Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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

nanoDSP crossover, suggestions please
nanoDSP crossover, suggestions please
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 12th October 2014, 05:59 PM   #11
basreflex is offline basreflex  Spain
diyAudio Member
 
Join Date: Oct 2007
could be a valid point, but is here is my reasoning:
the german project and AD demo board used it before ..
the switching freqs (52kHz) are well above audio and well below the image near 192khz (fs=96k). only the 208 khz spurious is 16khz away from 192khz..
I used an alu polymer output cap with very low series resistance.
kept the circulating currents away from the gnd planes
I hate throwing energy away ( i have designed pacemakers in the past, old habits....)
i'd like to make the supply as universal as possible..
the proof of the pudding is in the eating, and the boards will take some time to ship out of china as I was a bit cheap on the costs.. ( 10 boards for $30 shipping incl)
  Reply With Quote
Old 13th October 2014, 07:18 PM   #12
dudaindc is offline dudaindc  United States
diyAudio Member
 
dudaindc's Avatar
 
Join Date: Sep 2005
Location: Metro Washington DC
Nice project!
I would be interest when you are ready to sell boards...
__________________
"All measurements are wrong! Thus, measurement is the art of handling errors."
  Reply With Quote
Old 13th October 2014, 08:21 PM   #13
basreflex is offline basreflex  Spain
diyAudio Member
 
Join Date: Oct 2007
there will most probably be a rev2. talked to the germans and they suffer from a turn-on pop, so I did already design a fix for that. the writeback trigger circuit was wrongly designed in the AD demo board, (why do I trust these digital guys?), another fix . another thing is the total S/N. we could improve 10dB on it by adding a pre-emphasis (like in the berry 2496). then I would need to redesign the post amps and filters. this would be more interesting for the PA usage with high efficiency speakers. still I do not intend to deviate too much from the initial simplicity for cost reasons. or leave it tot the end users to add pre-emphasis components on the board and the de-emphasis in the digital domain. i'll make pads for components..
the input pre-emphasis adds more dynamic range to the the system ( for compression and limiting purposes) while we can tailor the outputs to fit the subsequent amps and speakers. so feedback is still appreciated ...

Last edited by basreflex; 13th October 2014 at 08:27 PM.
  Reply With Quote
Old 13th October 2014, 09:56 PM   #14
mhelin is offline mhelin
diyAudio Member
 
Join Date: Apr 2003
Location: Tampere Finland Europe
Not sure if the pre-emphasis is really worth it. I mean you will already get better SNR by using the balanced input scheme (assuming you implement it also in DSP). I guess most PA power amps used on active cabs anyway have some (audible) background hiss. Dynamic EQ might be useful in some cases (extending bass at low levels).

Regarding the volume control it might be good to have a fixed resistor from sweeper to GND just in case the pot breaks (to save your speakers). I would still first measure the PSU and if there is space on PCB use the switcher as pre-regulator (5V) and add a proper low-noise 3.3V LDO like ADM7150 or some cheaper one (it really doesn't take that much of space). The 1uF input caps btw. are way too small - ADI specifies 47 uF in data sheet.

Actually even though the XLR input is wired for mono/balanced use it could used as stereo input as well if you build a proper cable (2xRCA to pins 2,3 and GND to 1). Not bad.

Last edited by mhelin; 13th October 2014 at 10:00 PM.
  Reply With Quote
Old 14th October 2014, 05:52 AM   #15
basreflex is offline basreflex  Spain
diyAudio Member
 
Join Date: Oct 2007
1u 20k gives an 8hz -3dB high pass. I took 50V caps to resist accidental phantom powered lines into the unit.

I will implement stuff after the first board debug..
  Reply With Quote
Old 14th October 2014, 07:22 AM   #16
basreflex is offline basreflex  Spain
diyAudio Member
 
Join Date: Oct 2007
I only get better SNR if the left and right channels input noise is uncorrelated. if the noise is caused by a PLL spur , the advantage is gone. I guess that the noise is mostly related to the input impedance and input series resistor ratio. the input impedance is set by a sw C impedance and has the traditional kt/C noise...

Last edited by basreflex; 14th October 2014 at 07:42 AM.
  Reply With Quote
Old 3rd November 2014, 08:29 PM   #17
basreflex is offline basreflex  Spain
diyAudio Member
 
Join Date: Oct 2007
finally the first rev boards have arrived. I started with the DCDC and checked the ripple on the 3.3V supply when resistively loaded with 100mA . here is the spectral plot of the ac voltage on the 3.3V taken from the 2.2u across the 470uF polymer cap.
Attached Images
File Type: jpg supply noise_100mA.jpg (64.6 KB, 346 views)
  Reply With Quote
Old 3rd November 2014, 08:32 PM   #18
basreflex is offline basreflex  Spain
diyAudio Member
 
Join Date: Oct 2007
then I added the DSP and other components and keeping a list of fixes to be done for the 2nd rev. I designed a mute circuit using the bitclock as neg rail charge pump to be able to use a NPN transistor. originally I planned a maxim analog switch with neg rail capabilities , but distortion wise the NPN mute seems cleaner and cheaper. the power-on timer does not seem to work as intended. need to work on that.
  Reply With Quote
Old 4th November 2014, 07:06 PM   #19
basreflex is offline basreflex  Spain
diyAudio Member
 
Join Date: Oct 2007
good news: the XO part operates as planned.
most of the design time goes into the startup and power down glitches
the power-on transients are caused by residual charge on the coupling and filter caps. there is a glitch at 700usec after turn-on when the 3.3Vrail rises above 1V.
I have several options:
- drive the mute directly when raw supply is applied
- use a normally-on device like a Jfet to short the outputs (BF862).
- use a photomos or photo LDR as series element (bulky and expensive)

the neg rail runs off the wordclock charge pump and sits at -3.1V.
  Reply With Quote
Old 4th November 2014, 07:51 PM   #20
randytsuch is offline randytsuch
diyAudio Member
 
Join Date: Jan 2003
Location: LA
Another vote for cool project, and I would also be interested in a board.

I just bought a minidsp 2x4 balanced, but I'd still like to play with this.

As for the mute, driving it directly seems like the simplest approach, is there any reason not to go that route?

Randy
__________________
My system is here
http://randytsuch-audio.blogspot.com/2005/10/my-system.html
  Reply With Quote

Reply


nanoDSP crossover, suggestions pleaseHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Active crossover - suggestions? JRL Multi-Way 34 24th November 2013 04:09 PM
Crossover suggestions salvatorereda Multi-Way 13 10th April 2013 05:12 PM
Crossover suggestions creutz Multi-Way 7 12th September 2011 10:09 AM
Crossover suggestions? trunkmonkey Multi-Way 12 22nd April 2006 07:00 PM
Suggestions on my crossover design? JoeyDD Multi-Way 11 11th December 2005 02:05 PM


New To Site? Need Help?

All times are GMT. The time now is 01:16 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki