Voltage-out DAC without an output filter - diyAudio
Go Back   Home > Forums > Source & Line > Digital Source

Digital Source Digital Players and Recorders: CD , SACD , Tape, Memory Card, 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 16th September 2007, 06:51 PM   #1
mudihan is offline mudihan  United States
diyAudio Member
 
Join Date: Jan 2004
Location: Texas
Default Voltage-out DAC without an output filter

As a purist approach, one can connect the outputs of DACs with voltage out (such as TI's PCM1753) directly to the next stage (a preamp, a volume control, or a power amp). I was reading this article:

focus.ti.com/lit/an/sbaa055/sbaa055.pdf

and it talked adding an output filter (P6). Two of them are active, so I am not considering them. But the first one, the 1st order passive filter, involves only a resistor in series and a cap parallel. Is such a passive filter necessary? What are the advantages and disadvantages of using/not using such filter?

Since I am using a 10k stepped attenuator, I do not want the source output impedance to be to high (may change the attenuation curve).

Thanks!
  Reply With Quote
Old 16th September 2007, 07:56 PM   #2
diyAudio Member
 
jan.didden's Avatar
 
Join Date: May 2002
Location: Great City of Turnhout, Belgium
Blog Entries: 7
Red Book CD performance specs include the filtering to obtain the specified signalk to noise ratio. How much you have to filter depends on the sampling rate of your DAC. With a high sampling rate, the sampling noise is at a higher frequency so you can maybe get away with a simple RC filter.

Otherwise you need more steep filtering, either active or poassive L-C sections. You probably should research this a bit more.

Jan Didden
__________________
If you don't change your beliefs, your life will be like this forever. Is that good news? - W S Maugham
Check out Linear Audio!
  Reply With Quote
Old 17th September 2007, 11:20 PM   #3
ttan98 is offline ttan98  Australia
diyAudio Member
 
Join Date: Apr 2006
Location: Melb
I use a single low pass filter after the I/V amp., and then a buffer, it seems to work very well.

I think if you pick the correct I/V amp and buffer combo, it will sound very good.

I think the THS4031 used as I/V is ideal and LT1010 as buffer. Others think 4031 and buf such as BUF634 or OPA627(expensive) or AD825 are also applicable.

2 poles low pass filter need to use accurate and or non preferred values of capacitors, they are sometimes hard to get or matched esp. those that come from discrete comp not so much as from SMD cap. Jan may shed some light on this.
  Reply With Quote
Old 18th September 2007, 12:29 AM   #4
diyAudio Member
 
Join Date: Dec 2003
Location: Sydney
Default Re: Voltage-out DAC without an output filter

Quote:
Originally posted by mudihan
As a purist approach, one can connect the outputs of DACs with voltage out (such as TI's PCM1753) directly to the next stage (a preamp, a volume control, or a power amp). I was reading this article:

focus.ti.com/lit/an/sbaa055/sbaa055.pdf

and it talked adding an output filter (P6). Two of them are active, so I am not considering them. But the first one, the 1st order passive filter, involves only a resistor in series and a cap parallel. Is such a passive filter necessary? What are the advantages and disadvantages of using/not using such filter?

Since I am using a 10k stepped attenuator, I do not want the source output impedance to be to high (may change the attenuation curve).

Thanks!
I don't us any filtering at the DAC output, in particular if it is current out. Later on yes, but not at the I out.

In your case (V out) I suppose you can always check the amount and spectrum of digital rubbish you are getting, and act accordingly. Your amplification may be more sensitive to this rubbish, and could cause some overheating (in extreme cases) - but this can be tested as well: load the output with capacitive load (worst case) and check the amp for stability - see what comes thru to the speaker's end and how the amplifier handles this with difficult loads (donít forget that the speaker cables if capacitive, will make things even worse!)...

(Scared enough?)

Good luck,
Boky
  Reply With Quote
Old 18th September 2007, 03:20 PM   #5
diyAudio Member
 
hifimaker's Avatar
 
Join Date: Oct 2003
Location: San Jose
A couple of factors to consider...

1) Delta Sigma DAC's create a lot of high frequency noise that your tweeters must deal with, and a resulting loss of the contextual dynamics due to the the noise.

2) No active filtering will result in drive problems with the preamp. The DAC to preamp connection becomes VERY dependant on cables. With the right active filter design, much less exotic cabling is needed.

Just my own experience.

-David
  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
Filter Capacitor & correct voltage jomatecc Parts 3 28th October 2008 01:27 PM
filter choke voltage rating nhuwar Tubes / Valves 3 28th October 2008 02:45 AM
Can An Output Transformer Change A Voltage Amp's Output Impedance From 0.1 To 47 Ohms kelticwizard Everything Else 11 25th March 2007 05:17 AM
Voltage controlled filter with tubes ?? jim Tubes / Valves 3 28th September 2005 10:18 PM


New To Site? Need Help?

All times are GMT. The time now is 10:14 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