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Old 27th May 2015, 08:45 AM   #1
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Default Amp shutdown 'plop'

Hi All,

Just finished a P3A which sounds wonderful. It is equipped with a uPC1237 + relays soft start & DC protect so startup is nice and quiet.
At shutdown however a loud 'plop' is often heard in the speakers.
How can I avoid that? Thanks.

Jacques

Last edited by jacques antoine; 28th May 2015 at 07:59 AM.
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Old 27th May 2015, 06:09 PM   #2
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As well as Dc protection, uPC1237 is supposed to provide turn-on delay to prevent a "plop" when turning on some amplifiers and instantaneous turn off to prevent that turn-off "plop" as well. Unless the relay does drop out immediately, you possibly could still hear that plop.

According to Rod Elliott's notes on the P3a, it really doesn't need an output relay because it makes very little noise by design - if you build as specified. So it's surprising you hear a "plop" when you turn off, even with a relay fitted. I have set up 3 of these without relays and not heard a whisper on one and only faint clicks on the other 2, as I recall.

You need to review what is wrong with that protection relay kit or more likely, just the way it's timing circuit is set up, assuming this is one of a number of kits of your own choice for the features you list. Have you tested the amplifier as suggested, with no relay protection or soft turn-on? The latter is really unnecessary for a small amp like this anyway.
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Old 27th May 2015, 06:16 PM   #3
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How about correcting the mistakes you have done ?

uPC1237 is supposed to sense AC loss or power down and very quickly disconnect the load from the amplifier to avoid thumps and pops that might occur in either condition .

If the kit you used doesn't have this function means that this is a bad implementation of uPC1237 circuit ..

But here is the funny part !!!
P3A if made correctly doesn't produce start up or shut down noises meaning that if yours is producing something then there is some construction error in your construction .
Obviously if you have a preamp together in the same chassis thumps and pops might be produced by the preamp ....
Also uPC1237 might be powered by the wrong power supply to behave like that .

Let us know more pictures schematics of your project will be good also

Kind regards
Sakis
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Old 27th May 2015, 06:17 PM   #4
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Ian we hit the POST button in the same time .... How are you these days ?
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Old 27th May 2015, 06:21 PM   #5
sangram is offline sangram  India
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I agree with Ian. I've built a few amps derived from the P3A (using modern transistors and some changed parts to account for those) and it is almost totally silent at power-up and power down.

I do have one implementation that makes a loud pop and a dying squeal (not good!!) and that does need a fix. This is because of an active crossover output not shutting down properly and sending a lot of garbage into the input. I don't bother much as the woofer does not seem to mind it too much.

I would check if you still had the pop with the input shorted, would be surprised if it was the case.

The 1237 needs an AC detect to disconnect the relay almost immediately with power-down. Look at the datasheet, a few components are needed and the relay will shut down almost instantly as you power-off.
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Old 27th May 2015, 07:17 PM   #6
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Quote:
Originally Posted by east electronics View Post
How about correcting the mistakes you have done ?

uPC1237 is supposed to sense AC loss or power down and very quickly disconnect the load from the amplifier to avoid thumps and pops that might occur in either condition .

If the kit you used doesn't have this function means that this is a bad implementation of uPC1237 circuit ..

But here is the funny part !!!
P3A if made correctly doesn't produce start up or shut down noises meaning that if yours is producing something then there is some construction error in your construction .
Obviously if you have a preamp together in the same chassis thumps and pops might be produced by the preamp ....
Also uPC1237 might be powered by the wrong power supply to behave like that .

Let us know more pictures schematics of your project will be good also

Kind regards
Sakis
Hi Sakis,

I have used this implementation form BuildAudioAmps but added a transformer on the board: here's a pic
Attached Images
File Type: png uPC.png (423.2 KB, 104 views)
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Old 27th May 2015, 07:35 PM   #7
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Quote:
Originally Posted by sangram View Post
I agree with Ian. I've built a few amps derived from the P3A (using modern transistors and some changed parts to account for those) and it is almost totally silent at power-up and power down.

I do have one implementation that makes a loud pop and a dying squeal (not good!!) and that does need a fix. This is because of an active crossover output not shutting down properly and sending a lot of garbage into the input. I don't bother much as the woofer does not seem to mind it too much.

I would check if you still had the pop with the input shorted, would be surprised if it was the case.

The 1237 needs an AC detect to disconnect the relay almost immediately with power-down. Look at the datasheet, a few components are needed and the relay will shut down almost instantly as you power-off.
Hi Sangram,

The circuit I used has an AC detect but I noticed that the resistor I used connected to uPC pin 4 is higher than recommended on the datasheet (15K instead of 4K @12V x 0.7071) could that be the problem?

Last edited by jacques antoine; 27th May 2015 at 07:54 PM. Reason: Volt r.m.s !
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Old 27th May 2015, 07:45 PM   #8
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Quote:
Originally Posted by Ian Finch View Post
As well as Dc protection, uPC1237 is supposed to provide turn-on delay to prevent a "plop" when turning on some amplifiers and instantaneous turn off to prevent that turn-off "plop" as well. Unless the relay does drop out immediately, you possibly could still hear that plop.

According to Rod Elliott's notes on the P3a, it really doesn't need an output relay because it makes very little noise by design - if you build as specified. So it's surprising you hear a "plop" when you turn off, even with a relay fitted. I have set up 3 of these without relays and not heard a whisper on one and only faint clicks on the other 2, as I recall.

You need to review what is wrong with that protection relay kit or more likely, just the way it's timing circuit is set up, assuming this is one of a number of kits of your own choice for the features you list. Have you tested the amplifier as suggested, with no relay protection or soft turn-on? The latter is really unnecessary for a small amp like this anyway.
Hi Ian,

I added the uPC to protect my speakers against DC in case I want to abuse the system . Soft start came as a bonus....
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Old 27th May 2015, 09:00 PM   #9
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Quote:
Originally Posted by jacques antoine View Post
....I added the uPC to protect my speakers against DC in case I want to abuse the system . Soft start came as a bonus....
Sure, understood but to get the issue of your opening post, does the amplifier work OK without those features and or as Sangram suggested, with the input simply shorted or say, shunted with a 1k resistor?
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Old 28th May 2015, 06:43 AM   #10
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Quote:
Originally Posted by Ian Finch View Post
Sure, understood but to get the issue of your opening post, does the amplifier work OK without those features and or as Sangram suggested, with the input simply shorted or say, shunted with a 1k resistor?
Both P3A channels do work 'as advertised' without the uPC board. Very likely the board is faulty, not the P3A. Sorry about the misleading thread.

Jacques
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