Marantz amp question (Transformer).

[rainman]

You really should have gone for a basic EE course where they would have covered V=IR and P=IV and so on. That would really help your understanding of the basic circuit design. Calculus also helps, because you're talking about RC circuit design (http://othello.mech.northwestern.edu/ea3/book/elec5/RC.htm) and power supply design. In addition, you are throwing in semiconductor physics with the introduction of FETs.

Where your stray voltages are coming from: If you have -20 to +20 VAC coming out of your transformer (40V peak to peak), when you rectify it, you have approximately 0 to 18.6 V coming out of the rectifier (you lose 1.4V due to the silicon diodes in the rectifier, less if using germanium diodes). See http://content.answers.com/main/content/wp/en/6/6f/AC%2C_half-wave_and_full_wave_rectified_signals.PNG. Adding in the RC circuit will likely provide you with approximately 17.6 to 18.6 V (this is called 18.1VDC with a 1V peak to peak ripple). Not very clean. The tighter you design the RC circuit, the tighter the tolerances on your ripple voltage. There's a good power supply primer here: http://my.integritynet.com.au/purdic/power1.html

As to your question regarding the "shocking feeling" when touching the backside of your LM317...yes, you're now creating a new path to ground for the electrons in your circuit. Pin #2 on a TO-220 transistor package is hooked directly to the metal "back" of the case. That's why to add a heatsink to the TO-220 you need a mica insulator.

There's a reason we measure things with a multimeter and/or a laser thermometer. Touching things when you have electrons flowing is a very bad idea.


Also, you can do some reading here: http://www.allaboutcircuits.com

 

[macrospect]

You really should have gone for a basic EE course where they would have covered V=IR and P=IV and so on. That would really help your understanding of the basic circuit design. Calculus also helps, because you're talking about RC circuit design (http://othello.mech.northwestern.edu/ea3/book/elec5/RC.htm) and power supply design. In addition, you are throwing in semiconductor physics with the introduction of FETs.

Yes, I know I just havent had that type of schooling at my disposal, I am in college not, taking networking technology, so I know that course will be mandatory. For now, I just figure stuff out as I go along.

Where your stray voltages are coming from: If you have -20 to +20 VAC coming out of your transformer (40V peak to peak), when you rectify it, you have approximately 0 to 18.6 V coming out of the rectifier (you lose 1.4V due to the silicon diodes in the rectifier, less if using germanium diodes). See http://content.answers.com/main/content/wp/en/6/6f/AC%2C_half-wave_and_full_wave_rectified_signals.PNG. Adding in the RC circuit will likely provide you with approximately 17.6 to 18.6 V (this is called 18.1VDC with a 1V peak to peak ripple). Not very clean. The tighter you design the RC circuit, the tighter the tolerances on your ripple voltage. There's a good power supply primer here: http://my.integritynet.com.au/purdic/power1.html

That 50V is after the transformer voltage comes out of the rectifier, wasnt that the purpose of the rectivier, to get rid of that peak voltage. Still I dont know why all of a sudden I went from 24V to 50V?!

As to your question regarding the "shocking feeling" when touching the backside of your LM317...yes, you're now creating a new path to ground for the electrons in your circuit. Pin #2 on a TO-220 transistor package is hooked directly to the metal "back" of the case. That's why to add a heatsink to the TO-220 you need a mica insulator.

Ahh, ok thanks for explaining that to me. I did not know if that was normal or not.

There's a reason we measure things with a multimeter and/or a laser thermometer. Touching things when you have electrons flowing is a very bad idea.


Also, you can do some reading here: http://www.allaboutcircuits.com

Yes, I know its a bad idea. I did NOT do this on purpose, I was picking the board up, just after I turned the unit off (cap was still discharging) and was resting my arm on the metal casing. Thats how I discovered the back of LM317 carrys a little current.

I know not to use your finger to test if somethings live. Its sort of like saying, "I dont know if this 480V disconnect switch is live, let me test it out,) granted there is not that much power in the amp, I still know there is enough to knock you about.

In all thanks for your reply, I will check out those links. I am sure I will learn something new. For now, I am going to put the amp back together. Its not worth investing any more time or money into it.

 

[Mohonri]

I know not to use your finger to test if somethings live. Its sort of like saying, "I dont know if this 480V disconnect switch is live, let me test it out,) granted there is not that much power in the amp, I still know there is enough to knock you about.

After Hurricane Katrina, I was with a volunteer group in LA helping to clean up. We cleared some trees so an electrician could come and fix the power going to a pair of sewage pumps (very important, those!). I know the power going to them was at least 120V, probably 240V. The power was off, but just to make sure, the electrician tested it. With his fingers. You wonder sometimes...

 

[macrospect]

Seesh, some of the ideas people get....

They clearly do not know the true strength of electricity!