A New Take on the Classic Pass Labs D1 with an ESS Dac - Page 18 - diyAudio
Go Back   Home > Forums > Source & Line > Digital Line Level

Digital Line Level DACs, Digital Crossovers, Equalizers, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 28th May 2010, 01:14 PM   #171
opc is offline opc  Canada
diyAudio Member
 
opc's Avatar
 
Join Date: Oct 2004
Location: Ottawa, Ontario, Canada
Regal is absolutely correct in asking about the PCM63, and you guys really need to pay attention to some of the basics here.

You can't play the mix'n'match game with whatever you please and then post negative results as though they somehow apply in a blanket sense.

Samoloko:

If you're using a PCM63, then this circuit will not work for you. We've been over this twice before. The output current from the PCM63 is far too low, you won't get sufficient output voltage, and you're best off using the D1 in its original form if that's the DAC you have. You're probably also best off using the IRF610, since, as you said, it's what Nelson chose to use in that exact setup, and it's more than likely the best FET for that setup. In my circuit, with 13 times the current and 1.5 times the voltage, the FQA devices work best. That doesn't mean they'll be any good in the original D1. I'll test the IRF610 in my setup when I get some free time. Pierre has kindly offered to loan me a few of them, and I'll take him up on it when I get the chance.

Calvin:

Thanks for posting all the details, it's much easier to comment when all the information is available.

You've finally clarified that the poor measurement you're getting is the single ended measurement, and not the balanced one, but I'm not sure why you're surprised by that. These DAC's are not meant to be operated in a single-ended fashion the way you're doing it. Notice how there are no single ended performance numbers anywhere in the datasheet? That's because the DAC relies on you to use the differential output properly in order to get good performance. To be honest, I'm shocked you got such good performance using only a single side. I've mentioned before that this circuit is intended ONLY to be used with a balanced output. If you want good SE performance, you need to convert to SE after the differential output of the I/V stage using either a transformer or an op-amp or some other discrete diff to SE converter.

What is the performance of the DAC if you only use one side of the diff output? You'll have to measure that and use it as a starting point. I get the feeling it's not going to be that great. Using a balanced setup doesn't only cancel the 2nd harmonic of the I/V stage, but it cancels the 2nd harmonic of the DAC output. The performance numbers on the datasheet assume you're doing this. If you only use one side, then there's no telling what you'll get.

You are definitely correct about the voltage at the output of the DAC for the 1794. I should have double checked that before posting it. You want 0VDC there. I still think you should halve that resistance value (maybe 200 ohm instead of 365), keep the same rail voltage, and try the circuit like that. You'll double the dissipation and halve the gain, but you'll get better performance at 0dBFS and still get 2VRMS from the differential output. If you can take some measurements with this setup I'd really like to see them. You're already riding the limitations of the DAC, so I'd like to see if things get any better.

Cheers,
Owen
  Reply With Quote
Old 28th May 2010, 02:08 PM   #172
diyAudio Member
 
Join Date: Jun 2006
please don't get me wrong
I regard very much your work
I only would like to point out my impressions regarding sound of various FETs
I have said very clear that I use pcm63 and prometheus pcb
  Reply With Quote
Old 29th May 2010, 07:12 AM   #173
Calvin is offline Calvin  Germany
diyAudio Member
 
Calvin's Avatar
 
Join Date: Nov 2004
Location: close to Basel
Hi,

ahhh, see I missed the point about only balanced measurements. That explains alot ;-) Oh man, just one decent look at Your distortion plots should have made me think in the right direction
Well the PCM1794A doesnt need to be connected in a balanced fashion.
You can simply hardwire one of the outputs to gnd, or use a small valued resistor to gnd (<20Ohms), or use the same input stage as on the other output. The PCM1794A is very forgiving in this respect. Just make sure the second DAC-output is terminated with a current path to a lowimpedance point.
THD-Values remain nearly the same on a very low level (less than -105dB at 0dBfs), the differences beeing negligible (apart of course of the K2, K4, etc-values) compared to the capabilities of the analog stages.
At the moment I know of just one circuit running without global feedback that uses complementary JFETs and a kind of folded cascode stage, that reaches down to -100dB in singleended connection to the DAC. But Id prefer a simpler circuit to do the job, because in most cases I like the sonics of those simpe circuits more. Im afraid though that this is impossible and -80dB represents a limit to such circuits.

jauu
Calvin
  Reply With Quote
Old 29th May 2010, 11:53 AM   #174
diyAudio Member
 
Join Date: Jan 2002
Location: Cheltenham
Hi Owen,

Thanks for going to the trouble to make these measurements. They are certainly something to think about. I hope my questions were not seen as being negative towards your project.

I very much doubt ESS's 108dB THD figure was plucked out of the air, so I'd guess there is a configuration that is optimised for V out mode, much like your circuit needs to be optimised for best performance. However as you say there really isn't enough information in the datasheet to go on. At a guess I'd say it's relative to the impedance on the output, but who knows.

Another thing I've been curious about, that isn't covered in the datasheet, is the level of out of band noise coming out of the Sabre. As I'm sure you know, delta sigma chips traditionally put out a lot of ultrasonic junk, and this determines how much low pass filtering is required on the output. If you or anyone else was able to measure this, that would be fantastic. Me, I'm going to have to get a sound card with a good ADC so I can determine this stuff myself. Thanks again.

Dan


Quote:
Originally Posted by opc View Post
Hi Spartacus,

Well, I think this should be a lesson in trusting datasheets, especially those with unqualified distortion numbers.

