When I think of all the reasons to use an outboard microphone pre-amplifier, most salient is purity of sound. Manley Laboratories of Chino, California has produced the MIC/EQ 500 Combo with the sole purpose of providing the purist possible microphone signal path for direct recording. It has been designed to be the first choice for recording vocals, acoustic and electric guitars and even orchestral primary mics. Designed by David Manley, the MIC/EQ 500 Combo is a fine example of a classic tube circuit fully realized in a modern package using the best available components and manufacturing techniques.

The unit's genesis comes from two sources. The mic pre-amp section uses a fully differential Class A input stage similar to the amplifier circuit in the Manley Variable Mu Limiter/Compressor. The Variable Mu is considered the finest audio line amplifier currently being built. A fully differential design was also used in one version of Manley's $8.8K Reference 20-bit Digital-to-Analog converter. Secondly, the equalizer section is modeled after an existing vintage design by Arthur Davis. Davis worked for Altec Lansing, Cinema Products, Universal Audio and Langevin. His passive equalizer circuit is highly praised by mastering engineers and collectors of audiophile gear.

The fully differential input stage is a design departure from Manley's other mic preamplifiers: the Manley 40dB Dual Mono and Single Channel Microphone Preamps. The MIC/EQ 500 Combo is quieter, cleaner and smoother than the 40dB pre-amp. The 40dB use a "single-ended" tube circuit where the two triode sections are operated in cascade. The signal out of the mic input transformer is referenced to ground at the grid of the first tube stage. The 500 uses two triodes in a fully differential circuit to feed a second pair of push-pull triodes before the output transformer. The signal enters the first tube stage fully balanced and leaves the last stage fully balanced out of the transformer.

It is interesting that a small amount of negative feedback is accrued by connecting the cathodes of the output stage tubes to a separate winding on the final output transformer. As a rule, Manley designs use less than 12 dB of negative feedback to maximize transient response accuracy. Transient response accuracy is a subjective quantification and cannot be empirically measured. Fully differential topology also has the propensity to cancel out even order harmonic distortion products. A similar differential circuit is used in the popular Telefunken V77 mic pre-amp. (It makes sense here to mention David Manley's long association with EMI Research, Engineering, Design & Development or REDD. The V77 units were used by EMI Studios at Abbey Road)

Maximum gain is 55dB. That's enough for 98% of all studio recordings but may be a little lean for some Foley sounds or extremely quiet ambient or nature recordings. (This would, of course, also greatly depend on the gain of the microphone you are using as well as the I/O analog level setting of your recording system) I certainly had no gain starvation problems ever in any of the applications I use the two units I received. Frequency response is 10Hz to 22kHz @ +0 or-1dB. Signal-to-noise ratio from mic to line out is 95dB. I can tell you this is one of the quietest pre-amps I have ever come across. You will start to hear the noise floor of your microphone, your room noise, your A/C noise and your console electronics. I also had no problems with microphonics or other typical vacuum tube maladies. This reflects the fact each unit is hand assembled with carefully matched and tested tubes.

The passive equalizer follows the pre-amp section and is switched in by way of a front panel routing switch. The routing switch either divides or unites the pre-amp and equalizer sections. You may operate the mic pre-amp as a stand alone unit without the equalizer by using the pre-amp's output XLR connector. Likewise, you may use only the equalizer by using the line input and output jacks. When you use them together the line amplifier (another fully differential circuit) has about 10dB of user-adjustable variable gain that makes up the insertion loss of the passive equalizer circuit. This configuration makes a convenient insertion point for connection of external processors such as a compressor or de-esser before the equalizer.

The equalizer is a two-band, high/low type with peak and shelving switches. Manley added the shelving feature to the original Davis circuit in a very simple fashion. Frequencies are: LF Band 40Hz and 100Hz; HF Band 3kHz, 5kHz, 7kHz, 10kHz, and 15kHz. The boost/cut controls are switches rather than pots and are in two dB steps from -10dB to +10dB. The switches are Greyhill custom built with gold contacts and ensures clean, reliable and resetable operation. There are only three components in the equalizer signal path: one resistor; one inductor and one capacitor.

To match the rest of the entire Manley product line, the MIC/EQ 500 Combo is housed in an aluminum framed cabinet with a thick, engraved front panel. The overall solid feel and sturdy construction of the two-rack space unit is not betrayed by the internal construction. Inside a large, thick printed circuit board holds all components with the attendant wiring neatly wrapped and bundled together. There is an overall handmade craftsmanship throughout with clean applications of shielding for all sources of stray magnetic fields. Top grade components are used throughout with gold plated terminals, switches and XLR connectors. I object to the quality of the small output VU meter and wonder why the same meter used in the Variable Mu Limiter wasn't used. (Actually, an output meter is redundant since you should be measuring VU/Peak levels at your master recorder's meters.)

In operation the MIC/EQ 500 is an impressive unit. I recorded solo violin using a Milab microphone with and without the equalizer path. There is no difference in sound with the equalizer in or out (with the EQ flat of course) other than the 10dB gain change. I like to characterized sound as "very close" to you in the sense that I was hearing the violin exactly as the microphone was hearing it. I could tell there is less electronics between the sound source and my ears. I was rediscovering my mic collection. I found little need to use the equalizer beyond compensation for microphone shortcomings. I wish there was an easy way to simply add the make-up gain if you elect to insert the equalizer after you have already arrived at a proper recording level without it. Perhaps if the front panel engraving had accurate hash marks indicating gain in dB's, you could add the gain without having to guess. While on the subject, it would also be good to have a "mute" button. I love direct recording except for the fact if you want to erase an inadvertent noise you will have to physically unpatch the output of the pre-amp. Hutch, over at Manley assures me that if the output control and/or the mic gain control is turned all the way down, you would effectively mute the output. (-100dB) However, having said that, I would like to know that I have returned to the same exact level.

Recording vocals also revealed the striking differences between microphones as well as mic placement. This newly found resolution I attribute to the pristine audio path. Singers could hear themselves better and didn't complain of a "veil" over their voices. I used less EQ and a little less compression. I think getting a great sound was never easier. Retail price is $2,900.

I would like to thank Hutch, David and EveAnna Manley and everyone else at Manley Labs for their help with my preparation of this review. Manley Laboratories, Inc., 13880 Magnolia Avenue, Chino, California 91710 Phone: 909-627-4256 FAX 909-628-2482