ZynAuCon - troubleshooting left output

I’m working on my official 4.4 kit and looking to make use of both audio channels. Just realizing that there seems to be something weird going on with the left output channel.

I typically use a balanced TRS cable to connect to a mixer, but when using both L and R channels, the right channel is consistently hotter than the left. When I listen through an unbalanced connection, the left channel is completely dead. I fed both into my audio interface, and did a sine wave generator test. I gradually raised the master output volume on both channels from 0 to 100. Here’s what I saw in Ardour:

It took dropping the output volume on the right channel by 20 (e.g. L: 100; R: 80) to get the signals to match.

Could this be a short on the ZynAuCon board? Or something similar? I’m glad that I can at least use the right channel either balanced or unbalanced.

Thanks for the help.

If you use the audio recorder on the zynth what does it show?
This is a purely software record so is downstream of the card.

Built-in audio recording of the same thing looks about as interesting as white on rice:

image

It does shift the issue to the board.

Have you checked the Audio Levels page in Zynthian main UI? Digital Left and Digital Right should be at the same value to give balanced output.

I have just noticed that the PGA gain on mine is different (Left: 12.0 dB, Right: 37.0 dB). I’m not sure if that affects input or output (it looks to be with the output controls) but I don’t recall changing it so it may be similar for you. I am not at home to be able to listen to / measure the output level. (I am accessing the unit remotely via ssh.) By default the PGA gain is hidden from the Audio Levels page (and probably should be). They can be adjusted in the advanced view of webconf Audio (Mixer controls).

Thanks for the tip. The Digital Left and Right knobs are what I used to sweep from 0 to 100 and generate the comparison data in my post. I find that when the output levels are matching there’s a difference of about 7dB in the signal level (L is 7 dB lower than R), and in order to achieve matching signal levels, I need to set the Digital Right to a level about 20 less than Digital Left.

I checked my PGA gain levels and they were close but slightly off (PGA left: -1.5dB, PGA Right: -0.5dB). Unfortunately when I adjusted them it made no impact on the audio signal coming through the balanced outputs jacks.

What happens if you swap the L/R plugs over. Swapping the cables at the Zynthian end will identify if there is a cable or plug issue.

Your description sounds like you have lost or grounded one pole of the balanced output. I’m not sure if that can be configured, e.g. with jumpers. The inputs can be configured by the driver but I don’t see similar for outputs.

Swapping the L and R output cables puts the weak signal on the other channel. Swapping both ends yields the same result as the original test. So not a cable issue.

If one pole of the balanced output were lost or grounded, would that cause the signal to disappear completely with an unbalanced (TS) cable? I’m guessing it would have to be the signal to the tip that is lost, otherwise something would still come through a TS cable connection.

Do you have a multimeter? If so, remove power from the Zynthian and plug in a TRS cable to the left output then measure resistance between T-S, then R-S on the jack at the free end of the cable. Repeat for the right output using the same cable and compare the results. You should have comparable T-S readings for both outputs and similarly comparable readings for R-S for both outputs.

Are there any jumpers on the audio board? (I am not near one this week to check.)

[Edit] I remembered I took pictures whilst constructing my V4. There are DIL pins on the soundcard. None should have any bridges. The only connection should be to the 1/4" socket board.

I assume you have the 4 x 1/4" sockets mounted on a PCB with a ribbon cable linking to the soundcard. (Early models had individual sockets on flying leads.) There could be a short circuit on that board, most likely due to a solder bridge on the DIL header to which the ribbon cable connects. Check for shorts on that connector and at the corresponding 1/4" output socket.

Loss of signal using a TS (mono unbalanced) cable suggests no signal on the tip (hot / + / mono) which could be caused by a short circuit to ground or by having completely missing signal, e.g. due to a dry joint. Dry joints can often be recognised as a solder joint where the solder does not form a conical shape, sometimes being a ball or sometimes there being excessive flux (red / brown material) at the joint. Check out the post with pictures (5th response) here.

