U47 maximum SPL

[c1184701]

Hi everyone. I’m looking for any advice/experience about using U47-type mics in high spl situations. My main question is: can you position a U47 within 5 feet of a loud drumkit and get a usable signal?

I had a U47 clone made for me last year by a small-ish boutique mic company, and when it arrived I quickly ran into problems using it as a mono drum overhead. On loud snare hits there would be an odd distortion, almost like a cheap limiter crushing the transient. I took a look at the waveform and noticed these unusual low-frequency wobbles, around 10-30Hz. Here's a picture (the large peaks are snare drum hits)



After some negotiation my mic went back to the company, who found an issue with the tension of the membrane. They also suggested changing the biasing method to self-bias. My mic is now back at my studio and is still distorting with the wobbly waveform.

Has anyone experienced anything like this before?

Thanks

 

[gyraf]

at least the real (berlin, vf14) version gets a lot of use in situations like that around here, and never craps out

 

[thomasdf]

+1

"boutique" means either top handcrafted microphone, or marketed crap. What is it like ? What capsule, what tube, what output transformer ? What power supply ? What preamp and outboard are you using ? There are many parts that can crap out on transient or loud signals

 

[c1184701]

at least the real (berlin, vf14) version gets a lot of use in situations like that around here, and never craps out

Thanks Gyraf that is good to know. So mono drum overhead, front of kit, with reasonably loud drummers? I'm not expecting to close mic a snare drum with this mic of course. The waveform above was recorded with the mic in this position, which seems like something it should be able to handle:

 

[c1184701]

+1

"boutique" means either top handcrafted microphone, or marketed crap. What is it like ? What capsule, what tube, what output transformer ? What power supply ? What preamp and outboard are you using ? There are many parts that can crap out on transient or loud signals

Hi Thomas thanks for your input. It is a Heiserman H47. So their HK47 capsule, custom made BV08 transformer, NOS EF8XX tube.

I get the same issue through any preamp (Cali VP26, EZ1073, Avedis MA5 etc) or even when connecting directly to line input on my audio interface.

 

[craigmorris74]

Mics of this type can produce a pretty hot signal. Have you tried using a pad before your preamp?

 

[Biula]

Hi everyone. I’m looking for any advice/experience about using U47-type mics in high spl situations. My main question is: can you position a U47 within 5 feet of a loud drumkit and get a usable signal?

I had a U47 clone made for me last year by a small-ish boutique mic company, and when it arrived I quickly ran into problems using it as a mono drum overhead. On loud snare hits there would be an odd distortion, almost like a cheap limiter crushing the transient. I took a look at the waveform and noticed these unusual low-frequency wobbles, around 10-30Hz. Here's a picture (the large peaks are snare drum hits)

View attachment 134917

After some negotiation my mic went back to the company, who found an issue with the tension of the membrane. They also suggested changing the biasing method to self-bias. My mic is now back at my studio and is still distorting with the wobbly waveform.

Has anyone experienced anything like this before?

Thanks

Seems like a power issue to me: this kind of 10-30 Hz oscillations may be a lack of tube power feed during hard transients, with the circuit trying to recover and surge in this odd manner... in this perspective, self-bias method seems a good advice from the company itself: have them modified it, considering you still have the problem?

 

[Accelerator]

@c1184701​

For the drums the “ideal U-47” is the U-47 Fet Condenser Microphone, as it can handles up to 147 dBA for Max. SPL for 0,5 THD at 1KHz…

For your Heiserman H-47 Tube Microphone with EF800 Tube, there aren’t any “official” or not measurements on their site about the Heiserman H-47 Tube Microphone ‘s Max. SPL dBA handling, so keep in your mind craigmorris74’s advice about an external pad before your preamp, some bigger distance (at least more than 6 feets…) and the gain of your microphone preamp(s). low…

 

[emrr]

The MK47 here gets used for OH all the time, many loud drummers.

Don’t recall what I’ve used for preamp but certainly either something naturally low gain or something with an inline pad.

The spikes look as much like lack of shock absorption or something rattling in the mic as anything.

 

[c1184701]

Mics of this type can produce a pretty hot signal. Have you tried using a pad before your preamp?

Thanks for all of the replies everybody.

Yes my preamps are generally padded when using condenser mics on drums. I have also tried this H47 directly into a line input, and the wobbly waveform and associated distortion is still present.

In addition, this really doesn't look like preamp clipping to me. I have done this in the past for special effect, using the output attenuators or inline pads to avoid clipping the interface. That results in quite a hard-knee squared-off waveform.

 

[c1184701]

Seems like a power issue to me: this kind of 10-30 Hz oscillations may be a lack of tube power feed during hard transients, with the circuit trying to recover and surge in this odd manner... in this perspective, self-bias method seems a good advice from the company itself: have them modified it, considering you still have the problem?

