I'm a bit puzzled on the PCM1794a Mono mode: it's clear that in Mono mode, the one channel's analog output is inverted to allow balanced operation. However, it's not clear on WHICH channel is inverted! Absolute polarity is important in my application as I'm building interchangeable DAC cards for a DSP application where the polarity needs to be consistent.
When the DAC is set to Mono mode left channel, I would presume the right channel's polarity is inverted, and vice versa for the other way round.
Table4 on p17 stipulates that a digital full-scale positive is represented by a full-scale positive voltage output when using the datasheet standard opamp I/V and summing circuit.
The Mono mode in Figure27 p22 then shows how the output of the Left output in Mono mode is called "OUT+" yet it goes to XLR pin3/cold.
Similarly the Right output is called OUT- but goes to XLR pin2/hot.
The question therefore is:
- In mono mode, is the polarity inversion applied to the opposite or selected channel?
- Does this mean for a dual-mono application with 2 identical circuits but one strapped for left and the other for right, the one channel would need to invert its polarity at the XLR plug to retain phase?
When the DAC is set to Mono mode left channel, I would presume the right channel's polarity is inverted, and vice versa for the other way round.
Table4 on p17 stipulates that a digital full-scale positive is represented by a full-scale positive voltage output when using the datasheet standard opamp I/V and summing circuit.
The Mono mode in Figure27 p22 then shows how the output of the Left output in Mono mode is called "OUT+" yet it goes to XLR pin3/cold.
Similarly the Right output is called OUT- but goes to XLR pin2/hot.
The question therefore is:
- In mono mode, is the polarity inversion applied to the opposite or selected channel?
- Does this mean for a dual-mono application with 2 identical circuits but one strapped for left and the other for right, the one channel would need to invert its polarity at the XLR plug to retain phase?
Thanks, yours was one of the first hits I got when I searched. However, board space prohibits external filters, and the measurements of NOS regardless of sonic attributes will not be acceptable by the Pro Audio customer. An initial prototype with the internal filter proved perfectly acceptable and now the goal is just to improve SNR since the application is mono anyway (active speaker).
In your application your method makes sense and is a novel approach, but when using the sharp rolloff internal filter and in I2S mono mode (but with current summing instead of the datasheet application note) the design should work fine without additional logic manipulation, unless there's some nasty unpublished behavioural issues in that mode?
In your application your method makes sense and is a novel approach, but when using the sharp rolloff internal filter and in I2S mono mode (but with current summing instead of the datasheet application note) the design should work fine without additional logic manipulation, unless there's some nasty unpublished behavioural issues in that mode?
I can not find clear Info about Iout phases of pcm1794 when we use dual chips In mono mode https://www.ti.com/lit/ds/symlink/pcm1794.pdf?ts=1587753574014
Would anyone confirm correct Iout phases (pins 17, 18, 25 and 26) In mono mode for Left selected and Right selected
Is this schematic (from Audiodesignguide) correct way to parallel Iout pins http://www.audiodesignguide.com/DAC_final/PCM179Xsch.jpg
Would anyone confirm correct Iout phases (pins 17, 18, 25 and 26) In mono mode for Left selected and Right selected
Is this schematic (from Audiodesignguide) correct way to parallel Iout pins http://www.audiodesignguide.com/DAC_final/PCM179Xsch.jpg
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Every DAC chip in mono mode, will output its channel as in datasheet, and the other channel inverted.
So, if a DAC is set for mono mode right channel, the right channel outputs will remain unchanged, but the other ones will be inverted:
IoutR- will be negative right, IoutR+ will be positive right
IoutL- will be positive right, IoutL+ will be negative right
For the left channel is the same behavior:
IoutR- will be positive left, IoutR+ will be negative left
IoutL- will be negative left, IoutL+ will be positive left
So, if a DAC is set for mono mode right channel, the right channel outputs will remain unchanged, but the other ones will be inverted:
IoutR- will be negative right, IoutR+ will be positive right
IoutL- will be positive right, IoutL+ will be negative right
For the left channel is the same behavior:
IoutR- will be positive left, IoutR+ will be negative left
IoutL- will be negative left, IoutL+ will be positive left
thanks for re-opening!
I have a question about mono mode I/V conversion... please bear with me because I'm still learning
in the AudioDesignGuide schematic posted, if I'm reading it correctly then for the left channel it shows IOUTL+ and IOUTR- currents summing together for L+, and IOUTL- and IOUTR+ summing together for L-
However I recently bought a DAC from Aliexpress (that actually sounds really good!), but the schematic shows the IOUTL+ and IOUTL- going to a dual opamp, and IOUTR+ and IOUTR- going to a different dual opamp, and the outputs of those each going to a single op-amp, in order to drive the XLR out
Am I right in thinking that it's just taking this inverted output and using it for the negative half of the XLR channel?
Also, is there an advantage to doing it this way, rather than the schematic posted by AudioDesignGuide where both currents sum together? It seems like this way there would be less opamps in the signal path, no?
Thanks for any help you can provide in setting me straight 🙂
Schematic from AudioDesignGuide:
Schematic from Aliexpress DAC:
I have a question about mono mode I/V conversion... please bear with me because I'm still learning
in the AudioDesignGuide schematic posted, if I'm reading it correctly then for the left channel it shows IOUTL+ and IOUTR- currents summing together for L+, and IOUTL- and IOUTR+ summing together for L-
However I recently bought a DAC from Aliexpress (that actually sounds really good!), but the schematic shows the IOUTL+ and IOUTL- going to a dual opamp, and IOUTR+ and IOUTR- going to a different dual opamp, and the outputs of those each going to a single op-amp, in order to drive the XLR out
Am I right in thinking that it's just taking this inverted output and using it for the negative half of the XLR channel?
Also, is there an advantage to doing it this way, rather than the schematic posted by AudioDesignGuide where both currents sum together? It seems like this way there would be less opamps in the signal path, no?
Thanks for any help you can provide in setting me straight 🙂
Schematic from AudioDesignGuide:
Schematic from Aliexpress DAC:
Schematic from the Audiodesign is correct. There are sort of "switched" phase in the mono mode.
Same as with the wolfson DACs...
But there are PDF data to check?
Same as with the wolfson DACs...
But there are PDF data to check?
OR just measure
Step response for + should going into positive range, - into the neg.
then connect all + and all -
,
ONE very important thing:
With Riv conversion +Io converts to -Vo. And oposite. But after the Single ended amplification it goes back in phase to +Vout
please check with simulations...
🙂
Step response for + should going into positive range, - into the neg.
then connect all + and all -
,
ONE very important thing:
With Riv conversion +Io converts to -Vo. And oposite. But after the Single ended amplification it goes back in phase to +Vout
please check with simulations...
🙂