Modding 7.1 Revolution.

[rosbacke]

This thread started in 'Alternative to M-Audio Delta 410' but I'm starting a new one since it was slightly off topic.

I've modded my revolution 7.1 by replacing the large capacitors on the power supply to 2.2milliF, changing three op amps to OPA 2134 and adding a 2.2microF capacitor to the three op-amps and the DAC for the front channels.
The sound is definitively better. The biggest impact was made by adding large, low ESR capacitors to the power supply line. However, after adding them my computer now makes 2-3 restarts i period of a couple of seconds when I start the computer. I guess it takes some time to charge the capacitors at startup.

I aslo tried to bypass the capacitors in the signal pathway but it made it worse.
The DAC converter (an AK 4381) has a separate on board +5V power supply where I added a small inductor (1.0microH, 0.5ohm) in series but later removed it since this made it worse.

A theory is that since the DAC uses 0 - 5 V as power, you actually need the capacitor to move the DC-level from 2.5 V to 0 V. But it is pure guessing from my part.

Overall a successful modification. If somebody only want to do part of it, I can recommend upgrading the large power supply capacitors. This will get you a long way and is fairly easy to do, compared to desoldering SO-8 surface mounted parts.

--- Mikael R

[lucpes]

Regarding the restart problem - what's your PC power supply rated wattage? I have a 350W one (not chinese watts!) and no troubles here with 2x3300uf on the Revo.

In what way did the bypassing the capacitors in the signal pathway made things worse?

[MWP]

Originally posted by lucpes
In what way did the bypassing the capacitors in the signal pathway made things worse?

They are DC biased out of the DAC/opamps.

Replace the ouput series DC blocking caps with caps of better quality, you cant just remove them

[rosbacke]

The power supply shouldn't be that bad. It's called 'Q-tec Psu Atx 350w Low Noise' and the system isn't to badly loaded with stuff. It's a PII 466Mhz celeron with a simple 2D graphics card, 3 network cards, a 200Gb hard drive, a CD ROM, 512Mb memory and an ASUS motherboard in addition to the soundcard. It could be a local problem that the PCI bus takes a lot of power but the overall system is OK on power.
The computer is mainly used as a gateway and firewall but has lately also been my main playing device for my stereo.
I didn't really try to characterize the sound but as I remember it was a rather large change. The bass mostly disappeared and some regions of the treble became stronger and I thought i heard some distortions.

--- Mikael R

[rosbacke]

MWP, My guess also. So next step is probably to try and find some good quality caps. At the moment I'm pretty satisfied with the sound but it shouldn't be to long before I start wondering how it would sound with just a little bit better quality. The DIY bug is hard to get rid of.

--- Mikael R

[Armers]

rosbacke:

You got a website off the top of your head for a guide to modding the maudio!?

I currently have a GTXP, which i am very happy with the sound (using the older style crystal chip. CS4630).

Basicly what i have read seen the "upgrade" would be the revo 7.1 (modded, of course).

I just need a guide and i'll be on my way.


Armers
ps, yo MWP!

[lucpes]

Originally posted by MWP


They are DC biased out of the DAC/opamps.

Replace the ouput series DC blocking caps with caps of better quality, you cant just remove them

The caps are directly after the I/V conversion stage or filter - I'm not sure (first opamp on the front channels). Having them removed (about two months ago...) I have -2mV and respectively 3mV of offset on the output. But you're right, the sound does get a little plasticky with those off, so I'm thinking Rubycon ZA 47uf/16V instead

[rosbacke]

Armers, I don't really have a website. I've mostly followed the image that lucpes showed me in another thread. Have look at http://diyaudio.com/forums/attachmen...&postid=416973 and the thread I mentioned in my first post.
It is a fairly easy card to understand since most of the components used have good datasheets available.

--- Mikael R

[MWP]

Originally posted by lucpes
The caps are directly after the I/V conversion stage or filter - I'm not sure (first opamp on the front channels). Having them removed (about two months ago...) I have -2mV and respectively 3mV of offset on the output. But you're right, the sound does get a little plasticky with those off, so I'm thinking Rubycon ZA 47uf/16V instead

Is that all??

Hmmm, the DACs have voltage ouputs, so no I/V is required.
The OPAMPs after the DACs are for buffering & headphone amps only.

Ill have to whip mine out of my PC and have a closer look.
Im not going to modify mine though as ill be removing its DACs and using those channels for SPDIF output at a later date.

BTW.... its the motherboard that makes the power supply to the PCI cards noisy... not the PSU.
I recently replaced my motherboard (and nothing else), now my Revo passes through quite a lot of background PC noise

If your game enough, you could cut the voltage supply tracks on the PCI edge connector, and supply the power via molex instead.
Should make quite a bit of a difference.

[rosbacke]

Cool idea. Building an external clean power supply and feeding the soundcard +-12V from that. Since the DAC already has an onboard fairly clean supply, that should get you close to optimum result with the DAC still on board.

--- Mikael R