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DIY Project # 3 - An AC-3 RF Output Upgrade for Laserdisc Players - April, 1997

By Ralph Calabria

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(If you would like to have your DIY project published in Secrets, please E-Mail Ralph Calabria at ralph_calabria@Merck.Com.)

Table of Contents (you can click on the list to go to specific item)

Introduction

What does the upgrade do?
The "Mod Squad"
The surgery (as performed on a Pioneer CLD-D703)
Construction tips
Testing your work
How did it sound?
Acknowledgments

Introduction

Wait! Don't throw out or replace your old laserdisc player just because it doesn't have an RF out for AC-3! There is an alternative. You can upgrade your old laserdisc player so it can extract the Dolby Digital signal from the right analog track.

O.K., I know some of you are saying, "But DVD is here, and laserdiscs are a thing of the past, and I don't want to spend any more money on it because the laserdisc format won't be supported in the future......... yada, yada, yada." While I certainly can't argue with some of those points, the fact of the matter is laserdisc is going to be in your face for a while, and if you're like a lot of the laserdisc collectors out there, you probably aren't going to be tossing out your laserdisc player or LD collection anytime soon. It will take some time for DVD to catch up with the 10,000+ titles already available on laserdisc. Chances are you already own several Dolby Digital encoded laserdiscs (well, maybe one anyway). Like most of us who've owned a massive collection of vinyl recordings, it's not likely you'll go out and buy the DVD version of a movie you already have on laserdisc (at least not right away). Interested in turning that scratchy, irritating sound coming out of your right analog track from an AC-3 LD into something bigger, better, and more dynamic than you've ever heard before at home? Read on.

What does the upgrade do?

Suffice it to say that DD completely replaces the right analog track on the laserdisc. If you try to play a DD encoded laserdisc in analog, you will hear a fuzzy distorted sound coming from your right channel. This in normal. In order to extract the DD signal from the laserdisc, the signal must be extracted before it sees the audio processing (DAC) stages. In general terms, that's what this upgrade accomplishes.

NOTE: Keep in mind, performing this upgrade will most likely void the manufacturer's warranty. Since most older players without the RF out are two years old or older, the warranty is probably expired anyway. So, keep reading!

The "Mod Squad"

The modification board was supplied by Charles Triola and Les Lavin from Houston, Texas (see Acknowledgments). They were responsible for acquiring the high quality parts that went into the mod board, as well as getting the board fabricated.

The modification is a generic board that works with just about every laserdisc player that can play both the digital and analog tracks of a laserdisc. The kit came with the fabricated mod board, miscellaneous parts to help with the installation, and complete custom instructions for installing the board in YOUR player.

The surgery (as performed on a Pioneer CLD-D703)

When I first got the kit in the mail, I read over the instructions about 3 or 4 times, stared at the board for about 20 minutes, and said, "How am I going to pull this off without destroying a perfectly good player?!" Those feelings were intensified when I finally built up the nerve to actually open the player. "Holy Toledo, Batman, those pins on the Printed Circuit Board (PCB) are awfully tiny and close together!!" Well, when it was all said and done, performing the mod was extremely easy. All my worrying was for nothing. All it took was a little planning (and praying).

I first removed the player's cover. This involved taking out two screws on each side and three screws from the back panel. The cover easily slid up and out. I then found a place where the board would reside. I used an existing screw that held the audio PCB in place, which was located at the front/center of the player. I installed the board with the components facing down so the components would not be protruding when the top was put back on. Following the kit instructions, I located the pins on the audio board to which I needed to make the connections. For the CLD-D703, all the pins were located right on top, so removing the board to access them was not necessary. The mod board has a strip wire consisting of four small color-coded wires. The wires are for the +5v, -5v, ground, and mute. The audio board on the player actually had all the pins labeled, so it made it that much easier to find the connections. The mod board also has two sets of 75 ohm cables, RF IN and RF OUT. The RF IN connects to the audio board, and the RF OUT connects to the supplied gold-plated RCA jack.

In order to easily install the RCA jack on the back of the player, I took off the back panel. This involved removing 12-14 small screws. Taking off the back made it easier to drill the hole for the RCA jack. This is also a safer way to install the jack, because if you get metal filings in the player, it could wreak havoc with the electronics. I drilled a 3/8" hole in a convenient spot in the back panel. I snaked the RF OUT coaxial cable in between the audio and video board, installed the RCA jack to the back of the player, then soldered the wires to the jack (including the supplied ground capacitor). I then found a grounding screw on the back of the player, attached the capacitor spade lug to it, and screwed the back panel back on. After all the other wires were soldered, I re-installed the player cover. It was that easy!

