Archive for January, 2010

I Built Your Amplifier

Thursday, January 28th, 2010


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?  🙂

Gratuitous Self Promotion

Monday, January 4th, 2010

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

Publishers Choice Most Wanted Components

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

Monday, January 4th, 2010

Concert Hall

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!