Hephaestus Audio

No, not an amplifier this time!  It’s my new little girl: Kilmney Arianwen - born February 22nd, 2010.  Mother and daughter are happy and healthy!

We received the Stereomojo 2009 Products of the Year award: Power Amplifier of the Year!

From Bill Schuchard of Stereomojo:

“The Hephaestus Audio HMA-1000 is a great monoblock amplifier. It sounds fast, clean, transparent, open, and airy with powerful but neutral bass and massive headroom. It worked well with a variety of speakers and sources, takes up very little shelf space, and produces quite a bit amount of power efficiently (1,000 watts per side). Those looking for a big shiny bauble with a fancy name to show off may be perturbed by the utilitarian look and understated size and miss out on some amazing sound. The $4900 list price per pair is a tough pill to swallow from a relatively unknown company; especially for those who are frugal like myself. The spoonful of sugar that makes the pill slip down is the sound. I am very pleased to announce my new reference amplifier; the Hephaestus Audio HMA-1000 monoblocks.”

Not only is Mr. Schuchard a wonderful reviewer, but also a wonderful customer!

Interest is picking up so this evening I am spending time soldering some new amplifiers!  I couldn’t help but think, “Gee, if I outsourced assembly of the PC boards, then I could just worry about final assembly and have some extra time…”

Is this how it has started for companies in the past?  It’s so easy to fall into the trap of offloading some of the more tedious tasks to somebody else – somebody who doesn’t know or care about your customers – somebody who is only doing a good job because you are paying them to do so.  There’s not a chance I’m going to do this!  Big amplifier manufacturers may scrap more units then I will ever build, but I’m not going to change how I’m doing it.  I like to know that my customers will receive something I have created with my mind and built with my hands.

Needless to say, when you purchase an amplifier from Hephaestus Audio, you may count on the fact that I built it for you – even if I occasionally toy with the idea of doing it another way.  Maybe it was just the solder fumes going to my head? 

We received the Stereo Times Publisher’s Choice Most Wanted Components award for 2009!

From Clement Perry, publisher of the Stereo Times:

“What immediately impressed me right out of the box was the improved dimensionality and the enriched harmonic overtones. This, from a kilo-watt powerhouse no less. Don’t let the small size of these dynamos (3.5 lbs) fool you either because they really do pack a punch!”

Mr. Perry is wonderful to work with.  He gave me real-world feedback early on in the life of the HMA-1000 that was instrumental to steering it in the right direction.  I’m thrilled to receive this recognition from the Stereo Times!

Signal to Noise Ratio (SNR), or Dynamic Range, is a measure of the maximum resolution of a piece of audio gear.  The larger the number, the greater the possible range from very, very quiet sounds to very, very loud sounds.  It is easy to calculate, for example:

Noise level with no input signal = 70uVrms
Signal level at full output = 1000Wrms into 4Ω → 63.25Vrms
SNR = 20 log (63.25Vrms / 70uVrms) = 119dB

Pretty simple, huh?

Now sometimes the Signal to Noise Ratio may mention that it is “A-Weighted“.  This is an attempt to adjust the value based (very roughly) on the way we hear – i.e. the “Fletcher-Munson” curves.  The end result is a higher Signal to Noise Ratio than if no weighting were used.  Is this simply cheating to improve the on-paper specifications?  Probably, but at least it has some basis in psychoacoustics.

Speaking of cheating, I came across an amplifier with the following specifications:

Noise level with no input signal = 90uVrms (A-Weighted)
Signal level at full output = 1000Wrms into 4Ω → 63.25Vrms
SNR (according to specifications) = 120dB (A-Weighted)
SNR (according to calculations) = 20 log (63.25Vrms / 90uVrms) = 117dB (A-Weighted)

What’s going on here?  There’s a 3dB discrepancy between the spec sheet SNR and the calculated SNR!  The trick in this case is that the manufacturer is using the peak output power (2000Wpeak) of the amplifier instead of the RMS output power (1000Wrms).  It is then compared against the RMS noise level – i.e. it’s not comparing apples to apples!  Here’s the calculation:

Noise level with no input signal = 90uVrms (A-Weighted)
Signal level at full output = 1000Wrms into 4Ω → 2000Wpeak into 4Ω → 89.44Vpeak
SNR = 20 log (89.44Vpeak / 70uVrms) = 120dB (A-Weighted)

There it is now!  So if you are simply “creative” with you calculations, you too can add 3dB to your amplifier’s SNR.  Is this cheating?  Yes, I believe it is.  However, you are now armed to check if the SNR numbers add up for a prospective piece of audio gear, to help weed out the cheaters.  Good luck!

This is a very tricky topic.  Any simple article is never going to be enough for a novice to really be able to design a class-D amplifier.  However in this article I attempt to outline the basic requirements and considerations for designing a class-D amplifier.  It isn’t complete, but it’s a good start!

Also, in the article I attempt to draw a parallel between some of the familiar elements of a linear amplifier and the perhaps not-so-familiar elements of a class-D amplifier.  The comparison isn’t perfect, but I hope it will serve as a springboard to those not yet familiar with the intricacies of class-D amplifier design.

