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U Boat 47


 Variable Diaphragm Tube Condenser Mic



27 Sonic Flavors From One Microphone

3 Capsule Segment Choices: Center, Edge, or Entire Capsule

9 Directional Pickup Patterns


Variable Diaphragm

Our patent pending diaphragm and capsule present a completely new concept in condenser microphones. Condenser mic diaphragms have been made  essentially the same way for around 70 years. The diaphragm in U Boat 47 is divided into selectable electrically insulated segments. So using just two switches, either the center segment of the diaphragm, the edge segment, or the entire diaphragm can be selected to be active.

Sonic differences between segments

The center segment sounds like a small diaphragm condenser, and as one would expect, using the entire diaphragm produces a large diaphragm sound. The edge segment presents an entirely new choice to audio engineers. The sound waves from an off axis sound source reach the edges of the capsule at different times. So for this size capsule, frequencies around 10 KHz, will have  the highest part of the wave reach one side of the edge, and the lowest part of the wave reach the other. So they substantially cancel each other. Keep in mind that part of the wave which reaches the center is substantially ignored by the capsule when only the edge segment is active. The overall effect of this is a darker tone from ambient sounds, and a brighter tone from sources in front. This creates a very pleasant mixture of the main sound source with sound reflections coming from the environment. Speaking only of frequency response, the edge segment resembles a medium sized diaphragm.

There are also resonance differences between the different segments. These are particularly relevant to tube mics. The reason tube mics have a "warmer" sound compared to transistor mics is that tubes amplify harmonic content of a signal, with even harmonics amplified more than odd harmonics. This creates a more pleasing and fuller sound which is also perceived as being louder. We will release sound samples and graphic explanation of sound flavor choices soon.

In general, sound from any segment is refined and they all sound very good. you would not have a "bad take" from any of the choices. The subtle differences are a tool for experienced audio engineers with trained ears who like to optimize the sound quality in a given recording situation.      



Individual wires are connected to center and edge segments on both sides of the capsule. This allows the user to select which segments of the capsules are used using switches on the microphone. The selected segments receive an electrical charge and form a capacitor between the back-plate (connected to white wire) and the selected segments of the diaphragm.

User Changeable Tube  


The heart of a tube mic is the tube!  There are sonic differences between different brands of tubes and we wanted to make it easy for recording engineers to experiment with them.


Removing only 2 screws provides easy access to the tube. There are no wires or components that need to be removed in the way.  


Initially, we will ship the mic with 7025 high performance tubes. These are compatible with 12AX7 and 12AU7 tubes. So there are many choices available.


the screws at the bottom are 2.5 mm hex key screws so frequent removal of them will not cause wear on the screw head.

Easy Access to The Tube

 Head-Grill Design

The reflections inside a head-grill have substantial effects on the sound of a tube mic. The reason why tube mics are preferred for recording, is not that the output is more linear. Transistor mics can produce more linear results. Tube mics are used because they can enhance a sound, producing recordings that are more favorable than the original sound.

We experimented with effects of different head-grill designs and chose the one that we found most effective in enhancing clarity and increasing the harmonic content of the signal.

Also an interesting feature of

Some of The Head-Grills Experimented with

Circuit Design

The simpler the circuit in a tube mic, the more pure the sound. So a simple circuit made with high quality components is used in U Boat 47.

The switches which select the diaphragm segments simply connect the appropriate segment to the circuit of the microphone. There are no additional electronic components used to achieve this.

There are no "pad" or "bass roll off" functions included to avoid additional components for those functions which would reduce the purity of the sound.


The circuit and all electronic components used

Pickup Pattern Switching

There are 9 pickup pattern choices; Cardioid, Figure 8, or Omni, and 6 more in-between choices. The selection is made using a rotary switch on the power supply.


Frequency Response Choices

The combination of switches and pickup pattern knob positions result in varying frequency responses of the microphone, which provide a lot of flexibility in selecting an optimal frequency response for a given sound source.  The provided 9 frequency response graphs here are actual output from a measurement system. They are not manipulated for marketing purposes. Other in-between positions of pattern knob would produce results in-between those shown here.

We will prepare a chart with suggested uses for these setting in the near future.

1-Pattern: Cardioid, Switches: Full (positions of Center/Edge have no effect)This produces the classic tube mic type of response with humps around 4 and 9KHz.

2- Pattern: Cardioid, Switches: Part & Center - The humps are less than classic tube sound.

3- Pattern: Cardioid, Switches: Part & Edge - This produces the most linear response.

4- Pattern: Omni, Switches: Full (positions of Center/Edge have no effect) -There is a dip around 5 to 6 KHz.

Frequency Response Choices ... continued

5- Pattern: Figure 8, Switches: Full (positions of Center/Edge have no effect)- The hump at 4 KHz is more pronounced. The second line represents back side of mic.