What about the small ribbon cable connecting the ZynADAC and the ZynAuCon? Have you checked it for continuity and CC?

Regards,

So I measured the resistance at each point, here’s what I found:

  1. Right channel (working as expected)
  • tip to sleeve: 7.52 ohms
  • ring to sleeve: 7.50 ohms
  1. Left channel (the suspect jack)
  • tip to sleeve: 0.0 ohms
  • ring to sleeve: 4.65 ohms

Seems consistent with the dead tip signal theory, but why would the ring be reading so much lower than the other channel?

I visually inspected the solder joints, and there are a couple joints on the socket array that just might be on the verge of a cold joint as they’re more rounded on top but it’s hard for me (a noob with soldering) to say. I took photos, tried to get as clean a shot as possible:


Thanks @jofemodo, that’s definitely worth checking - do you have any suggestions for the best way to do a continuity test on a ribbon cable? My multimeter tips are too large. I have some spare jumper cables and a breadboard lying around…

Also, what do you mean by CC?

The short between tip and sleeve is your issue. We need to figure out where that is happening. The likely reason for the lower impedance between ring and sleeve is because there will be some components common with the tip and ring hence the tip being shorted will impact the ring too.

The 20-way DIL header on the audio breakout board mostly looks okay. There are a couple of pins which aren’t perfectly soldered but we are not looking for a short rather than an open circuit hence we are looking for bridges. I can’t see from the picture if any of the opposing pins are bridged. There are a couple that might be but a picture from directly above may help. Also a picture of both sides of the HiFiBerry soundcard may help diagnostics.

I think @jofemodo meant short (or closed) circuit, i.e. checking that adjacent pins are not connected. You can cut short bits of wire and insert them into the ends of the DIL headers to expose the connectors. I don’t think this beneficial. We are looking for short circuits which is quite rare with a ribbon cable. A visual inspection of the cable should suffice (until it is the last thing to check :wink:). Maybe a photo of that would also be in order.

Yes, i mean “closed circuit”, a spanish-like expression. “Short-circuit” is better :wink:

You can check continuity using this method too.
Of course, I would send you a replacement as soon as you identify where the problem is.

Regards,

So my Zynthian components just got through quite a photo shoot.

From my (quite limited) perspective, there is nothing visually indicating a short circuit like a solder bridge. I also tested the ribbon cable (thanks for the tips, was quite easy) and it passed for continuity on all 20 wires.

I haven’t gone through a short circuit test yet on the ribbon cable as I want to verify where to focus my testing. Based on this diagram in the wiki I would be looking for a short involving pin #19, correct? (Usually the tip of a TRS balanced signal is the positive, right?)

So I should check the connectors at both ends of the cable, testing pin 19 against all the other pins to make sure they aren’t bridged internally? Please correct me if my logic is off.

Here are the new photos:









I got to running a few more tests and came across something strange (to me, at least).

Every continuity test for R+, R-, L+ and L- passed all the way from the loose end of a TRS cable to the 20-pin header on the ZynADAC card. I also checked to see if the suspect L output tip showed continuity with ground at several points, and found nothing. When I checked the grounds, however, one thing stood out on the ZynAuCon board.

For both L and R output ring circuits, there is no continuity in the ground-side. The tips seem to be grounded on the pin opposite the ‘hot’ pin, and the sleeve is grounded on both sides. Forgive me if my terminology is imprecise or unclear. I checked the balanced input jacks the same way and they are both grounded as you would expect - both pins of the sleeve and the ‘cold’ side of both tip and ring. So its the input jacks that are either wired differently or perhaps malfunctioned.

Is this expected? Or could it be related to the issue I’m troubleshooting? It seems strange to me that both the L and R outputs have the same apparent wiring issue when it’s only the L output that is not performing as expected. Perhaps there’s an explanation.

One other thing I noticed, using this diagram for reference, the R/L + and R/L - were backwards from what I expected. That is, i found continuity between these points:

  • R ring: pin 17
  • R tip: pin 18
  • L ring: pin 19
  • L tip: pin 20