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Post by Deleted on Feb 9, 2017 12:56:40 GMT -6
Quick question... I've been modding a used Apex 460, nothing crazy, just the Brian Fox mod and I'm pretty happy with the way it sounds for what I need it to do, even with the stock capsule. I noticed however, that the noise floor is significantly lower when its in full Fig-8 than when it is in straight up Cardioid, or even in any of the detents in between cardioid and fig 8. In cardioid it's much noisier than my FET mics, which is to be expected I suppose, but in full Fig-8, it's just about the same noise level as my FET mics. The tube I have in there is a fairly new EH6072, I've been burning it in for just over a week straight.
Is this usual or unusual?
Also, is this an indication that possibly the backside of the capsule is better, or in better condition, than the front side and maybe I should reverse the capsule?
I really like how it sounds in fig-8, so whatever is going on, it's working for me, but I thought I'd ask in case reversing the capsule could further improve the sound.
And yes, I'll probably change out the capsule at some point with something better, but as this is intended to be used as a VO mic for certain types of reads, the sound I am going after is one similar to my Sennheiser 416, but with a bit more meat in the low mids, which it currently has even with the stock 32mm capsule.
Thanks in advance!
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Post by Deleted on Feb 9, 2017 17:16:24 GMT -6
The noise floor in figure 8 can be also lower because of the side signal rejection. In full fig 8 you completely eliminate side signal and depending on the recording place this can be a big and by chance the biggest factor in the difference of noisefloor behaviour. I would look into this first and see if there is something to improve for the cardiodid setting in your place. (room acoustics)
As for the different sides of the capsule, you can check that e.g. if you record a signal in fig8, then turn the mic 180 degree and record again. Most probably one of the recordings sound better or louder. This is the side you want to have frontwise in cardiodid. I guess this is the easiest way to find out if it makes sense to open the mic and flip the capsule.
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Post by Deleted on Feb 9, 2017 17:38:31 GMT -6
If you are talking about voice recording, there is another effect, that can easily have an effect on noise floor. It is the proximity effect. Despite many people claim a multipattern condenser always has strong proximity effect, this is actually not the truth. They behave like fixed pattern in the according positions. In fact, the proximity is twice as strong in the fig8 pattern as it is in the cardiodid pattern and it is completely absent in omni pattern. So, if your signal is near the mic and the proximity effect is kicking in and you have content below 200 Hz, you might have a better noisefloor behaviour because you have more bass content but same noise, if your noise is not in the bass range, which is unlikely or, more precise, depends on the noise sources. Bass signals behave differently over distance than higher frequency content. They fade much faster, so it is unlikely you get bass noise, especially if you use a spider mount to minimize bass impact from the studio floor. So you get more signal content in the bass, but same noise if the bass noise is absent or low. So you get noticably different noisefloor, with improvement in the fig8 position. Neumann has done some research on the different proximity effects to prove this behaviour, pretty interesting.... www.neumann.com/homestudio/en/what-is-the-proximity-effect
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Post by Deleted on Feb 9, 2017 17:57:30 GMT -6
Hm, i am not sure about if this topic might fit better in the Pro Audio forum section, since it's more about mic behaviour than actual modification or diy electronics, Johnkenn ?
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Post by Deleted on Feb 9, 2017 18:46:16 GMT -6
Smallbutfine, Thanks for the input. Luckily, I can rule out room acoustics being the culprit. The booth I work in every day is pretty spot on. Great suggestion about turning the mic around. I'll give that a shot tomorrow morning during my warmups.
Admittedly, my observations on noise floor levels are unscientific and based upon VU meter readings with the mic on with no gate, booth door shut and comparing that with when I switch to my 416 or one of my other modded FET mics. I'm also using Rycote mounts on my booth mics which have definitely worked better than other mounts for me regarding rumble, etc.
