Hi Soundcheck,
- of course 5V only is a cheap and easy solution, BUT it is a very strong limitation of the analog stage. Internal output stages are CMOS devices and the negative voltage has to be supplied by a charge-pump, better to be avoided.
- the used OPA1642 is a very good FET op-amp. Hard to beat by an discrete circuit. And a good designed class-A stage would take probably more space on the board. Too much for a HAT, I think. Transformers are a complete different story, and not usable for this voltage output dac.
- no reclocker is required, works fine just with the Raspi and a power supply.
- I don't have a Boss, waiting for Greg's answer.
- of course 5V only is a cheap and easy solution, BUT it is a very strong limitation of the analog stage. Internal output stages are CMOS devices and the negative voltage has to be supplied by a charge-pump, better to be avoided.
- the used OPA1642 is a very good FET op-amp. Hard to beat by an discrete circuit. And a good designed class-A stage would take probably more space on the board. Too much for a HAT, I think. Transformers are a complete different story, and not usable for this voltage output dac.
- no reclocker is required, works fine just with the Raspi and a power supply.
- I don't have a Boss, waiting for Greg's answer.
Short answer, YES!
@soundcheck...
I posted a short (for me) summary of my current takes on the RPi DACs I have here on Ian's IsolatorPi thread yesterday:
http://www.diyaudio.com/forums/pc-b...tor-hat-native-dsd-decoder-5.html#post5101590
To set context, over the past 10 years I've been on a quest to understand what's important in getting good sound out of digital AND have tried AND modified a lot of setups. What I'm hearing from Alex's DAC is just another step on that journey... and it sets a new high bar for RPi setups for me.
Soundcheck, I agree with what you said about the power requirements of the DIAL DAC adding hassle and cost, that it is only an OpAmp output stage.
AND I also agree with Alex that the benefits of the +-15V GOOD opamp are VERY WORTHWHILE in this implementation. I don't know how you can get these results without them.
On whether it would beat my Boss setup, I said:
I wanted to hedge my comments then as I hadn't yet done any head-to-head comparisons. Now I have.
As for using a reclocker (Kali), I mentioned this in my IsolatorPi comments... the Boss directly on a Pi running in master mode is my baseline good quality sound setup for RPi playback. It gets better with separate power and even moreso with an IsolatorPi (tested only with 44.1 ripped CD source material).
AND the Boss TO MY EARS AND IN MY SETUPS gets even better on a Kali in slave mode (this is also true of the HiFiBerry DAC+ Pro, the other master mode RPi DAC I have).
My top +5V-powered RPi setup is currently RPi -> IsolatorPi -> Kali -> Boss. Of course it sounds best with separate supplies for each board, but it does very well with the Kali powering the Boss too... and a Piano 2.1 in 'twinned' mode using the stock I2S driver is very close to this, with a somewhat different sonic portrayal and signature (some might prefer it to the Boss).
Then I have listened to the Dial DAC with/without a Kali... it is reasonable without. Though I did not do a direct comparison, I'd say it is roughly equal to the Boss in master mode directly on the RPi. BUT as with every other setup I've tried, reclocking the I2S datastream out of the RPi yields the best results NO MATTER THE DAC!
The two areas where the Dial DAC shine are in the aliveness of the overall sonic portrayal/tonal qualities and dynamics, especially in the bass. I attribute these to:
- NO ceramic caps! The sound of the Dial DAC reminds me of my modified Sony HAP Z1-ES which also just uses good electrolytics and SMD film caps around the DAC and output stages.
- Outputs running from +-15V rails. I tested this somewhat with a different +-15V power supply... a Jan Didden Silent Switcher fed by an Uptone Audio LPS-1 (to give it the lowest noise source supply I have). While still good, the magic is diminished with the Silent Switcher. It is just much more alive and exciting with the shunt regs I'm using (similar to Salas).
- Better output active device. The OPA1642 used beats any of the CMOS OpAmps PLUS charge-pump -V outputs built into DAC chips like the PCM5122/5142/ES9023.
- The DAC chip. Middle-high end in the Burr-Brown lineup, though a much older chip.
I do have one caveot on the Dial DAC... using the I2S driver in PiCorePlayer 3.20 Audio I get a strange sound on some cymbals on a few recordings... say a small portion of 1 track of every 20-30 I've tried. It sounds like digital overload... I'm playing with digital levels and plan trying other distros & player & some other things to diagnose it. It happens on both the stock DAC and my HotRod, using my shunt regulators or the Silent Switcher, and with/without the Kali. I will report more on this as I try some options... but it is so rare & everything else is so good if I can't resolve it, I'll learn to live with it.
Greg in Mississippi
P.S. AND I do intend to try this DAC with transformer outputs replacing the active stage... I'll report my results.
@soundcheck...
I posted a short (for me) summary of my current takes on the RPi DACs I have here on Ian's IsolatorPi thread yesterday:
http://www.diyaudio.com/forums/pc-b...tor-hat-native-dsd-decoder-5.html#post5101590
To set context, over the past 10 years I've been on a quest to understand what's important in getting good sound out of digital AND have tried AND modified a lot of setups. What I'm hearing from Alex's DAC is just another step on that journey... and it sets a new high bar for RPi setups for me.
Soundcheck, I agree with what you said about the power requirements of the DIAL DAC adding hassle and cost, that it is only an OpAmp output stage.
AND I also agree with Alex that the benefits of the +-15V GOOD opamp are VERY WORTHWHILE in this implementation. I don't know how you can get these results without them.
On whether it would beat my Boss setup, I said:
I wanted to hedge my comments then as I hadn't yet done any head-to-head comparisons. Now I have.
