124 replies to this topic

[Brer Frog]

Here are a few more photos which show the output of the PAM8610. One channel is connected to a speaker & the other connected to a 7 ohm dummy load to which the oscilloscope was connected.

First one shows the amp’s output with the volume at zero.

 IMG_2882C.jpg   110.5KB   12 downloads

 

Second one is with a 1KHz input signal & both the PC and amp volume at 50%. Obviously not pretty. Even if the noise was not there it still does not look like a sine wave.

 IMG_2883C.jpg   111.98KB   11 downloads

 

 

[rickh]

Here are a few more photos which show the output of the PAM8610. One channel is connected to a speaker & the other connected to a 7 ohm dummy load to which the oscilloscope was connected.

First one shows the amp’s output with the volume at zero.

IMG_2882C.jpg

 

Second one is with a 1KHz input signal & both the PC and amp volume at 50%. Obviously not pretty. Even if the noise was not there it still does not look like a sine wave.

IMG_2883C.jpg

 

 

I was not able to cobble a suitable filter, this is what I got using a sig gen with 1kHz sine wave, ~1%[email protected].  The PAM 8610 amplifier volume is at half volume. 

Notice all the HF garbage, but as you can see the sine wave is there.  As I increased volume I noticed some distortion just before the the device started to clip.  If I can get a suitable filter I might be able to make a suitable noise measurement.  BTW- This is one of the few Class D amps I have seen that does not have any LP filters, making it painful to do a real scope measurement.

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[Brer Frog]

Not having a LP filter may make it difficult to do a real scope measurement. But doesn't that also mean the HF garbage gets passed to the speakers? Is it just to high to be heard as any form of noise?

 

That being said, all that noise on the 12V supply on the circuit board can't be good. Since it shows up on the scope using the same time base as used to display a 1KHz signal, wouldn't that mean the noise, at least some of it, is not that HF? What am I overlooking?

 

If the HF noise is not responsible for messing it up the 1KHz signal then what could be the problem?

[rickh]

Not having a LP filter may make it difficult to do a real scope measurement. But doesn't that also mean the HF garbage gets passed to the speakers? Is it just to high to be heard as any form of noise?

 

That being said, all that noise on the 12V supply on the circuit board can't be good. Since it shows up on the scope using the same time base as used to display a 1KHz signal, wouldn't that mean the noise, at least some of it, is not that HF? What am I overlooking?

 

If the HF noise is not responsible for messing it up the 1KHz signal then what could be the problem?

A normal speaker is purely an inductive load (~430uH).  Inductance acts as an open for HF, so in theory it should not have much affect (saturation) on the speaker.  Capacitors are the opposite of inductors, as they allow the passage of HF and act as an open to DC and lower frequencies.  As mentioned, I did see some distortion prior to clipping (or compression), but will need to build a suitable filter and resistive shunt (CVR) before I can make quantitative measurement.  So, I don't know what the problem is at this point.   BTW- I do have an FFT function on my scope so I can make a spectral measurement on harmonics.  

Attached Files

•  FFT of sig gen.jpg   118.93KB   6 downloads

[Brer Frog]

I am measuring across a 7 ohm resistor. When looking at the signal across a speaker it was really a mess!

 

Could the wall wart power supply be part of the problem, even when the volume control is at zero or very low? When not connected the wall wart looks pretty good. IOW could its inductance or capacitance be interacting with the amplifier?

[rickh]

I am measuring across a 7 ohm resistor. When looking at the signal across a speaker it was really a mess!

 

Could the wall wart power supply be part of the problem, even when the volume control is at zero or very low? When not connected the wall wart looks pretty good. IOW could its inductance or capacitance be interacting with the amplifier?

Mike, 

 

No, there is a big filter cap on that amp.  I am going to try a new test setup tonight using a current viewing resistor (which I am going to attach the scope to) in series with the speaker.  The coil in the speaker will not pass the PWM modulation, so it will not produce any current across the resistor.  I should only see the modulation.  Lets see if that works....... 

[Brer Frog]

Rick,

The amp, speaker, scope, & wall wart are all kind of clustered around the PC.

Short version: Over the last few days I noticed that sometimes it appeared I was shorting out the power to the amplifier when connecting the scope’s probe to the amp. First thought was that I just was not careful. But it happened several times.

Turns out the scope’s ground was the problem. The scope can be, and is, powered by a step-up converter which is made for the scope.

I’ve been using a PC USB port to power the converter. Consequently this makes the USB ground the same as scope’s probe ground. Depending on how the scope is connected it could cause a short.

So I connected a LiPo battery to the converter in order to isolate the scope’s ground. Amazingly this dramatically affected the amplifier’s output signal, at least as viewed on the scope.

The first photo is the 1KHz signal taken across a 7.5 ohm dummy load. The PC & amp volume are both at 50% and the LiPo battery is powering the converter. It looks more like a sine wave than all those other photos I’ve taken.

