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Chip Amps Amplifiers based on integrated circuits

Power on/off 'Pop'
Power on/off 'Pop'
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Old 6th July 2018, 03:27 PM   #11
tomchr is offline tomchr  Canada
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+1 for the X capacitor. Also note that the C usually has an R in series to tame the Q. 10-47 nF + 39 Ω seems common.

Tom
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Old 6th July 2018, 04:37 PM   #12
Fast Eddie D is offline Fast Eddie D  United States
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Quote:
Originally Posted by tomchr View Post
Even with a mute circuit in place, you can still have a small pop due to the charge injection of the switch or due to differences in DC offset between the source and the load. Those are obviously much, much lower than the typical rail-to-rail pops you get without the mute circuit, so the mute circuit does offer a significant improvement.
That's true. There is a tiny "tick" noise audible when you turn it off. It is only audible with no program.

I think that could be eliminated with a more elaborate control circuit. I also think it's not even worth it.

Quote:
It's important to use an X capacitor which is rated for across the line.
http://www.kemet.com/Lists/Filestore...aRFIandSMD.pdf
I knew that and forgot it. Lame excuse. I do have some of those X capacitors because I always save them when I strip a chassis.
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Old 12th July 2018, 07:47 PM   #13
Autotat is offline Autotat  United Kingdom
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Thank you for the replies, your help is much appreciated. Sorry I haven't been back sooner but I have been busy with work.

Having taken the lid off the pre-amp and had a look around it already has a capacitor across the on/off switch.

Following the advice of an electrician at work I have try'd powering onand off with first the lower output part of the PSU for the control circuits and then the higher output for the pre-amp stage.

With the lower voltage side unplugged the pop was stll there but with the higher output unplugged there was no pop.

I will try to post up some photos when I dig them out.

Cheers.
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Old 12th July 2018, 08:49 PM   #14
CharlieLaub is offline CharlieLaub  United States
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Just a thought here on a possible source for this problem:

You mentioned that when you replaced the offending preamp with another (different MFG) unit the pop on power-down went away. One possible cause that I did not see mentioned is a single-ended, AC-coupled gain stage in the preamp. In that circuit, a coupling cap is used to remove/filter the DC bias voltage from the output. If the power supply rail collapses when the AC mains is shut off, you will reach a point in time where the bias voltage is rapidly falling back to zero. The output filter (just a cap, so first order) handles this like a step change and there IS a significant transient event that appears on the output, possibly a couple of volts at Vmax. This might be your "pop", since that is just passed on to the amps (which are still "on'). One solution would be to add a bunch of capacitance to the preamp power supply, so that you have some time (e.g. 10 sec or more) before the supply collapses to turn off the amps, or to trigger muting (speaker) relays after the amps that will disconnect the speakers from amps.
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Old 12th July 2018, 09:29 PM   #15
Autotat is offline Autotat  United Kingdom
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That is an idea but I would have to have some way of automatically decoupling the output such as the relays you mention as the family won't necessarily turn everything off.

I have dug out some photos but it appears that I need to host them somewhere and link to them for them to appear here. Unless I have missed something.
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Old 13th July 2018, 01:26 AM   #16
PRR is offline PRR  United States
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> it appears that I need to host them somewhere and link to them for them to appear here. Unless I have missed something.

Start reply, Go Advanced, there is an Attachments system.
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Old 13th July 2018, 07:21 AM   #17
Mooly is offline Mooly  United Kingdom
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Power on/off 'Pop'
Like this:
How to attach images to your posts.
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Old 13th July 2018, 09:58 PM   #18
Autotat is offline Autotat  United Kingdom
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Aha, well in that case:

Please note that the manual is for the intergrated version of this amp so there may be some differences.
Attached Images
File Type: jpg C500 c.jpg (88.0 KB, 61 views)
File Type: jpg C500 h.jpg (63.7 KB, 59 views)
File Type: jpg C500 d.jpg (61.3 KB, 59 views)
File Type: jpg C500 e.jpg (67.4 KB, 59 views)
File Type: jpg C500 f.jpg (70.1 KB, 58 views)
Attached Files
File Type: pdf CambridgeA500intsch.pdf (572.2 KB, 4 views)

Last edited by Autotat; 13th July 2018 at 10:03 PM.
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Old 13th July 2018, 11:41 PM   #19
CharlieLaub is offline CharlieLaub  United States
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Why don't you just go and find an ADCOM ACE-515 e.g. on Ebay. Turns on and off preamps and power amps in sequence with a delay that completely avoids the problem you are experiences. It has a "power switch" of its own, so you tell all the others in the household "USE THIS SWITCH ONLY" and all will be good.
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Old 14th July 2018, 12:11 PM   #20
Autotat is offline Autotat  United Kingdom
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I'd never even heard of such a thing but by chance that would actually solve two issues as then nothing would be left on (or off). I take it that there are 240V versions for over here in the UK.
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