Audio Amplifier Power Issues/ Design Issues PAM8019 - Page 1
Forum section: electronics / beginners

author: onemanonelaptop
author_rank: Contributor
timestamp: October 20, 2023, 11:21:34 am
content: Hi all, hoping someone can help me diagnose a problem i am having with a test circuit.Issue OverviewAudio output is clipping at anything over approximately half the volume. This clipping is accompanied by large drops in voltage (see images later).DetailsAudio IC : PAM 8019https://www.diodes.com/assets/Datasheets/PAM8019.pdfAudio Source : Game Gear handheld console.Speakers : 2 x 8ohm 1WCircuit DiagramI've reverted back to the example application from the datasheet to eliminate any of my own introduced errors.Here is the circuit taken from the datasheet linked aboveTest BoardIncoming Audio and Power SignalsAs these are coming from an existing device (i.e. Sega Game Gear Console) i have to work with what i get and manipulate from there.5V powerAudioThe IssueWhen turned the volume up to about half the amp starts to clip and I am unsure of the cause, when it clips i can see on the scope large voltage drops, if i am reading my scope right thats a 1.4v momentray drop.I can only assume that this drop in voltage when the amp is presumably drawing more current is triggering one of the following:Non Clip Power Limit (NCPL) Function: I doubt it is this as i have left the PL pin floating so should be disabled.Under voltage Protection: this seems more likely, i have left the UVP as no connect, The datasheet is unclear to my untrained eye, but i assume that its default is VDD - 1.2V as its threshold to shutdown.Solving the issueSo my question is ultimately how to solve this issue, before i start throwing components at it i wanted a sense check on a few things.Options:Linear Voltage Regulator: I thought this might help, but driving 5V output from a 5V rail doesn't seem like it will achieve much if anything, but happy to stand corrected if an LDO with high output capactiance could suppress the transient load.Bulk Capacitance: Bank of capactitors on the incoming 5V input to take up the slack?Capacitance at the power pins: I thought of adding another cap in addition to the 0.1uf cap that is decoupling each of the power pins, but not sure if this is the right place or even what value makes sense here.Other unthought of solution... inductor maybeI'm not too proud to admit i am likely lacking in some knowledge here, so a steer in the right direction would be massively appreciated.How can i beef up the existing 5V power rail to cope with the demands of this amp chip.

author: Dan123456
author_rank: Regular Contributor
timestamp: October 20, 2023, 12:19:06 pm
content: You have said you are using 2 8speakers but the first wiring diagram says to use 2 4speakers.Could that be it?It just immediately jumped to my eye as double the resistance and issues above half volume. Sounded logical at a glance

author: onemanonelaptop
author_rank: Contributor
timestamp: October 20, 2023, 12:27:53 pm
content: Quote from: Dan123456 on October 20, 2023, 12:19:06 pmThankyou for the reply.The datasheet seems to imply (again if im reading it correctly) that i can use 4Ohm speakers, just have reduced power as a resultQuoteI will see if i have some 4Ohm speakers around to try though to see what the difference is.

author: CountChocula
author_rank: Unknown
timestamp: October 20, 2023, 12:36:07 pm
content: According to the datasheet, the amplifier can drive ~1.4-1.7W into an 8Ω load (though, at the high end, you're already looking at 10% THD), which means that, at maximum volume, it will want to draw around 400-500mA from the power rail. Do you know if the power supply can provide that much current? You could check by attaching a DC load and checking how the voltage sags as you draw more and more current.If that's the problem, some bulk capacitancemighthelp if you're only experiencing clipping during peaks, but it could also just be that you're asking too much out of the supply. Are you sure that you need all that power? If you don't, you can simply limit the volume to an acceptable range that doesn't cause clipping.—CC

author: Dan123456
author_rank: Regular Contributor
timestamp: October 20, 2023, 12:39:00 pm
content: Quote from: onemanonelaptop on October 20, 2023, 12:27:53 pmNo stress at allI imagine it is probably something else but just noticed that off the bat and thought I’d mention it just in caseThere is nothing worse than spending days diagnosing something only to find it was the simple answer the whole time (happened to me just the other week where I had just forgot to remove a track on a strip board)!

author: CountChocula
author_rank: Unknown
timestamp: October 20, 2023, 12:40:49 pm
content: Oh, also worth checking the signal you're getting in input… if it's too high, you may just be overdriving the amplifier.

author: onemanonelaptop
author_rank: Contributor
timestamp: October 20, 2023, 12:56:05 pm
content: Quote from: CountChocula on October 20, 2023, 12:36:07 pmSo clipping currently starts with the volume at 2.3V on pin 8 which according to the data sheet is7.5dB Gain, Its fairly close to being loud enough, and cutting out the top 10-15 steps of the volume control probably makes some sense thankyou just would like to be able to squeeze some more out of it.Quote from: CountChocula on October 20, 2023, 12:36:07 pmCan you elaborate on this for me? I think id like to run this test but not 100% sure how to go about it.

