The new Kit v4.1 is out: Balanced Input & Output!

I actually prefer these:


I loved combi sockets when they appeared.


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.


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.


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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?


The only documentation i know is the technical datasheet of the ADC chip, the PCM1863:

and the ALSA driver’s source code :wink:

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. .


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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.