Radial-Blue Report on DI Boxes 电路图.pdf

INTRODUCTION The Radial Blue Report is a comparative study that presents the professional audio engineer and system designer with a complete review of the features, construction and specifi cations of four of the most popular active direct boxes used in professional touring today: the Radial J48, the Countryman Type 85, the BSS AR133 and the Klark-Teknik DN-100. It is important to note at the outset that all of these direct boxes are produced by quality manufacturers and are well deserving of the success they have enjoyed in the market. The intent of the Blue Report is not to dishonor any of our esteemed competition, but to compare all of these units using the same test equipment under the same conditions so that the audio engineer can make a proper informed decision with respect to his or her direct box requirements. As with any piece of audio gear, the user must balance his or her personal taste with factual measurements. For instance, some engineers may prefer the sound of a given pre-amp or direct box over another, even though both pieces may measure the same. Subjective listening will always play a part in any purchase. This of course brings to bear ones philosophy behind a given product - do you want a direct box to sound like something? Or do you feel that a direct box should take the sound of the instrument and pass it along to the mixing console to allow the engineer to make the musical decision? At Radial, we believe our task is to be true to the music. In other words, it is our job to provide the very best interface possible given restraints such as features, convenience, size, available power, budget and so on. Therefore, we do not believe it is our task to change the tone of that pre-CBS Fender Jazz Bass or adding sizzle to that new $5,000 Martin D45. Our job is to provide the most invisible and natural sounding interface possible so that the distinctiveness of the instrument shines through. To this end, the Radial engineering team works diligently to remove all types of distortion that may hamper the audio circuit. This includes ensuring an ultra-wide linear bandwidth, reducing harmonic distortion at all frequencies, attaining the very lowest phase distortion, reducing inter-modulation distortion, eliminating residual noise and providing the maximum dynamic signal handling for todays high output instruments. By going to this extreme, a funny thing happens: Odd as this may sound, less distortion sounds better. Or maybe, we should say, it does not sound at all. Enjoy! Peter Janis President Radial Engineering Ltd. Page History of the active DI . 1 Test result summary . 2 Frequency Response . 3 Distortion vs. Frequency . 4 Distortion vs. Amplitude . 5 Phase Distortion . 6 Inter-Modulation Distortion . 7 Fast Fourier Transform the preamplifi er overloads causing distortion. In our view the most critical zone is between -20dB and +3dB. This is where the instrument will likely be in level during real world performance. It is important to note that when testing the output of these devices, all four direct boxes performed differently with respect to input level and output response. The Radial J48 output level dropped by 1.5dB. The BSS and Klark-Teknik showed a 6dB drop and the Countryman showed a 16dB drop. In the real world, one would simply adjust the input trim or pad on the direct box to compensate for levels. Once again, all levels were normalized to provide proper comparative graphs. DistortionRadial J48BSS 133KT DN-100Countryman 85 +0dB0.005%0.004%0.004%0.3% -10dB0.002%0.004%0.004%0.05% -20dB0.005%0.004%0.006%0.1% -50-40 dBV 0.005 0.002 0.001 0.0005 0.0002 0.0001 0.01 0.02 0.05 0.01 0.2 0.5 1 2 5 10 -30-20-10+0+6 RADIAL J48 - THD vs AMPLITUDE % -50-40 0.005 0.002 0.001 0.0005 0.0002 0.0001 0.01 0.02 0.05 0.01 0.2 0.5 1 2 5 10 -30-20-10+0+6 BSS AR-133 - THD vs AMPLITUDE dBV % -50-40 0.005 0.002 0.001 0.0005 0.0002 0.0001 0.01 0.02 0.05 0.01 0.2 0.5 1 2 5 10 -30-20-10+0+6 KT DN-100 - THD vs AMPLITUDE dBV % -50-40 0.005 0.002 0.001 0.0005 0.0002 0.0001 0.01 0.02 0.05 0.01 0.2 0.5 1 2 5 10 -30-20-10+0+6 COUNTRYMAN T85 - THD vs AMPLITUDE dBV % The Radial J48 performs well at -50dB measuring only 0.01% distortion. Like all op-amps it performs best when driven hard. This is clearly shown with less than 0.005% at the nominal +0dB level. The BSS AR-133 performs well in the bottom end with less 0.01% distortion and shows impressive signal handling throughout and above the nominal level coming in at under 0.005%. The KT DN-100 performs well in the bottom end at just 0.1% distortion and shows impressive signal handling above the +0dB nominal level coming in at under 0.005%. The Countryman does not fare well with over 2% distortion at -50dB and another signifi cant rise to almost 1% distortion when pushed beyond the nominal range. 