need simple anti-thump

[sondadareas]

Hi,

i'm building a medium-sized power amp & don't need a complex relay-type of anti-thump.

Years ago I saw a simple circuit using a fet on the very input of the power amp; I recall that this device momentarily shorts the onrushing turn-on votage, then from here on it doesn't count.

Anybody seen this circuit?

I think it's also possible to extend this circuit to double as overload protection for the input.

thanks.

[indianajo]

Some people use current limiters, sold by GE as CL-## where the number refer to different resistances. See the datasheets on datasheetcatalog.com. These are thermistors that decrease in resistance as they get hot. The GE originals are black. The oriental manufactured similar devices (found in the inputs of switching power supplies like PC power supplies) are shaped like a disk capacitor and are green. I found a 2.5 ohm resistance device that goes to 1.7 ohm in front of a hair dryer, in a 450 watt PC power supply. I just installed a CL-90 with over 100 ohm cold resistance in series with the power transformer of a mixer preamp, fused for 1 amp but probably using a lot less. It cut the turn on click I was experiencing if I turned the mixer on before the power amp. Some people, including the power supply manufacturers, wrap these devices in plastic to ensure they don't go cold if the music goes soft (on an amp).

[Bigun]

This is what you are looking for if you wish to do it in the power supply:

http://www.pmeweb.co.uk/audio/psu.pdf

It has the potential to address turn-on thumps and protect the output from over-current.

[sondadareas]

thanks!

The circuit I want comes between the input cap & just before the input darlington pair.

I have just built the classic 1977 NS/Hitachi mosfet amp using a 2sk1058 & 2sj162, to 50 watts. I used the usual permanent ink to hand-draw the PCB artwork & hand-etched the excess copper.

I found that 2n5401's & MJE 340/350's work as well besides the 2sa872 & 2sd756/sb716.

I still can't upload the PCB design so others can try their hands but I'm working on it.

thanks.

[sakis]

read esp pages ... Rods articles about ltp stages current sources protection and delay methods and so on and on .....you may find more than one option to fit your needs ...you may also be able to cure the situation in an other way ...

regards sakis

[sondadareas]

Sakis,

2sa1302? I thought they's been discontinued cuz of fakes from the East!. Years ago I upgraded a friend's power amp by putting a 1302 & it's complement rather than replacing the broken ones which were not as good as these.

I built one anti-thump from Slone's & I might try the one from Self. But this morning I looked at my old book the Electric Guitar Handbook & I found one circuit with the fet anti-thump, by Gibson.

[smartx21]

What you are looking for has been published in this forum by user APEXAUDIO. Send private message to him asking for this circuit. Or search over his threads.
Regards,
Max.

[smartx21]

Take a look at this post: 100W Ultimate Fidelity Amplifier

[smartx21]

The circuit is attached in this post.
Watch to both 1N4007 diodes. They have to be connected BEFORE the bridge, not as is in this drawing.
Regards,
Max.

[Tekko]

I made a simple anti thump circuit using a small relay, a transistor, a capacitor and 2 resistors to form a delay circuit that delays the speaker beeing connected to the amp output.