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Manley Core

Reference Channel Strip
Published December 2014
By Bob Thomas

Manley Core

Billed as their ‘greatest hits’ package, Manley’s Core packs a lot into a package that’s less expensive than their previous offerings.

The cost of designing and manufacturing in–house in the US is one reason Manley have previously aimed their music production gear at the professional end of the market. Their new single–channel Core Reference Channel Strip, though, has been designed to deliver their signature circuitry and audio quality in a more cost–effective package: it’s not ‘cheap’, but they’ve put it within the reach of the serious home and project studio user.

To The Core

The stylish 2U purplish–blue, brushed–metal front panel carries five laser–engraved, recessed sections: Input, Compressor, EQ and Limiter. A large, blue–lit VU is switchable to indicate output level or gain reduction. The 48V phantom power is also switchable, and there’s also a 180–degree polarity–invert switch. The input section also hosts an instrument DI socket, but all the other I/O is on the rear. The mic and line inputs, and direct (pre–EQ and limiter) and main outputs are on XLR connectors, and there’s a TRS jack for the pre–EQ insert.

The mic input feeds a 1:8 Manley ‘Iron’ input transformer that provides almost 18dB of gain. Despite the name, the transformer laminations are primarily nickel, with the whole encased in a mu–metal can to eliminate hum pickup. Manley have been winding their own transformers since 1994 and several, including this one, are based on the Sowter models used in earlier products. The mic/line selector and the switched jack on the DI input route the three input signals via two relays. One selects between the line and DI inputs, while the other switches between the mic input transformer and the source selected by the other relay. It’s a versatile setup that I found really useful. After the input selection comes a switchable 120Hz high–pass filter, which is followed by a variable input–level attenuator and associated Hi/Low gain switch. In the Low position, with the level control fully clockwise, the mic input gives about 40dB and the line input 20dB of gain. Switching to Hi brings in an additional 20dB of gain.


The Core’s electro–optical Elop compressor comes before the valve preamp to prevent the latter from clipping. The circuit topology is the same as in Manley’s Voxbox, and is similar to the limiters found in their Elop and Slam! With a fixed 3:1 compression ratio, the attack, release and ‘Compression’ (threshold) controls give you an intuitive interface. The maximum gain reduction is 16dB, and a silent bypass switch allows the original and compressed signals to be compared instantly.

The compressor is based on modern Vactrol technology. Vactrol was once the brand name of Vactec’s bulb–based Resistive Opto–isolator (RO), but has become the generic term for any RO used in audio equipment, including faster, more modern LED-based designs like this. In very simple terms, an RO uses a rectified sample of audio to turn on a light source, which shines onto a Light Dependent Resistor (LDR). The brighter the light, the lower the LDR’s resistance. Pairing an RO with a fixed resistance creates a voltage divider that acts as a smart volume control — the louder the signal, the brighter the light and the greater the attenuation.


The preamp is a new implementation of the Class–A circuit that Manley use in their Voxbox and Mono and Dual Mono mic preamps. The valves are run on a 300V plate voltage, courtesy of the switch–mode power supply, giving the Core’s preamp loads of headroom and plenty of drive at its output.

The preamp features a 12AX7WA (ECC83) dual–triode valve for gain, and this is followed by a 6922 (ECC88) dual–triode as a Class–A, single–ended, White Cathode Follower (WCF) output stage. Originally developed by Philips for use in television tuners, the 6922 valve became popular in the hi–fi world. In a WCF configuration, the two halves of the 6922 operate in push–pull mode, without the need for a phase–splitter.

On the subject of outputs, the Core’s preamp feeds not only the balanced XLR Direct Out (O/P 1), but also the input to the EQ section. A TRS insert send/return jack sits between the preamp and the EQ, and this gives you the option of inserting an effects unit in the signal path, or of taking a second, unbalanced, ‘sniff’ feed from the preamp for some other nefarious audio practice. You could also, if you wished, use the insert return to route an external source through the Core’s EQ and limiter sections.


The EQ section features a three–band Baxandall EQ, with shelving low– and high–frequency controls at 90Hz and 12kHz respectively, plus a semi–parametric mid–range that can be swept over two ranges, 100Hz–1kHz and 1kHz–10kHz. The overlap between the three ranges gives you plenty of control, but a surprising omission is an EQ in/out switch — comparing the effect of any EQ with the original signal means toggling somehow between the Core’s Main Output (O/P 2) and either O/P 1 or the insert send.The rear panel includes a  clear indication of the signal path. While you might expect to find the compressor after the preamp and EQ, Manley prefer to place it earlier in the chain, to avoid clipping the valve preamp.The rear panel includes a clear indication of the signal path. While you might expect to find the compressor after the preamp and EQ, Manley prefer to place it earlier in the chain, to avoid clipping the valve preamp.