 

The second photo is using the USB to power the scope’s converter. Everything else remained the same as above. This shows the typical crappy sine wave that I was previously getting.

 

 IMG_2887C.jpg   138.16KB   7 downloads     IMG_2889C.jpg   143.17KB   7 downloads

Still not sure what is going on. IOW why does the amp sound harsh? Is it noise or distortion?

And why would the scope’s power source affect its displayed signal? The LiPo battery may be a perfect DC supply, but it and the USB power were fed into the same step-up converter. Is it a ground problem?
 

 

[rickh]

Mike,

I don't have the components handy to build a suitable filter, but i have played with the amp some more and discovered that there are step transitions in amplitude where I detect more distortion than others.  I encountered a total of three of these transitions during the full volume excursion, I must have missed this on my initial evaluation.  Anyway, glad you were able to find the problem with your o'scope.  BTW- If you have a math function of Channel A and B you can make a differential measurement.  

[Brer Frog]

Wish I knew why there was a problem with the o'scope when using one power supply vs another for it.

 

Could noise on the amplifier have been fed back to the o'scope because of the common ground between them?

 

No Channel A and B, there is only a single channel on this cheap scope.

[rickh]

Wish I knew why there was a problem with the o'scope when using one power supply vs another for it.

 

Could noise on the amplifier have been fed back to the o'scope because of the common ground between them?

 

No Channel A and B, there is only a single channel on this cheap scope.

The inexpensive scopes have common mode issues which limits their use.  However, if the instrument is independent from any other interface (besides a power supply that should be isolated) it should not have any issue if using a single channel.   BTW- I just purchased a DROK TDA7297 (TDA7297 15W+15W) amplifier and should have a review by mid October.  The amp was only $9 USD. 

[Brer Frog]

The PAM8610 with the 2" speakers sound OK when playing VP. It just sounds harsh when playing music.As mentioned earlier, it just may be that the new 2" speakers are delivering a wider & higher range of sounds than I'm used to hearing when using my old PC desktop speakers with built-in amp. I don't know. But when I saw that o'scope display it was an area of concern.

 

That being said, you mentioned using the PAM8610 to power the exciters for haptic feedback which is my intent. It's just temporarily connected to the backbox speakers to try it out.

 

I'd try the TPA3116D2 2.1 amplifier but at the moment don't have a way of connecting its RCA input jacks to the PC.

[Brer Frog]

I found an audio cable to connect the PC to the RCA jacks of the TPA3116D2 2.1 amplifier. Connected the speakers & grabbed my 19V Chromebook power supply. But the 19V supply has a real small power plug & won’t fit the amplifier. Bummer.

The amplifier listing does say it works with 12V - 25V so I powered up the old 12V wall wart. I was not expecting the loudest volume but figured it should give me something. The 12V plug won’t fit the amplifier. Looks like the center pin of the amplifier’s jack is just a tiny bit larger than the center pin of the PAM8610’s power jack. IOW the wall wart fits one amplifier but not the other. And both supposedly work with 12V.

Are there really different size 12V jacks & plugs, or do I have a defect/reject?

 

Update -

Googled and it appears these can be either 2.1 mm or 2.5mm ID. Guess I've just been lucky because I have a few power supplies & never had a problem.

Edited by Brer Frog, 27 September 2017 - 12:03 AM.

[rickh]

I found an audio cable to connect the PC to the RCA jacks of the TPA3116D2 2.1 amplifier. Connected the speakers & grabbed my 19V Chromebook power supply. But the 19V supply has a real small power plug & won’t fit the amplifier. Bummer.

The amplifier listing does say it works with 12V - 25V so I powered up the old 12V wall wart. I was not expecting the loudest volume but figured it should give me something. The 12V plug won’t fit the amplifier. Looks like the center pin of the amplifier’s jack is just a tiny bit larger than the center pin of the PAM8610’s power jack. IOW the wall wart fits one amplifier but not the other. And both supposedly work with 12V.

Are there really different size 12V jacks & plugs, or do I have a defect/reject?

 

Update -

Googled and it appears these can be either 2.1 mm or 2.5mm ID. Guess I've just been lucky because I have a few power supplies & never had a problem.

Mike,

 

There are loose standards governing these connectors,  I think that there are at least 5 types, perhaps more.  Generally these connectors sizes increase in proportion to the power requirements.  More importantly is the polarity, as this will normally release the magic smoke that makes your device work. 

[xantari]

Hows the good, better, best list coming along? Care to share a preview?

[rickh]

Hows the good, better, best list coming along? Care to share a preview?

I shared part of the review already in a previous post, but I am retesting a couple of amplifiers and adding yet another to my collection. 

