Mr White's "Opus", designing a simple balanced DAC - Page 63 - diyAudio
Go Back   Home > Forums > Commercial Sector > Manufacturers > Twisted Pear

Twisted Pear Superior quality electronic kits

Reply
 
Thread Tools Search this Thread
Old 23rd August 2007, 12:57 AM   #621
diyAudio Member
 
Join Date: Jul 2007
Send a message via ICQ to fierce_freak Send a message via AIM to fierce_freak Send a message via MSN to fierce_freak Send a message via Yahoo to fierce_freak
I'd love to try the Ballsie out...in fact, once you guys get the pre-order or ordering up for the new Opus modules and the Ballsie, I'll probably spring on a set. I chose to go with the zapfilter for now because I've used one before and liked what it did for the DAC I used it in and because I really like its design (I actually haven't really looked at Ballsie yet).

A thought that just occured to me...I forgot to bypass the caps on the output of the DAC boards. I can't imagine that would have anything to do with the hum issue, but at least having to deal with the hum issue allowed me to remember to short the caps.

-edit- btw, the opus with the zapfilter (aside from the hum) sounds flippin' fantastic. some stuff sounds spookily real coming from it.
  Reply With Quote
Old 23rd August 2007, 03:50 AM   #622
diyAudio Member
 
wigginjs's Avatar
 
Join Date: Dec 2003
Location: Columbia, SC
I'd be really interested to hear impressions of this DAC w/ and w/o the Zapfilter (and w/ and w/o the Ballsie too infact).
__________________
The Four Chairs
DIY Home Theater
  Reply With Quote
Old 23rd August 2007, 03:52 AM   #623
diyAudio Member
 
wigginjs's Avatar
 
Join Date: Dec 2003
Location: Columbia, SC
"The I2S bus separates clock and data signals, resulting in a very low jitter connection."

http://en.wikipedia.org/wiki/I2S

Hmm......
__________________
The Four Chairs
DIY Home Theater
  Reply With Quote
Old 23rd August 2007, 08:18 AM   #624
neb001 is offline neb001  United States
diyAudio Member
 
Join Date: Mar 2007
Quote:
Originally posted by m0tion
I'd be really interested to hear impressions of this DAC w/ and w/o the Zapfilter (and w/ and w/o the Ballsie too infact).
Same here, I'm curious to hear how the Ballsie compares vs the Zapfilter. With my limited understanding, it seems the two are basically doing the same thing.

Btw, what exactly does the filter in the Ballsie do? I've been trying to access the wolfson datasheet to find out, but for some reason can't connect to their site right now.
  Reply With Quote
Old 23rd August 2007, 09:05 AM   #625
diyAudio Member
 
Join Date: Mar 2007
Quote:
Originally posted by neb001


Same here, I'm curious to hear how the Ballsie compares vs the Zapfilter. With my limited understanding, it seems the two are basically doing the same thing.

Btw, what exactly does the filter in the Ballsie do? I've been trying to access the wolfson datasheet to find out, but for some reason can't connect to their site right now.
The datasheet doesn't explain the circuit at all, nor does it provide much information on the internal lowpass.

Without analyzing the circuit in question, I would guess that it's a lowpass tuned to a lower frequency than the ultra conservative (to keep responses flat) builtin analogue lowpass filter. This would serve to filter out additional digital noise and improve SNR and THD+N. How much, I'm not sure. I'd guess a few dB SNR at least.

My own question: how does using the builtin filter scaling affect sound quality? Are these digital filters going to lose bits when attenuating the signal, or are they past the stage where that matters (I'm really not totally clear on delta sigma operation...but is this filtering process not what converts the 24bit input to 6bits for the DAC itself anyway)? If so, with the impressive specs, I may add a passthrough input to my preamp project and seamlessly control the DAC IC instead of the PGA2310...
  Reply With Quote
Old 23rd August 2007, 12:46 PM   #626
diyAudio Member
 
Russ White's Avatar
 
Join Date: Jan 2005
Location: Nashville, TN, USA
Send a message via Yahoo to Russ White
Hi Folks,

Just a couple notes:

1) The main design goal for ballsie was to provide balanced and SE outputs at the same level from the DAC, and to allow for filtering all while presenting identical load to both parallel DAC outputs when used in dual differential mode.... phew... One other design goal was to be able to drive SE and BAL simultaneously from just one DAC while still providing optimal loading to the DAC and not compromising either signal. If you drive a Balanced amp from an Opus and tap one of the outputs(say out+ from each side) for something like a subwoofer amp, then you are loading the outputs of that channel differently. This sorta defeats the purpose of a balanced output.

