JimElliott
New Member
There was much discussion here about isolating the RCA input connector from the chassis...DON'T! As a broadcast (FCC 1st Class) engineer, one of the first rules learned is ONE ground point to chassis at the input. With the old tube consoles sometimes literally a few feet from the transmitter, this was the only way to prevent RF and HF oscillations within the audio gear which, by the way, was never grounded to the power line via the "third pin" on the power cord.
One ground is good and more are worse because you create ground loops where current flows due to the minute differences in resistance between ground points. It usually sounds like the 120Hz buzz you referred to.
The best ground point was the one Heathkit chose, but some amps may not still be properly grounded, explaining the perceived improvement when lifted. I would sand all oxidation away from the chassis around the inside where the RCA jack is mounted and insure the jack is pristine, as well, so as to make a solid electrical connection to the chassis. Then install the old jack using star lockwashers under the heads of the mounting screws to penetrate the paint just for good measure. If you don't mind altering the original look a bit, a high quality, stud mount jack with nut would be even better, once the chassis is cleaned. This should be the one and only ground point connection to the chassis for the ground buss wire that extends throughout the amp. If I were doing a total rebuild, I would use 12ga copper from some scrap romex house wire instead of the wimpy stuff Heath supplied, which is small enough to have a minute loss from one end to the other, adding noise.
In radio stations we used 4 inch wide copper sheet with the transmitter bonded to one end and the audio console to the other, and braided copper strap to every turntable and tape machine chassis. No shields were connected at both ends for the same reason, only at the input of the console.
In the W-5M, connect the shield to the RCA jack only or, better yet, to the ground buss at V1, which is the real input to the amp.
And bypass that V1 input capacitor for tighter bass. Auricaps, Sonicaps and Obbligatos can't hold a candle to a straight wire. The best amplifiers are the ones with the fewest coupling caps.
One ground is good and more are worse because you create ground loops where current flows due to the minute differences in resistance between ground points. It usually sounds like the 120Hz buzz you referred to.
The best ground point was the one Heathkit chose, but some amps may not still be properly grounded, explaining the perceived improvement when lifted. I would sand all oxidation away from the chassis around the inside where the RCA jack is mounted and insure the jack is pristine, as well, so as to make a solid electrical connection to the chassis. Then install the old jack using star lockwashers under the heads of the mounting screws to penetrate the paint just for good measure. If you don't mind altering the original look a bit, a high quality, stud mount jack with nut would be even better, once the chassis is cleaned. This should be the one and only ground point connection to the chassis for the ground buss wire that extends throughout the amp. If I were doing a total rebuild, I would use 12ga copper from some scrap romex house wire instead of the wimpy stuff Heath supplied, which is small enough to have a minute loss from one end to the other, adding noise.
In radio stations we used 4 inch wide copper sheet with the transmitter bonded to one end and the audio console to the other, and braided copper strap to every turntable and tape machine chassis. No shields were connected at both ends for the same reason, only at the input of the console.
In the W-5M, connect the shield to the RCA jack only or, better yet, to the ground buss at V1, which is the real input to the amp.
And bypass that V1 input capacitor for tighter bass. Auricaps, Sonicaps and Obbligatos can't hold a candle to a straight wire. The best amplifiers are the ones with the fewest coupling caps.