Construction tips

The most important aspect regarding the success of the upgrade is proper soldering technique. Because the pins on the IC are small and close together, there isn't much room to work. All wires on the mod board were tinned, that is, a coating of solder was put on the bare part of the wire. This is critical for a good solder connection. If you decide to cut the wires to make them fit better in your player, you must re-tin the freshly cut wires.

Using the proper solder and soldering iron is also important. The solder used must be rosin core (not acid core), since acid core will most surely destroy the wires over time. The iron should be fairly low wattage, about 15-25 watts. The tip should also be of the pencil variety to get into those close quarters without touching unwanted connections. Both rosin core solder and the iron described above could be found in Radio Shack or any other electronics store. Be sure to tin the soldering iron tip as well. In between each connection, wipe the tip of the iron free of any oxidized lead. The tip should have a silvery-shiny appearance.

When making the connections on the board, place the wire parallel with the board. Place the wire directly on top of the pin to be soldered, and press the wire down on the pin with the iron until the solder on the pin and wire melts and the connection is solid. Do not apply the heat very long, as this may damage the IC. If the iron and wire are tinned properly, the soldering of each wire should only take a few seconds. Gently pull on the connection to ensure that a proper bond was made.

After speaking with Charles Triola about the installation, I expressed my concern about soldering the big ground lead of the coaxial cable of the RF IN to the audio board. He stated that this connection really wasn't necessary, so I opted to eliminate this connection. If you also opt to eliminate this connection, be sure to properly shield the ground wire using shrink-wrap shielding material.

Testing your work

Once everything is put back in place, I plugged in the lasedisc player. Much to my surprise, there were no sparks or explosions! I used a volt meter on the AC-3 RF output jack to check that everything was connected properly. When the unit is on and in stop or pause, the voltmeter should read 0 volts DC. When the unit is in play mode, the voltmeter should read approximately 4.5 volts DC. In my case, it read 4.6 volts DC in play and 0 volts DC in stop and pause. The reading really depends on the player and how much voltage loss is incurred, but the voltage should be something less than 5 volts. The range usually falls between 3.6 and 4.6 volts DC.

How did it sound?

The system used to demo the mod was a B&K AVP-2000 preamp, B&K AV-5000 power amp, Marantz DP-870 Dolby Digital Processor, the modified Pioneer CLD-D703 laserdisc player, DIY Audax A652 left and right main speakers, Paradigm CC-300 center channel speaker, and ADP-150 adapted-dipole surrounds, Yamaha YST-SW200 subwoofer, and Audioquest Quartz interconnect cables throughout.

I guess the first question our readers will ask is, "Does it work?" First I played a disc using the left and right digital tracks in Dolby Pro Logic mode, just to make sure I didn't destroy the audio board. Mission accomplished! No problems so far.

I selected several Dolby Digital encoded laserdiscs from my LD collection to audition and switched to Dolby Digital. Discs included "Twister", "Stargate", "The Mask", "Star Trek: Generations", "Independence Day", "Primal Fear", and "Last of the Mohicans" .

Based on the little red AC-3 indicator light on the DP-870, I immediately knew that the AC-3 signal was being read and locked in. But what about the sound? Knowing that volts DC output was correct, my main concern was external noise. If the board was not installed properly, there is a potential for generating 60 cycle hum or buzzing, caused by poor grounding and external RF frequencies. Well, I'm happy to report that all discs demoed were drop-dead quiet during quiet passages. In fact, there was less noise during DD playback when I compared it to the Pro Logic soundtrack. This is an indication that the mod was installed properly, which included the proper connection of grounding capacitor on the back of the chassis. Using several key chapters in the demo movies, I checked the steering of all channels. As expected, sound quality and steering were right on as well.

If you've heard Dolby Digital before, then I don't have to tell you what the experience is like. If you haven't given a listen to DD, I wholeheartedly suggest that you do. It is by far more dynamic and lifelike than Dolby Pro Logic. If you have a pre-DD-ready laserdisc player, and you want to get into the DD game, I can't recommend this mod enough. It will bring your home theater to the next level.

Acknowledgments

I would like to thank Charles Triola and Les Lavin for making this mod available and for all the advice given in guiding me through this project. Unfortunately, Charles Triola is no longer building these mod boards for sale. However, there are several alternatives available to you should you decide to pursue this modification. Check out the Q&A section here at Secrets, #16 June 17, 1997. You might also want to look at a generic schematic diagram of an AC-3 mod board at http://home.powertech.no/espenb/ac3/output.html Kevin Nakano has a very nice web page dedicated to modifying LD players to AC-3. His web site is at http://users.aol.com/knakanoz28/ac3mod.html.

Ralph Calabria


© Copyright 1997 Secrets of Home Theater & High Fidelity
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