Tubes vs Transistors - Perception of Loudness, Clarity, Distortion, Sound Quality
People often ask, how does the BaM-235ab compare, in terms of sound quality and loudness, to a transistor amp?
It's a simple question that uncovers many complexities. One answer is it's so subjective, because the character of amplification and overload sound different; therefore, it comes down to approximation and personal preference. Please keep in mind we are necessarily speaking in broad, general terms.
In general, tubes overload softer and don't hard-clip like transistors overdriven - giving more 'cushion' and 'headroom' before distortion becomes objectionable. Also, the overdriven spectra of a tube amp sounds different: softer, more full, not as harsh. So, when pushed hard, transistor amp distortion generally sounds much nastier than tube amp distortion. Guitarists (who often seek "good sounding" distortion using tube amps) have solidly demonstrated this for many decades, which is why we make GAGA.
This is one aspect of 'tube sound'. There's also the resolution of nuance and fine detail, something which tubes excel at without sounding overly bright or brittle.
Technically, tubes amplify without requiring as much corrective negative feedback as transistors, allowing for simpler circuitry -- and simpler generally sounds better. Very broadly, tubes would seem to be naturally more adept at amplification, more inherently amenable to being used to amplify, because they require less commanding circuitry to perform well - they don't have to be forced.
Together, these open up new dimensions into the music because you can generally get "better" (more detailed, more involving) sound up to higher levels with tube amplification.
General perception holds that a tube amp can sound two- to four-times louder than a transistor amp of equal power. Since 10x measured power is required to give a doubling of perceived power, the 60 Watt tube BaM 'sounds at least about as loud as' a 600 Watt transistor amp, with some variance due to the "two- to four-times" loudness difference most often reported by listeners, across different types of music and other factors such as speakers, wiring, equipment, installation, etc. This is entirely consistent with Earl Zausmer's famous competition car, which uses two BaM amps (about 120 tube Watts) and 1,200 Watts of (transistorized amp) power on the subwoofers.
So, in general, with other variables held steady, as the power rating goes up dramatically (10x), the perception of loudness only doubles. 3,000 Watts sounds only "four-times louder" than 30 Watts. It seems unlikely, but measurements and much anecdotal evidence have consistently shown it is generally true.
"Last week, I played a 35W amp on full blast (but not clipping) through [speakers] which have a sensitivity of 100dB. I took out a sound pressure level meter and put it 10 feet away from the speakers. The 35W amp produced a clean power level of 117dB, which is only 3dB quieter than an airplane landing." »
Speaker efficiency - or a speaker's ability to produce sound pressure level from input wattage - also plays a crucial role in loudness. Power rating without efficiency is about as pointless as latitude without longitude.
Frequency range is also a consideration. Since tube amps generally don't amplify low-frequencies as accurately (because their output transformers can saturate, and they generally have a higher output impedance) as transistor amps, using a tube amp on the midrange and high-frequencies makes sense in high-powered systems, which is why we created the TC crossovers, to split the audio spectrum approximately in half, below 100Hz for transistor amps on the subwoofers and above 100Hz for tube amplification via the BaM.
Material herein added and updated constantly; presented for inspirational and educational purposes per Fair Use.
Last modified 16 Feb 2024
