I just measured pin 20 on the AP2322. Via the digital output (I2S) played like a 1kHz signal (other Freq. behave the same ...). Now you get a d2 and d4 on pin 20 with levels of like 30-50uV. The rest is noise at a level of 3uV (per frequency package as this is FFT of course). But clearly these peaks are there. WITHOUT a signal, there is only this noise (the 3uV) it is also almost independent ( 😕 ) of the level of the sine wave... 0dB or -120 dB does NOT make a big difference... like from 50uV to 30uV. Only when no signal is applied the peaks disappear...
The interesting part now is that you would expect this signal to show up in the output through the "mirror function" we expect in the DAC. On DC it is 25x multiplier at least. Easy to see at low input signal levels as you would expect that the "bias d2 and d4" would prevail in the output, when playing signals like -120dB. Well... it does NOT. The output is dead flat on d2 and d4 at low signal levels, so no peaks coming through
Still very mysterious thing 😉 I think we need the empirical approach. Just connect a 0.4mA current sink to pin 20. I think a simple JFET solution will do the trick to see if there is a noticeable difference to start with...
I asked Brian Lowe, who is one of the smartest people I have had the honor to meet, if he knew anything about the PCM1794 and especially the mysterious PIN 20 - he says he does have some familiarity with it and is going to tell me what he knows when he gets the time. Sometime in the next day or so.
I mentioned to him the desire to come up with a sink and asked for his expertise.
I did pose it as something to sell - so I do not expect a give-away but who knows. I meant a product to sell, not a drawing! But this guy knows his stuff. His wife is an expert SMD components solderer! Now that's a unbeatable combination. Brian is good at miniaturization which would be good with the lack of board space after one tightens up the regulator positions to be intimate with the DAC chip.
Still hoping the best option is a TX2575 but that would be too easy - though it is not uncommon for simplicity to be the best solution in audio.
AS soon as I get the note I will post it.
I mentioned to him the desire to come up with a sink and asked for his expertise.
I did pose it as something to sell - so I do not expect a give-away but who knows. I meant a product to sell, not a drawing! But this guy knows his stuff. His wife is an expert SMD components solderer! Now that's a unbeatable combination. Brian is good at miniaturization which would be good with the lack of board space after one tightens up the regulator positions to be intimate with the DAC chip.
Still hoping the best option is a TX2575 but that would be too easy - though it is not uncommon for simplicity to be the best solution in audio.
AS soon as I get the note I will post it.
Just put a vishay vsmp 6k in there might be something in it
Need more listening to confirm
Have the diode on the way too
Need more listening to confirm
Have the diode on the way too
think im on my own testing this for unbalanced
http://web12491.serv4.spacequadrat.de/html/DAC_Nitro_DAB_V10.pdf
but it has me well confused
the iv resistor values im using 33r (r1)and 150r(r2) which i landed at by experimentation and listening but it should sound awful in theory
im pretty convinced its one of the best tweaks ive done yet
there very well could be better r combos
this is the calc speadsheet for calc best r values http://web12491.serv4.spacequadrat.de/html/DAB.xls
but it doesnt correlate with the listening experience
does anyone know what the measured currents for digi silence , max pos & max neg are?
that would be a great start
or is the datasheet spec just conservative?
http://web12491.serv4.spacequadrat.de/html/DAC_Nitro_DAB_V10.pdf
but it has me well confused
the iv resistor values im using 33r (r1)and 150r(r2) which i landed at by experimentation and listening but it should sound awful in theory
im pretty convinced its one of the best tweaks ive done yet
there very well could be better r combos
this is the calc speadsheet for calc best r values http://web12491.serv4.spacequadrat.de/html/DAB.xls
but it doesnt correlate with the listening experience
does anyone know what the measured currents for digi silence , max pos & max neg are?
that would be a great start
or is the datasheet spec just conservative?
use proper Widlar CCSink (say small bjt as programming and small darlington as programmed part) and bang it to negative PSU rail , to achieve proper/greater headroom/performance
Here is a reference from ecdesigns to get rid of vref on tda1543
http://www.diyaudio.com/forums/digi...e-nos-dac-using-tda1541a-416.html#post2866509
http://www.diyaudio.com/forums/digi...e-nos-dac-using-tda1541a-416.html#post2866509
take 9V battery for test and then , if result is worth the trouble , you can use almost any sort of aux. PSU , due to CCS isolation
Very intresting article and nice circuit suggestion. Should be easy to do a quick mockup.