I'm glad to hear that all of your thoughts on this topic are along the lines of the noise floor fluctuations being naturally occurring issues rather than mechanical ones though. I did try a different tube, a 12AU7, and it didn't noticeably change the noise floor--I'm not ruling out the tube or ruling out trying a better tube, but for now, after reading your thoughts, I'm starting to feel more confident that this is just probably normal for this mic and not an anomalous occurrence or something I botched in the mod.
Thanks again!
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Post by Deleted on Feb 9, 2017 21:06:19 GMT -6
Self-noise of a mic really is an important measure. So in the end all depends how much noise there is practically in your recordings. Best way to figure this out is to leave the mic in the booth and just see how much noise you actually get in your DAW. The specs of mics usually specify A-weighted self-noise, so the spectral behavior of the noise matters. A-weighted means it is taken into account that psychoacoustically we percieve basses in noise less much less than higher frequencies. This said, there are some guidelines what is acceptable noise. The quietest mics there are can reach below 10dB self-noise, which is better than what almost every recording room adds to the noisefloor. Most people find everything below 20dBA totally sufficient for everything except for recording of very quiet sources. Above that the noise becomes noticable, definitely. More than 24dBA is unacceptable except on very loud sources and normally does not qialify for studio works. Signal-to-noise levels are measured by standard with a sound pressure level of 94dB/1 pascal, so the calculation is Signal-to-noise level A-weighted (dBA) = 94dB - Self-Noise A-weighted(dBA) However, what you see in your DAW's VUs normally is unweighted, so it is definitely higher. This all said, what matters for you is the *actual* noise you get in your track. So, to get a reality based figure, set your levels to get an RMS recording level of -18dB shown in your DAW, loudest peaks shall not go hotter than -6dB at any time. This way you get nice dynamic recordings. Now see, what actual noisefloor you get if you let the mic alone and verify subjectively, how obstrusive you percieve the noise if you set the playback level of your monitoring at a comfortable level you normally use. If you are picky, you can start a frequency/noise measurement sweep in the recording booth to see the spectral behaviour of the noise with one of the PC-based analyzing programs, don't know if there are similar programs for Mac... But your DAW software most probably has possibilities to show up the spectrum of the noise you get. And from this you can come closer to the sources of the noise and if there is something obviously wrong and can be improved. You may also see hum etc.. To get a good picture of the noise content, just record 30-60 seconds of the mic alone in the booth, normalize this and watch in the analyzer of your DAW. Now you can see which frequencies are critical, or if there is more like white noise (all over the place) and so on. After setting up the conservative level as i wrote before, how much noise and hum shows up in the meter anyway? less than -75 dB? I would not bother at all. At least if you don't record 24 channels thru the tube mic in your mix (noise DOES add up with track count). I would be perfectly happy when achieving -73...-72 or even -70 dB on my DAWs scale across the audio band (22khz) this way, maybe even more noise depending how the spectral behaviour is and first - how *perceivable* it really is. Your ear IS a very good measurement instrument to decide how acceptable the noise is. There can be very annoying noise or maybe even a smooth warm unobstrusive floor, you can not see that with a VU meter. Also, use a clean pre with the tube mic if noise bothers you. As clean and quiet as possible. Make sure you do not hear the pre noise and blame the mic if your pre is noisy at the maybe 30dB gain you might only need. Use good mic cable. Sometimes a lower impedance input on the micpre which might have to be compensated with more gain does the trick.
Wow, now i wrote much more than i intended to. I hope you can make use of it to check if you can live with the noise of your mic. It does matter that you can go to record beeing relaxed and not beeing unsure about the noisefloor...
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Post by Ward on Feb 9, 2017 23:18:14 GMT -6
Not that an unusual find. Every TLM170 I have owned, own or have used has a tiny bit less noise in Figure of 8 then cardioid or omni
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Post by Deleted on Feb 10, 2017 11:12:22 GMT -6
First off, thank you both for your input.
Smallbutfine: I appreciate the lesson. I'm happy to learn more about ways to analyze my gear's performance and hopefully how to optimize my work product. I tried what you suggested about turning the mic around in Fig-8 and discovered that backside of the capsule actually (and not shockingly) sounds like crap compared to the front so I'll definitely be replacing that sooner than later, but after I give it a noise floor check as you described for better comparison.
