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Art Djpre II Modifications
Art Djpre II Modifications
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Old 15th June 2018, 12:25 AM   #1
chd_diy is offline chd_diy  United States
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Join Date: Nov 2009
Default Art Djpre II Modifications

I just finished a few modifications on my Art Djpre II, and thought I'd share them with the DIY community.
The first thing I changed was the power supply.
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.
Cheap upgrade for Art DJ Pre ii owners : vinyl
I looked at the one they suggested from Parts Express, but given that it is made by Mean Well, who to my knowledge only makes switching type supplies (which would introduce a lot of switching noise) I chose instead to build my own ripple filtered & regulated supply.
The original wall wart was 9VAC, which is rectified inside the chassis with small SMD diodes in a full wave bridge configuration.
The first filter cap is a 470uf, immediately after which the voltage is regulated down to 5VDC.
Since battery power improves the sound so much, my assumption is that everything after the regulator is of sufficient quality that little improvement could be made from there on.
So, I saw the 470uf cap as a good place to start.
The original is made by Junfu.
They are generally considered low grade crap, so I began the hunt for something better, and decided after reading probably way too much about the subject that an Elna Silmic II would be a substantial upgrade.

The first change was to replace the first filter cap C5 with an Elna Silmic II 470uf @ 25V.

The Elna is slightly larger than the original, but did fit with a slight bend in the leads.

The power supply I came up with is pretty straight forward, and has a nice clean output.

It should be adjusted to 12VDC.

I was a bit skeptical of the difference these changes would make, but listening tests confirmed what others have noticed.
Quieter, more dynamic, improved depth & clarity.

I could have quit at that point, but then I had another small thing to work out.

I am using the Djpre II with an Ortofon 2M Blue.
The inductance of this cartridge is rated at 700mh, which I confirmed measures 728mh with an inductance meter.
With the capacitance of the tonearm cable, interconnects, and the Djpre II internal loading capacitance of 100pf, I was getting a resonant peak at roughly 11.4khz give or take, which was readily apparent in listening tests.

This page has a calculator to estimate resonant peaking with various capacitance loads, and explains really well the effects of changing the cartridge load.
Hagerman Technology LLC: Cartridge Loading

So, it seemed pretty clear that I needed to shed every pf I could to get closer to ideal frequency response from this cartridge.
I tried low capacitance cables, which helped a bit, but it still wasn't low enough capacitance to get rid of that resonant peak within my hearing range.
I briefly considered going with a lower inductance cartridge like a Grado, but where's the fun in that?

I contacted ART and asked for a schematic, but they said that they no longer provide schematics for their current line of products, because they have had some of their designs stolen by other companies.

Since I was only looking to tune the input capacitance, I really didn't need the entire schematic, so I contacted them again and described my problem, and what I was trying to do.
The ART QC engineer consulted the Design engineer who both shared their knowledge of this circuit and helped me to get rid of that last 100pf load capacitance, which in turn got rid of the resonant peak (at least to my ears).

I would like to thank both of them for their help.
It was much appreciated.

So, here it is.

C20 & C23 are the 100pf cartridge load capacitors.
They stay across the input all the time.
C36 & C37 are both 100pf capacitors which are switched in parallel with the fixed capacitors (C20 & C23) to achieve 200pf loading.

Removing C20 & C23 gives you 0pf load on the 100pf setting, and 100pf load on the 200pf setting.

It's as simple as that.

Without giving away any of their trade secrets, I made the overly simplified schematic of the input loading circuit as a way to visualize the effect of removing C20 & C23.
Attached Images
File Type: png DJPRE II Loading CKT.png (4.6 KB, 50 views)
File Type: png C.H. Diamond Art Djpre II Power Supply.png (24.4 KB, 53 views)
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