[Triode Pete]

I'm a very recent & happy owner of a T-8 DAC (Serial No. 1016086). I noticed that some AC posters mentioned that use older (NOS?) 6N1P tubes. Is there anything special about these Russian tubes? Are there any worthy US, English, Dutch or German tubes (or substitutes) worth considering?

Also, I have not upgraded the two chips to the Burr-Brown type. Has anyone with a T-8 DAC done this & what are the sonic benefits? Is it very subtle or pretty noticeable?

All opinions appreciated as well non-warranty breaking tweak suggestions!

Thanks
Pete

[richidoo]

When I had T8 preamp for a short time I experimented with swapping 6N1P tubes. I compared stock sovteks, Svetlana from 90s and original Russian military 1960s which were also cryoed.  My preference was the Svets, then NOS, then Sovtek.

[Art_Chicago]

I'm a very recent & happy owner of a T-8 DAC (Serial No. 1016086). I noticed that some AC posters mentioned that use older (NOS?) 6N1P tubes. Is there anything special about these Russian tubes? Are there any worthy US, English, Dutch or German tubes (or substitutes) worth considering?

Hey, Pete,
I think neither Netherlands nor Great Britain make the vacuum tubes anymore even if they did. I do not know about the US producers, but doubtful. German Telefunken made good tubes (it is under Siemens now). They are usually twice as expensive as Svetlana. I do not know if there is an analogue to 6n1p, though. Frank is the man who knows this for sure.
I am curious, however, why the origin of the vacuum tubes bugs your mind if you are a happy owner  of the T-8 DAC, produced in Minnesota?

Art

[Triode Pete]

Not completely happy...getting quite a bit of tube rush from the DAC..my SET monoblocks as well as tube preamp with separate tube regulated power supplies are dead silent with my 104 dB speakers...the last thing I expected was excessive noise from a digital source...

I have been pursuing Nirvana from my Audio System...started in 1998 with solid state McIntosh equipment (amp & pre-amp)...my current tube amps & tube preamp is much quiter than the McIntosh gear...wish the DAC was as good...

[JerryM]

Also, I have not upgraded the two chips to the Burr-Brown type. Has anyone with a T-8 DAC done this & what are the sonic benefits? Is it very subtle or pretty noticeable?
Thanks
Pete

Pete,

This past Monday I received from Frank chips for my T8 DAC.

I've got Friday off. I'll be chip rolling early. 

I'll let you know what my ears tell me.

Have fun,
Jerry

[Art_Chicago]

I'm a very recent & happy owner of a T-8 DAC (Serial No. 1016086).

How old is the unit? I can't tell from the serial number. You may want to change the tubes if it is about 2 years old or older. I can hear some background hiss from my  T-8 preamp only at very high volume ( from 3 to 5 o'clock), the loudspeakers' sensitivity is 88 dB, 130 wats power amp. But again it is just me, some may be more sensitive.

[Triode Pete]

Made in November 2008; about 60 hrs on it.

The T-8 DAC has a very effective muting circuit at idle...but when it's playing or paused, there is some tube hash/hiss coming through my speakers. I can notice it pretty easily with my 104 dB horns.

I just received a Blue Jeans Cable (Belden) heavily shielded digital cable today. Hopefully that might improve / eliminate the background noise.

Any other ideas out there? Is this normal (tube rush) behavior for the Transcendence 8 DAC???

Thanks,
Pete

[oneinthepipe]

I am not sure what you are experiencing, but I just compared my Insight DAC and T8 DAC for noise.  I can try something else if this is not adequate.  I powered up the amp then preamp, DACs, and CDP.  Alternating between the DACs, I turned the volume on the preamp up all the way, without a CD in the CDP  , and the floor noise/hiss was nearly identical between the Insight DAC and the T8 DAC (after I moved the digital coax cable between the DACs and the preamp's source selector switch to the respective input).

[Triode Pete]

  Alternating between the DACs, I turned the volume on the preamp up all the way, without a CD in the CDP  , and the floor noise/hiss was nearly identical between the Insight DAC and the T8 DAC (after I moved the digital coax cable between the DACs and the preamp's source selector switch to the respective input).

