Modding my EMU 0404: Can someone please verify

[bg4533]

I am about to order some parts to mod my EMU 0404. Below is a link to a picture of what I want to do. I only care about improving the analog output of this card.

Picture

Color Codes:
Yellow: 10uF/16V caps, replace w/ Panasonic FC 10uF/25V (16V unavailable)
Red: 100uF/25V caps, replace w/ Panasonic FC 100uF/25V
Pink: 47uF/16V caps, replace w/ Panasonic FC 47uF/16V
Green: Output caps and buffers, remove and jumper
Orange: Opamp, replace with LT1364, bypass cap, Bias to class A with ~1.5mA CRD

Removing buffers:
The datasheet lists the pinout of these opamps as:
1. A Output
2. A- Input
3. A+ Input
4. V-
5. B+ Input
6. B- Input
7. B Output
8. V+
I obviously have to bridge A output to one (or both) A input, but which? The same goes for B.

Bypass caps:
I think I am just going to use a Panasonic ECQP Polypropylene here. I have not yet decided on a size. Should I bypass from rail-rail or rail-ground? Rail to rail will be easier. What are the benefits of each method (I want to know this for future projects mainly). If I go rail to ground can I use the silver box by the buffers as ground? Anywhere better for ground?

CRDs:
I have been unable to find these on Digikey. Anyone know any part numbers?

Capacitors:
I want to keep this a fairly cheap mod, so I am going to stick with Panasonic FCs for now. Are there any other caps on this board I should upgrade or are there any that I am upgrading that don't pertain to analog output? Provided the caps fit, could there be any problems with using a larger capacitance cap? Prices are about the same, so I might as well use larger ones if it won't hurt.

Thanks for the help.

[BrianL]

First, I'd probably just replace all electrolytics on the board.

In general, if they'll fit, use larger capacitance values.

I don't know if Panasonic PP will fit for bypass. Consider
0.01uF C0G ceramic. Having long-ish leads on the
supposedly better bypass caps pretty much negates
the benefit of the better caps. Note also, that there's
a lot of HF/RF hash to kill, so your bypasses have to work
up into the RF region.

Which parts are the buffers and why do you think that?
Before just jerking them out, I'd replace with a better op-amp.
If the buffers are truly buffers, -input is connected to output.
You'd jumper from +input to output. But you need to trace
the circuit to make sure it doesn't have gain, isn't an inverting
amp, etc.

My choice for op-amp would be something like AD8610/20 or
OPA2132 (or 2134)

CRDs: One could use a JFET connected as a constant current
load or maybe just a resistor. Pick a resistor so that it
draws about 3 mA from the output to the negative supply
on the op-amp (ground, if single-ended supply)

[Werner]

Have you studied the datasheet of that AK4395?

http://www.asahi-kasei.co.jp/akm/en/...395/ek4395.pdf

Pins VREFH, VREFL, and VCOM are probably the most critical ones,
aside from the analogue supply.


Swapping capacitors may seem fun, but if (part of) your power supply voltages are generated by a switching regulator or DC/DC convertor, then strange things may happen all over the place.

Try to measure the DAC's output through the board's ADC, for instance with Rightmark freeware, and monitor the noise floor after each modification.

[ngiachin]

would you be willing to post details about the mods when you are finished? I would really like to mod my 0404, but guys are charging like 160.00 to do it. Thanks.

Nik

[bg4533]

Originally posted by ngiachin
would you be willing to post details about the mods when you are finished? I would really like to mod my 0404, but guys are charging like 160.00 to do it. Thanks.

Nik

I am a regular poster over at the Head-Fi forums. Not too many people over there have modded their cards yet and few people understand what they are doing anyway. I posted here to see if anyone here has modded these cards or if there is any other advice.

I ordered all of the parts I need to mod this card from Digikey yesterday. I couldn't find CRDs there, so I am just going to wait on that. I got the opamp, Panasonic FC caps, and some ceramic caps for bypass. It is probably around $15 in parts.

I am planning on making a bit of a modding tutorial for the people at Head-Fi. I will post it here when I finish too. Will probably be 2 weeks before I can mod the card and write something up.