In order to evaluate two components in an AB test, it is essential that they are carefully level matched.  If the gain differs by only one dB, the louder unit will almost always be perceived as sounding better.  Unfortunately, this phenomena has been exploited by unscrupulous hi-fi dealers to promote overpriced components, as I have personally witnessed:

My friends and I once went to a local hi-fi shop to check out the goodies.  There were some very lovely components we had the opportunity to see and hear, but there was also a one meter length of heavy power cord retailing for about $2,000 (this was over 10 years ago).  The salesman conducting the demos (err…Jim) saved this gem for last – here’s the process he used (I watched very carefully):

• Carefully set volume knob to specific level
• Play track from reference CD to completion
• Turn down volume knob to zero
• Insert special power cord between power strip (!) and amplifier
• Carefully set volume knob to specific level
• Play track from reference CD to completion
• Turn down volume knob to zero

Sure enough the second time the track was played it sounded significantly better!  It would have been truly amazing if I had not been paying really close attention: When Salesman Jim carefully adjusted the volume knob the second time – the time with the special power cord in circuit - he turned it up just a little bit higher!  It wasn’t enough to notice it was louder, but it was enough for all of us to think it sounded much better.

My friends had unfortunately not noticed this scoundrel’s trick.  I’m sure I only did because I knew to look for it.  I quizzed Salesman Jim on exactly what made this power cord work.  At first he tried to dodge the question, but then it went something like this:

Salesman Jim: “Okay, okay it’s a ‘PFM Circuit’.”
Me: “A ‘PFM Circuit’?  I’ve never heard of that – what’s it mean?”
Salesman Jim: [laughing] “Pure Fricking Magic.” [note: slightly edited]
Me: “Okay, ha ha, seriously what is it?”
Salesman Jim: [growing annoyance with this punk] “Hey Bob, what’s the technology of this [brand] power cord?”
Salesman Bob: “Uh…geometry and metallurgy.”
Me: “Geometry and metallurgy?”
Salesman Bob: “Yup, that’s it.”
Me: [sigh] “Okay, well thank you guys for your time.”

So there you have it folks - the secrets to any mysterious audio gizmo: PFM Circuitry and Geometry/Metallurgy – what will they think of next!

Please forgive the bitter tone that follows in this post, but recently I came across an “audiophile” device that I feel may damage the already precarious position of the audiophile industry.  First however a little necessary physics background…

A “Blackbody” is an object that does not reflect electromagnetic energy incident upon it, or allow any to pass through it.  Any emission from it is entirely thermal in nature with no characteristic emission/absorption lines from any element.  This is referred to as “Blackbody Radiation”.  Classical theory describes this spectrum with the Rayleigh-Jeans Law:

is the power per unit area
is the speed of light
is Boltzmann’s constant
is the temperature in Kelvin
is the wavelength

This is in agreement with observation at lower frequencies, however the problem with this result is that at higher frequencies (i.e. as ) the power approaches infinity!  This is certainly not in agreement with observation and has been referred to as the “ultraviolet catastrophe”.

A physicist by the name of Max Plank made an amazing assumption that was to prove instrumental not only for resolving the paradox of the Rayleigh-Jeans law, but for all of quantum mechanics.  The assumption is that radiation can only only assume discrete energy values:

is the energy level
is Planck’s constant
is the frequency.

Therefore the energy between two adjacent energy states is given by:

The power per unit area spectrum that results from this important assumption agrees with observation and is given by the following expression:

Now I return to the bitter part of my post.  As I make clear in my Engineering Perspective article, I am not a big fan of overpriced audio interconnects.  I am not saying there isn’t a subjective improvement, but that it may not provide the greatest benefit to cost ratio for the audiophile.

However, at least these overpriced interconnects are functional.  At worst, they get the signal from point A to point B.  Even something as esoteric as a special wooden volume knob that improves your sound at least allows you to turn up the volume!  But a product that claims to dramatically improve your system by acting as an electromagnetic blackbody for your equipment is a complete waste.

There are people in this world with incredible perception that can detect “impossible” subtleties.  The purpose of the audiophile industry is to cater to these individuals – those for whom minute differences matter.  Please try to give these gifted individuals the audio experience they deserve and not just another piece of junk backed up with horrible pseudoscience.

I love to set personal goals.  The feeling of always reaching for something that you can just barely touch with your fingertips.  The above picture is my father-in-law John performing the “Iron Cross” on the gymnastic rings.  He used to perform the “Flying Rings” on Muscle Beach back in the day.  Wow.  Gymnasts make it look so easy, but the most humbling experience you can have is to actually try it.

Like I said I love to set goals for myself, and not just in audio endeavors (e.g. design a great new amp).  I’m not what you would call an “in-shape” person – in fact just two months ago I couldn’t do a single chin up!  Now I can do a single good one (no kicking, swinging, etc.)  I have installed a pair of gymnastic rings in the garage and my personal goal is: to perform a single “Muscle Up” on the rings!

My next goal is to someday perform the Iron Cross on the rings…hey, it’s important to have dreams! 

There is much debate about optimum grounding strategies in audio electronics.  This article explores a ”Star Ground” versus a “Ground Plane”.

It may come as a surprise that, despite the common use of the star ground approach in audio electronics, the ground plane is superior.

Also included in the article is a list of helpful advice for a successful layout, particularly for high-power switching audio designs.

Enjoy!