If I've followed all of this correctly, you've perceived the problem with two different speakers, two different tube amps, two different preamps (one of them being a phono stage used as a preamp), two different sources (one vinyl, one CD), and a variety of different cables.
If so, it seems to me that there are likely to be two different problems that have been present, which are causing somewhat similar symptoms.
What may be an important point regarding the possibility of clipping the amp: Depending on how the Ref 150 is designed, by providing it with a single-ended signal you MIGHT in effect be using only one-half of its balanced signal path, which would reduce its 150 watt power capability to possibly as little as 1/4 of that amount (37.5 watts). I'd suggest contacting ARC and asking them if providing the amp with a single-ended signal would affect its power capability, or have other adverse consequences.
If that turns out to be an issue, converting single-ended to balanced with a suitably chosen transformer from Jensen Transformers or (at a higher price point) SMc Audio (Steve McCormack) would be a solution.
Mofi, thanks very much for the nice words. Coming from someone with your extremely extensive experience, that's a meaningful compliment indeed.
Best regards,
-- Al
If so, it seems to me that there are likely to be two different problems that have been present, which are causing somewhat similar symptoms.
I also tried listening closely to the speakers and found that the distortion appears almost on all frequency including bass while cranking up the volume.I would infer from this that the distortion at low frequencies is more subtle than the distortion you described earlier which was evident mainly on high volume high frequency content. And my guess is that the distortion that is evident at low frequencies is the result of amplifier clipping, while the other problem (evident especially on female vocals and piano) is due to something else. At this point I'm as mystified as you are as to what the "something else" may be.
What may be an important point regarding the possibility of clipping the amp: Depending on how the Ref 150 is designed, by providing it with a single-ended signal you MIGHT in effect be using only one-half of its balanced signal path, which would reduce its 150 watt power capability to possibly as little as 1/4 of that amount (37.5 watts). I'd suggest contacting ARC and asking them if providing the amp with a single-ended signal would affect its power capability, or have other adverse consequences.
If that turns out to be an issue, converting single-ended to balanced with a suitably chosen transformer from Jensen Transformers or (at a higher price point) SMc Audio (Steve McCormack) would be a solution.
Mofi, thanks very much for the nice words. Coming from someone with your extremely extensive experience, that's a meaningful compliment indeed.
Best regards,
-- Al