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Recommendation for 5-10W amp.
Recommendation for 5-10W amp.
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Old 16th October 2014, 11:34 PM   #271
dobrivoje is offline dobrivoje  Serbia
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You can get rid of thump if you use standard power supply with transformer, rectifier and cap multiplier.
Look at schematic. Also Juma, also single supply. I've made it and there is no any thump.
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Old 16th October 2014, 11:45 PM   #272
e_fortier is online now e_fortier  Canada
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Recommendation for 5-10W amp.
I am already aware of this, I'm looking for a solution with my current set-up. I do not want to rebuilt the amp, it's already finished. Your amp is different than the one I have built.

Why does it work with closing SW1 and not with closing SW2 is the question. Very tough question to answer, I know.

Thanks,
Eric
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Old 16th October 2014, 11:54 PM   #273
Zen Mod is offline Zen Mod  Serbia
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Recommendation for 5-10W amp.
what I meant is - put switch in mains
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Old 17th October 2014, 12:01 AM   #274
Bigun is offline Bigun  Canada
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Recommendation for 5-10W amp.
I would hazard that your amplifier power rails collapse too quickly compared with the supply to the protection board - so the protection board doesn't cut off the speaker on power down before the amplifier rails collapse.

If this is the correct diagnosis then one option is to reverse engineer your protection circuit - that chip has a pin that detects when the power goes off so maybe you can have that pin monitor the amplifier power rails directly ?

Another options is to slow down the collapse of the amplifier power rails - not sure on your options there other than a lot more rail capacitance, which your SMPS may complain about on power-up. And you'll need a lot of capacitance for a Class A amplifier - yeah, scrap that thought.

Actually, I'm surprised the protection circuit doesn't cut off faster - is it working properly ?
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Last edited by Bigun; 17th October 2014 at 12:03 AM.
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Old 17th October 2014, 12:02 AM   #275
propitious is offline propitious  United States
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Recommendation for 5-10W amp.
Quote:
Originally Posted by e_fortier View Post
I am already aware of this, I'm looking for a solution with my current set-up. I do not want to rebuilt the amp, it's already finished. Your amp is different than the one I have built.

Why does it work with closing SW1 and not with closing SW2 is the question. Very tough question to answer, I know.

Thanks,
Eric
Zen Mod gave the answer. The 12 vac is not the lowest current loop. It has 10 times the current of the 120 vac feeding it. You want to switch the 120 vac side (of both PS's) like you are doing with the power strip switch. If you do not like that switch, make your own in a setup where you can reach it. BTW, one way to not get a turn on thump with the standard ACA is to unplug the PS from the wall outlet, instead of using the switch on the DC side. But, of course, the outlet might wear out eventually.
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Old 17th October 2014, 12:25 AM   #276
dobrivoje is offline dobrivoje  Serbia
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Sorry, Eric, I was not clear enough. Cap multiplier slowly rises voltage unless capacitor gets full.
Your smps also has capacitor at the output. If you turn on SW1 after SW2, voltage rises until capacitor gets full. In this case time is much shorter compared with cap multiplier due to much higher frequency and smaller capacitance.
If you turn on SW2 after SW1, you don't have voltage rise, you get nominal voltage at the moment when you connect load, so you get huge voltage peak. That peak goes thru amp to speaker and you hear thump.
Now, when you turn off your amp you have the same situation, but reversed. Voltage goes from nominal to zero, capacitor gets empty. If you turn off SW2, you divide amp from capacitor, voltage on amp goes to zero in one cycle, again you get voltage peak, only reversed, and, do I need to say, thump.
Edit: While I was writing, smarter people already answered.

Last edited by dobrivoje; 17th October 2014 at 12:32 AM.
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Old 17th October 2014, 12:51 AM   #277
e_fortier is online now e_fortier  Canada
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Recommendation for 5-10W amp.
Quote:
Originally Posted by Bigun View Post
I would hazard that your amplifier power rails collapse too quickly compared with the supply to the protection board - so the protection board doesn't cut off the speaker on power down before the amplifier rails collapse.

If this is the correct diagnosis then one option is to reverse engineer your protection circuit - that chip has a pin that detects when the power goes off so maybe you can have that pin monitor the amplifier power rails directly ?

Another options is to slow down the collapse of the amplifier power rails - not sure on your options there other than a lot more rail capacitance, which your SMPS may complain about on power-up. And you'll need a lot of capacitance for a Class A amplifier - yeah, scrap that thought.

Actually, I'm surprised the protection circuit doesn't cut off faster - is it working properly ?
BINGO !! Problem solved. You were correct, I simply added a 6800uF, 35V cap across the 24Vdc and now everything is great, no more pop of any kind. I'm thrilled !

Thanks to everyone, what a great forum.

Time to go enjoy some music

BR,
Eric
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Old 17th October 2014, 06:36 AM   #278
AndrewT is offline AndrewT  Scotland
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Does the prot IC have an instant OFF facility?
Find it, read up on how to implement it.
Use it.
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