This is interesting thanks. The mic has already been converted to self-bias, yet the problem remains. So you think it could be a power supply issue? I have to assume they checked over the voltages when I sent the mic back to them, but I will ask them.

 

[c1184701]

@c1184701​

For the drums the “ideal U-47” is the U-47 Fet Condenser Microphone, as it can handles up to 147 dBA for Max. SPL for 0,5 THD at 1KHz…

For your Heiserman H-47 Tube Microphone with EF800 Tube, there aren’t any “official” or not measurements on their site about the Heiserman H-47 Tube Microphone ‘s Max. SPL dBA handling, so keep in your mind craigmorris74’s advice about an external pad before your preamp, some bigger distance (at least more than 6 feets…) and the gain of your microphone preamp(s). low…

I have a pair of U47 Fets that I built in BM800 bodies using @mihi_fuchs PCBs, which work very well on drums as close mics on kick and toms. I'm certainly not expecting to put this H47 anywhere near a drum as a close mic, but I was hoping to use it as a mono drum overhead and front-of-kit mic.

My preamp would always be padded, and as mentioned above I've ran the mic straight into a line input (no preamp!) and the problem remains.

 

[c1184701]

The MK47 here gets used for OH all the time, many loud drummers.

Don’t recall what I’ve used for preamp but certainly either something naturally low gain or something with an inline pad.

The spikes look as much like lack of shock absorption or something rattling in the mic as anything.

Thanks Doug, so this is a vote for yes, you can use a U47 as a drum overhead.

The mic is properly mounted in its shock mount, and through the process of troubleshooting it has been put up next to Sony C38b, diy U47fet, diy U87, and none of these mics are exhibiting the same wobbles. In fact my diy U47/U87 mount with simple right-angle clips, no shock mounts, so they should expose any floor vibration that might be causing this.

 

[c1184701]

View attachment front of kit1.wav
View attachment front of kit2.wav
View attachment front of kit3.wav
View attachment mono ohd1.wav
View attachment mono ohd2.wav
View attachment mono ohd3.wav

I thought I would attach some audio samples in case anybody has a moment to take a listen. The first three are with the mic positioned fairly close to the drums directly in front of the kit (as in the photo earlier in the thread). The other audio clips are withe the mic positioned as a low-ish mono overhead, perhaps 6 inches above the drummer's forehead.

It's a very unusual type of distortion, almost like a short sag in the audio signal. I've been tracking for over 17 years, and I haven't heard any other microphone or preamp distort like this.

 

[Accelerator]

Let’s Cathode Biased it properly…

For an Oliver Archut U47 Alternative Tube circuit with the EF80(0) Pentode tube wired as a Triode, at 105 DC Volts Vb, with R4 = 100KΩ + R8 = 30KΩ aka RL = 130KΩ, if we want to have the Quiescent Operating Point at 52.5 Vq(V) as center bias for Max. Headroom, then the Grid Bias Voltage (V): -1.01Volts and the Iq(mA): 0.40mA.

1.01Volts / 0.40mA = 2525Ω (preferable) Cathode Resistor...

 

[paulcheeba]

Hi Thomas thanks for your input. It is a Heiserman H47. So their HK47 capsule, custom made BV08 transformer, NOS EF8XX tube.

I get the same issue through any preamp (Cali VP26, EZ1073, Avedis MA5 etc) or even when connecting directly to line input on my audio interface.

I use a pair of these exact mics in a similar position with no issues. In fact they sound great. It’s strange you’re having this problem.

 

[c1184701]

I use a pair of these exact mics in a similar position with no issues. In fact they sound great. It’s strange you’re having this problem.

Thanks Paul this is exactly what I needed to hear. I've seen your posts on Gearspace about these mics, and I was going to reach out to see if you had experienced any problems like this.

So when you say similar position, we're talking lowish drum overheads? Have you noticed any weird oscillations on your waveforms like my screen grab earlier in the thread?

 

[paulcheeba]

No I've never seen any waveforms like that but I imagine being in stereo I'm naturally off axis so I'm not getting the full blast. Have you tried the obvious things like an XLR pad in the cable or tilting the mic up a bit. I've never known such an issue, I mean we use fet 47's as Kick mics. Same kind of capsule right?

 

[c1184701]

No I've never seen any waveforms like that but I imagine being in stereo I'm naturally off axis so I'm not getting the full blast. Have you tried the obvious things like an XLR pad in the cable or tilting the mic up a bit. I've never known such an issue, I mean we use fet 47's as Kick mics. Same kind of capsule right?

I've tried every preamp I own with their pads engaged, with no success. I can record Fet47 inches from a kick drum without any distortion, so I'm certain my preamps aren't the issue. I also tried running the xlr directly into a line input, which is obviously far less sensitive, again no improvement.

Thanks for your input everybody, I'm certain this mic is faulty and has to be returned.

 

[paulcheeba]

Yes it sounds like a lemon and needs replacing.