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Last Update:3/23/2005

M-Audio (Midiman) SuperDAC 2496

In my quest to improve my home system, I realized that I needed a very good DAC with modding potential at a reasonable price. During my quest, I came across the M-Audio SuperDAC 2496 on several of the audio forums. Most folks raved that this little box was a diamond in the rough. I began checking E-bay and Audiogon for several DACs, and the SuperDAC happened to be the first one that became avaiable. I quickly purchased it from the seller, who included an upgraded power supply transformer (3 amp, 9VAC Trak Microcomputer).

Even with my (then) meager setup, it became very apparent that this would be a great addition to my "Frugalphile" system. I don't believe that most high-end audio gear is worth the asking price. I do, however, believe that pro-audio gear makes a great platform for home audiogear, albeit with a few tweaks.

I began researching the DAC, through forums and google, which lead me to a great group on Yahoo, http://groups.yahoo.com/group/M-Audio_SuperDAC_2496. These guys are dedicated to modifying this DAC.It became readily apparent that with a little elbow grease and a few choice components, this DAC could be turned into a top piece of kit for a paltry investment in parts.


DAC Layout

Power Supply:

The power supply on the SuperDAC consists of three sections: digital, analog, and the local bypasses.

The digital supply consists of D5, a 1N4001 diode, half-wave rectifying the 9VAC and feeding C11, a 2200uF/16v Capacitor. This in turn feeds a LM7805CV regulator, filtered by a 470uF/16v (C12) cap at it's output. This supply powers all of the digital components on the board (AKM4393, CS8414, PIC, etc.).

The analog supplies consist of two full-wave voltage doublers, formed by D1-D4, C3 and C6. These in turn each feed a 7815CV and 7915CV voltage regulator. Each regulator is filtered by a 470uF/16v (C2 & C8) capacitor, and provides +/- 15v to the opamp section.

Supply Bypassing:

The opamp bypass section consists of 12x 10uF/35v electrolytic capacitors (C49-51, 55-57, 69-71, 75-77), each bypassed with .1uF ceramic capacitors (C52-54, 58-60, C72-74, C78-80). The DAC (AKM4393) is bypassed with 3x 10uF/35v electrolytic capacitors (C33, 37 and 39) bypassed with 3x .1uF ceramics (C34, C38 and C40). Finally, the CS8414 is bypassed with 2x 1uF/50v (C20, 21) electroyltic capacitors and 2x .1uF ceramics (C22, 23).

Analog Output Section:

The analog output of the AKM4393 is fed into 4x 47uF capacitors (C42, 46, 48 and 52), which act as DC-blocking capacitors. This in turn feeds the output section, which consists of 6 opamps, JRC 5532s, 3 for each channel. The first pair of opamps (U9, 10 for the Left channel, U12, 13 for the Right Channel) are configured for a gain of 5.82, and feed the XLR outputs (7V peak-to-peak output). The third pair of opamps (U11 for Left, U14 for Right) take the output of the first pair of opamps and reduce the voltage, while creating a single-ended output.

Note that the opamps connected to the DAC are configured for inverting operation. This gives the output signal proper phase, since the AKM4393 inverts absolute phase.


Modifications

Power Supply

The rectifier diodes are the first to get removed. These are all replaced with MUR860 ultra-fast rectifier diodes. Purportedly these help with the switching noise caused by the transition from positive to negative on the AC waveform. When the sinewave goes from positive to negative, and the diodes clamp shut, it generates spurious noise. These ultrafast diodes minimize the time period that this noise is generated for.

Next, the generic electrolytics are removed.  

On the analog power supply, I replaced the 4x 470uF/35v capacitors with 1000uF/35v Panasonic FM capacitors. Technically, you could squeeze 1200uF Panasonic FM's into these spots. I then replaced the 470uF/16v post-regulator Capacitors with Elna Cerafines. I should note that the caps around the 7805/7905 are a tight fit -- you will need to leave the leads a little longer and do some creative maneuvering to get the capacitors to sit flush. I recommend removing the caps and the diodes, then first installing the diodes, followed by the pre/post regulator caps altogether. You will need to squeeze the caps a little to get them to fit correctly. I also recommend desoldering and resoldering the regulators so that the thickened portion of the leads are flush with the top of the PCB. Then, bend the regulator back and you will gain more room by not having the regulator pins in the way of the base of the cap.