author: onemanonelaptop
author_rank: Contributor
timestamp: October 20, 2023, 01:04:04 pm
content: Quote from: CountChocula on October 20, 2023, 12:40:49 pmHmm.... the clipping seems to coincide with peak input levels of 200-240mv (again never sure if im reading my new scope right). The datasheet doesnt specificaly state its input sensitiviy

author: CountChocula
author_rank: Unknown
timestamp: October 20, 2023, 01:43:43 pm
content: Quote from: onemanonelaptop on October 20, 2023, 12:56:05 pmAssuming that the problem is with the ability of the supply to provide sufficient current, there are two things you need to worry about: Average power and peak power. The latter is the ability to supply sufficient current within a small amount of time, which is what happens when you have a sudden peak in the output. The former is the ability to provide enough current to power the amplifier over a given period of time.The reason why you want to treat these differently is that you can create a limited supply of current (using bulk caps) that the amplifier can tap into when it needs a to take a sudden gulp from the supply, but you can't rely on that trick for the long term, and so the supply has to be able to provide a baseline amount of current to power your circuit.An electronic load is basically a variable resistor that you can set to accurately draw a given amount of current from a power source. The idea here is that you could apply the same load as your amp and check whether the voltage sags to an unacceptable level, which would indicate that your supply can't satisfy the average power requirements of the circuit.However, it sounds like your experiencing clipping during peaks, so here's a simple experiment that you could try: Connect a large electrolytic cap (say, 220µF or so) between the supply rails of your amplifier chip and see if that helps.

author: onemanonelaptop
author_rank: Contributor
timestamp: October 20, 2023, 02:14:06 pm
content: Quote from: CountChocula on October 20, 2023, 01:43:43 pmThankyou.So adding 1 220uf of the lowest quality caps in the world, while did clean the wave form made no difference.. adding 2 x 220uf electrolytics, did allow me to take the volume up up to 2.1V which is a gain of 8.6db progess for sure... however not sure i can hear the difference between the two levels.

author: onemanonelaptop
author_rank: Contributor
timestamp: October 20, 2023, 04:10:11 pm
content: Looking again at the datasheet it states that the Operating Voltage is 2.8V to 5.5VI am wondering if i would get better results and have less of current issue if i used a voltage regulator to drop it down to 3.3V and run it at the lower voltage...These are what i have to hand....https://www.mouser.co.uk/ProductDetail/Texas-Instruments/LP2985A-33DBVR?qs=paYhMW8qfis6dkQ9X%2FZDvw%3D%3Dhttps://www.mouser.co.uk/ProductDetail/Texas-Instruments/TLV76133DCYR?qs=9vOqFld9vZV5BPjUhjTZUA%3D%3DCant hurt to try at the very least.*Edit:Acutally thinking clearly about this, the current draw will likely increase, so back to the drawingboard....

author: themadhippy
author_rank: Super Contributor
timestamp: October 20, 2023, 04:51:25 pm
content: QuoteNot many do,however the gains given,and you know the output level your after, so work backwards.

author: CountChocula
author_rank: Unknown
timestamp: October 20, 2023, 05:21:01 pm
content: Quote from: onemanonelaptop on October 20, 2023, 02:14:06 pmHmmm… do you have another set of larger/more powerful speakers you can try?

author: onemanonelaptop
author_rank: Contributor
timestamp: October 20, 2023, 05:27:33 pm
content: Quote from: CountChocula on October 20, 2023, 05:21:01 pmI ordered some 4Ohm speakers that will arrive tomorrow, but i'm restricted by the 27mm diameter that fits in the housing of the game gear console.However for testing purposes ill collate a bunch of different speaker options i think and try them out.

author: onemanonelaptop
author_rank: Contributor
timestamp: October 22, 2023, 09:17:53 am
content: So i tried out the 4ohm speakers instead of the 8Ohm and they sound great and are reasonably louder, predictably though the amp clips at exactly the same volume setting on the dial. But we are louder at this point.Next StepsI will limit the allowed volume by adding a resistor to the potentiometer track.I am thinking of adding this to the design, to try and help with sudden peaks of current draw.....I am pretty sure this is a good idea, the extra capacitance seems to help.Questions1. I am thinking of adding an inductor into the mix but am struggling on understanding if it will do anything to help and if so what value it should be if required. Does anyone have any guidance on the benefits of inductors in stabilizing a 5v power rail from current surges?2. I currently have a 0.1uf Decoupling and a 10uf capacitor at each of the power pins, does anyone think that adding some bulk caps at the pins would make a difference considering the bank of capacitors i am already going to add?