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Tubed DAC problems,opinions please.

Hi to all.
Recently I purchased a used AUDIO RESEARCH DAC-3 Tubed DAC with four 6922's output stage. When I hooked it up to my system I heard pops coming from the speakers and first blamed my ARC line stage LS3B and thought that volume control was dusty or something. I actually started a thread on AMPS-PREAMPS about it.
I was about ready to take my line stage in for check-up but the last minute I decided to re-check my whole set-up one more time.
Today after carefull ispection I realised that the DAC-3 is creating the pops and very low volume level (I mean low,to the point that at 11:00 pm position of volume control on the LS3B LINE STAGE the sound is barely noticeable).
Note that the DAC-3 is feeding my LS3B LINE STAGE which is driving a CONRAD JOHNSON MV55.
There is no doubt that something is wrong with DAC-3 .
The previous owner claims that it left his house in good working condition,but the FEDEX must of dropped it.
Do you think the problem got to do with the 6922,s tubes or must be something more serious.
I mean could the tubes produce above problems and by replacing with new ones everything gets fixed, the previous owner was using telefunken NOS and just put the stock 6922's in prior to shipping. But he says he checked two times and everything worked ,before shipping it to me.
I am confused,and not an expert ,please let me know your thoughts
Best regards
George
128x128yioryos
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ncarv
983 posts
 
I'm using an Audio Logic with 6922's and have never had that problem.
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yioryos's avatar
yioryos OP
723 posts
 
hi jea48
It is not the cable ,or transport,or pre-amp,or anything else. It is beyond any doubt the ARC DAC-3 (FOUR 6922 OUTPUT STAGE) .Reason I know is because I eliminated every component in the system by ex-changing with another one .
I mean I used a second spare dac (stax talent) and another cd transport (musical fidelity A3 used as transport via digital output and as a stand alone cd player)and a different power-amp (mark levinson 27.5) and another line stage(used the HARMAN KARDON home theater receiver).
I mean I turned my system heads down till I was sure.
Every time that DAC-3 was feeding the signal upstream in the system the problem was there,and every time it was out ,the problem was gone.
Another words the signal coming from the DAC-3 is week and lifeless and lucking punch and dynamics,it's like listening to your alarm clock to wake up in the morning.
It is of that reason that I am wondering whether the tubes need to be replaced because they reached their usefull life.
If you take a look of the tubes they show a dark ,black dicoloration crown on their tops.
This is my opinion though and I would like to hear from somebody who knows better than me.
My knowledge is minimal in these matters.I am new into tubes too.

thanks in advance
George
cytocycle
1,043 posts
 
Call ARC on Monday, they have awesome support, also 6922 tubes don't cost much so get a new set from ARC before you ship it back for repairs... I wouldn't have shipped it with the tubes installed
s23chang
619 posts
 
First of all, the stock 6922 tubes are not even close to most of NOS tubes. That's why the seller didn't include those with the DAC.
As I replied you in your LS3B preamp question, I didn't think there was anything wrong with your preamp's volume control.
How was the tubes packed? if they were shipped inside of the DAC then it is possible that they could damaged from shipping. The damaged tubes would give you pop and hiss sound. "Lifeless and weak" has more to do with tube character itself. Get yourself Some NOS Amperex or Siemens 6DJ8s. If you want a lower noise type ( I would usually prefer lower noise for DAC but they're less liquid sounding) then get yourself some NOS Amperex/Siemens 7308 tubes.
garyk
30 posts
 
I recently had the same problem with my Kora Hermes II dac. At first I thought it was a problem with my integrated amp, so I swapped in another amp and it was still there.

In discussing the problem with my local tech, he suggested the dac's output voltage may be overdriving the integrated's preamp section. He mentioned that a lot of tube dacs dump a high (7+) voltage unfiltered signal to the pre that (typically) is expecting only the industry standard 2 volts.

I don't know what the DAC-3's output voltage is but I'd ask the ARC tech support if this might be an issue.
yioryos's avatar
yioryos OP
723 posts
 
HI GARYK
My DAC-3 is still bad as ever,the output voltage is 1.5Vrms
and note that I am using a same brand linestage as my DAC.
That's Audio Research.I would think that both units coming from the same manufacturer are compatible. At this moment I am waiting (previous owner offering)for a set of different tubes so I can swap and see what happens.I am almost conviced that I experience a case of one or more bad tubes.
Thanks
George
chryslers_rule
32 posts
 

Not sure if all four tubes are needed at once but if they are two per channel try to use just one channel/set and swap around to see if the problem goes away. Somewhat rare to have all four tubes go at once although not impossible.
rcprince
3,070 posts
 
I'd call ARC as well, their customer service is excellent. It sounds like it could be tubes, but if it's in both channels it would be unusual for all the tubes to go bad at once. I have had 6DJ8/6922s (Sovteks) go bad in my Audio Logic, and they can make some nasty pops, which get louder over time, so I'd get it fixed sooner rather than later.
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