I wasn't planning to take the dac apart for a few days as I'm still burning in the last mods.
The data sheet says:
I/V Section
The current of the PCM1794 on each of the output pins (IOUTL+, IOUTL–, IOUTR+, IOUTR–) is 7.8 mA p-p at 0 dB (full
scale). The voltage output level of the I/V converter (Vi) is given by following equation:
Vi = 7.8 mA p–p × Rf (Rf : feedback resistance of I/V converter)
The current of the PCM1794 on each of the output pins (IOUTL+, IOUTL–, IOUTR+, IOUTR–) is 7.8 mA p-p at 0 dB (full
scale). The voltage output level of the I/V converter (Vi) is given by following equation:
Vi = 7.8 mA p–p × Rf (Rf : feedback resistance of I/V converter)
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see this in the datasheet: on page 25
that the max current output is 10.1ma
i wondering now as were using mono mode does that translate to 20.2ma max output?
but then from from Deode's notes
I learned, that the following was the optimal situation
Vcc 8 Volt
R ref 6,1KOhm
R Load 270 Ohm, resulting in a Bias of 2,72 Volt
Current Output at zero signal ~ 10mA allowing headroom for full scale current (6,3mA)
just that using ohms law using various r values (i used this http://www.rapidtables.com/calc/electric/ohms-law-calculator.html because im lazy)
2.72v bias at 266r (2x 133r) is 10ma
3v bias at 300r is 10ma
3.66v bias @ 366r is 10ma
so its 10ma?
so the optimum bias is supposed to be 2.7v
the dab calc suggests 22r and 82r by my entries, which would bias at 2.04v
which would have to be weak vol wise
even if use 270r as the base using 33r and 100r resistors the volume would be less than stock
however i think it would be able to cope with at least 40r and 133r without any distortion
im still using 33r and 150r i cant hear any distortion
I'm confused... Are you using the method described here to convert the balanced output to an unbalanced one, or just following the half of the theory and using the split I/V resistors?
I saw your diagram a few days ago, but don't recall you joining the pos and neg together with a capacitor like that guide explains to do.
At that stage i hadn't tried the cap I was just trying to figure out the correct r values
Even at that level I thought the potential was good enough to discuss here
There will be all sorts of varients of this iv that should sound good
Even at that level I thought the potential was good enough to discuss here
There will be all sorts of varients of this iv that should sound good
Hi,
I plan to build DDDAC. So nobody use LIFEPO4 A123 power ? I think to use two battery one for 3.3-3.4 V dirctly without regulator (10 * A123 in // very low impedance 0.2 mohm 25ah) and second 10.2 V (3 * 10 A123 in // 25ah ) with 8 V belleson regulator . What do you think of that ?
I plan to build DDDAC. So nobody use LIFEPO4 A123 power ? I think to use two battery one for 3.3-3.4 V dirctly without regulator (10 * A123 in // very low impedance 0.2 mohm 25ah) and second 10.2 V (3 * 10 A123 in // 25ah ) with 8 V belleson regulator . What do you think of that ?
Oh, well, my nearly breathless post from yesterday has come to nothing.
Brian must have confused PCM1794 with another DAC.
He did suggest seeing what happens with a bypass cap on the resistor but could not guarantee this would not destroy the DAC.
Sorry for the drama.
I did ask him if he could come up with a tiny module to replace the resistor when and if someone finds this is the way to go.
Walked out of the house without the RAKK DAC board so it will be Monday. The numbers are so small I could not read them. Hoping I can scan the board at high resolution and be able to zoom in. No scanner at home.
Brian must have confused PCM1794 with another DAC.
He did suggest seeing what happens with a bypass cap on the resistor but could not guarantee this would not destroy the DAC.
Sorry for the drama.
I did ask him if he could come up with a tiny module to replace the resistor when and if someone finds this is the way to go.
Walked out of the house without the RAKK DAC board so it will be Monday. The numbers are so small I could not read them. Hoping I can scan the board at high resolution and be able to zoom in. No scanner at home.
Any half decent camera should be able to capture enough detail surely? I've used my phone camera before for teeny smd stuff before and it's been good enough.
