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LCDuino on γ3 - strange volume behaviour

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LCDuino on γ3 - strange volume behaviour

Postby Balcmeg » August 15th, 2019, 6:21 pm

My volume control on the Gamma3 has started misbehaving and I wanted to check in to see if anyone could suggest a cause before I start digging. The processor side of things is probably what I have the least knowledge of.

I noticed it yesterday at first - when I change the volume up or down doesn't matter, the digits on the display set to value - let's say -30db. after maybe a second, it then makes a jump of 8 to 20 dB in the same direction as I adjusted the volume and after this big jump, it changes in small er increments, 2, 1, 0.5 dB or so. it's not the same steps every time.

    The issue is not happening every time to change the volume
    The audible volume is also affected so its not only a display issue.
    It does not seem to matter if the volume is adjusted from remote or the volume pot.

I have also been having an issue where the right channel seems to suddenly go quiet, or at least go on a very low volume. I doubt these are related since this right channel situation have been showing up sporadically for several years. Right now it is, as far as I know, working ok again. I tried once by swapping the cables to the power amp, as well as swapping the alpha24 amps and the issue seems to be in the Gamma24 board, because of the intermittent issue of the problem I never got further than that, but I did try to resolder the DAC-chip. When I sorted the volume issue I will get back to this. (I also seem to have a lower volume of the right - but I cannot be certain this is not because of less than ideal speaker placement.)
/Stefan
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LCDuino on γ3 - strange volume behaviour

Postby amb » August 16th, 2019, 5:48 pm

Maybe the motor pot has wiper contact issues (oxidation?). Are you using an Alps RK16812? Also check the wiring to the pot to make sure all electrical contacts are good.

As for your channel imbalance, verify it by playing a mono test tone and measure the AC voltage at the left and right channel outputs at maximum volume (and at other lower settings) to compare. You can download a 16b/48K 1KHz 0dBFS sine WAV file here:

https://www.amb.org/audio/files/sine_mo ... 16b48k.wav

If there is more than a small fraction of a dB of differencce between channels, then you probably have a soldering issue at the DAC chips' analog output pins, the summing resistors, or the α24 boards. To see if the α24s are the problem, you can swap the two board and see if the imbalance changes sides.
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Re: LCDuino on γ3 - strange volume behaviour

Postby Balcmeg » August 17th, 2019, 9:40 pm

HI Ti,
amb wrote:Maybe the motor pot has wiper contact issues (oxidation?). Are you using an Alps RK16812? Also, check the wiring to the pot to make sure all electrical contacts are good.

Will drag it out of the system on Monday and check - which is the best way to check if there are any potentiometer issues?

amb wrote:As for your channel imbalance, verify it by playing a mono test tone and measure the AC voltage at the left and right channel outputs at maximum volume (and at other lower settings) to compare. You can download a 16b/48K 1KHz 0dBFS sine WAV file here:
https://www.amb.org/audio/files/sine_mo ... 16b48k.wav
If there is more than a small fraction of a dB of difference between channels, then you probably have a soldering issue at the DAC chips' analog output pins, the summing resistors, or the α24 boards. To see if the α24s are the problem, you can swap the two board and see if the imbalance changes sides.

Will check this too - I did read your post some while back about you having a similar problem, although judging from the sound, the difference is far more than a fraction of a dB, more like "almost totally no sound", maybe even "no sound" but I need to confirm this first.
Still, will not hurt to try a reflow again - last time I did trace the problem to the DAC board (but no further), but that doesn't mean it what happened now.
/Stefan
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Re: LCDuino on γ3 - strange volume behaviour

Postby amb » August 17th, 2019, 9:57 pm

You can unplug the pot, reconfigure LCDuino-1 to run with no pot in the menu setup, then use the remote control to change the volume. Does the problem occur in this configuration?

If not, then you’ve isolated the problem to either the pot itself, or something related to it.
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Re: LCDuino on γ3 - strange volume behaviour

Postby Balcmeg » August 18th, 2019, 12:30 am

amb wrote:You can unplug the pot, reconfigure LCDuino-1 to run with no pot in the menu setup, then use the remote control to change the volume. Does the problem occur in this configuration?

If not, then you’ve isolated the problem to either the pot itself or something related to it.


Thanks, took me a couple of minutes after posting to realize this.
Anyway, unplugging the pot did the trick and seems to be caused by the connection of the pot to the board, wouldn't be surprised if it is just some oxidation. After plugging it in and out a number of times I can no longer replicate the problem.

Over to the imbalance while I am at it. Good opportunity to try out the Picoscope I just bought.
/Stefan
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Re: LCDuino on γ3 - strange volume behaviour

Postby Balcmeg » August 18th, 2019, 1:06 am

Balcmeg wrote:HI Ti,
amb wrote:Maybe the motor pot has wiper contact issues (oxidation?). Are you using an Alps RK16812? Also, check the wiring to the pot to make sure all electrical contacts are good.

Will drag it out of the system on Monday and check - which is the best way to check if there are any potentiometer issues?

Something new happened, On the left, I now measure over 40Vpp, with the volume set to 0dB, while the right channel show 5.615Vpp. Switching the a24 give the same results, and I can also confirm that both a24 give 5.615Vpp when connected to right channel.
The previous issue must have been caused by the DAC unit.
EDIT: After putting back the a24, I couldn't get a good measure. I removed them again and on both channels OUTPUT from the DAC (54/55 and 64/64 pin) I only see ca +2.4 DC

Will take a break now, but this doesn't really look good.
/Stefan
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Re: LCDuino on γ3 - strange volume behaviour

Postby amb » August 18th, 2019, 1:24 am

That’s the correct DC “offset” at each of the WM8741’s analog output pins. You should be measuring the AC signal voltage while playing the test tone.
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Re: LCDuino on γ3 - strange volume behaviour

Postby Balcmeg » August 18th, 2019, 3:19 am

amb wrote:That’s the correct DC “offset” at each of the WM8741’s analog output pins. You should be measuring the AC signal voltage while playing the test tone.

Yes, right.. been a while since i did this.

Must check my setup, Im getting LEFT channel 60Vpp 50hz on both a24 INPUTS, moving it reduce the voltage to 16V...
Same result with both my Picoscope and OWON oscilloscope.

I will try again tomorrow and make some more free space with cleaner cabling - and try to figure out where the heck mu DWM went AWOL.
/Stefan
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Re: LCDuino on γ3 - strange volume behaviour

Postby Balcmeg » August 18th, 2019, 3:54 am

OK did find my DVM, i do measure the Dc offset as it should be

The CD inputs are ok, although GVDD low? 4,65VDC

Apart from that I can't get any AC on the outputs, and i connected my OPPO Mobile DAC as a Line amp to the outputs and now i have no sounds (it does work with my gamma2), to make sure its not the USB input that's messing things up I used my iMacs optical output to optical input and there are no sound.
Either something happened on the DAC board, and/or its related to the volume control issue i had before. The display and motor all look ok - but i guess it could have got the DACs stick on full attenuation?
/Stefan
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Re: LCDuino on γ3 - strange volume behaviour

Postby amb » August 18th, 2019, 3:41 pm

Balcmeg wrote:Im getting LEFT channel 60Vpp 50hz on both a24 INPUTS, moving it reduce the voltage to 16V...

Those are impossibly high voltages. You're probably not measuring or reading the results properly...

Just use a good 'ol DMM in AC V mode for this.

GVDD is a bit low at 4.65V. Check the molex connector J14 on the γ3 backplane.
Check all other voltage test points on the γ24 board, as well as the supply voltages to the α24 boards.
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