I actually prefer these:
I loved combi sockets when they appeared.
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Oh ok… but I know which one I’d rather hand make a panel for …
This is not necessarily so. The input circuit needs to be designed to provide this feature. It may appear to work but audio quality may deteriorate. Does anyone have diagrams of the audio input stage?
While we’re talking about mono I/O, is there currently a software way to downmix the output to either the left or the right channel?
I use the stereo mixer lv2 plugin
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If i plug a guitar into one of the inputs using a standard mono TR 1/4" (6.35mm) plug I get nothing. If I partially insert it I get high level (distorted) audio. Is there a configuration that will allow both balanced and unbalanced input? I would guess that many (most?) Zynthian users will be using unbalanced audio devices and hence this is a significant problem for them. Ideally inputs and outputs should work for both balanced and unbalanced signals.
HI @riban !
It should work. I’ve tested my 4.1 zynthians with both balanced and unbalanced input and it works like a charm. When connecting an unbalanced input, one of the pairs is connected to ground, so the phase cancellation circuit simply do nothing (1/2 signal + GND = 1/2 signal). This is the normal behaviour of almost all balanced input circuits iin any device.
Your problems could be related with a bad cable or perhaps, bad wiring.
Regards,
The cable is fine. I tested with other cables but it is a simple mono jack to mono jack cable. Internally I use the PCB with 4 jack sockets which connects to the HifiBerry via a ribbon cable so not much room for error there. I checked inside this morning and it looks okay. If I plug in an unbalanced source, e.g. guitar, synth, etc. I get nothing out.
Have you tried to change the selector “ADC Left/Right Input” from the “Audio Levels” (ALSA Mixer). Try choosing VNL2/VNR2 instead of VNL1/VNR1. Also, it should work by selecting the last option for differential input.
Regards,
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Thanks @jofemodo. That did it. Is there any documentation on what those settings do? I can’t remember what value they were in the fresh image but do remember playing with them trying to figure out their meaning.
[Edit] I just looked at alsamixer and see lots of settings for the Hifiberry dac plus pro. From what I can make out the ADC input settings are:
- Disabled
- Ring only
- Tip only
- Tip and ring sum
- Tip and ring difference (balanced)
The last setting gives -6dB for an unbalanced input. The fourth setting looks optimal for unbalanced as it will allow a stereo source to be plugged in and mono version derived or it will take a mono signal. The other options seem of little use. I wonder if it is worth tweaking the display to present a toggle between the last two labelled balanced / unbalanced?
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The only documentation i know is the technical datasheet of the ADC chip, the PCM1863:
and the ALSA driver’s source code 
But the ADC input setting is just as you say, except that i would say that the balanced (difference) option gives +6dB when signal is balanced. Unbalanced signal is -6dB weaker than balanced. Also, i don’t understand the “sum” option. I tested this option with a good balanced signal from a SM-58., expecting to ear only the noise. If the “diff” option cancels the noise and doubles the signal (+ 6dB), the “sum” option should cancel the signal, amplifying the noise, is it? Not in my test. Although the noise is stronger, the signal is not canceled at all.
Anyway, as you say, the interesting options are “Tip only” and “Balanced”. And yes, we could tweak the ALSA mixer class for “improving” the UX of “official kit users”. I will think about it and will add some lines to the wiki. .
Regards,
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Ooh I got a bit excited when I read the datasheet that we may have a 4 channel device but this is the model down with 2 ADC. It is still very versatile and we could expose some more features (in time). I disagree that tip-only is the best option. By using tip+ring we allow both mono and stereo signals to be plugged in to each channel. Plugging a TRS stereo signal would mono it, summing both channels of the stereo which is advantageous. It means we can take two mono or stereo signals into our two independent channels, e.g. mono microphone on A and stereo feed on B.
I hope it’s ok to revive this old topic, but since it’s topic is balanced output connectros to hifiberry dac it seems the right place and it might be better to just keep similar topics together. Yesterday I finished my encoder/mcs23107 setup with the help of so many, primarily @wyleu , so thank you all for being so helpful and empowering!
Before I put everything into the wooden cigar box, I want to solve the presumably last problem: Connecting the Hifiberry Dac2 Adc Pro input and output connectors to 1/4" balanced jacks.
My current working setup is: Hifiberry to RPi5 (with active cooler), mcp23107 encoder circuit to Hifiberry DSP header. Parts I have at home related to that question are the following:
So I connected the female dupont end to the respective output connector on the Hifiberry and soldered + to tip, - to ring and GND to sleeve. It sounded horrible, it was very quiet, had humming and I thought I could hear raspberry’s calculating operations through my speakers.
I already searched this forum, there were some posts mentioning using unbalanced connectors would be the best solution in any way, but actually the V3 and V4 kit’s building wiki say to connect all of the 6 pins each.
So here are my questions:
- Are these dupont cables (dividable, but connected) suitable for the tasks or should I use separate 2.54 jst cables? May there be possibly something like a minimum thickness of these kind of cables?
- Do I have to setup a balanced output option anywhere in webconf or somewhere else? By now I just found different alsa configuration options for the input connector, but not for output.
- Any other things I might not think of? So how was I able to hear some noise which sounded like digital data noise?
- If I succeed, how would be a setup which would be compatible to both balanced and unbalanced use?
- Should I maybe go fully unbalanced?
Thanks in advance. Hope we’ll see each other soon in the “success cases” section.
So here’s what happens:
The output from the RCA outs is completely fine.
When connecting the balanced out jacks, it sounds like this (boot to shutdown):
As you can see here I spared the last pop in the rendering to be nice to your playback devices and lowered the volume for the few test tones:
So, can anybody day what’s going on here?
However, connected to input the jacks work fine, at least with a unbalanced TS electric guitar plugged in.
I can suggest
- triple check your audio wirings/solderings.
- unplug the Dupont connectors from Hifiberry to audio jacks and see what happens (
- alsa pcm1863 driver is configurable for single ended or balanced signals. I do believe Zynthian has a built in config tool in webconf for this, if not, alsamixer will do the job.
- if possible (with an other SDcard) see how it goes with a basic RaspiOs system
good luck
Thanks for looking into this.
I think since a) using the same plugs as input at the J4 input connector works without noise and using the card just with the RCA connector works as well there should be no problem on this side.
I’m afraid that does apply for the input, right?
I might try this, if I find out to configure the hifiberry there. But the sound is also there in off state after shutdown.
Can somebody confirm that the TRS connection should be (G - +)?
Ok, I tested just connect + and gnd and leave - out and that is ok. So what could I do from here?
The DAC 2 ADC Pro does not have balanced (differential) outputs. The connector has +5V which explains the noise you were hearing.
You posted in this thread which is about the zynthian soundcard, not the Hifiberry soundcard. They are different.
Wow, don’t know why I thought that it was balanced… Thanks so much to point me there. Probably I thought when it has 6 pins it must be balanced somehow. Now I try to find out why it even has the other 2. Maybe to connect two different outputs?