As for using a reclocker (Kali), I mentioned this in my IsolatorPi comments... the Boss directly on a Pi running in master mode is my baseline good quality sound setup for RPi playback. It gets better with separate power and even moreso with an IsolatorPi (tested only with 44.1 ripped CD source material).
AND the Boss TO MY EARS AND IN MY SETUPS gets even better on a Kali in slave mode (this is also true of the HiFiBerry DAC+ Pro, the other master mode RPi DAC I have).
My top +5V-powered RPi setup is currently RPi -> IsolatorPi -> Kali -> Boss. Of course it sounds best with separate supplies for each board, but it does very well with the Kali powering the Boss too... and a Piano 2.1 in 'twinned' mode using the stock I2S driver is very close to this, with a somewhat different sonic portrayal and signature (some might prefer it to the Boss).
Then I have listened to the Dial DAC with/without a Kali... it is reasonable without. Though I did not do a direct comparison, I'd say it is roughly equal to the Boss in master mode directly on the RPi. BUT as with every other setup I've tried, reclocking the I2S datastream out of the RPi yields the best results NO MATTER THE DAC!
The two areas where the Dial DAC shine are in the aliveness of the overall sonic portrayal/tonal qualities and dynamics, especially in the bass. I attribute these to:
- NO ceramic caps! The sound of the Dial DAC reminds me of my modified Sony HAP Z1-ES which also just uses good electrolytics and SMD film caps around the DAC and output stages.
- Outputs running from +-15V rails. I tested this somewhat with a different +-15V power supply... a Jan Didden Silent Switcher fed by an Uptone Audio LPS-1 (to give it the lowest noise source supply I have). While still good, the magic is diminished with the Silent Switcher. It is just much more alive and exciting with the shunt regs I'm using (similar to Salas).
- Better output active device. The OPA1642 used beats any of the CMOS OpAmps PLUS charge-pump -V outputs built into DAC chips like the PCM5122/5142/ES9023.
- The DAC chip. Middle-high end in the Burr-Brown lineup, though a much older chip.
I do have one caveot on the Dial DAC... using the I2S driver in PiCorePlayer 3.20 Audio I get a strange sound on some cymbals on a few recordings... say a small portion of 1 track of every 20-30 I've tried. It sounds like digital overload... I'm playing with digital levels and plan trying other distros & player & some other things to diagnose it. It happens on both the stock DAC and my HotRod, using my shunt regulators or the Silent Switcher, and with/without the Kali. I will report more on this as I try some options... but it is so rare & everything else is so good if I can't resolve it, I'll learn to live with it.
Greg in Mississippi
P.S. AND I do intend to try this DAC with transformer outputs replacing the active stage... I'll report my results.
See my comments above on what I think of the stock Dial DAC... short version, if you can deal with providing good +-15V supplies AND put it on a Kali (and adding an IsolatorPi makes it even better), you will get very good results.
But even before I setup and listened to the stock Dial DAC I liked what I saw. So I also got a bare board from him and did a HotRod version... what I did was:
- Powering the DAC 3.3V & 5V from higher quality (IMHO) regulators with each being fed from a separate rail instead of being fed from the +15v
- Upgraded to PPS caps from mylar for the DAC and output rail bypasses
- Used 3 22uF PPS caps on the 5V DAC rail instead of a 47uf Nichicon Fine Gold (this will get upgraded with a 4th 22uF soon)
- Going to conductive polymer caps (IMHO, better for digital circuits) on the 3.3v rail again instead of a 47uf Nichicon Fine Gold
- Adding a 33F/5.5v Supercap after the regulator for both the 3.3V & 5V rails on the DAC chip
- Going to larger 220uf Nichicon Muse instead of 100uf Nichicon Fine Gold on the output stage +-15V rails
- Converting the output stage filter caps from Wima polyprops to PPS (I am planning to go back to the polyprop caps Alex uses here, I am not sure this was a good choice)
It has been running 2-3 weeks now and is currently at the top of my RPi-mounted DAC setups.
See attached pix of the HotRod build in-progress.
IF you care to build SMD boards AND want a very good RPi DAC, I suggest you look at getting one of these boards from Alex. I ordered 2 more myself... 1 to try with an OPA1632-based balanced output stage and the other to try with some transformer outputs instead of active stages.
Greg in Mississippi
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I say scrap the Pi and go with an ASUS TinkerBoard instead. Faster chip. If you need to use it, it/s on board dac is tolerable. USB out is much, much better than Pi, so you can plug TB into an existing DAC. Volumio runs great on it. Many of the Pi HATs work on the TinkerBoard with Volumio. Costs more but worth it. New TinkerBoard version has superior memory. I have old TinkerBoard but it runs great with Volumio, including wireless, off my NAS, off my phone, whatever.
@fab:
I use the OPA1642 in this circuit, because it has a very good noise and distortion performance and stable input capacitance. This op-amp is well-suited for active filter circuits like this.
And the most importand thing is the sound of course. In my experiences it was the best, detailed musically sounding and a wide holografic soundstage. But in the end it is all a matter of taste and other op-amps can be used.
I use the OPA1642 in this circuit, because it has a very good noise and distortion performance and stable input capacitance. This op-amp is well-suited for active filter circuits like this.
And the most importand thing is the sound of course. In my experiences it was the best, detailed musically sounding and a wide holografic soundstage. But in the end it is all a matter of taste and other op-amps can be used.
Thanks for the info. I agree that this opamp sounds very nice. However, sometimes the OPA1612 gives a better balance (but reduced soundstage) with more bass depending on the dac. Some AD opamps also sound very nice. The AD4001 has an very wide soundstage.
Can I obtain one board with the Opamp not installed so I can select mine?
Fab
Can I obtain one board with the Opamp not installed so I can select mine?
Fab
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