I'm new to the tube world having recently acquired an ST-70. I made some mods including moving the power switch to the front panel, adding a volume control, added a second input jack (stereo mini) on the back panel and replaced the stereo/mono switch with a front/back input selector. In the process of doing this, I noticed that the grounds of each input go through a separate 10 ohm resistor to amp ground. I'm puzzled at the purpose of these resistors. Aren't the input grounds already grounded together at the source equipment? I had already made all my mods which essentially has all of the input grounds connected directly to chassis ground before noticing the 10 ohm resistors and the amp seems to play just fine.
2 posters
Technical question concerning input grounds
gabe- Posts : 6
Join date : 2014-09-26
GP49- Posts : 792
Join date : 2009-04-30
Location : East of the sun and west of the moon
It lifts the input grounds to help avoid a ground loop through the two shields of the cable connecting the power amplifier to the (assumedly common-grounded) preamplifier. If you are not getting hum, as you probably would not if you are using the three-conductor stereo mini jack, you can leave it alone.
If you removed them, don't forget you did that...in case you run into a ground loop problem later.
If you removed them, don't forget you did that...in case you run into a ground loop problem later.