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CharterOak ProAudio - Microphones, Signal Processors, Headphones

Pressure Gradient
Single 1.00" 6 micron thick gold sputtered Mylar (side terminated)
13mV/Pa 0dB=1V/Pa@1kHz
< 200 Ohms
> 200 Ohms
22dB A weighted IEC651
128dB for 0.5% total harmonic distortion @ 1000Hz
Custom supply 115V or 230V operation with IEC type 2 AC Cable
| CharterOak S600 Cardioid Stereo Mic |

The CharterOak Acoustic Devices S600 is a front address vacuum tube condenser microphone. Delivered in sequentially numbered pairs with a lockable fight case, dual power supply, and two shock mounts and is extremely well suited for stereo recording.

The S600, like all CharterOak products, features extremely rigid construction and a clean and simple electronic design.

The CharterOak S600 uses a custom made side terminated 1.00" gold sputtered Mylar capsule and custom made output transformer. Its rich and particularly non-sibilant eq make it a perfect choice when used as a stereo overhead pair on the drum kit. The result is clean and rich cymbals with lots of sustain while picking up all of the transient peaks of the snare and tom toms.

The extended bass frequency response of the S600 makes a single S600 a perfect choice for recording bass guitar and its particularly smooth treble response makes it a perfect choice for recording bright electric guitars.

It is hard to imagine a more versatile tool in the studio than a pair of CharterOak S600 vacuum tube condenser microphones.

The microphones are delivered with a lifetime warranty on all parts and labor and easy access to factory technical support.

With good looks and a unique sonic character, there's plenty to commend these mics.- Hugh Robjohns

Charter Oak are relatively new microphone producers, having formed only five years ago, in 2002. The business is based upon sourcing component parts from around the world (mainly China), then hand-assembling them in Connecticut in the USA, and tailoring the complete system to provide a 'boutique' quality high-end sound. One of the key differences between the Charter Oak mics and their source Chinese designs lies in the choice and quality of electronic components — especially the selected valves and capacitors — which have a significant effect on the sound quality, even if they don't necessarily show in the technical specifications.

The S600 is a very chunky, end-fire, large-diaphragm, cardioid valve microphone, and is supplied only in matched stereo pairs, in a sturdy, lockable metal attaché case, complete with dual-channel power supply, cables, and a pair of shockmount cradles. The mic itself measures roughly 210mm in length and 40mm in diameter, and weighs about 590 grams, so this is a substantial item! Its body is finished in a highly polished piano-black, with anodised capsule grille and integral wire-mesh screen. At the base of the mic is a threaded XLR stem, which fits into the rotating collar of the shockmount. The seven-pin XLR connection accepts power from the supplied PSU, and provides the audio output through that unit in the usual way. Etched on the body is the mic's serial number, along with the Charter Oak logo, but there are no other facilities: no filter or pad switches, for example.

The capsule is a traditional one-inch, side-terminated design with a Mylar diaphragm, sputtered with a six-micron layer of gold. A frequency response of 18Hz to 20kHz is quoted, but no limits are given. The frequency response charts supplied with the mics show a pretty flat response, but not as flat as the generic trace published on the company's web site. They were both within a couple of dB from 60Hz to 7kHz, with a modest resonant peak at about 9kHz, above which the level falls off gracefully. The matching of the two mics is very close indeed, with only a minor discrepancy around 5kHz on the review models, so there are no problems there. The mic has a pronounced proximity effect if used closer than about six inches.

Sensitivity is given as 13mV/Pa, which is quite healthy, but the self noise is a surprisingly high 22dB A-weighted. For comparison, the Neumann M147 cardioid valve mic has a self-noise of 12dBA. Maximum SPL for the S600 is 125dB for 0.5 percent distortion, which means that it will cope with most musical sources, even with close placement.

Unusually for a large-diaphragm mic, the S600 is an end-fire design: you have to point it at the source, instead of facing the side to the source like a U87 or C414. This looks very odd when mounted in the traditionally designed, elasticated shockmount — although it seems to work well enough. This is an American-built mic, and the stand adaptor with the review models had a 5/8-inch thread; no 3/8-inch European adaptors were supplied. The knuckle joint is tightened with a large butterfly bolt, which proved able to tighten securely and release easily during testing.

The power supply is a large, black, metal brick, with IEC mains inlet, illuminated power switch and voltage selector on one end, and two pairs of mic-in and signal-out XLRs at the other.


The S600 sounds like a hand-tailored large-diaphragm mic. It quite definitely has a character, which is slightly warm and quite rich, despite the apparently flat frequency response. Presumably this character is the result of a combination of subtle capsule, valve and custom output-transformer distortions. The gently falling high end gives it a fairly smooth sound too, without any trace of resonant brightness or sibilance on most vocalists.

Charter Oak suggest using S600s as overhead pairs on drum kits, and I can see the sense in that, particularly for rock drum kits where a little extra character and shimmery cymbals would be useful. Another suggested application is for electric guitars and bass guitars, building on the mic's solid low end and smooth, resonance-free treble.

