I've read a few EMU 0404 USB mods on the internet and decided to take on this modding project. Some guides were informative, others were not. There still seems to be some unanswered questions relating to what each component does and which ones to replace. I look the liberty to hook up my oscilloscope and poked around in a few places and did the hard work. Here is my end result: (sorry, I only took pics after the mods, so I do not have the before pics to point out which ones are to be replaced)
DAC decoupling capacitors
From the looks of it and my PCB analysis, the DAC has 4 outputs: Left -,+ and Right -,+. You need to replace the stock 47uf caps (x4) with some good ones of your choice. The other 3 around that area are supply caps (10uf I believe) and are used only for filtering. (Be cautioned: I used 1500 uf Rubycons only to find out DC-DC converter cannot handle the inrush current at turn-on. The unit kept on going in an endless power cycle, sometimes it works, most of the time it doesn't. I played around with the values and 470uf seems to be a good limit on all the supply caps.) Supplying the opamps is -+6V, so there must be some DC-DC conversion going on here. (Noise!)
Four 220uf ELNA Cerafine audio de-coupling caps and rubycon 1600uf filter caps (later replaced with smaller values)
The remaining two G-Luxon caps are also used for filtering. They are 220uf, Replace them.
The Op Amps
I just chose the 2132 because I am familiar with them. You can almost choose any opamp you want, a majority of them will be a direct replacement with a few exceptions. As far as audio output goes, you only need to replace the headphone amp, (x1) gain stage, (x2) the output/buffer stage. (x2)
The signal path goes to the first pair of opamps to the right of the caps. Then it is split between the headphone and output stage. In other words, whether you are modding the headphone or direct line out, this first pair must be replaced. (Why not do all 5 while you're at it?)
Burr Brown OPA 2132U opamps. (need five)
Output stage pair on the right and one gain stage opamp is showing on the left. There is one more right under the caps.
Lowered the supply caps to 470uf as 1500uf was excessive. I also soldered some silver wire to get some balanced XLR connectors out to my main system.
I used a LM7805 linear regulator to replace the wall-wart. You will need to use pass transistor to supply the current since most regulators are rated at 500mA. The one shown is rated at 1A and still could not power on the unit. The MOSFET mounted sideways is the pass transistor. I also had to use a small DC fan running at 7V to keep the heatsink cool.
A nice extra supply of filter capacitors is always good. (But don't go too overboard) Use some snubbing capacitors (100nf is a good choice) on the diodes as well.
Sound? I will let you be the judge of that. Whats the fun in DIY if you know the results? I will say that putting in the larger caps gave some nice surprises in the low end.
That is it for now. I will edit this as users post comments/questions. Time for bed.
Edited by lhowing884 - 9/20/10 at 11:50am