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Bock Audio 251 Tube Condenser Microphone  From Bock

One of the BEST modern day recreations of the coveted Elam 251.  Looking for the sound of the 251 without the vintage headache? Look no further than the Bock 251.

Bock Audio

What We Think

At Sound Pure we have always felt the 251 is one of the most versatile mics for all mic lockers, and the Bock 251 is one of the best 251s money can buy. 251s capture the performance like no other mic, and they do it without overstepping sonic boundaries. Many other vintage style mics can be heavy handed and change the performance, but the 251 simply captures the detail of the performance while adding just a touch of warmth and excitement. Anytime the performance in the room sounds great, the 251 is the right mic.

The Bock 251 is such a great example of what we love about 251 microphones. It has all the detail and presence that you are looking for in a vocal performance, or on your favorite instrument. One of the attributes we love the most is how easy it is to get the recording of a 251 to sit in both sparse, low track count mixes as well as big highly produced mixes. It responds to EQ so well (partially due to the flat response), that you really can place this mic just about anywhere in the mix. If you are looking for that one great mic that will take your studio to the next level, the Bock 251 must be on your short list of mics to look at.  

With Sound Pure's unique "Try Before You Buy" program, there is nothing to lose. If you have interest in this mic, give us a call and let us send you one to try in your studio!


251 Style Vocal Mic Shootout: Telefunken 251E v. Bock 251 v. Upton 251 v. Neumann M149

In this video we present a 251 style vocal microphone shootout using the Telefunken 251E, the Bock 251, the Upton 251, and the Neumann M149. Can you tell which one's which? If you are interested in hearing the results and/or getting ahold of the audio files from this shootout, give us a shout, we'd love to hear from you!

Manufacturer's Description from Bock

What Is It?

The vintage 251 is THE vocal sound people ask for, but the original (vintage) versions are 50+ years old and sound very different from one another. Repairing, rebuilding and “nursing” original 251s along has been David Bock’s work spanning over 30 years. The risk for a modern studio or end user to depend on a vintage mic on a daily basis is increasingly problematic. 

The Bock 251 is David Bock’s answer to the vintage mic dilemma of getting “that sound” without the headaches. It is a premier lead microphone for premier voices. It is built to last and provide the studio and user with many years of daily, high end performance. 

What Makes It Different? 

The Bock 251 provides the user with absolute confidence that this is the mic you put in the most critical situations. The Bock 251 uses a proprietary hand made German capsule, a proprietary hand wound multi sectioned audio transformer, a NOS tube in the mic amplifier, a hand built outboard power supply and a custom low capacitance audio cable. This is one of the best overall mic packages available on the market at any price. The Bock 251 is the ideal microphone to choose when there is a variety of applications that must met with absolute top recording quality. With frequency response that extends well beyond the normal range of typical studio microphones, the Bock 251 sets new standards. 

For vocals, the Bock 251 instantly delivers that huge vocal sound you have wanted for years. It sounds equally impressive on females and males. It will capture the most intimate and subtle details of a vocal yet maintain integrity at high SPL’s. It holds up track after track, “sitting on top” in extremely dense mixes without EQ. 

For instruments, the Bock 251 offers very high end performance on critical stringed instruments, orchestras, choirs and small ensembles. The outstanding transient response reveals elusive harmonic details that spell the difference between good and great in your recordings.

How Do I Use It? 

The Bock 251 cardioid pattern shuts off the back of the capsule to deliver extraordinary vocals when worked very close. It is recommended to use a pop filter on less experienced vocalists to enable closer working distances to take advantage of the magical proximity effect. There is no low frequency filtering used on a Bock 251 so you will hear low frequency content you’ve never heard before. 

At distance, the Bock 251 delivers a level of definition that is amazing. The high end does not fade with distance like so many other condensers and the power and depth of the low end response is a joy to hear. The omni and Figure 8 patterns prove useful in these non-voice applications.

System Includes 6 pin Tuchel cable, AC cable, wood box, spider shock mount, and shipping system.

Technical advantages the 251:

1) True transformer balanced output using hybrid lamination four section transformer*. Our transformer is ten times the size of the original so you get no rolloff in the low end until 8Hz (with no loss of high frequencies), making our mic more full bandwidth than the original.

2) NOS dual triode** with traditional resistive (not transistor) load and enhanced original circuitry for unique vintage amplification curve and dynamics response!

3) Selected ck12 type capsule.

4) True linear power supply featuring choke fed, passive shunt regulated B+ voltage and new super-quiet heater regulation, providing a better hum and noise spec than the original.

5) Original headgrille dimensions and wire mesh layers are maintained for faithful replication of classic 251 headgrille resonance effects.

6) Higher wattage resistors reduce noise effects due to heating inside the mic.

7) Shock mounted ceramic tube socket unlike any other in the industry reduces in-band tube resonance & increases s/n while ensuring long trouble free life.

8) Switchable three patterns on mic: omni, cardioid, fig 8. Cardioid completely removes the rear membrane and it’s associated circuitry from the signal path ensuring an optimized tone and s/n.

9) P251 power supply has power on indicators located at both ends for quick and easy “power on/off” status verification.


*(four section transformers cost much more than the common unsectioned or two sectioned device but have a greater ability to resolve complex program material)

**(most NewOldStock tubes perform better than any currently made tubes in microphones, and we have secured adequate stock for many years to come and will not run into shortage problems like those seen with VF14’s and 6072’s)

Bock Audio

About Manufacturer

Inside every Bock microphone is a collection of very high end and unique-to-Bock parts influenced by experience rather than textbooks.  The direct knowledge of the studio of what made two great vintage mics sound different from each other proved invaluable to David in designing Bock Microphones.  All brass hand built hand tensioned capsules with the more robust 6 micron diaphragms, offer transparency without artificial brightness.   Multisectioned Bock design transformers offer a deeper and smoother low end than found in any other production microphone.  Inductor based old school power supplies offer dynamic range for our discrete audio amplifier and longevity for our tubes that is only found in vintage models.  The sum of Bock’s unique parts and David’s design make a big difference in inspiring and capturing a great performance.

Bock manufacturing employs all hand construction techniques with mics all built 5 or 10 at a time using techniques that are impossible to execute in high quantity.    Bock mics are easy to repair and service.  This is why higher volume production microphones that are designed to be manufactured but not repaired cannot compare to Bock hand built mics.  We are very proud of our business model in a world of “more is better” and “one size fits all” mass production.  

Bock Microphones offer the highest level of performance, equal or better to the classics, proving it IS possible to “build it like they used to”.  With Bock Microphones, you own a microphone destined for a lifetime of extraordinary studio use.


Patterns: Cardioid, omni, Figure of 8 Switchable from mic
Frequency Range:10Hz to 18kHz, +/-2dB
Equivalent Noise:18dB (“A” weighted) 32dB (unweighted)
Distortion vs.SPL @1kHz: 
  • 112dB = 0.5% THD 
  • 118dB = 1% THD
  • 129dB = 2% THD
(increasing distortion is non-exponential, nearly linear, and primarily 2nd harmonic)
Impedance:200 Ohms true transformer balanced
Recommended load:1.2k Ohms
Dynamic range (maxSPL-"A"noise): 94dB
S/N (94dB-noise):76dB “A”, 62dB unweighted
Capsule size:1” diameter, dual asymmetrical backplate CK12 type
Tube type:New Old Stock 6201 
Dimensions:2” dia x 8.5” oal (52x216mm)
Weight:1lb 9.3oz (1.58lbs) =716g
Shipping weight:12 lbs
Power Supply: P251 true linear, factory wired 115v or 230v operation





251 Data Sheet & Frequency Response