For the Digital power supply, I swapped out the 1N4001 for another MUR860. The 2200uF/16v generic smoothing capacitor was replaced with a 2200uF/16v Panasonic FM. You can technically fit up to a 2700uF/16v Panasonic FM capacitor in this position. For the post regulator capacitor, I used another 470uF/16v Elna Cerafine. During the course of this, I did manage to install the diode backwards and blow the 2200uF Cap and the 7805 regulator. Fortunately, after switching the diode around and swapping the regulator for a new 7805, everything still worked fine. Just remember to double check your part orientation against the datasheet, and don't do this when you're tired.

Bypassing

Changes here were similar to the power supply mods. Basically, all of the electrolytic caps were swapped for Elna Cerafines.

When changing the bypass caps on the opamps, I realized that the Cerafines would not fit in the stock capacitor spots if I installed the sockets for the opamps. To remedy this, I swapped the electroyltic and it's respective ceramic bypass cap. This actually brings the bypass cap closer to the opamp. I then proceeded to install the 10uF Cerafines.

For bypassing the other parts, I exchanged the 1uF Electrolytic capacitors around the CS8414 and PIC for 10uF Elna Cerafines (C18, 20, 21). I also swapped the 10uF caps around the DAC for Cerafines as well.

Analog Output Stage

The worst aspect of this DAC's design, in my opinion, is the fact that they use 47uF/35v electrolytics (C42, 46, 62, 66) in the signal path. These were immediately swapped for 47uF/35v Cerafines. They barely fit in these spots. A better choice might well be 47uF/6.3 Black Gate non-polar NX Hi-Q. My understanding is that the output of the dac is no more than +/- 2.5v peak-to-peak. I have these on the way and will post an update once I swap them in.

UPDATE: I have swapped the Cerafines for the Black Gate NX-HiQ's and recommend going this route over the cerafines. First off, they sound better. Second, they fit the spot and are easier than trying to shoehorn in the Cerafines. They are available for $2.19 each at http://www.kyoto-electro.com.

The next step was to desolder the JRC NE5532 opamps and replace them with sockets. These sockets wee then stuffed with the "Audiophile Approved" (tm) OPA627's. I really didn't have any particular reason for choosing these other than they have a great reputation and sound fantastic in my headphone amps. Other alternatives may be the TI/Burr-Brown OPA132/134, OPA604, or the Analog Devices AD8610, the AD744, or the AD8065. You should keep in mind that the power supply provides +/- 15V to the opamps, and many of the new opamps from Analog Devices are not rated for more than +/-12V supplies.

Connectors

The final item that needed to be fixed were the stock jacks that came with the DAC. The SuperDAC utilizes 1/4" jacks for the single-ended outputs, need to be replaced with quality RCA Jacks. The S/PDIF Digital Input is also a generic "gold plated" RCA plug. All 3 of these jacks would be replaced with WBT 0201-style PC-Board mount jacks.


Parts-list

PCB Part# Original Part Replacement Part Cost Where to Buy
 C1, 3, 6, 7  470 uF/35v  Panasonic FM 1000 uF/35v  $3.80  Digikey P12405-ND
 C2, 8, 12  470uF/16v  Elna Cerafine 470 uF/16v  $4.80  Welborne Labs ROA472
 C11  2200uF/16v  Panasonic FM 2200uF/16v  $0.95  Digikey P12369-ND
 C33, 37, 39, 49-51, 55-57, 69-71, 75-77  10uF/50v  Elna Cerafine 10 uF/35v  $9.00  Welborne Labs ROA100
 C42, 46, 62, 66  47uF/16v  Black Gate NX-Hi-Q 47uF/6.3v  $8.40  Kyoto-Electro
 C15  22uF/35v  Panasonic FC 22uF/35v  $0.34  Digikey P11230-ND
 C18, 20, 21  1uF/50v  1uF/63v BC Metallized Polypropylene  $1.16  Digikey BC2076-ND
 D1-5  1N4001  ON Semi MUR860 Ultra-fast rectifier  $5.70  Digikey BC2076-ND
 U9-14  JRC NE5532 Op-amp  TI/Burr-Brown OPA627AP  $110.28  Digikey OPA627AP-ND
 Opt. Sockets for U9-14  n/a  Assmann IC Socket, .3u Gold 8-pin DIP  $7.44  Digikey AE7313
 RCA Jacks  n/a  WBT 0244 RCA Female Chassis Mount Jack  $75  Partsconnexion WBT-62409
   Estimated Total Price:  $226.87  


