Saturday, February 20, 2016

Radial JDV MK5 (VERY) Active Direct Box

Peter Janis
I have been a distant fan of Radial for years. I've never used any of their gear, but seeing it, reading about it and holding the occasional piece in my hands left me with one impression - very solid stuff. 

I saw the JDV MK5, read the cut sheet and asked Peter Janis if he'd forward one for this review. Peter was my "go to" guy when he was working with Gefell Microphones. I had heard that there was something special about the nickle-membraned Gefell M294, M295 and M296 condenser mics. Indeed there was. If you want to read that review, you can download it here.

Vintage imp-2
There are hundreds of them out there, ranging from my vintage Whirlwind imp-2 passive direct box, from the early 1970s, which consists of a couple of 1/4" jacks on one end, an XLR on the other and a small transformer inside. Direct boxes are used to convert a high impedance, unbalanced guitar or other instrument into a a low impedance, balanced mic signal. A transformer is used to correct the impedance mismatch. It also balances the line and sends it out as a three conductor connection; either on XLR or TRS. A balanced, low impedance mic level signal can run over longer lengths* (see notes at the end of this review). For the high impedance output of a guitar or keyboard, best practices says cables shouldn't be longer than twenty feet.

You still might run into problems even if you do stay within twenty feet. There are small mixers that say you can plug a high impedance instrument right into them. Yes, in some cases, but in other cases, the circuits are very unforgiving and the gain structure is wonky and you end up with "TCS", total crap sound!
Radial JDV Mk 5 front and back panels

Radial JDV MK
At $449, the Radial JDV MK5 is not passive nor is it your average active direct box. The 14-gauge steel used in the chassis and outer shell let you know this is just the tip of the iceberg.

The JDV MK5 has two channels, each with discrete, single-ended, Class A input circuitry, for electric or acoustic instruments.
It is decidedly not a stomp box unless you get  the JR-2 footswitch. 

Seen below, the two switches are for MUTE on the left and A/B select on the right. The JR-2 ($99) connects to the device using a standard balanced audio cable with choice of ¼" TRS or XLR connections. The JR-2 is unique in that it derives its power from the device being controlled which in turn illuminates the on-board LED indicators to show the remote.
Radial JR-2 Remote Control

According to Paul Blake, in the support department at Radial, these switches allow you to switch an instrument plugged into input one to either input A or input B, should you want to change the sound of your instrument for different parts of a song. The JDV MK5 would sit on an amp or somewhere nearby; close enough to plug in your instrument(s). You would not normally need to adjust anything on it during a performance.

The front/back image of the JDV MK5 above indicates that this is a busy box. There are two separate 1/4" TS unbalanced jacks, one for each input. Each input has its own input level control. Each channel also has a variable high-pass filter. The PHAZER knob and switch on the right allow you to time-align the two inputs. This would be for situations in which you had two pickups on the same instrument or a pickup and a strapped-on mic on the same instrument. The small switch below the knob lets you choose 0 to 180 degrees or 180 to 360 degrees. You then use the knob to align the two signals before the mono balanced XLR and other outputs. The other front panel adjustments are for compensating for different kinds of pickups. 

JDV MK5 Front Panel
Front Panel
Input A has a switch that changes the input impedance from 10 M Ohm for piezo systems to continuously variable DRAG for magnetic pickupsThe continuously variable resistive DRAG control allows you to compensate for the load from 22K Ohm to 500K Ohm for passive pickups. Input B can be switched from 10 M Ohms for piezos to 220 Ohms, typically for magnetic pickups

I have a K&K Pure Western Mini (now called a Pure Mini) piezoelectric passive pickup installed in my D28S Martin, thanks to the gentle and intelligent hands of John Thurston before he abandoned Baltimore for an obviously better way of life at Guitar Tex, in San Antonio, TX. This is a great pickup choice for that guitar, especially for finger-style playing, because there's little if any quack. 

