E-MU 0404 USB Modification? - Page 4 - diyAudio
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Old 3rd March 2010, 08:55 PM   #31
iko is offline iko  Canada
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That's good info, thanks Jim!

For what it's worth, I've seen high frequency ripple on the -5V rail (about 160kHz) with the card connected to absolutely nothing. I'm not sure, but this HF ripple may be a side-effect of the DC-DC inverting converter, the TPS6755, which works on a switching frequency of 160kHz.
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Old 3rd March 2010, 11:34 PM   #32
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Jim- good work. My 0202 has the same noisy output and I was a bit confounded trying to reconcile the published specs with what I saw on the scope. I was able to reduce it by changing computer settings (can't remember what) but it was still useless as a signal source. IMO, there's some synchronization going on when using Visual Analyzer and good measurements can be made, but the stuff is still there. Thus my basic distrust of sound card based measurements unless some traditional means can be used to verify at least a couple points. My results have always been very set-up specific.

Best,
Conrad
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Old 8th March 2010, 01:19 PM   #33
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I have performed some mods in my EMU 0404 USB too. I have changed all those crappy electrolytics caps for some nices Panasonics FM and FC. I still have to change the output opamps and the headphone opamps to LM4562. I am a bit afraid of skrewing up something because of the tiny smd components.

Another big improvement will be bypassing the output pot. Seems to be a really cheap one, in RMAA tests it showed a bit unbalance in tracking between channels (depending of pot position).
Add to that the fact that I have been using it as a preamp through a daily whole year usage, that means it should sound significatly worse than when it was factory new.
I think I will bridge the pot and use my brand new DCB1 preamp with stepped attenuator.
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Old 8th March 2010, 02:26 PM   #34
Salas is online now Salas  Greece
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Quote:
Originally Posted by Conrad Hoffman View Post
Jim- good work. My 0202 has the same noisy output and I was a bit confounded trying to reconcile the published specs with what I saw on the scope. I was able to reduce it by changing computer settings (can't remember what) but it was still useless as a signal source. IMO, there's some synchronization going on when using Visual Analyzer and good measurements can be made, but the stuff is still there. Thus my basic distrust of sound card based measurements unless some traditional means can be used to verify at least a couple points. My results have always been very set-up specific.

Best,
Conrad
I have seen high output noise on my scope too from my Emu tracker. Even sine waves produced by it are obviously dirty VS my analogue old generator on the scope's screen. But when looped with measurement software, it ignores it, and it compares very well for THD readings and SNR of DUT VS normal measurement equipment. A guy in a local forum made an extensive analysis and comparison with his HP gear, and beyond square wave generation that was ringing, he found the EMU very useful when looped with measurement software, but not as a stand alone generator. Especially not beyond 48kHz sampling rate. Big noise starts at 35kHz and he made a filter. That helped if there is need for an AF only capable stand alone generator and it must be the EMU, for economic and utilization reasons if its already in hand. They also proposed buffered attenuation for its input so it can be used on measuring high voltage signals too.
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Old 21st May 2010, 12:36 PM   #35
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Someone have got the output from the DAC chip to skip the problem of output stage ?

This will resolve the problem of the negative power supply because is not used in DAC section but only in the output stage, I think.
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Old 21st May 2010, 02:58 PM   #36
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I think it outputs a balanced out. Someone looking at the chip datasheet may confirm...
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Old 21st May 2010, 10:10 PM   #37
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I have change the power supply electrolytics near the DAC chip and I have got the balanced output on this chip.

All the opamp and all the capacitors on the signal path are bypassed .

The balanced signals with the +2.5Vdc has been connected on a Lundahl transformers like in the my DAc final (DAC Final).

Very simpe this modification, no more of 1 hour.

Index of /HiResolution/EMU0404
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Old 21st May 2010, 10:27 PM   #38
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Did it make a measurable/audible difference?
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Old 22nd May 2010, 12:52 PM   #39
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still no measurements but the sound is fantastic

Hi-Resolution System Intro + 192KHz 24bit

The thd is about 0.1% with transformers
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Old 22nd May 2010, 06:58 PM   #40
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Looks very interesting, really nice information. You gave me the idea to do something similar. What of the approach for outputs have you used? You explain it with a transformer, with discrete solid state, hybrid and pure tubes.
Have you constructed and tried all of them? What differences have you noticed.

Leaving still connected the old output stage, is not gonna make some kind of influence? Like input impedance is divided if you place 2 output stages in parallel.

Regards,
Regi
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