Images

Note: These pictures do not reflect the current state of the DAC. They still show 3x 1uF Metallized Polypropylene in the spots the 1uF/50v electrolytics occupied. These have since been replaced with 10uF/35v Elna Cerafines.






Further Tweaks

Power Supply

The seller on Audiogon that I purchased my DAC from included a 9VAC/3amp transformer. This is pretty much the first upgrade that should be done to get the most out of your DAC. The standard PSU looks like it probably cannot sustain high current demands if the DAC should require them. A few options are out there:

1) Buy a ready made one. These transformers were common with old Atari computers. Ebay or Google may yield somewhere to buy them.

2) Build your own. 9VAC/1.5AMP or better toroidal or R-core transformer should be sufficient. Put it in a small aluminum enclosure, wire up a fused IEC connection, and run a cable with a 2.5mm jack on the end of it to the SuperDAC.

I've been giving the power supply more thought, lately, and my ideal way of dealing with it would require removing the SuperDAC from it's enclosure entirely. Then, strip all of the pre-regulator caps and rectification diodes. Finally, build 3 outboard power supplies, +15v, -15v and +5v around Jung-style superregulators. I would use a 15VAC/2amp transformer with two secondaries, each going through full-wave rectification via MUR860 or another ultrafast rectifier diode. This, plus 2,200-4,700uF of capacitence per rail would power the +/- 15v section of the DAC. A second 6VAC-9VAC single-secondary toroid with full-wave rectification would power the +5v sectionThis should yield a great improvement on the analog output stage

Yes, this is probably overkill to the extreme, but isn't DIY more fun that way?

Resistors

There are approximately 24 resistors in the Analog output stage. Almost all of these are either feedback resistors or directly in the signal path. The stock resistors look like standard 1% or 2% tolerence metal films. Replacing these with a higher quality (Caddock MK132 or Vishay S102) resistor should yield significant improvements -- if resistors are actually audible :) I still haven't decided whether or not I believe it, but I can acquire these parts fairly inexpensively, so it may be worth trying out at a later date.

Clocking

Based on the discussion I've read, the SuperDAC benefits greatly from an accurate clock source. Unfortunately, the DAC itself does not have a way to be reclocked, so the best bet is to go with an external clock source, such as a Monarchy DIP. While you're at it, you may want to get the DIP Upsampler. It not only provides the jitter control that the original DIP does, but it also upsamples the S/PDIF data from 16bit/44.1khz to 24bit/96khz to feed the DAC. The only downside to these is that the upsampler costs the same as what a brand-new, unmodified SuperDAC went for. Otherwise, you could probably stick with the standard Monarchy DIPs.


Links

Audiogon: http://www.audiogon.com
Digikey: http://www.digikey.com
Parts Connexion: http://www.partsconnexion.com
Welborne Labs: http://www.welbornelabs.com
Yahoo SuperDAC Group:http://groups.yahoo.com/group/M-Audio_SuperDAC_2496/


Acknowledgements

Thanks to Harry from the Yahoo SuperDAC group for posting schematics on both the PSU and Output stage. Furthermore, thanks to whomever started the Yahoo Group, since it helped catalyze me moving forward with my modifications on the DAC. Finally, thanks to the guys over at Boulder Audio and the other mod places for inspiring me to mod mine to at least their levels, or hopefully exceed it!