A New Take on the Classic Pass Labs D1 with an ESS Dac - Page 19 - diyAudio
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Old 13th June 2010, 10:31 AM   #181
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Its actually 22 bit , so if you offset 6-12dB you still have many bits left, so saturation at 0dB would go unnoticed ( not read what the levels were at -10dB).
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Old 13th June 2010, 10:43 AM   #182
EUVL is offline EUVL  Europe
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I know it's a bit off topic. Sorry to disturb.

For those low-current, 0V nominal, zero IV input impedance DACS like PCM63, PCM1704, AD1865, ...., I personally think that the Hawksford IV circuit is hard to beat. It works very similar to the Pass D1, except that it allows current amplification. And it does not have output coupling caps.

Here is my attempt for one version using the LU1014D power JFET in triode mode and a current gain of 12 (i.e. equal to paralleling 12 DAC chips together).

Hawksford Discrete IV with a Twist

LU1014 in triode mode :

Some other Source Follower COnfigurations

No time to build yet, but WILL do eventually.


Patrick

Last edited by EUVL; 13th June 2010 at 10:51 AM.
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Old 13th June 2010, 05:20 PM   #183
opc is offline opc  Canada
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Hi Guys,

Sorry for the 2 week absence, I was on vacation, and then had a lot of work to catch up on which didn't leave much time for anything else.

I've also been busy installing the 50 drivers in my latest line-array project, which is taking far more time than I was hoping.

Before I left, I measured the circuit as built on Pierre's PCB with a very closely matched pair of fets (for both Vgs and TC). I'm now riding the measurement limit of the Audio Precision at -112dB THD+N. I'm fairly sure the system is actually better than that, but even if I loop the AP straight from generator output to analog input, the best I get is -112dB with a 2VRMS signal. I would say that the circuit itself is definitely finalized, and I'm more than thrilled with that level of performance. Even the best op-amp based circuits would struggle to perform that well, and this does it with no feedback, and only a single device / gain stage.

qusp:

I'll snap a few pictures and post them tomorrow. I've got both channels done, and I've listened to the whole thing using a lab supply. The next step will be to make a regulated +/-50V supply to go along with it. When I'm happy with everything, and done some tweaking of the PSU, then I'll finally make the final PCB.

I know it has been a long time coming, but at least when it's done, it'll be perfect. There's nothing worse than making a PCB that isn't everything you wanted it to be.

Samoloko:

Lowering the resistor values does indeed lower the gain, and there's nothing you can do to change that basic fact, other than adding another gain stage. I would say that the sweet spot is really the lowest gain you can tolerate, which in my case is 2VRMS at 0dBFS. If you can live with 1VRMS, then by all means, you can lower the resistors values and get even more current through the fets for a given voltage level.

Calvin:

The voltage mode measurements were taken with only a pair of 750 ohm resistors on each output to ground. I soldered the resistors directly to the XLR jack, and ran 2" leads from the DAC output to the XLR jack. I verified the setup several times since I was quite surprised by the poor results.

The generator is the AP built in digital generator which gives -148dB THD+N when looped back to the digital input at 24 bit, 192kHz. The limits of the analog analyzer is about -112dB THD+N, so that's not what was causing the poor measurements.

Realistically, the DAC isn't designed to be run in "Voltage Mode" and for all I know, they might have a very specific circuit that qualifies as "Voltage Mode". What I can tell you though, is that performance into a pair or resistors isn't good, and doesn't come anywhere close to the number on the datasheet at 0dBFS.

If someone else here has measured this and gotten better results, let me know what you did, and I'll try it again.

Cheers,
Owen
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Old 14th June 2010, 04:18 AM   #184
qusp is offline qusp  Australia
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Quote:
Originally Posted by opc View Post
Hi Guys,

Sorry for the 2 week absence, I was on vacation, and then had a lot of work to catch up on which didn't leave much time for anything else.

I've also been busy installing the 50 drivers in my latest line-array project, which is taking far more time than I was hoping.

Before I left, I measured the circuit as built on Pierre's PCB with a very closely matched pair of fets (for both Vgs and TC). I'm now riding the measurement limit of the Audio Precision at -112dB THD+N. I'm fairly sure the system is actually better than that, but even if I loop the AP straight from generator output to analog input, the best I get is -112dB with a 2VRMS signal. I would say that the circuit itself is definitely finalized, and I'm more than thrilled with that level of performance. Even the best op-amp based circuits would struggle to perform that well, and this does it with no feedback, and only a single device / gain stage.

qusp:

I'll snap a few pictures and post them tomorrow. I've got both channels done, and I've listened to the whole thing using a lab supply. The next step will be to make a regulated +/-50V supply to go along with it. When I'm happy with everything, and done some tweaking of the PSU, then I'll finally make the final PCB.