The Pure Mini is three electronically paralleled piezo pickups mounted inside on the bridge plate. According to K&K, it wants to be plugged into a 1 Meg Ohm or higher input. Straight into my Fishman SoloAmp, it sounds better than I thought it would. I was curious about the Fishman SoloAmp 1/4" instrument input so I reached out to Derek Alves in the support department at Fishman. Alves confirmed that the input impedance of the 1/4" input is 5 Meg Ohm, so good to go for plugging straight in, but what about through the JDV MK5 and out its XLR to the Fishman SoloAmp?

I plugged the Martin into input A of the JDV MK5 and began to turn the drag control which requires a screw diver. The thought being that once you get it set, you don't want to accidentally change it. The D28S isn't as boomy as a regular D28, but it's still quite full. I found a position fully clockwise with the DRAG control - so, 500K Ohm, and about mid-point in the rotation with the high-pass filter that tucked in the bass a bit and the sound was more "finished", with a broader, flatter frequency responseAt this point I was coming out of the JDV MK5's XLR out and into the SoloAmp XLR input. Nice!  

I expected more of a difference with tonality when adjusting the DRAG and other impedance switches. With my guitars the effects were very subtle. Regardless, the difference was mostly about gain. Full clockwise (500K Ohms) on the DRAG control was best; YMMV with different pickups. 
Turns out, if you have piezo pickups, you should stick with the 10 M Ohm input positions on the JDV MK5. The DRAG control was designed more for magnetic pickups. 

The effect of the high-pass filters were more noticeable. None of my guitars, the Martin D28s, Fender Thinline with humbuckers or Martin Grand J28-LSE Baritone with active electronics ever got close to exceeding the input level and I had any guitar and JDV MK5 gains turned all the way up; so plenty of head room.

JDV MK5 Back Panel
The back of the JDV MK5 is no less busy. There's a four pin locking XLR to bring power to the unit from the external power supply. 

The next connection is a balanced 3-pin XLR fed from a Jensen JT-11-YMPC transformer, designed to feed a live sound board or recorder. 

The next four controls grouped together under the Radial logo offer some savvy help. The first one flips the polarity 180 degrees. The second one lifts the ground on pin 1 of the XLR output. The third one inserts a Jensen JT-11-YMPC transformer to isolate the XLR output signal path. These two may help you deal with your good friends Hum and Buzz. The fourth bumps the JDV MK5 output up to +20 line level. 

Continuing across the back panel are the jack for the footswitch that allows muting and switching between the two channels and an always-on 1/4" unbalanced, high-impedance out that can feed a tuner, amp or other device. There are two 1/4" unbalanced instrument inputs, one for each of the two inputs. There's a separate 1/4" unbalanced THRU output normally used to feed a stage amp and a separate 1/4" balanced TRS jack for microphone inputs. 

The 1/4" TRS microphone input jack is only routed through the input A. It has 48 V Phantom Power. According to Blake at Radial, "With phantom power, the two 6.8K ohm resistors limit the current to phantom powered devices to 10mA." That's more than enough for the hungriest condenser mic.

An LED under the DRAG control on the front panel lights when Phantom Power is active. As a safety precaution, the Phantom Power turns off when the JDV MK5 is powered down and has to be re-engaged by the small push switch in the side panel upon power up.

Both my Neumann TLM 103 (23 mV/Pa) and Audio-Technica AE5400 (10.0 mV/Pa) condenser mics overpowered the mic input when worked any closer than a foot, lighting the O/D lights on the front panel. Engaging the 10 dB pad on the AE5400 dropped the signal below clipping. I really like the Audio-Technica AE5400 for live vocals. I reviewed it back in 2003 when it came out. It uses one half the capsule of an AT4050 and has a 10 dB pad and high-pass filter. I'd put it up there with a Neumann KMS 104 and KMS 105. If all you have is high-sensitivity condensers with no on-board pads, I guess you could add a pad to the mic cable. My Shure SM86 (3.15 mV/Pa) hand-held condenser worked just fine with no pad, requiring the input trim to be about halfway up at 12 o'clock. My vintage dynamic Sennheiser MD421 (2.0 mV/Pa) also did well, also at about 12 o'clock. 

