[warrior05]

over the weekend i received a Pacific Valve modified DAC-AH. i'm trying to determine if some distortion i'm hearing is due to the unit or it is making my set-up so revealing that i'm hearing a production flaw in the music.

this first became very apparent while listening to an ambient track from Alva Noto and Ryuichi Sakamoto's collaboration - Vrioon. this is a very minimalist CD with Noto's use of various clicks, pops and other noises in conjunction with Sakamoto's simple piano playing. i know this CD very well and Sakamoto's playing has always been crystal clear. but listening through the DAC, when he sharply hits some higher notes i'm hearing a clipping distortion as best i can describe.

so here's my set-up: PC > FLAC files (ripped via EAC) > Juli@ > DAC-AH (via glass toslink) > Headfive > K701

to narrow it down to the DAC i plugged my H5 via analog out to my Juli@ - no distortion. tried a different optical cable - distortion. tried rca digital (keep in mind, the Juli@ has no 75 ohm coax s/pdif out - there is a rca jack via break out so i actually did regular rca to rca run) - distortion.

for a track more of you would probably know, i tried KT Tunstall's song Under the Weather. around the 1:11 mark she sings "sorry for being so bold". on the word "bold" backing vocals kick in and it is the same kind of distortion. what's got me kind of wondering if it is production flaw i'm hearing is that i can detect the distortion via analog out but it is pretty subtle. through the DAC i can clearly hear it. i went back to the Vrioon track via analog and upped the volume but i'm not detecting any distortion on the same notes i'm clearly hearing through the DAC.

thoughts?

 

[Jahn]

if it's not a persistent distortion or noise floor issue, i'd say it was the source recording. norah jones is the same way - sounds fine in the minivan, horrendous on my home rig (where i use the DAC-ah too). that dac isn't as revealing as, say, an Esoteric, but it's still revealing enough to show those kinds of flaws in the production.

edit- plus, you faintly heard it using the juli's internal DAC when you used the analog out. which means it definitely is the source recording. the DAC-ah is just more revealing than your soundcard DAC.

 

[warrior05]

yeah, i was afraid it would be the source recording. i guess it's a drawback of heading towards high-end kit. the noise floor is definitely not an issue. i've got such great blackground with my set-up.

how is it that they can release recordings with that much distortion? annoying!

 

[mindthegap]

The DAC AH, brilliant on dynamics, great on bass.

However, a bad recording or a recording with a sour note - an output with an even worse sounding recording and worse sour note. Conversely a good recording - great music.

If this really bothers you, you can:

1. I have had their modified unit. It does you a lot of good to let break in for a couple of weeks.

2. If that still does not please you, upgrade to the DAC AM, which is what I did. It has a much smoother presentation.

 

[Jahn]

one of the casualties of upgrading your kit is the reduction of listenable tracks. for instance, i have about 300 tracks of rare stuff i pulled from the web in headier days - can't listen to any of it now, it's all in 64 MP3 bitrate, lol, artifacts are horrendous.

 

[TheMarsVolta]

Quote:

Originally Posted by mindthegap However, a bad recording or a recording with a sour note - an output with an even worse sounding recording and worse sour note. Conversely a good recording - great music.

I'm finding the same with my DAC-AH. I find some albums have some distortion in the bass, some 'fuzziness' down low but otherwise very clear sounding. After doing the passive mod but not upgrading the power supply caps or the I/V resistor (not yet, parts are on the way), I wondered if the DAC chips aren't getting enough juice, or if it's just revealing clipping/distortion in the source file. Another option is to adjust the Vref trim pot, playing with that makes an audible difference.

 

[sevenjohn]

I also have some distortion coming through from my dac ah. It seems to appear not just from low frequency but more from a full signal. Makes me think that the output from the dac is easily overloaded. I used the volume bar in itunes to reduce the output via the optical to 75% and this has minimised the distortion, but it's not a "solution".
I'm going to fire up my PC and do some tone sweeps through the dac ah and try to isolate the frequencies/levels that cause the clipping. I won't be shipping the dac back to HK so I'd prefer if i could sort it out myself. Impressive dac for the money though.

 

[warrior05]

Quote:

Originally Posted by sevenjohn I also have some distortion coming through from my dac ah. It seems to appear not just from low frequency but more from a full signal. Makes me think that the output from the dac is easily overloaded. I used the volume bar in itunes to reduce the output via the optical to 75% and this has minimised the distortion, but it's not a "solution".

i essentially did the same thing. i lowered the output volume within foobar to about 90% and that has greatly reduced the distortion but as you mentioned, it really isn't a solution. i really do like the sound of this DAC and plan to keep it. since i'm a tweaker i have no problem in opening her up to see what can be done but i have zero experience with DACs and wouldn't know what to tweak.

 

[Jahn]

whoa now that's something else. if your line signal is coming in too hot, it's just too hot. for me, the itunes and system volume is jacked all the way up with no clipping, so i know the signal's full and clean before it gets broken up into zeros and ones going through the soundcard's optical out to the DAC-ah. but if it was redlining on the computer side, i'd back it down a bit.

 

[sevenjohn]

I have isolated the problem to the dac, as optical output from my iriver and CDP give the same type of distortion, but with no means of reducing the output level.
I too have little experience with modding, just re-capping my X-can, but I would have imagined that the clipping may occur in the op-amp section of the dac, and have read that this can be by-passed, So if anyone has clear instructions, I'd be happy. But I'm very happy putting up with the defect for a while anyway- sounds way better than line out

 

[Jahn]

you know, that could be the case. i had the opamps taken out of mine, it's a passive output stage now with big ol caps in there instead.

 

[regal]

Have you tried Foobar with clipping limiter ?

 

[sevenjohn]

well you know i only got the dac two weeks ago, and a new set of DT880s last week, I've been to busy listening to this setup to try to get to the root of the problem. But with holidays next week I'll have some time to fire up my pc, and take a first look inside the dac.
Guess I'm stalling on sorting out the sq for the moment, cause i'm to busy listening to the music!

 

[warrior05]

Quote:

Originally Posted by regal Have you tried Foobar with clipping limiter ?

no - please tell me more. i'm fairly new to foobar and just looked into doing the UI mods. i'm assuming you are talking about the DSP Manager. i see "Advanced Limiter" and "Hard -6db Limiter". are you referring to one of those? if i move either one under Active DSPs i can't seem to configure them. guess i'll go do some searching but i would appreciate some insight as well.

EDIT: nevermind my inquiry. it makes sense that i keep my windows volume maxed and my foobar volume around 90%. my headfive is at my fingertips so i can adjust volume easily enough. so after all is said and done i was hearing clipping from what foobar was outputting it would seem. i've listened to a couple of CDs since adjusting and all sounds good now. thank goodness that sometimes it is the easy answer. though i still wouldn't mind tweaking this thing!

 

[odmanca]

Quote:

Originally Posted by Jahn one of the casualties of upgrading your kit is the reduction of listenable tracks.

Well said!!!