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Most people who now listen to tube amplifiers began with a transistor amp, and know from experience that a tube amp of a given measured power output sounds louder than its nominally identical transistorized equivalent. The unofficial consensus is that you need two to four times the transistor power to achieve the same loudness as you would using tubes. In other words, given the (subjectively) undistorted sound level a 25W (footnote 1) tube amplifier can provide, if you want the same loudness from solid-state technology you would have to replace it with at least a 50W transistor amp (footnote…
First, I loaded a 25W transistor amp with 8 ohms resistive. It clipped at almost 17Vp (peak) on a continuous sinewave (fig.1). (Note that the vertical scale used here is 5V/division.) I then connected the amp to my main speakers (Audio Note E's) and cued Touch to five seconds into the first track, where the percussionist hits a tambourine very hard—so hard that, during recording, he broke two tambourines. The 'scope was triggered to capture the first 8ms of this stroke, which sets off a train of pulses at basically 600Hz—so I also chose 600Hz as the frequency for the sinewave measurements.…
By now I had grown pretty curious about how my 4W push-pull triode would fare. Fig.5 gives the 8 ohm situation: Vp is about 8.5V. (As this is a lower-output amp, the vertical scale is again back to 5V/div.) Defining clipping as 3% THD, the 'scope indicates a 4.2W RMS power rating. Pushing further leads to hard clipping at 10.5Vp output. Playing Touch at 0:05, the speaker load managed to produce fig.6, with a positive Vp of 15V—not as shocking as with the 300B, but this still implies almost a doubling of the Vp under steady-state conditions, and represents a quadrupled transient output power…
Letters in response appeared in the November and December 2000 issues:
Tubes do sound louder
Editor: I can directly confirm Peter van Willenswaard's observation that tubes sound louder than solid-state amplifiers (September 2000, pp.55-59). The excellent graphs Peter provided allow me to make an educated guess as to what is going on below the surface.
Back in 1981, when MOSFET amplifiers were all the rage, I borrowed a 75W Nikko from my employer. Its competition was a Leak Point One with EL84 output tubes, weighing in at about 15W. I hooked up the Nikko, put on a record,…
A Followup appeared in June 2001 (Vol.24 No.6):
In the September 2000 issue I wrote an article about tube amplifiers sounding louder than transistor amps, given the same nominal RMS power output. The measurements showed that the greater perceived loudness was not a subjective phenomenon but objective fact.
However, the evidence produced was based on experiments with a single recorded tambourine stroke, and the measurement was a pure electrical one. Reflecting on the project, I thought it would be interesting to see if it also worked with, for instance, a soprano voice and with…
Next, the more demanding, wide-range fff fragment of choir and orchestra: I had to reduce the gain of the mike amp and readjust the 'scope to 2V/div.; there is therefore no direct level relationship between figs.1-3 and figs.4-6. This is perhaps regrettable in hindsight; however, I was not trying to record absolute SPL levels, just making comparisons among the three amplifiers using two different musical signals.
Fig.4 is the 25W solid-state amp again, now generating 7.6V p-p at the mike amp output. The 10W 300B easily beats it at 11.3V p-p (fig.5), and even the 4W EL84 amp excites the…
The following letters were received in response to "Tubes Do Something Special":
Congratulations
Editor: Congratulations on your June 2001 issue, which contains several interesting articles. With the death of Audio magazine, there are few places for the consumer to see this kind of technical information. I have been trying to understand the apparent disparity between measurements and critical reports for some time and the article by Ben Duncan is a good example of a real attempt to throw light on this.
I am a little more perplexed by Peter van Willeswaard's follow-up on "…
I used to be an audio cheapskate even worse than Sam Tellig. Anytime I saw an interesting device for sale, I immediately began to figure out how I might build it for myself for a fraction of the cost.
Time no longer permits me to do much of that, but the cheapskate spirit hasn't died. When I saw Canadian company Monsoon Audio's new FPF speakers on the main floor at CES, not at the high-end venue, I got the old chill in my miserly bones: three-way planar-magnetic hybrids at $600–$1600/pair! The prototypes looked and sounded great, even though the demo was a bit too whiz-bang for my…
When I played some of my standard discs for low-frequency evaluation, the FPF never strained at levels that stressed my ears, but also never achieved the palpable impact obtained with the Revel Ultima Studios or other big speakers. Indeed, I've heard what seemed a better semblance of lower lows from the much smaller Paradigm Reference Studio/20, with its single 6.5" woofer. The FPF pumped much more air around the room and played much, much louder than the Studio/20 or the dual-woofered Studio/60, but I suspect that Monsoon has designed bass loading to maximize power output rather than…
Sidebar 1: Specifications
Description: Three-way, reflex-loaded, floorstanding loudspeaker with low-compression port. Drive-units: planar magnetic tweeter, two planar magnetic midranges, two 6.5" polypropylene-cone woofers. Crossover frequencies: 400Hz, 5kHz. Frequency response: 32Hz–20kHz, –6dB. Impedance: 4 ohms. Sensitivity: 88dB/2.83V/m. Recommended amplification: 30–250W.
Dimensions: 52" H by 10" W by 12.5" D. Internal volume of woofer bin: 20-liter. Shipping weight: 75 lbs each.
Finishes: walnut veneer, matte black.
Serial numbers of units reviewed: None. (The speakers…