I was easily able to plug a mic into input A and my guitar into input B, control the levels with input trim and alter the frequency response with the separate high-pass filters. Everything sounded just fine at mic level going into my Fishman 220 SoloAmp. I could have also chosen the +20 output on the side of the JDV MK5 and gone line level for recording or to a FOH console. 

Drilling down a bit more into the guts of this beast. It's very common to use negative feedback in a circuit to improve fidelity. Negative feedback is not the only way to go, but it's a very common way. The Radial JDV MK5 does not use negative feedback and achieves its performance with single-ended Class A circuitry. Class A circuits are usually less efficient, generate more heat and exhibit better high frequency performance and fewer higher-order harmonic problems. Here's a great rabbit hole about amplifier modes.

Radial bought Jensen in mid 2014, so they now own one of the best makers of audio transformers in the business. Bill Whitlock, the former President, said Radial was their biggest client and in as much as he was turning 70, he wanted to ensure that Jensen's good name would continue. Quality transformers may not seem to be that essential, but they are a very big deal. 
A little bit of finely-crafted iron can really smooth the edges of your audio. 
John Hardy

John Hardy makes high-quality mic preamps, including one of my all time favorites, the Jensen Twin Servo, and knows quite a bit about Jensen transformers and circuit design. "Most traditional audio transformers use core material that is 97% iron. Most of the Jensen transformers use core material that is 80% nickel. I know that "iron" is a commonly used term when referring to transformers generically, but I like to make the distinction that the best transformers use the 80% nickel core material. Nickel is much more expensive than iron, but it performs better."  (and there we are, back at the magical properties of nickel. More about nickel here)

Being able to consistently and accurately turn out great transformers is very important. Hardy says. "Early Jensen transformers were wound by Reichenbach engineering. They were good, but Jensen is now winding in-house with more precise winders, so the piece to piece consistency is even better."

I found the JDV MK5 to be a very well-made and versatile piece of gear. It does a lot of different things and could be expected to become the hub of a performing musician's cluster of gear. The solo performer could use it to simply control one vocal and a mono instrument to one mono output, or other more complex configurations. Please continue to scroll below the specs for more information.


2/20/16: Just before I returned the JDV MK5, I noticed a strange little noise on the ring out of notes on input B. I sent word and an audio file to Ryan Juchnowski, Custom Shop Manager / Trade Show / Radial Technical Support. He said this was unusual and would get back to me. Keep an eye on this space for an update!

3/1/2016: This is what they had to say; “We had engineering test a few of the units off the shelf and found that sometimes, when the signal LED begins to dim/discharge, that the strange noise becomes present. Luckily this is an easy fix and we have changed the resistor values in all new units so that this intermittent problem has been eliminated. Should users find that this issue is present in units which they already own, all they need to do is contact and in typical Radial fashion, they will be taken care of immediately.”



Hold on a minute! There is documented evidence that even running long mic level signals back to FOH mixers also results in signal degradation. Fortunately, the JDV MK5 can also run +20 line level. 

Years ago, I spoke with John Hardy for a review in MIX magazine. He recounted events at which Randy Ezratty's Effanel remote recording rig was used to record major concerts. They found that they got a better signal in the truck if racks of mic preamps were put on stage. Makes sense, right? Shorter mic to preamp runs sounded better than long mic runs. (Yes, they had to have an extra tech stage-side to oversee the mic pre levels.) The take away lesson was that if you're running long lines, it's better to have them at line level than mic level. 

Even if you do this in live sound, your mixer and speakers may not be good enough to let you hear the difference. I walked into a singer-songwriter event here in Baltimore one night and noticed an AKG C1000S set up for acoustic guitar. I thought the sound would surely suck, but to my great surprise it didn't!

I'm guessing that the PA company owner hadn't had his C1000S modified. It must have been the compromises of the PA system that scraped the edge off of the C1000S. If you have one, try it in the studio and for live PA and see for yourself. If you have an AKG C1000S and are in search of a mod, try Mark Fouxman at Samar Audio. Last time I checked, he was charging $169 USD for the mod. 

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