Hi guys,
I just bought myself a piece of Essence One and I'm quite happy about it.
Of course, I'm already thinking of modding it:
- according to csarrow and mach3: replace KT with KA caps, increase PSU's caps
- add tantalums for+/-12V and +5V
- add 3 x 2.2uF in parallel with trafo's secondary coils;
- add EMI/RFI filter (capacitors and coils);
- replace BK10 with 4-gangs equivalent logarithmic from BOURNE (Mouser has something)
- according to MaestroSfai (https://audiofilifiorentini.files.wordpress.com/2014/04/modifiche-sonore-al-dac-asus-one-che-risorgerc3a0.pdf): replace output caps with dc-servo circuit with TL072, like is already implemented in E1's headphone amp with LME49720.
Well, I still love E1's warranty right now, so...I'll probably wait a couple of years till starting these quite intrusive/obvious mods.
Meantime, after swapping some opams (NE5532, LM4562, OPA2604, OPA1602) in different positions I realized that best sound I could get is having OPA2604 in I/V and OPA1602 in LPF. Best soundstage indeed, but too bad I can't keep the OPA2604 in IV anymore, because of overheating: around 65C with case open and most likely 75C or even more with case closed.
Will not try adding heatsinks on OPA2604 because I really think they are oscillating, so I'll try finding an oscilloscope first or I'll just try OPA1642 in IV soon.
Speaking of opening and closing E1's case, while keeping my AKG 550's on my head with volume pot at max. (E1's mute button = ON) I realized that I have an audible hum around 100-200Hz when case is closed or even partially-closed, but not hum at all while case is fully open. Same hum, but a little bit less disturbing, was heard with my Grado SR60i L-cush, so looks like thick aluminium case is reflecting trafo's hum/noise back inside the DAC's circuit.
Then, I realized there are tests proving the existence of this noise: http://www.homemedia.fr/tests/i/mesures/asus-essence-one-rmaa/ASUS%20Xonar%20Essence%20One%2096%20khz.htm and http://archimago.blogspot.ro/2013/02/measurement-asus-xonar-essence-one.html.
So, I found out that trafo needs to be repositioned and least hum-noise I could get is placing it vice-versa (yes, with bottom on top) and angled with about 30 degrees, like in pictures attached. This decreased the hum-noise with more than half. I've used 1 x clothes-pin and 1 x rubber-band to do this "trafo rearrangement", but I'm sure this can be done way much better looking.
Just to be sure noise will decrease further, I've also added a ferrite-core around the power cord and a small DIY RC filter between chassis ground and mains power ground (5K/4Watts resistor || 330nF cap), somehow similar with what Meier Corda does in his amps.
Is anyone else able to hear that hum I'm speaking about or just my E1 has this issue?
Thanks,
Raul.