bleeder resistor for ZenV4 power supply; and ancllary matters

[roddyama]

Originally posted by Zapped
...so want to make sure its safe to stick my mitts into the amp to make adjustments.

So Larry, if there's the slighest doubt, measure the voltage.

[roddyama]

This thread is reopened for discussion. Lets be considerate of the less experienced members and not suggest unsafe practices.

[Zapped]

With 5K ohm at 2 watt across the filter caps (23,400microfarads each) I also found it took a heck of a long time for the caps to discharge. And the Blue LED was almost heliarc bright. Experimenting last week, I dropped the bleeder resistance to 2 K at 5 watt (sandstone type) and separately (in parallel with the bleeder resisters) tried a bunch of increasing R's-in-series-with-the-LED to get the blue light down to a low glow. At about 50K ohm (!) in series with the LED, it is a nice mellow glow, amazingly still very visible across the room. The caps discharge quite a bit quicker with the 2 K ohm R's, which only get a couple of degrees above body temperature when doing their bleeder duty. Don't know if I will be wasting current capability this way when I connect the supply to the audio circuitry, but I feel safe now anyway.

Thanks for the advice and especially concern for avoiding unsafe practices. I am already Zapped; always want to avoid becoming more zapped.

Larry Wright
Seattle area

[mrfeedback]

Originally posted by jam
Well lets see. A 100w amp will have 100v dc between the rails and a 200w amp will have 140v between rails........I would say you would have something to worry about.

And if the amp had 100,00uf of capacitance the stored energy would be ...1/2 CVsquared (Joules).

I would say that if you got zapped , you would have a lot to write home about.


Regards,
Jam

Big PA amplifiers can run + and - 120V rails.
Going across these rails gives up to 240V DC.
DC is rather more dangerous than AC because DC can cause muscle spasm and 'lock-on'.
That said 240V AC can cause lock-on too - been there, done that.
The old rule about working with hazardous voltages is to keep one hand in a pocket, and perform measurements with the other hand only.
Grey, you now know that solid state voltages CAN be high enough to be hazardous.

Eric.