From: eBayZilla Subject: The "Quit VECTREX" Date: Monday, November 01, 1999 1:54 AM Classicgamer14 wrote: > Has anyone performed the surgery needed to eliminate the audio > hum (see no_buzz.zip file)? Is this procedure easy for the > novice and where can the parts be purchased (Radio Shack?)? > Is there any way to lower the hum by some how shielding the > audio cable and where is the best place for the cable to be > positioned? Any input is greatly appreciated... > > Well I read the no_buzz.zip file and I can't say I care for the idea much. It is way too complicated and over the head of about 99% of the VECTREX owners. Don't get me wrong, it probably works just fine. I thing it is partly based on a lot of assumptions that are not true. But I give credit to the author because it does look like a lot of work went into it. The no_buzz.zip concept is to add a pre-amp between the logic board and the power board. For the laymen, they put a gain stage before the amplifier to help make it less sensitive to noise. Why bother? As an alternate solution, I would suggest that you could get a small piece of Vector board and a LM386N-3 ($0.50ea) and just build another version of the stock circuit. Mount it next to the front of the logic board with short leads that won't pick up noise. The problem was that the amp should have bee placed on the logic board because it sure doesn't make any sense having it on the power board with all the electronic noise. I have never tried this but I do like the sound of it. The proper name is the "VECTREX Buzz". It is there at the same level and does not change when you turn up the volume. It measures typically 70 to 75 dB (Decibels) and I have seen it as high as 85 dB. This is as measured with a Radio Shack sound pressure meter at 1/4-inch from the speaker grill. The reason is one poor job of laying out the power board. The power amp is placed near the yoke driver circuit. The 13- inch audio cable acts as an antenna and also feedbacks the signal of the magnetic flux from the yoke. The resulting feedback and ground loop problem produces as buzz. The "VECTREX Buzz". What you see on the screen, comes out the speaker. Ground loop defined - When 2 or more points within a system are defined as ground and the resulting fluctuations in voltage between the ground points creates feedback and produces undesirable oscillations in that system. The VECTREX is on giant ground loop. We had a lot of video problem and I talked my boss into letting me off from my regular duties for 2 weeks and I did a top down analysis of the current VECTREX System in production. I came up with a list of 7 major problems. I believe they acted on only 4. There is a giant ground strap on the side that connects the power and logic boards. It was added due to FCC regulations. But then why is the green wire on the 4-wire cable assembly still connected? The director of engineering responded "whoops". It was removed for units produced after April 1983. You can take a pair of wire cutters and cut it in half. This was another ground loop! Just put heat shrink tubing on both ends. This typically results in 0 to 6 dB reduction in noise. My solution? This was the "Quit VECTREX" Proposal. If the ground gets all messy by the time it gets to the ends of the audio cable, then the solution is to ground the power board and logic board at that point using the audio cable itself. I removed the green ground wire, the ground strap (near game connector) and used a piece of heavy duty shielded coax (RG-11 I believe). It has to have a good braided outer shield and not that cheap foil stuff. This is going to be your new system ground line. I will give details to the solder_guy and let him try it first. Be patient. Advantages? Nothing to buy but a short piece of cable. If you can solder, you probably can do it yourself. I made this conversion to "Goliath" in April 1983. "Goliath" is the name of my personal development VECTREX that I used on both the "Quit VECTREX" and the "Head Phone" proposals. It also had the right-handed control panel prototype hooked up to it until I sold it. The "Quit VECTREX" Proposal violates FCC regulations for Class-J computing devices and would have required the system to be qualified again. It was rejected very quickly. But, a lot of the gang modified their own units. "Goliath"? With the volume up to its max, you have to put your head next to the speaker to hear a buzz. Typical 25 to 30 dB noise reduction. Regards fellow VECTREX owners, eBayZilla http://members.tripod.com/gceinc/buzz/ Sent via Deja.com http://www.deja.com/ Before you buy.