ART DJPRE II Phono/Line Pre-Amplifier

Product Information

Many owners of this unit report that it sounds much better on battery power, or as reported in this post it can sound just as nice with a good quality regulated supply. Even its mediocre THD-N is shown at near real situation as sum of THD with Noise at AV=20dB gain amplification, VO=5V, RL=2kΩ, f=1kHz and it is THD-N is 0,001% The original wall wart was 9VAC, which is rectified inside the chassis with small SMD diodes in a full wave bridge configuration.

As you can see in pictures, now the case is pretty crowded and moreover wires soldered to 0603 SMD pads are delicate, so I wouldn't want to open it again, since last time I had to open and close 3 times before everything was safe and connected in place (every time 1 wire broken its solder). If the turntable has a different ground wire, connect it to the DJPRE II's Ground port to eliminate hum. Here we have three graphs: one for Pluto and two for DJPRE II with its filter switch to Flat and Low Cut. When set to flat, the DJPRE indeed has a flat response that extends past 50 kHz. The Pluto has a low-cut built-in per specification. So for a good solution we need any bipolar Op.Amp that can give at least SVR of -110/120dB, and below 8nV/√Hz at 10, 100Hz and even at 1kHz (and not in the ultrasonic range at 100kHz like TS972).220p input, and the treble peak wants to eat your ears for breakfast (though it sounds clean otherwise, so I doubt it's the stylus - I bought a spare just in case). Originally the cable would have been much shorter, and the phono input in the amplifier that went with the unit had 47 pF of input C, bringing the total close to the upper end of the recommended 100-200 pF load range. We've never lost the motivation that comes with the development of developing technologies over the previous four decades, and we appreciate you, as well as the thousands of ART users, for your continuous support and commitment. This firm proudly manufactures pro Audio DJPRE II.

I think that both these items show a failing in modern Phono preamps, that of limited headroom. Preamps need an absolute minimum of 20dB above their nominal sensitivity, which needs to be in the range of 3.5mV to 5mV for 500mV output, and therefore with a maximum output of 5V before clipping.When Ti put in spec for OPA1612 as stellar level for THD-N like 0.000015%, we must have in mind that it is mesured on no gain platform AV=+1 so that real condition Pre.Amp wil degrade that for any aplification level it performs, so at AV=100 (20dB relative) it is = A-weighted signal to noise ratio ("SINAD") is 83 dB for DJPREE II beating the 80 db for Pluto. Both companies spec 90 dB.

A-weighted signal to noise+distortion ratio ("SINAD") is 83 dB for DJPREE II beating the 80 db for Pluto. Both companies spec 90 dB. Here, it is Pluto's turn to nail the phase response with essentially zero deviation at all frequencies. The DJPRe II though starts to have a negative phase shift below 1 kHz and it progressively gets worse down to 20 Hz at some 66 degrees. Selecting the low-cut filter makes things better with a positive phase shift that starts at 50 hz and goes up 20 degrees or so at 20 Hz. I am not sure what is going with the DJPRE II here. I can see a phase compensation at higher frequencies but not lower.

Customer Reviews

Why is it, because someone concluded that a simple CMOS op-amp with low en. of 4nV/Hz (at 100kHz!) is enough to get a solution that will be Low-Noise, "well, litle tomorrow, maybe never". The ST TS972 has a typical SVR of -70dB which means it attenuates the noise level in the power supply by about 3162 times, before it appears as a parasitic value at the input of the Op.Amp. We all know that after that it will be 100 to 178 times more amplified. And the result of all that is the hum that can be heard and clearly seen on spectrographs.

And it has specified and garanted RIAA caracteristics NJM2068D Equivalent Input Noise Voltage is as FLAT+JIS A, on RS=300Ω at 0.44 to max 0.56μVp-p As you see, the DJPRE II has "low cut" filter switch together with input capacitance selector (100 or 200 pf). It also has a clipping indicator and variable gain switch. I posted this about my observations after setting the gain on the Art to -6db on another forum, and wanted to include it here also: Both are great bargains from what I can see. Personally I find the DJPRE II a more flexible unit so if I had to buy one, it would be that if I could hide it some place.

Both devices are remarkably the same with one significant difference: the pluto bleeds noise from its power supply rectifier into its output. You can see this in harmonics of mains 60 Hz in blue. The DJPRE II actually has higher mains hum at 60 Hz, but it is otherwise much cleaner relative to power supply noise. thank you all for giving me insight into the potential and possibilities for improving an already very solid pre-amplifier design. added 1000uF alu-polymer cap on opamp pins (I assume they have the same rails so doesn't matter which one)