I tried the mic on a couple of different electric guitar/amp combinations and found it did indeed work very well, capturing the required sound in a pleasing, musical way, with plenty of detail but without harshness. A lot of capacitor mics can sound rather brittle on electric guitars, but not so the S600. The proximity effect doesn't really come into play until you get within about six inches of the source, as mentioned earlier, but close miking can certainly be used to take advantage of the additional warmth and body that results.

As a vocal mic, I was a little less impressed with the S600. The relatively high self-noise was more of an issue for me in this role, especially with delicate vocals. I was able to use a recently acquired AEA mic preamp to raise the S600's output to line level, which yielded decent enough results. This preamp design was intended for ribbon mics, but works well with valve mics too, and is extremely quiet. Using more standard-fare mic preamps (Mackie VLZ Pro, Focusrite ISA428) revealed slightly higher noise — not so much as to make the mic unusable in any way, though personally I think I'd stick to using the S600 as an instrument mic, rather than for vocalists or as distant mics.


At around £1400 for a stereo pair, these are fairly expensive mics — and if you're only looking for a single mic, this sort of money will open the doors to a wide range of very respectable and high-quality models, both solid state and valve. There are also more versatile mics that might be a more appropriate starting point for a collection. However, the sonic quality and character of the S600s will justify the cost for many and they would certainly enhance an already well-stocked mic cupboard. The kit of parts is also nicely fitted out, with the cables, shockmounts, mics and power supply all in a solid, professional-looking case.

Finally, they are also, without question, things of beauty, which will generate interest and comment: not least the inevitable questions about whether you are pointing them in the right direction!


Reviews. CharterOak SA538, SA538B, E700 & S600

“CharterOak microphones reviews in PROSOUND April ’07 Edition”

CharterOak condenser microphones are manufactured in the factory located in
Connecticut, U.S.A. Only the parts with well selected and passing the very severe
quality criteria are assembled in the rigid body which is being machining from the brass. And, furthermore, after 7 days aging for the tubes and testing in the studio
environment for more than 30 minutes, the microphones will be delivered to the
customers. In addition to this, such accessories as the flight case, the power supply, theshock mount, the cables, etc. will be checked severely. By taking care of this
fundamental points in order to manufacture the products, the credibility will be
increased and the products will attract customers’ attention and the firm position of the products will be established, which is a short cut to be successful for the products.

The products which I would now like to introduce you this time are 4 types of the
condenser microphones manufactured by CHARTEROAK ACOUSTIC DEVICES in
U.S.A. They are SA538, SA538B, S600 and E700.

First of all, from the external appearance of the microphones, the black shiny finish is afeeling like having its very expensive products and the microphones have a feeling of having its enough weight. Furthermore, except E700 which is solid state type, the exclusive power supply will come with the microphones. About SA538 and SA538B, as they equip the switch with 9 steps of which the directivity can be selected from non-directivity to cardioid.

Let’s try to test them!

First, let’s start from SA538. This is a dual diaphragm tube type condenser
microphone(SA538B is the same.).

Checking it with vocal, it sounds like thinking of a vintage microphone and the
bandwidth ranging from mid-low sound to low sound is solid. Nevertheless, it is not
like a dull sound, but, it has apparently a feeling of existence against the sound source in the back. Listening to only the vocal track carefully, it is understood well that the room noise was not almost felt. Then, after recording while selecting the directivity newly, with transferring gradually from non-directivity to cardioid(middle value), the noise is becoming decreased and it is a feeling that I went to the country side where has clean air, being away from the city. In doing like that, the high technique is necessary in order to decrease only the noise, without spoiling a feeling of air. I feel that CHARTEROAK ACOUSTIC DEVICES has very high technology research level. SA538B is being the same, but, as this is a side termination type, the high frequency sound is much extending with a feeling of hybrid.

Depending upon the vocalist is if it is a male or a female, it is fat or thin, utterance is strong or not, what is the performance style of the back, etc., the choice will be changed. In the studio, I would like to have both. In either way, the microphones can realize sound image very well for which the vocalist is in the very front position of the stage and they are superb microphones, and they are also easy for mixing.

E700 is the low cost version for the above 2 microphones. This is a gold depositioned myler diaphragm and pure class A solid state type microphone. The microphone equips the switch which can be selected from 3 types of the directivity(cardioid/omni/figure 8) and the attenuator of -10dB/-20dB(sensitivity switch).Though this microphone is in the low priced range, the sound is fairly good and a feeling of clear air with less noise can be realized well.

S600 is a front address type and the tube type, but, this microphone is different in appearance from the above microphones. The top portion of the microphone is aimed at the recording object and I think it is for the purpose of recording the musical instruments. I recorded the Conga which is my favorite musical instrument. Although it is a same feeling as sounding with a feeling of existence, this microphone is likely flat in its frequency response. In its good aspect, it has a sound with non-peculiarity and wide dynamic range.

For myself, in case of recording in stereo against the recording object(2 microphones), especially to drams and percussion(also piano), not standing the microphone inside from outside, reversely, I always request to stand it outside from inside. This means that I consider it phase, but, with using this microphone, when I tried to make both settings and to compare them, I realized that there are big difference in a feeling of existence and a clearness of sound. In some sense, I am impressed with this microphone that it is honest.


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