2) Ballsie is not exactly the same filter as either of the filters (there are two) found in the datasheet (but very close). It is actually a hybrid of the two. I will graph the response and post in a bit.

3) I do not find the ballsie filter necessary at all, but some may like it better, so I chose to include it. In fact the DAC sound great just directly coupled to an amp using the DAC's internal volume control. I look forward to some long tests with both the filtered and unfiltered ballsie though.

4) The digital volume control works extremely well and does not appear, at least to me, to have any serious drawbacks. In fact I would say I am finding the presentation possibly a bit more dynamic then it was going through an attenuator. Now that said, you should know this... ANY analog device has a certain degree of noise present on the output. A DAC is no exception. One benefit of using an attenuator and/or preamp is that the output from the DAC is always full scale. So the audio signal is present at a much larger level than the natural device noise. To comfortably listen to the DAC you have to attenuate the signal, this attenuates both the noise and the audio signal and since the noise is already tiny and it will get even smaller you get lower noise floor with an attenuator than without. When you use the digital volume control you loose this "noise attenuation", the signal is attenuated, but not the noise. Now, this is not actually very worrisome as my testing so far proves that the noise output of the DAC even direct couple to an AMP is very very low. I can't hear it. These facts are also true of other analog devices (say a phono stage). What it means to you, potentially, is if you goal is the absolute lowest possible noise floor at very low listening level you will likely want an external attenuator like the Joshua Tree. Wow thats a long paragraph.

5) I spent yesterday doing some A/B tests with both the slow filter roll-off and the normal roll-off. So far I can't say I like one more than the other, but I am going to leave it in slow roll-off mode for a week or two, then switch back to normal and see if I detect a difference then.

Cheers!
Russ
__________________
Less pulp more juice Twisted Pear Audio.
  Reply With Quote
Old 23rd August 2007, 01:59 PM   #627
diyAudio Member
 
Russ White's Avatar
 
Join Date: Jan 2005
Location: Nashville, TN, USA
Send a message via Yahoo to Russ White
Default Ballsie response with filter caps

When configured with the suggested filter caps this is what the response of the ballsie should look like:

The signal is 3db down at 550Khz

Cheers!
Russ
Attached Images
File Type: jpg ballsie_resp.jpg (94.2 KB, 807 views)
__________________
Less pulp more juice Twisted Pear Audio.
  Reply With Quote
Old 23rd August 2007, 05:09 PM   #628
diyAudio Member
 
Join Date: Jul 2007
Send a message via ICQ to fierce_freak Send a message via AIM to fierce_freak Send a message via MSN to fierce_freak Send a message via Yahoo to fierce_freak
An update on my hum problem: I've spent hours trying to troubleshoot this. It seems the hum only appears when there's a connection between - phase signals from the DAC to the zapfilter. In every other case, there's no hum. This even happens when I pull out one of the DAC boards and run the remaining one regularly. Any other ideas?
  Reply With Quote
Old 23rd August 2007, 05:33 PM   #629
diyAudio Member
 
Russ White's Avatar
 
Join Date: Jan 2005
Location: Nashville, TN, USA
Send a message via Yahoo to Russ White
Quote:
Originally posted by fierce_freak
An update on my hum problem: I've spent hours trying to troubleshoot this. It seems the hum only appears when there's a connection between - phase signals from the DAC to the zapfilter. In every other case, there's no hum. This even happens when I pull out one of the DAC boards and run the remaining one regularly. Any other ideas?

Sounds very frustrating... I know the feeling. It is still very likely a case/PS/device loop of some sort. Unfortunately its pretty much impossible to diagnose remotely.

One thing to do would to try grounding -in on the ZF. See if you still get any humm.
__________________
Less pulp more juice Twisted Pear Audio.
  Reply With Quote
Old 23rd August 2007, 06:04 PM   #630
diyAudio Member
 
wigginjs's Avatar
 
Join Date: Dec 2003
Location: Columbia, SC
Hmm... Another very interesting thing. The WM8804 S/PDIF receiver has a PLL and re-generates the clock of the S/PDIF signal it receives based on a local crystal. Maybe S/PDIF signal transmitted in this manner is not quite so bad?

Below is interesting reading on a similar, but more complicated method of attempting to correct S/PDIF jitter labeled "clock injection":

http://peufeu.free.fr/audio/extremist_dac/spdif.html
__________________
The Four Chairs
DIY Home Theater
  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



New To Site? Need Help?

All times are GMT. The time now is 10:10 AM.


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