Manley Laboratories Mic/EQ 500 Combo

By Barry Rudolph


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EQ500 Manley Laboratories of Chino, Calif., has produced the MIC/EQ 500 Combo with the sole purpose of providing the purest possible microphone signal path for direct recording. 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. Intended applications include use with primary orchestral mics and spot recording of vocals and acoustic and electric guitars.

The mic preamp section uses a fully differential Class A input stage similar to the amplifier circuit in the Manley Variable Mu Limiter/Compressor, considered by some to be the finest audio line amplifier currently being built. The MIC/EQ 500 Combo's equalizer section is modeled after a vintage design by Arthur Davis, who has worked for Altec Lansing (Cinema Products), Universal Audio and Langevin. Davis' 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 preamp, which uses a "single-ended" tube circuit and operates the two triode sections in cascade. Also, in the 40dB, the signal out of the mic input transformer is referenced to ground at the grid of the first tube stage.

Instead, the MIC/EQ 500 Combo 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." 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 preamp. (David Manley has a long association with EMI Research, Engineering, Design and Development or REDD. The V77 units were used by EMI Studios at Abbey Road.)

Maximum gain of the mic preamp section is 55 dB, enough for 98% of all studio recordings but maybe a little lean for some Foley sounds or extremely quiet ambient or nature recordings. (Of course, necessary gain greatly depends on the gain of the microphone and the analog input level of the recording system.) Frequency response is 10 to 22k Hz (+0/-1 dB), and signal-to-noise ratio from mic to line out is 95 dB.

This is one of the quietest preamps I have ever come across--you will start to hear the noise floor of your microphone, room noise, A/C noise and console electronics. I had no problems with microphonics or other typical vacuum tube maladies, no doubt a result of the fact that each unit is hand-assembled with carefully matched and tested tubes.

The passive equalizer that follows the preamp section is activated by a front panel routing switch that either divides or unites the preamp and equalizer sections. The mic preamp may be operated as a stand-alone unit without the equalizer by using the preamp's output XLR connector. Similarly, the equalizer may be used separately via the line input and output jacks. When preamp and EQ are used together, the line amplifier (another fully differential circuit) has about 10 dB of user-adjustable variable gain that makes up the insertion loss of the passive equalizer circuit. There is an 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. Frequencies are: LF Band (40 Hz and 100 Hz) and HF Band (3 kHz, 5 kHz, 7 kHz, 10 kHz and 15 kHz). The Boost/Cut controls are switches rather than pots and are in 2dB steps from -10 dB to +10 dB. The custom-built Greyhill switches feature gold contacts and ensure clean, reliable and resettable 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-rackspace 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 Combo 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 would characterize the sound as "very close," in the sense that I was hearing the violin exactly as the microphone was hearing it--I could "hear" the lack of electronics between the sound source and my ears. I found little need to use the equalizer, apart from compensating for microphone shortcomings.

One small point: 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, you could add the gain without having to guess. I would also like to see a Mute button. I love direct recording, except for the fact that if you want to erase an inadvertent noise and have no mute, you will have to physically unpatch the output of the preamp. 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 (-100 dB). However, without hash marks it would be difficult to return to the same exact level setting.

Recording vocals revealed striking differences between microphones, as well as mic placement. 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 is $2,900.

Manley Laboratories Inc., 13880 Magnolia Avenue, Chino, CA 91710; 909/627-4256; fax 909/628-2482. Web site: www.manleylabs.com.

Barry Rudolph is an L.A.-based recording engineer. Visit his Web site at: WWW.BARRYRUDOLPH.COM




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