Jump to content
Sign in to follow this  
ablaze

Emu 0404 modding

Recommended Posts

never did, and still don't understand electronics, but I CAN follow instructions and solder accordingly happy.gif

 

so following the thread here:

http://www4.head-fi.org/forums/showthread....25&page=1&pp=20

mainly summarised in this pic:

user posted image

 

we have this:

user posted image

 

basically swapped out the stock caps with slightly higher valued caps of the "purple" variety

removed buffer opamps, buffer caps

removed 2 560ohm output resistors too, so I can drive headphones directly

replaced jrc opamp with ad8620

 

anything else I should do (undo)?

Share this post


Link to post
Share on other sites
oh yes,

can someone give me EXPLICIT instructions on how to bias the AD8620 to class A?

Use the following for AD8610 family. It's better for this particular family of opamps and also because I'm not sure if the opamp receives dual or single rail power.

post-12-1108561130.gif

Share this post


Link to post
Share on other sites

i think you can make another sub card to arrange the analog parts.and insert the sub card to the other pci dock.

then the Emu 0404 card can small modify.the two cards connect by strip cable.

 

 

Share this post


Link to post
Share on other sites

The two left most yellow cap should be for bypassing of the voltage supply rails for the op-amp.

So you should need 12V cap at minimum.

You said that you have replace them with 1000uF caps, and from the photo you are using 8mm dia OS-cons.

I don't 1000uF OS-Con for 16V or higher exist, so something must be wrong here.

 

I'm not sure how 0404 regulate it's +-12V supply for op-amp, I will take it as there is a 4.7 ohm resistor before the yellow 10uF caps to filter noise. In that case 10uf should be quite fine. (PPA schematic used only film caps after the resistor)

 

Personally I think 10uF is fine, and more than 100uf is pointless, but there's nothing with using 1000uF either.

 

I don't see that there will be any major problem with changeing it to 1000uF.

But there's one potential danger in doing so. that is if I'm right that the caps are for bypassing +-12V supply for op-amp, there's 4.7 ohm resistors before them, and that there's no muting circuit when you turn on the power (as I have seen in 0202 with the huge 1000uF cap).

for 1000uF cap takes 100 times longer to be charged to a certain voltage compared to 10uF caps. And because the existence of the 4R7 resistors before it, the current supply to it is limited.

So for that few ms that the caps are charging up, the output op-amp will be getting voltage supply that's below its rating. And when this happen the op-amp will not be stable. (this is the main reason that you hear a pop when you turn on some instruments) The worst case will be it outputing huge DC offset (that could be up to rail voltage, who knows?)

In the worst case you connect the 0404 to a headphone amp with gain 11, and then to a earphone of Z=16ohm.

If you take the DC offset as 1V, the amp make it 11V, and since power=V^2/R, your tiny 16ohm imp earphone will be heated at a power of 7.56Watt, i.e. 7.56mJ per ms, which will burn burn it in just a few ms even if the diaphragm don't break with the loud pop.

For 1000uF to be charge to 12V with a 4R7 resistor, it takes 9.4ms (if my maths serve me right), and in that period of time each of the 4R7 resistor will converted 0.144J to heat (the initial peak power is 30.6W!!!), which I'm not sure is safe.

Luckily most op-amps are operational from +-5V onward. the popular AD8620 works well down to +-3V (personal experiance), and for it to output DC it may takes much lower voltages.

For 5V the time will be 2.5ms, for 3V it will be 1.33ms.

So in practice it's quite safe as long as you don't have a killer combi of a low Z phone with a high gain amp that's on when you switch on your computer.

 

well, things will be much easier if you just use 100uF or less...

 

Also can let me know where you get all your OS-CON from?

Edited by aaa

Share this post


Link to post
Share on other sites

sorry those were pics from my prev 0404 that had oscons

here're some updated pics:

user posted image

user posted image

 

most 10-40uF caps have been replaced with BG NX-HiQs 47uF, cept those 3 in the bottom right on the front, that're using 220uF NX-es

there're only three caps that need >12v, one of them's replaced with a cerafine (on the front of the card)

and of course the 2 huge caps at the back are 1000uF 25v NX-es

could large caps in those positions actually "slow" the sound, since they'll take a lil longer to charge up?

I'm running my headphones straight from the card. no amp happy.gif so no additional "gain" to worry about

dc offset's about 4-6mV

Share this post


Link to post
Share on other sites

When did your get these BGs and how much they cost?

Since your used such good parts for mod, I will suggest adding some 0.1uF MKP or MKS bypass caps.

They should be much better than the tiny X7R caps EMU used.

Share this post


Link to post
Share on other sites
When did your get these BGs and how much they cost?

Since your used such good parts for mod, I will suggest adding some 0.1uF MKP or MKS bypass caps.

They should be much better than the tiny X7R caps EMU used.

The BG NX-HiQ's are not meant to be bypassed. At least, that's what I gather from users' experience.. I'm not a BG fan anyway.. There wouldn't be much of an improvement bypassing them as they're already low-ESR caps. It's more of a tweak when non-low-ESR caps are used.

 

Adrian: How much is the EMU-0404? I might consider getting one.. Heh.. Been using onboard sound for too long.. LOL.. Have to get a proper soundcard since I've been handling lots of video media conversion and video edtiting work lately..

Share this post


Link to post
Share on other sites

aaa: yeah I do recall reading that BGs work best without being bypassed, and I got them from partsconnexion but Wellaudio stocks lots of the BGs too, I just found out.

firefox: I think its great. especially with the good deals going on at vrforums, you gotta check it out. its.. S$155 smile.gif

 

erm, nobody's answered my question. Could 1000uF caps "slow" down the sound?

Share this post


Link to post
Share on other sites

ablaze,

 

Never know that property of BG.

IMO, if you are at the stage of cosidering to buy 1000uF caps, and not knowing it's effect, then your question will be valid.

But now you have already got the caps and have them soldered on, maybe it should be time you doing some test (of soldering and desoldering) and let other potential modders know the result.

BTW you just need to unsolder one of the two legs for each cap, then you can solder a 10-100uF cap on the top side of the PCB.

Share this post


Link to post
Share on other sites
erm, nobody's answered my question. Could 1000uF caps "slow" down the sound?

Not if they're just used for signal coupling.

Share this post


Link to post
Share on other sites

Please sign in to comment

You will be able to leave a comment after signing in



Sign In Now
Sign in to follow this  

×
×
  • Create New...