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9 polar patternsCharterOak Acoustic Devices SA538

Multi-Pattern Tube Condenser Microphone

Charter Oak’s SA538 is a multipattern tube condenser with a large-diaphragm capsule.

Like all CharterOak’s mics, the SA538 was designed in the US, and is assembled and tested in the US using parts sourced from around the world. The mic has the most rigorous testing and burn-in procedure we’ve seen:


The process involves a seven (7) day burn in of the vacuum tube and no less than 1/2 hour spent with each microphone in a studio environment. Careful listening tests employ high quality microphone preamplifiers and high resolution monitoring systems. Quality checks on every component of each kit complete the process.

The capsule is CharterOak’s “S1” design. The specs describe a 1.06'' diaphragm, which presumably means a 34mm capsule. According to Michael Deming, this is a center-terminated, K67-style capsule.

(Note that the SoundOnSound review from 2006 claims that the SA538 is an edge-terminated design, but we believe the reviewer’s notes were reversed. It is the SA538B that uses an edge-terminated capsule.)

In an unusual move, Charter Oak imports capsule metalwork from a Chinese supplier, remachines the parts to ensure consistency, and then ships the parts back to China for diaphragm fitting and capsule assembly. This approach allows CharterOak to ensure consistent capsule quality.

The tube is an ECC83 (12AX7) dual-triode. The amplifier circuit into which it is built has a self-noise rating of 22dBA, which is the highest we’ve seen for large-diaphragm tube condenser mics.

SA583 kitThe SA538 ships with its tube power supply in a locking flight case with a shockmount and cables. The mic is covered by a lifetime warranty.

CharterOak celebrated the sale of SA538 #100 by creating a custom gold logo for the microphone body.

SoundOnSoundIn all cases the Charter Oak SA538 came across as both solid and present, cutting through a mix rather more assertively than most of the competition but without sounding edgy.

Tape Op

We took country singer Ian Thomas, who sounds strong regardless of mic choice and had him sing into the SA538 and a BLUE Kiwi at the same time. In blind A/B tests, I could not pick the Kiwi vs. the SA538. In fact, I was wrong 50% of the time.

The CharterOak Acoustic Devices SA538 is also known as: SA-538.

The mic was released in 2005.


Frequency Response - CardioidClick Graph to Compare!
SA538 Cardioid Frequency Response Chart
Pickup Patterns Pads & Filters
Omnidirectional (12 mV/Pa; 30 - 20,000 Hz)
Cardioid (12 mV/Pa; 30 - 20,000 Hz)
Bidirectional (12 mV/Pa; 30 - 20,000 Hz)
Capsule Dimensions Impedance SPL/Noise
Diaphragm diameter: 27mm
Diaphragm gauge: 6 microns
200 Ohms (Low) Max SPL: 128 dB
Self-noise: 22.0 dB(A)
Weight Length Max Diameter Interface(s)
n/a n/a n/a
  • 3-pin XLR male (1)
Power Specifications
  • Includes tube power supply

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