M-Audio Audiophile USB Mods

[rdf]

Now that my Google finger's completely worn out, has anyone tried modifying this USB DAC? A peek inside reveals a few options. A couple minutes with a multimeter (and no schematics) suggested the four 50 Uf electrolytics near the headphone and output level controls were in coupling positions. Since the DC across them measured 0.001 mv shorting them seemed safe and no harm appears to have come of it, sonically or via Rightmark. The rest of the circuit looks DC coupled throughout, leaving power supply bypasses the only caps worth considering next. Other than perhaps replacing the rectifier diodes with soft recover versions and trying some localized shielding (or maybe a new metal chassis) nothing jumps out that doesn't involve swapping SMD devices.

I bought this thing for amplifier measurements but you know how it is once you lift the lid. Any pointers appreciated.

[serengetiplains]

Rdf, there's a small thread on AA regarding this unit.

M-Audio Modding

[rdf]

Thanks serengetiplains! I did see that. A few things made me cautious about the recomendations, for example I think the author missed that the original design already has SMD ceramic bypasses everywhere. He also missed the very obvious 22 uF coupling caps in the chain. Incidentally, I just re-did the bypass and a full suite of tests pre and post confirm nothing was botched. All clean as a whistle.

Next up are probably low ESR caps and soft recovery rectifiers. Not sure how far I'll go, it's a great play thing and a terrific tool and all but hasn't left the bench yet since the stereo already has a Benchmark DAC1.

[pburke]

I have one of those sitting on my parts bench too. Great for USB-SPDIF, but the built-in DACs just don't cut it. I think replacing the caps in the power supply section and some of the smaller caps on the board (ignore the analog section) is all I will ever do, if anything. A decent BNC connector has to replace the RCA SPDIF as well. Beyond that, I think I'll just leave it alone.

A complete custom power supply in a custom case may be the over the top mod, but I have my doubts that it would do very much to alter the quality of the SPDIF coming from it.

But just like you, I have a USB-I2S DAC now and I don't really want to deal with SPDIF anymore, so the M-Audio box has become a backup unit at best. I do use it as a A-D box to digitize some old vinyl and analog tapes from time to time, but that's really not a critical application for me, so no mods in that section either.

Peter