5 -50-40 dBV 0.005 0.002 0.001 0.0005 0.0002 0.0001 0.01 0.02 0.05 0.01 0.2 0.5 1 2 5 10 -30-20-10+0+6 RADIAL J48 - THD vs AMPLITUDE % The most critical zone to test amplitude performance is between -20dB and 0dB where the signal is at optimum level. Radial Engineering Ltd.Blue Report - Active Direct Box Comparison PHASE DISTORTION In simple terms, phase distortion is a slowing down of some frequencies versus others as the signal passes through the direct box. In other words, bass, mid-range and high frequencies go in together, but come out at different times. Obviously this should be minimized as it will cause the instruments sound to change. Phase distortion is most readily heard in the bass frequencies due to the longer wavelengths. As the phase distortion increases, the bass becomes muddy and indistinct. A preamplifi ers ability to transfer a signal without phase distortion is one of the most diffi cult challenges in circuit design. It is usually only specifi ed at 1kHz which, in our view, is somewhat meaningless since the effect of phase distortion is most noticeable at low frequencies. Phase DistortionRadial J48BSS AR-133KT DN-100Countryman 85 20Hz+10+40+70+18.5 50Hz+2+10+25+10 1kHz0000 20kHz0-38.5-50-90 D E G Hz +150 20501002005001k2k5k10k20k +100 +50 +0 -50 -100 -150 RADIAL J48 - PHASE RESPONSE D E G Hz +150 20501002005001k2k5k10k20k +100 +50 +0 -50 -100 -150 BSS AR-133 - PHASE RESPONSE D E G Hz +150 20501002005001k2k5k10k20k +100 +50 +0 -50 -100 -150 KT DN-100 - PHASE RESPONSE D E G Hz +150 20501002005001k2k5k10k20k +100 +50 +0 -50 -100 -150 COUNTRYMAN T85 - PHASE RESPONSE The Radial J48 is impressive with a mere +10 phase shift at 20Hz and virtually 0 phase shift from 100Hz and above. This would indicate the J48 would be well suited for all instruments. The BSS AR-133 measures a disappointing +40 out of phase at 20Hz and reaches -38.5 at 20kHz. It only shows a perfectly stable phase response between 450Hz and 2kHz. The Klark-Teknik does not fare well with respect to its phase response showing close to +70 of phase shift at 20Hz and almost -50 off at 20kHz. It is only phase coherent between 300Hz and 1kHz. The Countryman shows a respectable +18.5 of phase shift at 20Hz but never seems to reach any stability. The top-end begins to shift at 1kHz and is almost off the scale measuring -90 out at 20kHz. 6 Radial Engineering Ltd.Blue Report - Active Direct Box Comparison INTER-MODULATION DISTORTION IMD or inter-modulation distortion is a test that consists of beating one frequency against another and measuring how the two frequencies interact together. This is like listening to dissonance on a piano. Great pianos sound amazing even when playing dissonant notes while lesser ones just plain sound bad. As with distortion versus amplitude, the critical zone is the nominal or normal level at which the device is used. For the direct box, this is usually between the -20dB and +0dB range. This test was performed using the standard SMPTE 60Hz/ 7kHz at a 4:1 ratio. IMDRadial J48BSS AR-133KT DN100Countryman 85 +0dB0.002%0.02%0.02%0.5% -10dB0.003%0.015%0.017%0.15% -20dB0.008%0.008%0.012%0.05% -50-40 dBV 0.005 0.002 0.001 0.0005 0.0002 0.0001 0.01 0.02 0.05 0.1 0.2 0.5 1 2 5 10 -30-20-10+0 RADIAL J48 - INTER-MODULATION (IMD 60Hz/7kHz 4:1) % -50-40 0.005 0.002 0.001 0.0005 0.0002 0.0001 0.01 0.02 0.05 0.1 0.2 0.5 1 2 5 10 -30-20-10+0 BSS AR133 - INTER-MODULATION (IMD 60Hz/7kHz 4:1) dBV % -50-40 0.005 0.002 0.001 0.0005 0.0002 0.0001 0.01 0.02 0.05 0.1 0.2 0.5 1 2 5 10 -30-20-10+0 KT DN100 - INTER-MODULATION (IMD 60Hz/7kHz 4:1) dBV % -50-40 0.005 0.002 0.001 0.0005 0.0002 0.0001 0.01 0.02 0.05 0.1 0.2 0.5 1 2 5 10 -30-20-10+0 COUNTRYMAN T85 - INTER-MODULATION (IMD 60Hz/7kHz 4:1) dBV % The Radial J48 shows exceptionally low inter-modulation distortion from 0dB down to -10dB at less than 0.002% and a mere 0.01% under the -20dB threshold. The BSS AR-133 measures a respectable 0.02% at 0dB and maintains low inter-modulation distortion throughout the range. Like the BSS AR-133, the Klark-Teknik DN-100 measures a respectable 0.02% at 0dB and maintains low inter- modulation distortion throughout the range. The Countryman Type-85 demonstrates reasonable inter- modulation distortion below 0.5% but is outdone by all others in the measurement group. 