The ESS datasheet does indeed specify -108dB THD+N in voltage mode, but there's not much more data there. I'd ask the following:

- At what output voltage?
- At what frequency?
- With what HF and LF noise filters?
- With what value of resistor?
- With what circuit following the output?

I started with a pair of 200 ohm resistors, but that only gave me 1VRMS output. I ended up with 750 ohm resistors which was giving me 1.75VRMS output. Still not high enough to be a fair comparison to the circuit I'm using.

The following THD+N graphs were measured the exact same way as I've been measuring the circuit I've been working on. Same Buffalo 32 DAC, same channel, 192kHz, 24 bit.

The best I could get was -102dB THD+N but that was only at 1kHz and only at -13 dBFS. At 0 dBFS you're looking at closer to -80dB THD+N best case.

I'm not sure how they got the numbers they did... maybe you need an op-amp buffer, maybe they have an actual circuit that counts as "Voltage Mode" but you're not going to get that kind of performance with just resistors. Worse yet, almost all the distortion is 3rd order, which means there's probably large amounts or second order if you don't run balanced outputs. If anyone out there is using this single-ended with a resistor in voltage mode, then you're probably getting terrible results. This is part of the reason you should never design solely "by ear".

To answer your initial question, the IV stage buys us 30dB better distortion and lower output impedance. That's the point in using it.

Always be wary of THD+N measurements when there's no circuit, no graph, and no other measurement data than a single number.

Cheers,
Owen
  Reply With Quote
Old 31st May 2010, 07:49 PM   #175
opc is offline opc  Canada
diyAudio Member
 
opc's Avatar
 
Join Date: Oct 2004
Location: Ottawa, Ontario, Canada
Hi Guys,

Just a quick update to say that I've built up one channel of the latest circuit using one of Pierre's PCB's (Thanks Pierre!). It took a few jumpers, but everything fit nicely.

I've got some Ohmite thin film 15 watt resistors for the 400 ohm, and some Caddock 930's for the 200 ohm resistors. Those along with the mosfets are mounted on some oversized heatsinks so I should be able to run pretty much any voltage I want to see where performance stops getting better.

I'm looking forward to doing some serious listening with that setup as well, which should be nice. I'll be comparing just a resistor, an Analog Devices reference board, and then the circuit I've come up with at a few different voltage points.

Calvin:

I don't think you've really hit the wall yet, and you should try a higher voltage to get a little more Vds and Id for that fet. I think you mentioned that you were getting decent performance at less than 0dBFS, so if I were you I'd try a higher voltage.

Spartacus:

Certainly no offense taken from the question, that's what the discussion is all about! I actually did a double take when you mentioned the Vout spec, since I had never even considered it.

As you mentioned, I'm sure ESS came across that number somehow, but it wasn't with a resistor. It's either a specific circuit, or maybe even a "theoretical capability" spec. It would also be interesting to see some actual measurements of the best people have done with op-amps. I remember some discussion on the first Buffalo thread about people not being able to get full performance, but I don't remember how close people got.

Samoloko:

Again, no offense taken, and you're right, you did specify how you were listening to it, which is the important part. All I was trying to say was that what applies to one circuit doesn't necessarily apply to others.

Cheers,
Owen

Last edited by opc; 31st May 2010 at 08:10 PM.
  Reply With Quote
Old 1st June 2010, 01:20 AM   #176
qusp is offline qusp  Australia
diyAudio Member
 
qusp's Avatar
 
Join Date: Oct 2009
Location: Brisbane, Australia
owen, I would be very interested in seeing how you have set up pierre's PCB, since i'm just about to stuff it. I have caddock 930 for both 400 and 200
  Reply With Quote
Old 3rd June 2010, 06:16 AM   #177
diyAudio Member
 
Join Date: Jun 2006
I would like to ask you about gain - when you lower those resistors you lower gain
how compensate this and Is there a sweet pot
  Reply With Quote
Old 3rd June 2010, 06:29 AM   #178
qusp is offline qusp  Australia
diyAudio Member
 
qusp's Avatar
 
Join Date: Oct 2009
Location: Brisbane, Australia
yeah its touchy really isnt it, because lowering the resistors lowers noise in the IV, but then you must add more gain in your amp, more noise component...
  Reply With Quote
Old 12th June 2010, 06:35 AM   #179
qusp is offline qusp  Australia
diyAudio Member
 
qusp's Avatar
 
Join Date: Oct 2009
Location: Brisbane, Australia
Any update on the PCB Owen? any pics of how you set up pierres PCB to suit the new schematic?
  Reply With Quote
Old 13th June 2010, 10:18 AM   #180
Calvin is offline Calvin  Germany
diyAudio Member
 
Calvin's Avatar
 
Join Date: Nov 2004
Location: close to Basel
Hi,

Owen, how did You measure the distortion values of the ESS-chip?
Just -80dB@0dBfs would mean a ridicolously high value even for a 24Bit-DAC, let alone a DAC that rather claimes to be a new miracle.
Did You take the measurement of the pure DAC or with the MOSFET-I/V connected to the outputand how did You generate the input signal?

jauu
Calvin
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Pass Labs S/Ns ? dejanm Pass Labs 8 26th January 2007 07:35 AM
My opinion on Pass Labs and Mr. Pass (Nelson) himself b_online Pass Labs 11 21st May 2003 12:39 AM


New To Site? Need Help?

All times are GMT. The time now is 06:07 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2