Try playing a disc then pausing it... I noticed the muting circuit "takes hold" when there's no disc in the player & it should be silent. I can hear "hiss" when certain discs have quiet musical passages (a lot of classical music) and also when I "pause" it, there's a quite a bit of tube rush (white noise-like, ie- "ssshhhhhhhhhhh").

I wouldn't mention it if it wasn't noticeable...

Thanks,
Pete

[oneinthepipe]

OK, I compared the noise level when "pausing" a CD, and the T8 DAC was slightly noisier than the Insight DAC when the volume was cranked up to full and my ear was fairly close to the speaker.  The noise sounds like a very slightly louder layer of white noise/hiss.  I don't think that I would have noticed the noise if I didn't crank up the volume. 

[Art_Chicago]

We need you, Frank! Please respond, it is quite intriguing

  Alternating between the DACs, I turned the volume on the preamp up all the way, without a CD in the CDP  , and the floor noise/hiss was nearly identical between the Insight DAC and the T8 DAC (after I moved the digital coax cable between the DACs and the preamp's source selector switch to the respective input).

Try playing a disc then pausing it... I noticed the muting circuit "takes hold" when there's no disc in the player & it should be silent. I can hear "hiss" when certain discs have quiet musical passages (a lot of classical music) and also when I "pause" it, there's a quite a bit of tube rush (white noise-like, ie- "ssshhhhhhhhhhh").

I wouldn't mention it if it wasn't noticeable...

Thanks,
Pete

[avahifi]

The issue is the 104 dB efficiency of the speakers in question.  This will amplify any residual thermal noise from the electronics about five times as much as "normal efficiency" will.  It is not unexpected that this can make the otherwise quiet unit's thermal noise audible close to the speakers. Often we can put a voltage divider on the output of the preamp to reduce the gain of the preamp and the noise level at the same time. The "Low Gain" button on EC preamps will do this for you automatically.  However this is not applicable with a vacuum tube preamp.  The design techniques needed to suppress all the residual thermal noise are contrary to the design techniques to provide the best possible sound, and we design for the best possible sound, not the lowest possible noise in all cases.  We normally see about 1-3 mV broadband thermal noise from our equipment with shorted inputs. As long as the background noise level does not intrude on the music, we would not consider this to be an important issue.

Regards,

Frank Van Alstine

P.S.  The Burr Brown 627 chip upgrade may be helpful as they cut the noise level from that part of the circuit in half.

P.P.S.  It is always possible that your tubes went noisy prematurely.  Try swapping them from channel to channel and see if the noise characterises follow the tubes.

[Triode Pete]

Thanks for all the replies. I will reiterate that I am happy overall with the T-8 DAC but through a thorough evaluation, I did notice some anomalies, such as the "thermal noise" as described. The beauty of high efficiency speakers is the effortless dynamics & transparency; you can easily find the "weak link" in the system, if there is one. As far as compromising sound quality for a quiet, noise-free soundstage, that is untrue. My preamp & amplifiers are hand-built, point to point wired with great skill & knowledge by a gentleman and my friend, John Wiesner. His vast knowledge & history of electronics, including some long forgotten grounding schemes (secrets) borrowed from some hi-end tube radios of long ago, has contributed to my hi-fi system being extremely quiet and dynamic as all hell without losing PRAT.
One of John's philosophies (as well as Paul W. Klipsch), is that the Quality of the Design & Build is more important than the parts quality (including pixie dust!) Not saying that parts are not important, but build quality is more important. This is one of the main reasons I chose to purchase an AVA Transcendence 8 DAC.

Sorry for being long winded,
Pete

[Art_Chicago]

PM sent for oneinthepipe 

[Triode Pete]

Regards,

Frank Van Alstine

P.S.  The Burr Brown 627 chip upgrade may be helpful as they cut the noise level from that part of the circuit in half.

P.P.S.  It is always possible that your tubes went noisy prematurely.  Try swapping them from channel to channel and see if the noise characterises follow the tubes.

Performed the Burr Brown OPA627 chip upgrade this morning. Noise floor is much lower compared to the original AD chips. Tubes appear not to be the issue.

Impressed with the build quality & simple layout of circuits on my T-8 DAC. Currently listening to my 2nd CD this morning; sounds nice!

Anyone have any comments on "burn-in" of the new Burr-Brown chips or general "burn-in" of the T-8 DAC. I only have about 50 hrs on my DAC.

Thanks in advance,
Pete