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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
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
3,061 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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