AΩW The First and Last Watt

Is amplifier power like a motorcycle wheelie? This feature is about amplifier power, current and moto torque. My goal is to keep you engaged the whole way through. Talking about voltage amplification into an open circuit and sliding bias is Greek; together can we learn some language or improve our understanding to make your sound beautiful.

Looking under the hood. Left: Sonic Frontiers Line-1 tube preamplifier. Right: Threshold STATIS s/550e power amplifier.

One watt of power into your loudspeakers produces significant volume. Harley Lovegrove of Pearl Acoustics provides a demonstration of one watt into the 87 dB efficient Sibelius loudspeaker, check it out here.  

“The first watt is the most important watt.” Dick Olsher, Stereophile. The legendary amp designer Nelson Pass built a company around the First Watt.

Gordon Holt wrote, talking about the Threshold SA-1 mono amplifier; “Most audio perfectionists feel that 200 watts per channel is the minimum needed for clean crescendos.” All over social media we see stacks of large amplifiers. Is there a disconnect here; is the first or the last watt more important? Watch the guru Hans explain it, How many Watts do I need?

Louder is more audiophile right! How many watts are needed?

Tannoy Arden loudspeakers produce 0.89 Pa or 93dB SPL at one watt measured one meter from the speaker. Listening 3m away will sound ~4dB quieter; room boundaries increase sound pressure level (SPL). Doubling the power to 2W will increase the SPL 3dB to 96 and doubling power again to 4W will create a very intense 99 dB. Download Hans Beekhuyzen’s SPL calculator and see that for pop and rock music it’s desirable to have 14 dB of headroom (available power on demand), this requires an additional 20W. To achieve 20dB headroom for classical music requires 100W available power; note that 113 dB SPL will sound like a chainsaw at 1m.

Asking for more power than an amp can produce will clip the signal and can damage the speaker voice coil through heat. It’s more probable to damage a speaker with underpowered amps than with too much power. If you enjoy loud music, a 10, 25 or 60 watt/ch amp may not be for you; or perhaps you need highly sensitive horn loaded loudspeakers. Some quality speakers like Magnaplanar can present as a difficult load because of the impedance and will require MO-Power.  

Hans Beekhuyzen explains it very well; there are power requirements and current delivery requirements. Current is analogous to torque. To wheelie a motorcycle like me you need to have a big enough engine with low gearing. Alternatively, you can rev the engine under no load and dump the clutch to get a hit of instantaneous torque. I believe this analogy holds true for audio.

Commanding a wheelie; a modestly powered (50HP) single cylinder engine, such as this Honda CRF450x, produces gobs of torque.

Known as the Beast, the 1301cc LC8 KTM V-twin engine produces 180HP with 103 ft-lbf of torque.

The four-cylinder BMW S1000rr engine produces 205HP with 74 ft-lbf of torque.

Engine power and torque developed is highly dependent on RPM; maybe this analogous to current flow and speaker impedance; the resistance throughout 20-20kHz. A single cylinder engine has more torque at low RPM and thus makes it easier to command a wheelie from very low speed. In my experience, the S1000rr will not command a wheelie until above 7000 rpm; trying this at 5800 rpm has dramatically differing results - the moto will not move like it does at 7k. The torque beast LC8 engine has full command of the moto at any speed; but by nature of design will not go as fast as the BMW.

I don’t fully understand amplifier functions, sliding bias and STATIS design yet; I would like to. I wonder if the moto analogies hold true. It seems fair to think of current requirements at low frequencies (bass) much more demanding of the amplifier than at mids and high. It seems fair to think of some amps like a single cylinder engine, able to produce gobs or torque at low RPM. It also seems fair to think of some very high-power amps being able to hit high speeds, yet unable to command a wheelie; perhaps you could “dump the clutch” electronically? I welcome your feedback.

Commanding a motorcycle wheelie and commanding bass drivers feels analogous to me. Current will move and hold the drivers on command, especially big bass drivers. Drivers have inertia, they resist change in motion. If your amp is maxed out or cannot produce sustained current flow, it loses control of the drivers then distortion or bloating (overshoot due to stored energy or inertia) happens. The first watt is very critical, but current delivery has equal importance.

Gain Stage

In my previous feature describing the exaSound e62 digital-to-analog converter I noted that the perceived audio quality of the dCS Bartok could have a lot to do with the quality of its first watt, or gain stage. Yes, the first Watt is important; a quality preamplifier is critical stereo component because it is improving this first Watt.

On investment of the exaSound, I connected it directly to the 250W/Ch Master series NAD M22 stereo power amplifier. Looking back something was missing, but audio friends don’t leave audio friends hanging. My bud Mr. Awesome loaned to me - knowing through experience that I’d love it - the vintage audio Sonic Frontiers Line-1 6922-tube preamplifier. The M22 is quality amplifier but I don’t know if the first watt was good enough (I accept a challenge to this). I’ve upgraded the M22 to the Nelson Pass designed Threshold STATIS s/550e power amplifier and I still wouldn’t connect the e62 directly to the power amp. I think Dick Olsher was right, the first watt is the most important watt. I’m keen to agree with Gordon Holt, 200 watts per channel is around the minimum needed; however, we should be thinking about power is terms of torque or sustained current delivery.

Left: exaSound e62 DAC directly connected directly to the NAD M22, Right: addition of the Sonic Frontiers Line-1 tube preamplifier. Night and day difference!

January 16 is a very special birthday to someone who feels old. Age 40-60 can be the best years of our lives; hey, we are wise and experienced. Rock on Steve! Love ya brother.