Limiter & Output

Like both the Slam! and the Voxbox, the Core has a FET–based output limiter. At maximum limiting, this fast, high–ratio, brick–wall peak limiter can hold the Core’s +20dBu maximum output level to +3.5dBu, although there are sonic side effects (which you may like) if you overdo that. There are two rotary controls, Limiting (threshold) and Release. A red Limit LED illuminates when the signal crosses the threshold and goes out after the signal has dropped below the threshold and the release time has completed. With Limiting set to minimum, the Limit LED acts as an overload indicator (+20dBu). Finally, an active output gain stage, with a range of –6dB to +4dB, feeds the electronically balanced main output.

In Use

The Core powers up with its output muted until the valves have warmed up and are ready for action. The manual is pretty prescriptive about which of the Core’s XLR inputs and outputs should be used for balanced and/or unbalanced operation, and you’ll need to pay attention, since connecting an unbalanced cable to O/P 2 that has Pin 3 connected to earth could cause damage to the Core.

As you might expect from the presence of a transformer–balanced microphone input driving a Class-A valve preamp, the Manley Core has a distinct character. Taken as a whole, the Core feels accurate, open and dynamic, with a very natural and full–bodied character to the sound. Indeed, with a ±0.5dB frequency response of 10Hz–20kHz and a dynamic range of over 90dB, any limitations on performance are going to come from the source, rather than the Core.

Noise is down at –70dB, making the Core very quiet in operation. Even though there’s inevitably a noise penalty when you switch in the extra 20dB of gain, a bit of attention to the gain structure over the entire chain meant that I never had any problems in that regard. In any case, the only times I actually felt that I needed to use the extra gain was when I wanted to really hammer the compressor and a little noise wasn’t an issue.

The compressor was a pleasure to work with on sources such as acoustic instruments, DI’d electric guitar, bass and vocals, where a few dB of compression really helped to even things out. It’s capable of much more assertive gain reduction, though, which is good news if you’re into more creative crunching. For really heavy compression, the one missing feature is post–compression gain make-up, but all is not lost — you can add gain at the very end of the chain, where you’ve got 10dB of the Core’s +20dBu output capability to play with.

It’s the valve preamp, though, which to my ears makes the Core such a great–sounding device. Underlying the accuracy and clarity, there’s a depth that gives a real weight and body to vocals, acoustic instruments and percussion. DI’d instruments also come out well: an electric bass, with a bit of compression, sounded very fine indeed, and I was astounded by how good a sound I could coax from a passive Lloyd Baggs iBeam under-saddle acoustic guitar piezo pickup (with an additional 20dB of gain). The direct out from the preamp (O/P 1) sounded excellent, and I used it quite a lot for acoustic guitar during the test period. This worked well for me, as it meant I could record a clean feed while also recording through the Core with an effects unit patched into the insert point.

The EQ frequencies are well chosen, although the amount of overlap between them means you’re always working with it to shape a source’s overall character — it’s not a tool for surgically enhancing or removing specific frequencies. Personally, I’d have liked to have seen an EQ bypass switch, just so that I could sanity–check the effect of my EQ’ing, but you can’t have everything all of the time.

Finally, then, there’s the brick-wall limiter, with its very fast 115 s attack time. This enables the limiter to catch peaks that might cause clipping in the next stage in the proceedings — which in my case happened to be an A/D converter. I could actually see myself using this limiter in a live situation, but when working in the studio I tended to set the Core up so that the clip LED just came on with peaks at unity gain and then backed off the output gain control by 6dB to keep things safe.


On the basis of its price and performance alone, I’d have no hesitation in keeping the Core as the primary channel strip in my studio. On top of that, it is very well thought out electronically and operationally, delivering what Manley refer to as their ‘greatest hits’ in an easy–to–use package that’s more than capable of producing very professional–sounding results.

Although I’d have liked a bypass switch on the EQ section, and a post–compression make-up gain stage would have been nice, there’s actually nothing about the Core that would stop me from recommending it if you’re in the market for a simple-to-use, great–sounding, full–of–character channel strip in this price range. So I’m going to do just that, and recommend that you take a very close look at the Manley Core.


Although I can’t think of anything that’s directly comparable to the Manley Core — other than their Voxbox — you can find similarly priced valve channel strips from Thermionic Culture and Tree Audio, amongst others.

Published December 2014