Imbalanced Voltage Rails on Gainclone

[Kofi Annan]

First, I would like to say that this forum has been tremendously helpful for a newbie who only recently could not tell a resistor from a hole in the ground. Over the past few months, I have taught myself some basic electronics (although I still have more to learn) and I have built some VERY basic amplifiers (.3W to 7W).

I figured it was time for me to take the plunge, so I have ordered and received parts for a minimized "budget" Gainclone, using schematics and parts lists found on this forum. The best way for me to learn now is by doing, and I've already learned a lot-- I have completed the soldering of the amplifier circuit and the power supply. However, I've got a few questions that I would like to get answered before I supply power to the op amp.

1. The power supply works fine-- I'm using a +/- 18V 160 VA toroid which is giving me about +/- 17.3V across the bridge rectifier (I think the rectifiers drop about .7V). I am using 1000uF filter capacitors and (here's the question) the voltage across them is about 27.3V on the positive side and -26.9 on the negative side. Originally, I was getting a huge difference in voltage on the rails and I determined it was the ground. I fixed that and now since I only have a small difference, I was wondering if this is OK or if I need to get it exactly right. Any thoughts?

2. I am getting really confused about the grounds. I have the "earth" ground (round prong from the AC receptace) grounded to a 1/8" think aluminum rail in my wooden chassis. Also, I have the signal and power grounds attached to the same rail, although power is grounded to one screw, while signal is grounded to another. Is this going to cause a ground loop hum? Additionally, do I need to have EACH signal / power ground anchored SEPARATELY, or can I combine the grounds to one ground screw?

Any help you can offer would be greatly appreciated. I know about the "star ground" principle, but I don't understand why I would need to separate all the signal grounds and all the power grounds, then tie all signals to signals and powers to powers, then tie together signal and power. I can post pictures of my project if anyone cares to see it!

Thanks in advance!

[PRR]

> about 27.3V on the positive side and -26.9 on the negative side

Only 1%. Even a 10% unbalance is no big deal. And unloaded voltages are not too important, and often read higher than theory. You're cool.

> I don't understand why I would need to separate all the signal grounds and all the power grounds, then tie all signals to signals and powers to powers, then tie together signal and power.

Because you do not want POWER currents thundering through Signal conductors. No conductor is perfect. Big power currents through practical wires give "small" voltages. If this gets into the amplifier it makes trouble.

[Kofi Annan]

Thanks for the quick response! I completed the circuit last night and its working great!