 

Regards,

Rick

[xantari]

Thanks Rick. Since VPX 10.4 now includes surround sound capabilities to drive exciters for "poor mans DOF". What do you think about the Sure Electronics AA-AB34181 6x100W TDA7498 Class-D Amplifier Board available on amazon?

[Brer Frog]

What’s considered acceptable ripple voltage on a wall wart power supply?

I just got this 12V, 3A supply from Amazon. It had a lot of reviews & a decent rating.
https://www.amazon.c...0?ie=UTF8&psc=1

The first thing I did was look at the output with the oscilloscope & it had a 26mV p-p sawtooth waveform which I thought this was quite high. (First photo)

I then plugged it into the PAM8610 amplifier (no speakers were connected} to see how that load affected the ripple voltage. That reduced the ripple voltage to 8mV and frequency was jumping all over from about 100Hz to 400Hz. (Second photo)

Is this acceptable? My old 12V, 1250mA supply was a lot cleaner with no load.

 

 IMG_2913C_new 12V PS.jpg   112.24KB   7 downloads     IMG_2915C_New 12V PS on amp.jpg   114.79KB   7 downloads

[Brer Frog]

I spent the last few hours troubleshooting.

 

Connected the new 12V 3A power supply & speakers to the PAM8610 amp. I played some pinball & music & thought it sounded OK. Then all of sudden the amp started making a loud hum. The o'scope showed the 3A supply was OK. Connected the old 1.25A supply & no problem. WTF.

 

Unplugged the audio cable & no hum - until I touched the conductor's on the amp's audio jack. Appeared to be ground problem. If I grounded the amp's audio jack ground terminal the hum went away. What the heck changed?

 

The old power supply had a 3-prong AC plug. It's ground was continuous all the way to the 12V plug that in turn grounded the amp

 

The new 3A supply has a 2-prong AC plug & therefore it did not provide a ground connection to the amp.

 

But the amp should be grounded through the audio cable. Turns out the new audio cable has an intermittent ground conductor. This was no problem when using the old power supply because it provided a ground. Never would have known the audio cable was defective if I kept using the old wall wart power supply.

 

Now to get a another audio cable.

[rickh]

Thanks Rick. Since VPX 10.4 now includes surround sound capabilities to drive exciters for "poor mans DOF". What do you think about the Sure Electronics AA-AB34181 6x100W TDA7498 Class-D Amplifier Board available on amazon?

Xantari,  I'm shooting from the hip on this one, as I only reviewed the white papers on the TDA7498.  The amplifier chip appears to be a real monster!  Very high power output with low THD.   However, this beast will require a high voltage power source to bring out its full potential.  As with all class D amps with filters, the output impedance might be limited to 6 or 8 ohms.  4 ohm speakers may lower the performance, but not drastically.    

I spent the last few hours troubleshooting.

 

Connected the new 12V 3A power supply & speakers to the PAM8610 amp. I played some pinball & music & thought it sounded OK. Then all of sudden the amp started making a loud hum. The o'scope showed the 3A supply was OK. Connected the old 1.25A supply & no problem. WTF.

 

Unplugged the audio cable & no hum - until I touched the conductor's on the amp's audio jack. Appeared to be ground problem. If I grounded the amp's audio jack ground terminal the hum went away. What the heck changed?

 

The old power supply had a 3-prong AC plug. It's ground was continuous all the way to the 12V plug that in turn grounded the amp

 

The new 3A supply has a 2-prong AC plug & therefore it did not provide a ground connection to the amp.

 

But the amp should be grounded through the audio cable. Turns out the new audio cable has an intermittent ground conductor. This was no problem when using the old power supply because it provided a ground. Never would have known the audio cable was defective if I kept using the old wall wart power supply.

 

Now to get a another audio cable.

Mike,

I had a similar problem when I was scoping an amplifier. I traced it to a defective BNC cable.  It was driving me nuts!

What’s considered acceptable ripple voltage on a wall wart power supply?

I just got this 12V, 3A supply from Amazon. It had a lot of reviews & a decent rating.
https://www.amazon.c...0?ie=UTF8&psc=1

The first thing I did was look at the output with the oscilloscope & it had a 26mV p-p sawtooth waveform which I thought this was quite high. (First photo)

I then plugged it into the PAM8610 amplifier (no speakers were connected} to see how that load affected the ripple voltage. That reduced the ripple voltage to 8mV and frequency was jumping all over from about 100Hz to 400Hz. (Second photo)

Is this acceptable? My old 12V, 1250mA supply was a lot cleaner with no load.

 

IMG_2913C_new 12V PS.jpg    IMG_2915C_New 12V PS on amp.jpg

Mike,  the ripple shows a frequency of ~220kHz.  I didn't think your scope went this high.  However, I think the filter cap on the amplifier might be able to filter that noise out.  Regardless, I don't know if this ripple would be a detriment or not.

[Brer Frog]

Rick,

Initially I also thought it was ~220KHZ, but it's only 220Hz.