Ward: Thank you to you, too. I'm again relieved to hear that this particular issue is a non-issue.
For now, I'll consider the issue resolved. Thanks again, Dudes of RGO! We now return you to your current programming...
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Post by aamicrophones on Feb 10, 2017 15:27:12 GMT -6
Hello, I have done hundreds of these upgrades. I have not experienced any significant audible difference between the noise in Cardiod and Fig 8. I actually have one on the workbench that I just finished up for a client and I was getting feedback in the headphones before I could hear any noise in Cardiod. When I switched to FIG 8 there was no audible difference that I could hear or measure. However, our good friend Brian Fox will agree that the stock capsules are very inconsistent and this could be the problem. If you reverse the capsule wiring then you can determine if the capsule is compromised on one side. It is the capsule that produces the self-noise given in microphone ratings. If the diaphragm does not mate smoothly with the back-plate then self-noise will increase. We run a stress test on all our capsule to make sure the self noise does not increase. Now, as someone else had mentioned you do get more proximity effect in FIG 8 plus both sides of capsule are active so you will get a better signal to noise ratio. Short pin 2 of the tube to ground and then listen to the microphone. You have now shorted the input and all you are hearing is the tube/circuit noise. Brian also mentions on his site that there can be 16db difference is noise between EH6072a tubes. We use the EH6072a in some of our tube circuits and we generally find the pre-tested tubes we buy very quiet but we get about a 5% failure rate or ones we reject as being too noisy. We have also found in some of the APEX power supplies noisy Zener diodes. The APEX supply comes with two 72v zeners D4 and D4 in series which hold the plate supply voltage at 144v + or - 2%. We prefer 124v dc which means the capsule is polarized with about 60v not 70v. D4 & D5 in the power supply should be changed to 62v zeners. The difference in noise level between a FET microphone and a properly working tube microphone should be less than 2-3db in my experience. Our AK47 capsule will fit in the head grill which will probably give you more of the low mids you are looking for. Our 35mm AK67 capsule will not fit in that head grill. Our AK12 capsule fits and is what we usually use for 460 upgrades but this give the microphone a more C12 like sound while the AK47 is probably a better choice for voice-over work. Cheers, Dave Thomas aamicrophones.com Quick question... I've been modding a used Apex 460, nothing crazy, just the Brian Fox mod and I'm pretty happy with the way it sounds for what I need it to do, even with the stock capsule. I noticed however, that the noise floor is significantly lower when its in full Fig-8 than when it is in straight up Cardioid, or even in any of the detents in between cardioid and fig 8. In cardioid it's much noisier than my FET mics, which is to be expected I suppose, but in full Fig-8, it's just about the same noise level as my FET mics. The tube I have in there is a fairly new EH6072, I've been burning it in for just over a week straight. Is this usual or unusual? Also, is this an indication that possibly the backside of the capsule is better, or in better condition, than the front side and maybe I should reverse the capsule? I really like how it sounds in fig-8, so whatever is going on, it's working for me, but I thought I'd ask in case reversing the capsule could further improve the sound. And yes, I'll probably change out the capsule at some point with something better, but as this is intended to be used as a VO mic for certain types of reads, the sound I am going after is one similar to my Sennheiser 416, but with a bit more meat in the low mids, which it currently has even with the stock 32mm capsule. Thanks in advance!
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Post by Deleted on Feb 10, 2017 16:24:44 GMT -6
Thanks Dave! Yeah, I'm definitely going to replace those two Zeners in the PS with 1n4759's. I can probably rule out the tube since I've tried 3 different tubes: AY7, AX7 and AU7 and they all produce pretty much the same noise floor, the AX7 being a bit more noisy. Like you said, I'm fairly certain the capsule is the main culprit though. I'll give it some thought. I may just stick with some kind of 67/87 style cap though since that's the tonality that seems to work best for what I do and the sound my clients want from me.
