| ampage Tube Amps / Music Electronics |
For current discussions, please visit Music Electronics Forum. |
ampage archive
Vintage threads from the first ten years
Star Grounding Amplified
:
 6/3/2000 2:31 PM |
|
R.G. |
Star Grounding Amplified I fleshed out the star grounding example with some text to explain it a bit further, if you're interested. As always, additions and corrections welcome. |
|---|---|
| 6/7/2000 2:49 AM |
|
| Steve Ahola |
Question about Peavey grounding techniques R.G. The schematics for the Peavey Classic 20/30/50 amps show two ground points used throughout the amp, and they are seperated by a 47 ohm flameproof resistor ("47FP"). I believe that one of the ground points is in common with the chassis and the other, ur, isn't... Any thoughts on this? Here is the schematic for the Classic 20: http://www.ampage.org/blueguitar/c20schem.gif I believe that the ground point inside the circle is isolated from the chassis ground (no circle) by the 47 ohm resistor, but I may have that backwards... Steve Ahola P.S. Oops! The Classic 30 and 50 actually have three ground points using two 47 ohm resistors... |
|---|---|
| 6/7/2000 2:55 AM |
||
| R.G. |
Yeah, some. It's common to try to separate the signal ground from the chassis ground with a low resistor instead of a wire. This gives connection so there is no long term voltage imbalance, but enough separation to help with box-to-box ground loops, I think. I only addressed grounding within one box. Box-to-box grounding is sticky, too, as you can imagine. I saw one scheme to connect safety ground to signal ground with a 10 to 47 ohm resistor and a diode bridge with shorted + and - pins. This makes the signal and chassis grounds separated by a resistor until you get a voltage higher than two diodes, when the diodes start conducting like mad and prevent the signal ground from getting more than two diodes above chassis ground. This gives a form of "ground lift" to help with box-to-box hum while preserving some safety features. I don't know whether UL would agree, but that's the idea. As to the triple ground system - I'll have to look. | |
|---|---|---|
| 6/7/2000 6:10 AM |
|
| Peter S |
R.G., You're absolutely correct about this, and who cares what UL thinks  It does work to reduce ground hum between chassis. I've seen this grounding arrangement on quite a few pieces in recent years from different manufacturers, including Fender and Marshall.
PS |
|---|---|
| 6/7/2000 6:14 PM |
|
| R.G. | The Poop on Peavey grounding techniques 8-) They have three grounds there: (1) chassis ground, represented by the "rake" symbol (2) highest quality ground, represented by the uncircled ground symbol (3) medium quality ground - circled ground symbol The chassis and high quality ground are apparently connected at the input jack. The first two stages use that one. Note that the power decoupling cap for "B+" is attached to that ground. The medium quality ground is connected to the high quality ground through that 47 ohm resistor. All the circuits it feeds are the higher signal level circuits, including the power amp. |
|---|---|
| Page 1 of 1 |