let you know how it fares as you've been so kind to me on this bumpy venture. Wishing you both the best of evenings. I think I'm going to locate a pizza. :p


Share This Page