6- Pattern: Omni, Switches: Full (positions of Center/Edge have no effect)-This produces a linear response.

7- Pattern: Omni, Switches: Part & Edge

8- Pattern: Figure 8 , Switches: Part & Center

9- Pattern: Figure 8, Switches: Part & Edge


The included hard case has rubber seals to protect the equipment.

Microphone is shipped inside a padded pouch similar to those used for photography lenses.

A New Method for Measuring Tube Mic Performance


The customary frequency response curves paint an incomplete and potentially misleading picture when it comes to tube mics. This is because they do not show even and odd harmonic content of the output. Enhanced harmonic content is one of the primary benefits of tube mics. Normally, a frequency response curve is obtained by playing a sine wave with sweeping frequency in front of a mic. The problems with this customary approach are:

1- A sine wave does not have any harmonic content.

2- At any given moment a single frequency is fed to the mic and mic output is recorded at that particular frequency. Even if the sound source had harmonic content, those higher frequency would be ignored in this method of measurement.

We have devised a new measurement method where multiple frequencies are fed to the mic at the same time. So main frequencies and harmonic content are all simultaneously measured.

The following graphs illustrate the harmonic content from playing a C note on a Hammond organ and recording it using U Boat 47 versus a "flat" reference transistor mic.

The graphs illustrate that:

A- 1st “even” harmonic (around 500 Hz) is 5dB louder in output of U Boat 47. Higher “even” harmonics add a pleasing softness and richness to the sound.

B- Harmonics around 3 KHz and 4 KHz are much higher in the output of U Boat 47. These add clarity to the sound.


Pricing and Production


It took 5 years for kam (as a convention on this site,  lower case Kam is meant the company founder;  Kamran) and our team of engineers in electronics, mechanical engineering , and production fields to make this mic a reality. Manufacturing the new segmented capsules with so many additional wires needed innovations in not just the design but also manufacturing process.


It was an interesting adventure with purposely slowing things down to get every aspect right. This was not a project to just make a close copy of a great vintage mic, the aim was to make the greatest mic in the world which can also offer users the option to recreate the sound of the greatest vintage mics,   Should we be content with the best mic that could be produced 70 years ago? Or should we demand more?  U Boat 47 is a mic that shows respect for the vintage mics, but brings entirely new features and concept to the category.


KQMS quality management


K/\M instruments developed KQMS (KAM Quality Management System)  production method, which ensures highest quality. It is based on ISO 9000 family of standards but extended for our type of products. It encompasses from design testing stage to sub assembly testing and production station tracking.

When a flaw is detected, it can be traced to a part/person/machine in production stages to make sure it never happens again.


Production -  U Boat 47 quality management


U Boat 47 is the "crown jewel" of our company and one of  Kam's significant achievements. Aside from KQMS which covers production at factory site. There is significant testing performed in our Chicago locations. Each U Boat 47 mic and power supply get 20 to 30 hours of burn-in test period in our Chicago area facilities. This is because statistically it has been known that an electronic component that does not fail in the first 20 hours, has a significantly lower chance to fail in the next several thousand hours of operation. At the end of the burn it test period, Kam (Kamran) himself extensively tests each U Boat 47 mic fpr noise level and sound quality.


U Boat 47 mics are assembled overseas according to KQMS methodology to keep the prices as low as possible. But final testing and assembly checking done in our Illinois facilities ensure highest level of quality and durability.


 MSRP:  $1350, Availability: Nov 2018


Note: we plan to add a buy-it-now button using PayPal to this page by  November 15, 2018 or before that. Until then you can contact us by emailing info@Kaminstruments.com for direct discounted pricing. Make sure you include your zip code or city so that we can calculate shipping costs.





Capsule Type:                                                Segmented and dual sided

Capsule Diameter:                             34 mm, 1.34 Inch

Center Segment Diameter:               15 mm, 0.6 Inch        

Edge Segment Diameters::               From 16 mm to 25 mm,  From 0.64 inch to 1 Inch



Overall Frequency Response:          20-20,000 Hz

Self-Noise:                                          17 dB

Signal to Noise Ratio:                        76 dB

Max SPL:                                            120 dB for 0.5% THD



Type:                                                  Variable diaphragm and pattern tube condenser

Power Supply Voltage:                     110 to 120, 210 to 240, Switchable

Microphone Weight:                         955 g – 2.1 lb

Microphone Height:                          230 mm, 9 Inch

Microphone Diameter:                     72 mm, 2.8 Inch





Carrying Case and Pouch

Microphone Mount

Power Supply and cable

20 foot ,7 pin XLR cable (connects power supply to mic)


All specifications and pricing are subject to change without notice.