Am I wiring this correctly?

chuck55 · 04:26 PM

Hi, I made this DIY preamp and not sure if I have the grounding correct.
I am grounding the RED input / output together and the BLACK input / output. Is this correct? Do I star ground all together?
I tried not connecting the grounds (I think) and got a loud hummm. It went away when I connected it as shown in the pic.

chuck55 · 23rd June 2010, 04:30 PM

trying again with the photos.

chuck55 · 29th July 2010, 04:57 PM

Still looking for help.

Thanks

sreten · 29th July 2010, 05:12 PM

Hi,

You should have star point referenced to a metal case at the input.

/sreten.

DF96 · 29th July 2010, 06:47 PM

As you simply have a resistive attenuator in each line there is no need to connect the grounds of the two channels together. As you found, you do need to connect the input and output grounds for each channel because this provides an intact ground reference for the signal.

When you have to ground things, a star ground is a good idea. When you don't have to ground things, because they are grounded elsewhere and safety is not an issue, it is best to leave them floating. This avoids hum loops.

chuck55 · 30th July 2010, 10:53 AM

Thanks for the help.

Would a plastic case be okay? Even if metal, I don't know what grounding to that would accomplish as there is no power cord going to ground.

Quote:

As you simply have a resistive attenuator in each line there is no need to connect the grounds of the two channels together.

That is a star ground?

DF96 · 30th July 2010, 11:16 AM

A star ground is where all (or almost all) the ground connections in an amplifier are grounded at the same point. This may, or may not, be a chassis connection too.

If the pot works OK as it is then a plastic case should be OK. If you get hum or interference pickup, as your wires appear to be unscreened, then you would need a metal case. You should connect the grounds on one channel to the case. Then the case will act as a screen.

When a unit is powered, then the case should connect to the safety ground. The signal ground may be kept separate, or partially separate.

chuck55 · 31st July 2010, 12:48 AM

Very helpful. Thanks DF96.

23rd June 2010, 04:22 PM	#1
chuck55 diyAudio Member Join Date: Dec 2003 Location: New England	Am I wiring this correctly? Hi, I made this DIY preamp and not sure if I have the grounding correct. I am grounding the RED input / output together and the BLACK input / output. Is this correct? Do I star ground all together? I tried not connecting the grounds (I think) and got a loud hummm. It went away when I connected it as shown in the pic. Last edited by chuck55; 23rd June 2010 at 04:26 PM.

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29th July 2010, 04:57 PM	#3
chuck55 diyAudio Member Join Date: Dec 2003 Location: New England	Still looking for help. Thanks

29th July 2010, 05:12 PM	#4
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Hi, You should have star point referenced to a metal case at the input. /sreten.

29th July 2010, 06:47 PM	#5
DF96 diyAudio Member Join Date: May 2007	As you simply have a resistive attenuator in each line there is no need to connect the grounds of the two channels together. As you found, you do need to connect the input and output grounds for each channel because this provides an intact ground reference for the signal. When you have to ground things, a star ground is a good idea. When you don't have to ground things, because they are grounded elsewhere and safety is not an issue, it is best to leave them floating. This avoids hum loops.

30th July 2010, 11:16 AM	#7
DF96 diyAudio Member Join Date: May 2007	A star ground is where all (or almost all) the ground connections in an amplifier are grounded at the same point. This may, or may not, be a chassis connection too. If the pot works OK as it is then a plastic case should be OK. If you get hum or interference pickup, as your wires appear to be unscreened, then you would need a metal case. You should connect the grounds on one channel to the case. Then the case will act as a screen. When a unit is powered, then the case should connect to the safety ground. The signal ground may be kept separate, or partially separate.

31st July 2010, 12:48 AM	#8
chuck55 diyAudio Member Join Date: Dec 2003 Location: New England	Very helpful. Thanks DF96.

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