Low current thump silencer, good for preamp output

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schultzsch

schultzsch

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Joined 2009
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#1
As the title says this is module will keep the output of your preamp shorted to gnd with the condition this output is ac coupled.

Remember for when used for turn on thump protection! if you power off and don`t wait that the relay disengages and power on again you will get the power on thump or if the network drops and suddenly comes back then turn on thump can be present. It is more a protection for our bad memory.. 🙂)

It can be used for turn on or turn off thump.
It can be used up to 36vdc(probably more) and when assembled should look like in the image below.

tsl.jpg


One module can be used for 2 channels in a stereo setup if same power supply powers both channels. If you have a dual mono setup then one module goes for each channel.

To use it is simple, connect IN to the output of your preamp that has the turn on/off thump, gnd goes to gnd of your pre and V+ goes to V+ of your pre.

I have attached the schematic, bom and gerbers.


Edit.
Thanks to JP for his suggestion! I made a r1 version that includes this diode and updated all the files.

Later edit: Because of the added diode the cap that does the turn on delay discharges more quickly and if you turn off and back on(or when network power is lost) most probably you won`t get the turn on thump. JP is an amp saver this time 🙂 so thanks again 🙂
 

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#2
Hi, a relay based output muting circuit can be made so that it delays engaging the relay at power on but disengages the relay directly at power off. This because it does not matter if plops are caused at power on or off: both are unnecessary and can be prevented together with the circuit being user error tolerant. One extra diode. Please see the link. I made a revision of it suitable for both RCA and XLR that measures 32 x 22 mm.

Coicidentally I am working on a Kenwood device from 1980 that already had relay output muting. Why designs today lack it (just like input filtering) and have power on/off phenomena is incomprehensible.

iamwhoiam

Thread 'MOD: Mini Output Delay - a headphone / line-level audio output delay retrofit PCB'

BACKGROUND:
I needed to retrofit an audio output delay to an AC-coupled headphone amplifier design. The original protracted power-on transient of 6V would be enough to destroy some lower impedance headphone drivers. There are a few schematics available online, most of them had DC-offset protection too (something I did not require). For those who need continuously active DC protection, then Ti Kan created his e12 board. There are also solid-state implementations on these forums. Then this thread came to light discussing a circuit which seemed ideal with some...
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#5
Yes, Like I said in the first post it was a matter of populating or not the cap. Usually I had amps that thumped at power on or off but not both.
But now thanks to you I updated all the files and made it more universal. 🙂)
 
#6
All OK. A good preamp or source design has it implemented in the design. Any new design should have it as the pros outweigh the cons (a few Euro) big time. Power on/off phenomena = neglect.

If you add pads for solder blobs it can also be used shorting XLR outputs so GND free. I routed the GND tracks for RCA to the 4 pin connector to short outputs to their GND and not the circuits GND.
 
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