I know it has been a long time coming, but at least when it's done, it'll be perfect. There's nothing worse than making a PCB that isn't everything you wanted it to be.
hey Opc, thats excellent numbers mate and if its even better (which seems likely) then sounds like we found a winner so will you be providing PCBs for the regulated PSU to match as well? I have coffins minigold regs that will go up to 50v, but I dont have much else as I usually dont deal with such voltage, not being into tubes and being more into headphones than speakers. Most of mine top out at +/-35v, but yeah the minigold is quite good and will handle considerably more. I also have some of peranders RFB03 discrete rectifier PCBs to provide a nice raw DC supply from a center tapped 50-0-50 2A transformer (well actually the same iron has all the other voltages I need for this dac as well, custom wound by Richard Sumner (sumR)

so yeah if you can post those pics of the setup you got those numbers with thats well good enough for me to use pierre's PCB till you are finished yours, so theres no rush from me mate, happy for you to be perfectly satisfied youve made it as good as you want it to be.

cheers, hope you had a nice break, i'm jealous
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Old 14th June 2010, 09:25 AM   #185
Calvin is offline Calvin  Germany
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Hi,

thanks Owen. The ESS puts out tiny currents (what a weak whimp....nothing to drag a Tool Time Fan off behind the oven , howhowhow *lol*). Still though did You consider that 750Ohms could be so high that internal protection diodes start conducting -> hence increased THD-values? I dont know if the ESS features protection diodes on its outputs but the BB/TI current steering DACs like the PCM179x surely do.
As I understand the poor information from ESS, voltage mode and current mode differ only in the topology of the connected circuit. The outputs have an iimpedance value of 200Ohms, which is neither fish nor flesh. Too low for a decent current source and too high for a true voltage source. ESS might call this a feature ..... at the moment Id call it a bug. ;-(

jauu
Calvin
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Old 14th June 2010, 12:14 PM   #186
opc is offline opc  Canada
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Hi Calvin,

You made a good point with your internal protection diode idea which forced me to go back and take a second look at the datasheet to double check the stated voltage values at the output.

While doing so, I noticed that the stated maximum output voltage is 3.05Vpp, which I was reading as a peak value. That means in voltage mode, the most you can get out of the DAC is 1VRMS which means I was running too high an output voltage when I measured the resistor only configuration.

I'll re-measure with a lesser value of resistance, in this case just enough to get 1VRMS output, and I'll report back with my findings. I'll start with 80 ohms and go from there.

Keep in mind that this is the differential output voltage value, so for anyone out there using this thing with a resistor, make sure you double check your setup. If you're running differentially, you should have no more than 1VRMS output at 0dbFS, and if you're running SE, then it should be less than 0.5VRMS.

Cheers,
Owen
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Old 15th June 2010, 03:34 AM   #187
opc is offline opc  Canada
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Hi qusp,

As requested I've attached a photo of the DAC as I have it set up on Pierre's PCB's. There are a few jumpers, and the mosfets needed some lead bending to fit in the TO-220 outlines, but it all went together pretty well.

It's not the most portable setup, but it's the closest I've come to a finished design so far.

The final PCB will indeed have the power supplies built right in for the +/- 50V (adjustable if you want lower). I'm also going to toss one in for the DAC itself (5.5V), but using it/populating it will be optional. I kinda want an all-in-one solution that you can just drop the Buffalo II onto, and be finished. I will, however, provide for external power supply tie points for those wishing to use something fancier than an LM317/337.

Cheers,
Owen
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Old 15th June 2010, 07:29 AM   #188
qusp is offline qusp  Australia
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Hi mate, wow, now thats a mans dac IV so no changes to the values? yeah the FQA actually fit quite well with some coercing. pots are 100K yes? so FQR, 100K pots 200/400 and what BOM is the rest following?? the small blue caps are?? the large blue caps are?? and is there any jumpers under the board? oh and where did you get those clips that seem to be for more evenly distributing the heat from the fets and Rs from?
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Old 22nd June 2010, 06:40 AM   #189
gebi is offline gebi  Austria
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Default question for simulation in ltspice

Hi.
just playing around with some simulations. I have an buffalo DAC (ES9008)
The data-sheet is not really clear to me. The max differential output-current is 4.2mA and the DC offset is 1.65V correct ? For one channel half of current or ?

thx
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Old 22nd June 2010, 02:56 PM   #190
qusp is offline qusp  Australia
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it is with 9018/12, I dont have any experience with the 9008, but yes, if you are feeding it 3v3, yep it will have AVCC/2 offset. I take it you are not using balanced output? CMMR should take care of it, still better to sum the outputs in the IV to cancell
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