I have an AMR DP 777 SE which I bought used. I got it for a very good price. When I got it, it had only been played for approximately 150 hours.
It is certainly the best sounding DAC I have ever had or ever heard for that matter. I love this DAC and it was working perfectly in bypass mode with my Crayon CFA-1.2's preamp handling the volume control. My system was sounding near perfect to my ears.
But then I decided to see how good the DP 777 SE's preamp sounded so I set the AMR on its preamp setting and neutralized the CFA-1.2's preamp by turning the CFA's volume to max. This worked fine. The sound quality when using the AMR's preamp did not surpass that which was produced when I was using the CFA-1.2's preamp... but neither was the SQ diminished. It was equally as good. To my ears the difference was indistinguishable.
Well, it worked fine for one day.
I had let it play all night figuring that the preamp section had not been broken in since it had not been used. The DAC section had been played for easily 700 to 800 hours (I stopped counting after 500). The next day, the first time I tried changing the volume, I lost all sound from the left channel. Then when I hit the remote's volume button again the sound came back to both channels. Further experimenting with the volume caused the sound to be... sometimes lost in the left channel, sometimes lost in the right channel, sometimes lost in both channels... and sometimes it would be brought back to normal.
I never knew what to expect. So I called AMR and they told me to send it in to them.
Please note... this DAC is still under warranty. But as it turns out the problem was due to damage that occurred AS A RESULT OF TUBE ROLLING.
Now, I had not rolled any tubes. I don't even have any tubes to try and I had already read that AMR urges us not to do it. Plus I really like the sound of my DP 777 SE as it is so I did not feel any need to do any experimenting.
Actually, the tube rolling had been done prior to my taking possession of the DAC.
But here is the kicker.
If there is any damage due to tube rolling the warranty is invalidated and the owner has to pay for the repair out of pocket.
Now please know. AMR does not say that tube's cannot be rolled.
What they told me is this:
1. not all 9 pin tubes are compatible so if one wants to roll tubes and not risk damaging the unit then he/she had best know which tubes to try and which not to try.
2. even if you do know which tubes to try, the ones you actually use need to be top quality tubes (that means not compromised in any way).
According to AMR the demand for New Old Stock tubes is high and the supply is limited. Selling them is lucrative and this has spawned unscrupulous vendors who have jumped on the bandwagon and are selling Old Stock tubes that are not ''New'' but rather they have been pulled out of units in which they have been in service for God only knows how long.
Plugging one of these into the AMR could cause serious damage.
AMR did tell me that there are some tubes which indeed do improve the DP 777's performance by a small percentage. In AMR's opinion, however, there are only two different ones that do so and they are both very expensive. And they also told me that there were other, less expensive ways to improve the sound quality.
So at the end of the day, if one is willing to spend the money and should indeed want to try those tubes one needs to know that due to the fact that there is still the risk that the ones you actually buy may not be of top quality, AMR will take no responsibility (translation: will not honor the warranty) if damage results from tube rolling.
I am not going to name the tubes that AMR told me could actually improve the sound. If anyone is interested in knowing they can call AMR (or email them) to find out.
AMR has had my DP 777 SE for a couple of weeks and with shipping to and fro I will have been without it for almost 4 weeks and I have REALLY missed it.
It is now in transit back to me and should get to me in another 3 days.
I am anxiously awaiting its return. My Auralic Vega (which I am using in the interim) does NOT, in my opinion, even come close to it.
It is so incredibly musically satisfying!!!
(Once again, in my opinion).
