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How Did He Do It?
 
Periodically I get asked how something that I’ve accomplished works. Below I will shed some insight into a few solutions I’ve implemented as they pertain to various technical challenges. Some solutions are rather unique while others are relatively simple.
 
   
 
Before I tell you how I connected my PC and stereo together, let me first say how it was not done. I did not merely run audio cables between the Line In/Out jacks of the stereo and the Line In/Out jacks of the sound card on the PC. That method ties the ground connection of the PC to the ground connection of the stereo, which creates a “ground loop” that is notorious for background hum. Furthermore, such connections are “unbalanced” and consequently susceptible to magnetically induced interference. I also did not insert isolation transformers in the circuit because although they eliminate the ground loop, they do not typically have good frequency response. What I did was purchase some op-amps (integrated circuits) and wired them to convert from unbalanced signals to balanced and back again. This allowed me to use CAT5 cable to transmit the audio signals between the PC and stereo using a “balanced line.” The result is audio with no hum or interference.
 

 Digitize 78RPM Records
 
One of the items in my antique collection is an old wind-up Victrola, model VV-XI (VV stands for Victor-Victrola); it was made in 1917. This is a completely mechanical record player that uses ‘single play’ steel needles. It is an experience to hear this thing, and it can really crank out the sound, but I do not wish to unnecessarily wear out my old records or consume needles. So I have digitized my 78RPM record library. To do this, I purchased a ‘made for 78s’ styli which fits my Shure V15 cartridge. Since my direct drive turntable only plays at 33 & 45 RPM, I changed the resistor in the 45RPM circuit so it would spin at 78RPM. I then played the 78RPM records through my stereo while I recorded at the PC. Sonic Foundry makes some high end PC software that can remove pops & clicks and silence surface noise, but for the hobbyist the free program Audacity (http://audacity.sourceforge.net/) works OK.
 
 Configure Outlook on Multiple PCs
 
I have more than one PC that I use to read email. The way I make this work is that I configure Outlook to ‘leave a copy’ of my email on the server. This means my email can still be retrieved by a second (or third) PC later. I configure Outlook on my primary PC to delete emails only after a week, which limits the accumulation of email on the server. So as long as my laptop checks for email once a week or more, it has all my email. And if I want a copy of my sent mail on my other PCs, I BCC myself when sending that message. These settings can be found in Outlook by going into Account Settings | More Settings | Advanced.
 

 
“Loud is beautiful, if it’s clean.” That’s what it said on the stereo speakers I bought. And they will indeed play loud and clean. In fact, they are so efficient that they will put out 102db of sound with only 1 watt of signal. (That means they will play louder connected to a 10 watt amplifier than most speakers connected to a 100 watt amp. When purchasing speakers, one should pay more attention to efficiency than power handling.) But let’s digress for a moment. What happens when a stereo is turned up beyond its maximum power output? The answer is that because the bass requires the most power, the peaks of the bass notes will cause the vocals to distort when the peak instantaneous power of the amplifier is exceeded. At this point, loud is no longer beautiful. The normal solution is to buy a bigger amp. But another workaround is to separate the bass notes from the rest of the sound and use separate amplifiers for each signal. That is called bi-amping. (Want to know more? http://sound.westhost.com/bi-amp.htm explains it in detail.) To do this, I opened my speaker cabinets and separated out the woofer connections which I connected to an additional jack. I also built an electronic crossover circuit and incorporated it into my stereo, enabling it with a switch. I then ran the bass signal to a second amplifier to drive the woofers in my speakers. Now I can crank up the stereo until the bass distorts (which the human ear doesn’t object to very much) and the vocals are still crystal clear. The only problem that remains is when I turn it up to 110db or more, my wife promptly takes the phone off the hook (I have wired our phones to mute the stereo; otherwise we don’t hear the phone ring)!
 
 
Back in the days before Microsoft and PowerPoint, slide projectors were used for multimedia presentations. After seeing some very impressive shows during the 70’s, I decided to build my own two projector dissolve unit. I wanted it to run from a cassette deck, so I came up with my own design. I decided to control the projectors with a tone that ranged from 35-45Hz. Since low frequencies could saturate cassette tape, I recorded the tone at a level of -20db. To avoid conflicting with bass notes in the stereo background music track, I recorded the tone out of phase on the left & right channels. Since bass music is always mono (the ear cannot locate low bass), I could distinguish between my projector tone and bass in the music by splitting L+R and L-R at the low frequencies. Here’s how the circuit worked. I designed a crossover circuit that would send all frequencies above 50Hz to the sound system. Below 50Hz, I would send L+R to both the left and right sound system channels. Since the projector tone was out of phase between left and right, it would cancel itself out going to the sound system. To pick off my projector control tone from the audio below 50Hz, I inverted the phase of the right channel, added that to the left channel, and sent the sum to the projector controller. In this circuit, the mono bass audio would cancel itself out while the control signal would double in amplitude. It really work well. With a stereo cassette, I could get full range stereo audio and still control my projectors with an embedded tone that was not audible to the audience. To dissolve the projectors, I used a phased-locked-loop circuit to convert the control tone to a control voltage. This voltage caused one projector to go from dark to bright as the tone ranged from 36Hz to 44Hz, while the other projector went from bright to dark. At 35Hz and 45Hz, the dark projector was sent to pulse to advance to the next slide. One thing I thought was really advanced about my system was that the dissolve rate was infinitely variable, compared to the commercial products which only had fast, medium, and slow rates. In used this feature to advantage in one slide show where it took 20 seconds to transition from one slide to the next. The effect worked perfectly in that new objects seemed to appear out of nowhere because the transition was so subtle. (That presentation addressed the purpose of life; the special affect was to suddenly freeze all the busyness of life and then slowly morph it into a graveyard while the music faded away. It was very effective. It made you stop and think.)
  
 
After watching a demonstration of OnStar, I was curious if a regular cell phone could be integrated into a car radio. To test this, I bought a cheap wired cellphone headset and replaced the earpiece with a jack that could plug into an FM modulator. By substituting the FM modulator for the earpiece, I could then play the phone through the car radio. However, without echo cancellation circuitry, the volume could not be turned up very loud. The microphone worked best clipped to the visor, but as a practical matter a unit designed for this purpose worked better (such as http://www.myblueant.com/products/speakerphones/s4/index.php).
 
High Resolution Webcam
 
I do video conferencing. In fact, I consider it a necessity for Grandparents and Grandchildren. But some webcams do not work well; they are dim and blurry. My solution is to use a video camcorder as a webcam. This provides 720x480 30fps video, which qualifies as HD. And while ooVoo advertises HD video conferencing for a price, it can be done for free using Skype. My Sony camcorder will stream video over its USB connection, but this is only supported in XP. To do this under Windows 7, I have connected via FireWire rather than USB. Interestingly, Skype does not claim to support FireWire video connections. However, if the video signal is present when Skype is started (before the icon appears in the notification area), it recognizes the FireWire connection and streams quality video. (Note: I have come across a few PCs that have unreliable FireWire ports and they disconnect after 5 minutes.)