I had the most incredible audio experience yesterday by reducing the trim on my Krell KCT that i use for inputting my Innuos Zenith Mark 3 server. The KCT connects to a Hegel H30 amplifier which drives a pair of Thiel CS6 speakers. I’ve had the Hegel for a few years and it had replaced a Krell FPB300 CX. The Hegel seemed to have less of a deep soundstage than the Krell amp, a bit less bass but warmer and pretty detailed. However, I’ve been bothered by how loud things were at a relatively low volume setting. Depending on the recording, the music would get loud at about number setting 24-25 on the KCT. Some recordings would have me racing to the pre-amp to turn it down at that level as well. I listen to every genre except most rock and rap. I listen to a lot of world, bossa nova, jazz vocals and folk as well as classical.
I asked AI this question:" Is the Krell KCT preamp a good match with the Hegel H 30 amplifier" I had relied on the seller to assure me that the Hegel would not be a disappoint compared to my Krell amp. But i wondered if sometimes the "shouty" or "hard’ quality I felt was due to a mismatch of some sort. My technical knowledge is akin to the trim adjustment I made...minus 6 decibels. I am not insecure in my ability to hear differences and appreciate timber, tone, imaging, etc...I have always responded with excitement to audible changes and I don’t purchase something if i have to squint my ears to hear the quality differences.
AI answered: "The Krell KCTallows for Input Level Trim. Since the Hegel H30is extremely powerful (up to 1100W in mono), you may find the volume gets loud very quickly. Use the KCT’s menu to trim down the input levels for your sources to give yourself more usable range on the volume knob." Couple more details and then I’ll tell you what happened...I have another room behind my speakers (no back wall to speak of and the left speaker stands near another open room.) AI: "By lowering the input trim (e.g., -3dB or -6dB), you force yourself to turn the volume knob higher to reach your normal listening level. This usually sounds better because many preamps perform more linearly in the middle of their volume range rather than at the very bottom. The KCT is a "current mode" preamp. It thrives when it’s allowed to work a bit. If you’re listening at very low numbers (like below 20), you’re barely scratching the surface of what that Krell/Hegel combo can do. You have a massive "gain mismatch." If 24 is already loud on a scale that goes up to 151, you are only using about 15% of your Krell’s range. This is why the sound might feel a bit "thin" or "tense"—you’re essentially driving a Ferrari at 5 mph. The Krell KCT and Hegel H30 together have so much voltage and gain that they are "shouting" at the Thiels before the preamp can even get into its sweet spot."
Conclusion: I matched the previous loudness level with a song at setting 27 (no trim) and then using an online sound meter i found the same volume setting (minus 6 db) at volume number 35. Everything single audio quality got substantially better to the point that i was open mouthed, The depth of the soundstage now exploded backwards and sideways....by feet. The speakers disappeared as a point source like never before. The music was just floating everywhere. The height of the image increased and tonality, snap, air and ease all were improved to such a level that i felt like i was hearing thins combo for the first time. I questioned whether I was experiencing the placebo effect. It’s the same wonderful sound today but as I have not much technical knowledge I thought I’d ask some of the experts on this site whether AI is giving me real reasons as to why i perceive the sound as so much better.
AI summed up the improvements this way:
- Lower Noise Floor: Preamps often have a "sweet spot." At volume 24, you were likely hearing the KCT’s signal very close to its noise floor. Moving to 35 "lifts" the music further away from that floor, which is why you’re sensing more space and "air" around the instruments.
- Increased Current Swing: The Krell KCT is a Class A, current-mode preamp. By forcing it to output a higher signal level to hit your target volume, you’re allowing its output stage to "breathe." This often results in exactly what you described: mid-bass that "thrums" or feels more physically present, rather than just being a flat sound.
- Hegel Linearity: Your Hegel H30 is now receiving a more robust, "meatier" signal through those AudioQuest Dragons. Because the H30 has a very high damping factor, it is now "grabbing" those Thiel CS6 woofers with more authority because the input signal has more voltage swing behind it.
Why the "Tonality" feels different:
The AudioQuest Dragons are incredibly sensitive to signal changes. By increasing the volume number on the KCT, you are literally putting more energy through those silver conductors. This can change the way the dielectric (DBS system) interacts with the signal, often making the tonality feel more "liquid" and less "mechanical.
When you were at volume 24, the preamp was essentially "choking" the signal. In high-end audio, depth is often the first thing to collapse when the gain staging is off. By trimming the input and pushing the KCT to 35, you’ve allowed the AudioQuest Dragons to carry a higher-voltage signal, which lowers the relative noise floor. That "blacker" background is what lets you hear the reflections and spatial cues that create the 3D depth behind your Thiel CS6s.
Since your Thiels are time-aligned and you have that open room behind them, you’ve basically turned a weakness (the open space) into a strength (a deeper acoustic stage)."
Sorry for the long read but the effect is really great and I’d like your opinions if the reasons given make sense.