[SI-LIST] Re: Switch On & Switch Off Clicks due to Amplifier noise

  • From: "Tom Dagostino" <tom@xxxxxxxxxxxxx>
  • To: <rsefton@xxxxxxxxxxxxx>, <adeelmk@xxxxxxxxxxx>, <si-list@xxxxxxxxxxxxx>
  • Date: Sat, 12 Feb 2005 10:58:05 -0800

There are many reasons that will lead to clicks and pops when switching
audio signals.  You need to isolate the source of the problem.

From what you describe it sounds like you have some kind of audio source
that gets switched on to the analog input of the amplifier.  In many cases
the input to the amplifier is AC coupled.  If there are any leakage currents
in the system that allow the coupling cap to charge up then when the input
is turned on the cap discharges causing the click.  A simple solution to
this is to provide a DC path to ground on the switch side of the cap.  A
high value resistor, 100K, will likely work if this is the source of the
problem.

Tom Dagostino
Teraspeed Labs
13610 SW Harness Lane
Beaverton, OR 97008
503-430-1065
http://www.teraspeed.com
tom@xxxxxxxxxxxxx

Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
401-284-1827

Teraspeed is the registered service mark of
Teraspeed Consulting Group LLC

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx
[mailto:si-list-bounce@xxxxxxxxxxxxx]On Behalf Of Robert Sefton
Sent: Saturday, February 12, 2005 9:37 AM
To: adeelmk@xxxxxxxxxxx; si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Re: Switch On & Switch Off Clicks due to Amplifier
noise


Adeel -

What is the source of the sound you're playing back? If it's coming out of
an audio DAC and you're playing a stored audio clip through the DAC, then
your problem may be at the DAC input. I've seen circuits like this where the
input to the DAC is binary 0 before the track, transitions sharply at the
start of the clip (the first click you hear), then transitions sharply back
to 0 at the end of the track (the second click).

Just take a close look at these starting and ending transitions. If the
input to the DAC is unsigned, then "audio zero" whould be mid-range (e.g.,
0x8000 for 16-bit samples), not 0x0000. Whatever the case, if you're feeding
audio clips into a DAC you need to smooth out the DAC input. Consider it a
crude digital anti-aliasing filter.

Good luck,
Bob S.

-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] On
Behalf Of Adeel Malik
Sent: Saturday, February 12, 2005 2:38 AM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] Switch On & Switch Off Clicks due to Amplifier noise

Hi All,
            In my application I am using a Stereo quality Audio Amplifier
(TDA 7057A - Philips) for Sound Playback. I have kept the analog supply of
amplifier isolated from the rest of the system along with the addition of
high frequency by-pass capacitors as specified by the vendor. When I switch
on the sound, a noticeable 'click' is heard before the playing of the
message. The same 'click' is also heard after the sound playback.

I suspect that this may be due to some amplifier phenomenon.  Have someone
experienced this issue before while designing with audio amplifiers.?. If
yes, then how to resolve it ?.

Thanks and Regards,
Adeel Malik


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