Thanks again, Dave. Appreciate the input.
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Post by aamicrophones on Feb 10, 2017 17:43:54 GMT -6
Thanks Dave! Yeah, I'm definitely going to replace those two Zeners in the PS with 1n4759's. I can probably rule out the tube since I've tried 3 different tubes: AY7, AX7 and AU7 and they all produce pretty much the same noise floor, the AX7 being a bit more noisy. Like you said, I'm fairly certain the capsule is the main culprit though. I'll give it some thought. I may just stick with some kind of 67/87 style cap though since that's the tonality that seems to work best for what I do and the sound my clients want from me. Thanks again, Dave. Appreciate the input. Hello, I have lots of our AK89 (67 type) capsules which looks exactly like the capsule in the 460 except these are skinned with 6 micron mylar and come from the capsule makers we have been working with for over 10 years now. The are brighter than our 35mm AK67 which won't fit in the head grill of the 460. However, you can tame them by putting a 470pf to 1000pf capacitor across pin 1&9 of the tube socket. Its the capsule I use in our CM47fet. They are not on my site but I can sell them for $65 each. E-mail me directly at dave@advancedaudio.ca if you want to try one in the upgraded 460. It will have more low end than the stock capsule. Cheers, Dave
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Post by Deleted on Feb 11, 2017 14:11:18 GMT -6
That sounds pretty good. I'm in no rush so I'm going to give it some thought as to what I feel like ultimately accomplishing with this mic. I only do VO so my needs are pretty limited but its worth considering if I do want to go with another tonality just for grins and giggles. I'm sure I'll be in touch at some point!
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Post by EmRR on Nov 22, 2017 9:17:22 GMT -6
Brian also mentions on his site that there can be 16db difference is noise between EH6072a tubes. Having just gone through burn in of 30 of these for some console retuning/restorations, I can second that statement. As well, if you burn in at a higher current draw it appears noise increases permanently.
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Post by ericn on Nov 22, 2017 12:13:20 GMT -6
Yeah I would say the perceived self noise is often lower in figure 8 emphasis on perceived!
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Post by svart on Nov 22, 2017 12:25:48 GMT -6
I also have an Apex460 that's been "fox modded" by myself and I don't have an issue with noise. I'm using JJ 12AY7 though.
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Post by dandeurloo on Nov 22, 2017 19:51:45 GMT -6
Brian also mentions on his site that there can be 16db difference is noise between EH6072a tubes. Having just gone through burn in of 30 of these for some console retuning/restorations, I can second that statement. As well, if you burn in at a higher current draw it appears noise increases permanently. I've heard you can remove noise in a tube by burning them in at higher voltages. It is suppose burn the crud off the tubes. I have heard it can work but can also kill the tubes. So it is a gamble. But if the tube is noise and useless then I guess it is worth it.
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Post by EmRR on Nov 22, 2017 20:48:23 GMT -6
So how do you burn them in at higher voltage AND lower current? That's a see-saw.
Or are you mentioning the thing of running filament higher than spec, which is a rejuvenation method?
In the case I experienced, tubes with higher plate and cathode values did uniformly well, and a couple slots with lower value cathode and plate uniformly made for worst noise result.
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Post by dandeurloo on Nov 22, 2017 21:32:55 GMT -6
Or are you mentioning the thing of running cathode higher than spec, which is a rejuvenation method? In the case I experienced, tubes with higher plate and cathode values did uniformly well, and a couple slots with lower value cathode and plate uniformly made for worst noise result. I haven't tried it yet so I don't really know how it works or doesn't work.
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Post by EmRR on Nov 22, 2017 22:01:50 GMT -6
Or are you mentioning the thing of running filament higher than spec, which is a rejuvenation method? In the case I experienced, tubes with higher plate and cathode values did uniformly well, and a couple slots with lower value cathode and plate uniformly made for worst noise result. I haven't tried it yet so I don't really know how it works or doesn't work. Sorry, meant filament....fixed....
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