Hi. I've been lurking around Head-Fi for a couple years and really haven't posted that much. But I recently bought and received (today) a Leben CS300XS. I'm having some issues with the amp, which I already raised with my dealer and distributor and they do have me covered, though I'll have to wait a few weeks and live with the current amp in the meantime. However, the two issues are perplexing, and being somewhat reluctant to give up and wait.... I would love advice should anyone here have insight.
First, the amp sounds mostly fantastic. This is the best integrated and headphone amp I have owned. I was dazzled by feeling "in the music" today while listening to The Beatles 2009 Mono Box Set remasters through speakers.
Second, I have somewhat of a developed and trained ear being a musician for quite some time. I can hear differences in tubes and cables easily and this perception comes from years of playing guitar and using tube amps, and trying gear and listening carefully. If something sounds different or "off" I'll generally hear it.
Third, I realize my particular quesions may eventually turn into a technical / troubleshooting thread probably best placed in some other area of Head-Fi, BUT.... I beg leniency and would like to start here because I'm new to Leben, and hopefully this large thread has enough expertise to either lend appropriate advice on my issues as related to the CS300XS, and/or eventually point me in the right direction.
Now the issues...
The first issue - My 600ohm AKG K240M (made in Austria) phones are significantly lower in volume in the left channel through the CS300XS. I have ruled out the phones. They work with several other amps. Stereo separation is accurate, confirmed with other amps. Not the best phones, I know, but I have had them for years and years for mixing music and they are accurate and typically un-hyped / flat. Likewise my 32ohm Shure E4C (IEM) is slightly lower volume in the same left channel but only slightly compared to the AKGs. Again, it works fine with other amps.
I have ruled out IC's, source, input selection on the Leben, etc. I even swapped tubes from left to right, both the power and preamp tubes, first independently (EL84s only), then together (5751s & EL84s). The issue stayed on the left, regardless of tubes.
The second issue - while the amp sounds mostly fantastic with speakers, I have noticed that the opposite channel (right) has slightly diminished bass response. I'm estimating around 2-3db. I have asked a second party to listen and they confirmed. Just ruling out my hearing...
Again, this issue persists regardless of IC's, source, input selection on the Leben, and especially regardless of the speakers, which I swapped from left to right to rule them out. I confirmed the diminished bass using mono recordings and panning the balancer from hard left to hard right. The right definitely has lower bass response with the same monaural source material.
To summarize - left channel with phones is lower volume - significantly lower with 600ohm AKGs. The same left channel has roughly even volume to the right channel when using speakers, but the right channel has slightly less bass or low freq. response with speakers, around 2-3db down.
Any insights? With the quality of this amp as high as it is, it seems
highly unlikely something silly is in play like mis-wiring or cold solder joints. My gut says maybe the Leben doesn't like my two particular models of headphones. But why manifest as lower volume in just one channel, and then the opposite channel has less bass with speakers. Odd, and confounding. Any insights are welcomed and will be appreciated.