Look for the mistake - diyAudio
 Look for the mistake
 User Name Stay logged in? Password
 Home Forums Rules Articles diyAudio Store Gallery Wiki Blogs Register Donations FAQ Calendar Search Today's Posts Mark Forums Read Search

 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
diyAudio Member

Join Date: Aug 2001
Look for the mistake

Hi,

attached you find the output stage from my Perpetual Technologies P3-A with crystal CS 4396 DA convertor (voltage output, balanced).
Besides trying to understand this (especially the second opamp) I would like to convert this to something with a passive filter, x-bosoz with ccs (like Henrik showed in another thread) and keep everything balanced.

Just for fun I was looking what filter frequencies are in this standard output and hereīs where the problem starts.

If I look at the first low-pass (1k, 5n6//1k) I īm already 2.6dB down at 20.000Hz, The second stage (499R, 1n5) ads another 0,7dB to this so Iīm down over 3dB at 20000Hz. Since this certainly isnīt the case I must be making a mistake somewhere in this (very simple) calculation

Can somebody point out what I am doing wrong?

Hereīs the calculation:
z@20000Hz = 1/(2PifC) = 1/2pi*20000*5.6*10^-9 = 1421 ohm

1421//1000 = 587 ohm

587/(1000+587) = 0,3699

20Log0,3699 = -8,64dB (attenuation by cap + halving by second 1k)

8,64 + 6 = -2,64 dB

William
Attached Images
 p-3auitgangdiy.jpg (57.5 KB, 244 views)
__________________
een ooievaar is geen konijn want zijn oren zijn te klein!

 9th January 2004, 09:11 PM #2 diyAudio Member RIP   Join Date: Nov 2003 Location: Brighton UK Well the first mistake I can see is your first lowpass filter. The loop impedance seen by the bottom 5.6nF capacaitor to ground is 1k||Ik i.e. 500R assuming zero sourse impedance. sreten.
 9th January 2004, 09:13 PM #3 diyAudio Member RIP   Join Date: Nov 2003 Location: Brighton UK Well the first mistake I can see is your first lowpass filter. The loop impedance seen by the bottom 5.6nF capacitor to ground is 1k||1k i.e. 500R assuming zero source impedance. Plug it into a circuit simulator. sreten.
 10th January 2004, 07:40 AM #4 diyAudio Member     Join Date: Aug 2001 Location: Ingolstadt Germany sreten, could you explain a bit more or do a calculation so I can see where I went wrong/how it is done? (I also assumed 0 ohm output impedance, otherwise the attenuation would be even bigger) Circuit simulations are nice but donīt really help to understand how things work william __________________ een ooievaar is geen konijn want zijn oren zijn te klein!

 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 OffTrackbacks are Off Pingbacks are Off Refbacks are Off Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post Moondog55 Multi-Way 15 3rd January 2009 11:31 PM cjkpkg Tubelab 9 10th October 2008 10:01 PM rhart Full Range 25 5th February 2006 07:50 PM

 New To Site? Need Help?

All times are GMT. The time now is 01:39 AM.