7 -50-40 dBV 0.005 0.002 0.001 0.0005 0.0002 0.0001 0.01 0.02 0.05 0.1 0.2 0.5 1 2 5 10 -30-20-10+0 RADIAL J48 - INTER-MODULATION (IMD 60Hz/7kHz 4:1) % This diagram represents what happens when two signals are combined to create inter-modulation. In our view, one should evaluate how the device performs when it is driven hard into the hot zone from -20dB to 0dB. This is where performance is most critical. Radial Engineering Ltd.Blue Report - Active Direct Box Comparison FFT - FAST FOURIER TRANSFORM Audio Precision: SYSTEM-2622 CASCADE+ DSP Test Frequency: 1KHz Bandwidth: 22Hz - 22KHz not weighted Level: 0dbU (774.6 mV RMS) Source impedance: 600 ohms Test Load: 1,200 ohms (through 3 ft of twisted pair cable having 100 pfd approximate of total capacity) 10 Radial Engineering Ltd.Blue Report - Active Direct Box Comparison RECORDING magazine Radial JDI Mk3 & Radial J48 DI Boxes “. the real difference between passive boxes is entirely due to the quality and sound of the transformer. A better transformer will sound better.” “My quick RFI test of keying up a two-watt VHF transceiver (an old Motorola HT220. we use then a lot at festival gigs) was fl awless, with no RF pickup even with the antenna very near the cable.” “The JDI Mk3 is a great choice when you need a DI box for a synth, and instrument amp, and instrument with active pickups. (it will also work in reverse for some re-amping applications).” REVIEWS EQ magazine JDI Mk3 and Duplex - Radial juices up direct recording with two new direct boxes “. the best thing you can say about a direct box is that you forget its there. The JDIs are transparent and noise free, but theyre not forgettable. They performed very well on every source I fed them, including electric and acoustic guitar and bass. Even in an environment thats occasionally prone to grounding problems and noise from computers and monitors, the signal was ultra clean.” Audio Media magazine Radial J48 DI “I experimented with a handful of DIs on various instruments here in the studio. in every comparison, the Radial J48 was usually the fi nal choice, simply because it sounded more like I thought the instrument should sound like” . “While less expensive DIs are easy to fi nd, this one has proven its worth to me - I intend to buy a couple of them for my studio.” Keyboard magazine Short takes - Radial Engineering JDI, JDV & JD4 Direct boxes “.the JDI/JD4 and JDV sound - in a word - pure. Compared to these, my old standby active DI has a thinner and harsher tone. No matter what type of signal I put through them, the Radials sounded round and natural”. “Radial Engineering has done a superb job with these direct boxes - I couldnt come up with any gripes about them! I especially like the JDI. Plug it in and it sounds great. If you need a line level output or have a sensitive instrument that could be loaded by a transformer design, the JDV is for you.” “ . theyre pricier than some of the competition, but theyre worth every penny.” ARTISTS AND ENGINEERS CHICK COREA (Electrik Band, Miles Davis) “Radial direct boxes make everything I put through them warm, punchy and clear. They are great DIs!” Chick Corea ROBERT SCOVILL (Matchbox 20, Tom Petty, Rush) “The Radial products are the most transparent, technically comprehensive devices I have ever run across. They are right at the top of my list of gotta haves.” Robert Scovill TOM SIZE (Aerosmith, Journey, Steve Miller ) “We were using the Countryman and when we plugged in the Radial JDV, we noticed the sound was more clear, more open and more natural. To sum it up, The JDV sounds darn good!” Tom Size DAVE NATALE (Fleetwood Mac, Stevie nicks, Tina Turner, Lionel Ritchie, John Mellancamp) “Radials wide variety of direct boxes, iso transformers and splitters are built tough to take the abuse of the road. No one direct box or transformer is suited to the wide variety of applications that I encounter, thats why the choices offered by Radial are so valuable to me.” Dave Natale 11