Testing Prototypes

We've been building and testing catalyst prototypes for quite some time now.  I have previously posted a comparison showing testing done on the Audio Technica AT-PEQ3 vs the Lucid Labs Catalyst Phono Preamplifier.  This time I decided to take on a more expensive competitor the emotiva xps-1 phono preamplifier which retails for $149.  $69.00 more than an early bird backer special on our Kickstarter.  I used a QA400 Audio analyzer to complete this test and tested using a -40dBV 1khz input signal as emotiva has specified in their testing documentation.

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The results

• Lucid Labs Catalyst Phono Preamplifier:  0.00486% THD
• Emotiva XPS-1 Phono Preamplifier:  0.00811% THD

The QA400 doesn't do a great job with SNR values on phono preamps, the absolute number is usually 25-30db lower than when tested with an AP or other analyzer.  They are useful for relative values and testing showed that the Catalyst also had slightly better SNR values than the emotiva unit.  Why spend $60 more for theirs when ours sounds and tests better.

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5 songs I've been using to test my setup lately

Before I get a bunch of argumentative, hateful internet comments i'll preface this with these words.  These are not my absolute favorite songs, do I like them...sure, but the purpose of listening to these is my familiarity with how they sound on different systems and what each song highlights as far as audio reproduction is concerned.

In no particular order

1. David Gilmour-Wish you were here-Live in Gdansk.  If you happen to be a pink floyd fan, I highly recommend picking up this blu ray, its very well recorded and has a lot of David Gilmour singing songs from his Pink Floyd days.  This song in particular really highlights quite a bit of the spectrum, I typically listen specifically to hear the highs at 0:56 when the guitar comes in.

2. Dave Brubeck-Take Five.  A classic, well-recorded song for the audiophile.  I can't say i'd change anything about the way this song was recorded, and have listened to it enough times that I know how it should sound.  Horns showoff mids, symbols throughout add some highs, and the subtlety of the drums, particularly during the solo, make this a test song anytime I design a new piece of audio equipment or change something in my setup.  Bass heavy systems that aren't overly accurate really don't do the drums here justice.

3.  CC Coletti-You Shook me. I got this song on an audiophile sampler from HDTRACKS.COM.  Its really well recorded and neutral throughout.  On a good system soundstage is what I listen for here.  Really sounds like you're sitting in a studio with a bunch of musicians here rather than listening to a stereo or headphones.

4. Stevie Ray Vaughan-Tin Pan Alley.  This song off of the Cold Shot album is probably the first I go to anytime I change something on my analog system.  A great slow blues song driven mostly by guitar, Tin Pan Alley also features well recorded lyrics and crisp drum backing.    

5. Flight Facilities and Christine Hoberg-Claire De Lune. This song has some great subtle bass that extends a little lower than most of the songs on this list.  Vocals, strings, synthesizers, guitars, thumping bass...this song has a lot going on, An audio sampler platter if you will.  Keep in mind...they do lead in and out with record player tracking sounds...its the song not your stereo.

Honorable Mention 

Daft Punk-Something About Us. One of my favorite Daft Punk Tracks...and I have it on vinyl so its always been one I'll put on after making changes to the analog setup.

The Perfect Amplifier Power Supply

I have a lot of requests to make CMOY's that have DC jacks so that they can be plugged in.  I understand that certain applications may require a DC power supply, particularly if the amplifier will be on all of the time.  If this isn't the case I will argue until the end of the world that if the device has low enough power demands battery power is a better way to go.

First think about how an amplifier works, and do so by looking at the wikipedia definition of an amplifier.

Amplifier

"An electronic amplifier, amplifier, or (informally) amp is an electronic device that increases the power of a signal.

It does this by taking energy from a power supply and controlling the output to match the input signal shape but with a larger amplitude. In this sense, an amplifier modulates the output of the power supply to make the output signal stronger than the input signal."

Since we are taking energy from the power supply and using it to make a controlled output it would make sense that the cleaner, or closer to a perfect DC power supply we can get, the more accurate our output will be.  

Considering DC Power Supplies

Several steps usually take place in a DC power supply like those used in small audio amplifiers

1. Step Down Transformer:  A transformer steps the AC power down from the wall voltage 120v in the US to whatever the desired voltage is.  At this point we still have AC current in the form of a sine wave at a lower voltage

2.Rectification:  Using a recitifer Alternating current is converted to direct current.  Unfortunately this is really just taking the part of the sine wave that goes below zero volts and making it positive.  Instead of a constant DC voltage we have a constantly moving DC voltage

3. Filtering:  Using capacitors and other passive components this bouncing positive DC voltage is now filtered into a flatter, but still not perfectly flat waveform

4. LDO regulation:  Generally small signal audio amplifiers will employ a LDO regulator to regulate the bouncing waveform into a much flatter, more constant voltage DC output.  LDO regulators are notoriously inefficient and cannot perfectly remove all noise from the system.

All of these steps and you still have dirtier power than using a battery or two.  Cheap DC power supplies, the kind that come with lots of entry level equipment often have easily audible noise in their audio output.  Also think about the cost involved with all of these steps.  Transformers, large filtering capacitors, and regulator IC's are all expensive components, often the cost of creating clean DC power is a huge portion of the overall cost of amplifiers.  Which is why if you have a device, such as a headphone amplifier that uses very little power why not take advantage of the fact that you can use a much cheaper, better performing power supply known as a battery.  I highly recommend the tenergy centura brand rechargeable 9V batteries which can be charged and recharged over and over again yet still feature all of the benefits of a battery powered source.  We aren't the first people to think of this, there are several high end phono preamps and headphone amplifiers that utilize battery power to more accurately amplify.