Sime filter calculation help needed. - diyAudio
Go Back   Home > Forums > Design & Build > Parts

Parts Where to get, and how to make the best bits. PCB's, caps, transformers, 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 13th November 2006, 09:11 AM   #1
Nordic is offline Nordic  South Africa
diyAudio Member
 
Nordic's Avatar
 
Join Date: Sep 2005
Default Sime filter calculation help needed.

Click the image to open in full size.
Nuuk's class a buffer

Would someone please help me figure out what R3 is doing on the output?
Also how does R3 fit into the highpass filter on the output?
How would R3 be incorporated in calculations if you wanted to change the output cap.?

Also in another category, how would one calculate the gain for a circuit like this?
  Reply With Quote
Old 13th November 2006, 09:22 AM   #2
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
The 68R is to just provide resistive 'swamping' against possible likely cable (load) capacitance, any may offer a slight amount of protection against a momentary short on the output. It should not/does not form part of the 'output filter'.

The gain of the circuit is approximately unity (1) as it's an emitter follower with a current sink load.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 13th November 2006, 09:34 AM   #3
Nordic is offline Nordic  South Africa
diyAudio Member
 
Nordic's Avatar
 
Join Date: Sep 2005
Thanks RB.
So then in standard config that is a highpass filter set to 1Hz and corner frequency of .5Hz?

Halveing the value of the cap should thus give 2Hz with corner frequency at 1Hz... does this translate into an audiable effect...?
  Reply With Quote
Old 13th November 2006, 10:00 AM   #4
Did it Himself
diyAudio Member
 
richie00boy's Avatar
 
Join Date: Nov 2003
Location: Gloucestershire, England, UK
No. I was trying to highlight that C1, R3 & R4 are not a filter.

C1 blocks DC from getting to what is being driven and also protects the circuit against a DC fault on the driven circuit. The corner frequency will depend on the input impedance of what is being driven.

R3 is as I said previously. It's impedance is so low it's negilgible for anything else.

R4 is simply to provide a charge/drain path for C1 when the circuit is not connected to anything. It will be swamped by the input impedance of what is being driven.
__________________
www.readresearch.co.uk my website for UK diy audio people - designs, PCBs, kits and more.
  Reply With Quote
Old 13th November 2006, 08:35 PM   #5
Nordic is offline Nordic  South Africa
diyAudio Member
 
Nordic's Avatar
 
Join Date: Sep 2005
I think I got the bit about the funtcion of the 68R resistor. Also it carries less than 0.0068V for every volt over the outpu, so I'm willing to discount it...

If you don't mind bearing with me me a little longer until I have enough info to make it usefull, you could mabe check my understanding...?


So lets assume the next stage being powered has an input inpendance of also 100k, would I parallel that with the 100K of R4 to get 50K as part of the highpass filter?

Would that be a less than ideal load? as it demands more current? In other words
  Reply With Quote
Old 13th November 2006, 09:45 PM   #6
Nordic is offline Nordic  South Africa
diyAudio Member
 
Nordic's Avatar
 
Join Date: Sep 2005
Been cracking my head, so far only figured out the operation of the top transistor... I see now that its configuration makes that the input impendance of the next stage makes a very small change to load compared to using a simple voltage divider...
  Reply With Quote
Old 13th November 2006, 10:18 PM   #7
diyAudio Member
 
I_Forgot's Avatar
 
Join Date: Jan 2005
Location: Phoenix, Az.
Many of your questions a can be answered by spending a few minutes with SwitcherCAD. It's free, and it can save you a lot of time, if you invest a little time learning to use it.

I_F
Attached Images
File Type: jpg buffer.jpg (74.1 KB, 68 views)
  Reply With Quote
Old 13th November 2006, 10:23 PM   #8
diyAudio Member
 
I_Forgot's Avatar
 
Join Date: Jan 2005
Location: Phoenix, Az.
here's the ac response out to 1 MHz...

I_F
Attached Images
File Type: jpg buffer2.jpg (45.3 KB, 60 views)
  Reply With Quote
Old 13th November 2006, 10:26 PM   #9
diyAudio Member
 
I_Forgot's Avatar
 
Join Date: Jan 2005
Location: Phoenix, Az.
here's the DC operating point

I_F
Attached Images
File Type: jpg buffer3.jpg (48.5 KB, 54 views)
  Reply With Quote
Old 13th November 2006, 10:38 PM   #10
diyAudio Member
 
I_Forgot's Avatar
 
Join Date: Jan 2005
Location: Phoenix, Az.
here is what happens to the low freq response when the load resistance is stepped from 2k to 50k Ohms.

I_F
Attached Images
File Type: jpg buffer4.jpg (62.8 KB, 59 views)
  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
Powering F series amplifiers from sime power supply yoke Pass Labs 5 22nd December 2008 06:23 AM
Is Lowpass filter needed in 6ch amp? Wynand Chip Amps 4 24th November 2005 04:34 PM
SMPS Output filter inductor calculation. corrieb Car Audio 7 28th October 2005 03:47 PM
PLL 3rd Order Passive Loop Filter, calculation arguments cathode_leak Digital Source 0 24th February 2005 12:50 PM
Help needed for active filter k1jroth Chip Amps 0 23rd February 2005 03:14 PM


New To Site? Need Help?

All times are GMT. The time now is 02:22 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