Amp making a loud screeching sound while being turned on. How do I fix this?

[DustinNielsen]

So I finished installing my Amp 6 Basic a month or so ago. Everything was fine for a while. Now when I turn on the amp, it makes this horrible, loud screeching sound, similar to nails on a chalk board, but much louder. It used to make the thumping sound, when turned on, but that didnt seem like much of a problem.

It will only make this sound if it is plugged into an MP3 player/source. So say the amp is OFF, then plugged into an iPod, and then turned on, it will make the sound. Also, if the amp is not plugged into a source, like an ipod, it wont make a sound while it is turned on, but if I then plug it into a source while it is still on, it will make the sound while the plug is being inserted to the iPod.

Some facts about it that may help narrow down the reason why, although I cannot figure it out myself.

--The amp has been charged with an insufficient AC-DC adaptor, it is rated at only 200 mA MAX.
--The amp is used to power a boombox, so the amp is permanently installed to a 12V, 5 Amp hour SLA battery.
--The amp has an on/off power switch wired to it, but it does not go to the mute function (there is no mute function, the way it is wired), instead the switch cuts the power directly, so the switch is in between the battery and the positive terminal on the amp. It is worth noting that the amp used to make the thumping sound when turned on, since there was no mute function, but now it is just a very loud screeching sound, with no thump.

The only thing that I can think of is maybe the battery is not charging fully? Also, when I run the amp now, it cannot play at full volume without the sound going in and out of play, every few seconds.

Also, is there any chance that by not having the mute function working, that the surge of power directly to the amp may have screwed something up?

Any help would be very much appreciated, this is my second amp that I have had problems with, I am hoping that I don't have to buy another....

Dustin

[krilli]

That kind of sounds like the noise I got when my amp was either overheating or had an input overload. I'd say that there is something funny with the input - some short circuit somewhere I'd think.

Do you have another power supply to test with? You probably have a 12V 1-2A switcher brick around the house ... it'd be good to eliminate the battery + charger rig for experimentation.

[V-bro]

This problem I've had a few times as well. It's the switching frequency you hear, for some reason lowered to audible frequencies. Often the reason is indeed both shortage of current of the power supply combined with input overload. Sometimes the shortage of PS current is not due to a bad PS, but due to a bad solder or in worst case a damaged TA2020 chip... The shortage can also be caused by a short, leaving too little juice for the poor little amp to thrive on...

Do as Krilli said, change the PS and experiment some more with the source. Best would be to monitor the current consumption in the mean while....

An SLA should provide endless current.....

[Scratchy]

As per the Assembly Instructions here:
http://www.41hz.com/forums/content.p...I-AMP__6-Basic

Powering up for the first time
Always de-power the amp before doing any work! Never connect or disconnect signal connector or speaker cables with power connected as this can damage the amp. The Sleep/mute jumpers are the ONLY exception.

I've found this applies to all my Tripath amps.
I was getting that sound when powering off my pre-amp and leaving my AMP6 unmuted. I think it was kind of like a floating input.
You are asking for trouble by plugging and unplugging the inputs while the amp is powered up and unmuted...

[DustinNielsen]

As per the Assembly Instructions here:
http://www.41hz.com/forums/content.p...I-AMP__6-Basic

You are asking for trouble by plugging and unplugging the inputs while the amp is powered up and unmuted...

Do you think that I have ruined the amp at this point, or is this more of a slap on the wrist, and I can go back to having fun once I have figured out how to stop the screeching sound?

[Scratchy]

The amp is more than likely still OK.
This could also be due to some cold solder joints on the input circuitry as others have mentioned.

--The amp has been charged with an insufficient AC-DC adaptor, it is rated at only 200 mA MAX.

It sounds like you are just using an ordinary Wallwart to charge the SLA battery, which is not ideal.
It's better to use a proper charger for these if you want full output and rated charging cycles.
Normally the charging voltage can start out as high as 14.2 volts and tapers off to a float voltage of 13.75V.

Do a load test on your battery (turn up the volume and measure the voltage on the battery when the sound gets garbled).
I'm guessing if you are "charging" it with only 12VDC, the SLA has less than 1/4 capacity, even after 24 hours of charging.
This may be your problem.

[Haggis Basher]

The screeching sound at on / off, or when changing inputs etc. can be removed by fitting a mute switch and using it appropriately. It is more convenient to also fit an LED (to light) when the amp is muted. If you need further reassurances, see my recent posts and accurate replies from the mentors about my difficulties in attempting to use full switching of inputs via a “break before make” switch; on the thread “how to build your first Truepath”. If you want further background information, you could also search the Forum for intriguing solutions to the on / off screech, such as Audiophool’s (and if I remember rightly V-bro’s) use of relay breakers, which also act as speaker protection.

These screeching noises are usually due to the way the Tripath chips operate, and in my case, it was not due to poor soldering or other causes, more due to my stupidity and lack of knowledge! If the problem persists after fitting the mute switch then look elsewhere. If these nasty noises are due to the lack of a mute switch, the only damage caused by the screeches, would be on a long term basis to the speakers, and in your case unlikely.

Undoubtedly, your amplifier is clagging out, due to lack of juice. Buy a proper charger for the battery, charge the battery up disconnected from your amplifier, re-connect the fully charged battery, and you will be delighted with the super sound from the amp.

These are my interpretations from coping with similar problems, from a beginners perspective. Please ignore my short manner, as other, less enjoyable events are pressing me today.

Please post your results.

Ken.