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E-MU 0404 USB mod wiki
I decided to start this wiki to keep track of all info we can find about how to improve the E-MU 0404 USB (and possibly the Tracker Pre) sound interfaces.
Main modification topic is here
The contents of this section should be to identify on-board components and their function.
Detailed pics of EMU0404 are HERE
Image of the DAC section
Component identification (pic found on the web, thanks to the guy who made it)
PHKI = TPS62200DBV IC
PHOI = TPS61040DBV IC
PGVI = TPS73001DBVR IC
S28B = LM2704 IC
6755I = TPS6755I IC
OWNK Muting N-JFET transistors
The output stage has a summing filter first (opamp U22), very similar to what's given in the AK4396 datasheet. This is followed by a volume potentiometer, then a buffer (opamp U32).
The output of the buffer goes to the output jacks and also to another opamp (U39), in inverting unity amplifier configuration, that produces the inverted output for the balanced (!!) TRS
output jacks. Shown are left channel circuitry through main and headphone out. Diodes and JFETs other than the HP out aren't labeled with the right PCB name.
(Right channel takes the "B" of each opamp.)
Eagle 6.1.0 Schematic file
Original schematic drawn by pilli
You can swap out some of the filtering caps and putting new higher valued ones. This will (maybe) improve filtering. The DC/DC converters present in the PCB doesn't seem
to allow much changing in value though. Going too much up with value, will bring in an endless reset loop of the EMU.
Basically what you can do is:
ADDITIONAL NOTE: it seems that even 220uF value will make the board unstable, especially when EMU has been turned on for long periods. 100uF may be a good value (it's 10 times bigger than original, anyway)
better swap it with 63V still.
Don't even give a try changing the 2x220uF near U5 HP driver, because 470uF will make the board unstable.
Output stage Op Amps supply
An "easy" thing to do is to provide a linear regulated ±6V supply for the output stage opamps (U22, U16, U33, U39) with a dedicated power supply.
The ±6V rails reach the opamps through two jumper 0 Ohm resistors, components R149 and R157. If you remove these two, you can attach a new ±6V supply.
It is too tricky to solder on these tiny pads though. You'd better use the two local capacitors C103 and C109 pads, which are through-hole electrolytics. You'll need to attach your ground nearby on a pad nearby too.
Notice that the headphone driver U5 receives the same rails but through two other resistors, that are 1 Ohm, R83 and R74. These are larger, of course, because that's a low impedance driver (headphone). These have local elcos too, C30 and C39.
NOTE: ±6V seems a bit low. I would try ±12V.
Personally I wouldn't mind this mod because DAC resolution is fixed. Having higher supply voltages over opamps will give better resolution for the opamps themselves. But then, the wave coming from the DAC will still have AKM5385 resolution. As pilli told me in a PM, using ±9V didn't gave him much results (needs to be confirmed) (FixMetal)
Linear regulated +5V PSU
The other common mod is to create a linear regulated PSU with a 7805 and some bypass transistor. Note that you'll have to dissipate a great amount of heat. Some pics on the
web shows a fan over a heatsink for getting more heat out of it, but that way will most likely inject fan noise into your board (because of DC motor supplied by your regulator).
Keep in mind that you'll need a (at least) 1.2A transformer and a 12000uF input filtering capacitance to get a 5% ripple before the regulator. Spike smoother caps on the
diode bridge will surely improve the thing.
This mod won't (of course) eliminate the side effect of frequencies injected by DC-DC converters INSIDE the board. You should note that if the 160KHz (as supposed above) is the dominant noise in this board, it's 8 times over the audiable threshold! Even harmonics will go UP to 160KHz, not down, so there's really no chance for you to ear this (not even for your dog, I swear)
Not every opamp seem to be a good compromise being replaced instead of the original ones. I tried LT1364 in place of U33 and all I obtained was short between Vcc and OutB of the opamp. Same as above, I couldn't change U3 nor U7 with NE5532 without having HUGE pops, crackles and s**t over the 2 inputs too. There must be some decoupling/bias stuff that won't let some higher spec opamp work well.
It is up to you to decide wheter get rid of these or just raise the value . Many says that without these caps you get a better bass response and a more organic overall sounding board. The fact is you'd inject some DC into your speakers. BUT, there's a but. Since the EMU can't handle passive speakers, any that you will use will have some electronic between the board and the speaker itself, making your line out signal strong enough to drive the speaker. Any of these electronic stuff has surely a DC decoupling capacitor before whatever the signal goes in. Actually you don't really have to think about DC being injected into speaker.
If you're not enthusiast with this, you can always replace the 4x47uF decoupling caps with higher valued ones, like 220uF.
For somewhat reason Creative made a layout with lines prone to DC-DC converter and USB datarate noise. The left channel line is near an inductor, which of course induces noise to the line. Thanks to Sidiy on the forum, there's a fix for this. Instructions goes like Sidiy had
this done. Topic's here and here
Note: be very gentle while lifting the two resistors as the pads are real weak
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