Anti thump (will this work)

[rs1026]

I tried a spst switch just now.It works perfectly well!! No turn on thumps or no turn off thumps!!. The resistance of the switch is 1.5ohms so its like I have added 1.5 ohms in series with the speaker cables.I dont find any degradation in sonic qualities by adding this switch.

Initially capacitor was draining through the speakers when i switched of the amp.Now that problem is also solved.I am quite happy with this solution.

[rs1026]

I forgot to mention in my previous post.I measured the DC at the output of the amp.Basically I connected a multimeter to the output.Each channel measured 0.5mV DC.

[jackinnj]

the LM3886 and LM4780 have mute functions which can be slow-started -- see the ongoing thread on "Soft Start LM3886" -- you can also soft-start if you use an inrush current limiter -- the cold resistance is such that the power supply starts with an "RC" calculated delay.

Don't use too high an "On Resistance" since power supply regulation will be adversely affected., and will motorboat will the undervoltage protection is cycling on and off.

[djQUAN]

I've used the "delayed" relay in all the amps I made and all of them are silent at turn on and turn off.

turn off thumps are caused by the main supply caps draining and that lasts a few seconds at turn off. the relay opens in only a few msec so that's already too fast. if you get a thump right after turning off even if the caps haven't discharged, you're getting a pulse from the transformer primary (that happens if you don't use a snubber circuit across the primary winding).

the separate switch for the speakers and power may be fine today, I'll guess that by after a few weeks or months, you'll get tired of having to turn on two switches.

if you really want to disconnect the speaker after turning the amp off, use a programmable IC to control power and speaker switching.

[Bill Fitzpatrick]

Originally posted by rs1026
The resistance of the switch is 1.5ohms so . . .

1.5 ohms? That's ridiculously high.

[jackinnj]

Originally posted by djQUAN

turn off thumps are caused by the main supply caps draining and that lasts a few seconds at turn off. the relay opens in only a few msec so that's already too fast. if you get a thump right after turning off even if the caps haven't discharged, you're getting a pulse from the transformer primary (that happens if you don't use a snubber circuit across the primary winding).

the thump is also caused by the capacitors draining at different rates -- I was wondering whether it might not be better to switch some "R" in -- i.e. a DPDT relay

you need a rather beefy relay to do this.

[gmphadte]

If I use a power on delay relay then how to eliminate power off thump?

This is a timing juglary, the solution is somewhat like...

When I connected speakers I have noticed that thump off's are gone. Power LED is the only thing I have changed in whole amplifier, so my only explanation is that this LED consumes everything what's left ine elco's.