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 21st February 2003, 01:28 PM   #1
ijhill is offline ijhill  United Kingdom
diyAudio Member
 
Join Date: Feb 2003
Location: UK
Default Output Impedance

Do anyone know the output impedance of the Philips CD880, or can they advise how I can measure this myself with a multimeter.

Ian
  Reply With Quote
Old 21st February 2003, 11:15 PM   #2
biff584 is offline biff584  United States
diyAudio Member
 
Join Date: Jun 2002
Location: Villanova, PA
Send a message via AIM to biff584
Default measuring impedance

You can measure the impedance- but it will require a few extra things. You can do this by modeling the output stage with a Thevenin equivalent circuit.

First, you need a CD with test-tones of different frequencies on it. To measure the impedance at a given frequency follow these steps:

1. Using an oscilloscope, accurately measure the voltage output at an RCA jack while a test frequency is played. Record this voltage as Vs.

2. Now, get several resistors that are approximately the estimated output impedance (if you don't know, just get random resistors). Be sure to measure the resistances with an ohm-meter even if you know their values- you need to get a precise reading- record the value of the resistor you use as R.

3. Connect the resistor from the signal wire of the audio output to the ground. Play the same audio frequency as you used earlier.

4. Connect the oscilloscope across the resistor and measure the output voltage. Record this voltage as VL. (If VL is not much different (i.e. about 1/2) of Vs, then try a larger resistor.

5. Using ohm's law, the impedance and the resistor form a voltage divider. To find the output impedance, take the numbers you found earlier and plug them into this equation:

Zout = [ R * (Vs-VL) ] / VL

I attached a picture showing the the Thevenin model.

Good luck.

Brian
Attached Images
File Type: jpg impedance.jpg (22.8 KB, 316 views)
  Reply With Quote
Old 22nd February 2003, 07:46 AM   #3
Electrons are yellow and more is better!
diyAudio Member
 
peranders's Avatar
 
Join Date: Apr 2002
Location: Göteborg, Sweden
Blog Entries: 4
Default Re: Output Impedance

Quote:
Originally posted by ijhill
Do anyone know the output impedance of the Philips CD880, or can they advise how I can measure this myself with a multimeter.
May I ask why you wonder this? Modern gear can drive at least 10 kohm without any problem and I think even down to 2-1 kohms is also possible.
__________________
/Per-Anders (my first name) or P-A as my friends call me
Tube Buffered Gainclone in work |Thread || Diamond buffer |Thread for the group buy | Wiki
  Reply With Quote
Old 22nd February 2003, 07:58 AM   #4
diyAudio Member
 
Tube_Dude's Avatar
 
Join Date: Mar 2002
Location: Aveiro-Portugal
Default output impedance

The target for the NE5534 is to drive with ease 600 Ohms loads!

It is still one of my favorits ,besides the fashions!!

Regards

Jorge Santos
  Reply With Quote
Old 23rd February 2003, 02:57 PM   #5
diyAudio Member
 
Join Date: Jul 2001
Location: Orleans, France
Yes, Jorge,

But, the lower is the load, the higher is the distortion.

10 kohms is a good value for domestic hi-fi standard purposes.

Beware of loading such device with a transformer (passive preamp) , distortion can occurs at low frequencies because of the insufficient inductance of the transformer.

Regards, Pierre Lacombe.
  Reply With Quote
Old 23rd February 2003, 04:37 PM   #6
diyAudio Member
 
Join Date: May 2001
Location: London UK
Default Re: output impedance

The target for the NE5534 is to drive with ease 600 Ohms loads!

It is still one of my favorits ,besides the fashions!!

Jorge Santos
[/QUOTE]
---------------------------------

The 5534 is the designer/pros favourite. Low noise and cheap. But l;ook at the circuitry, comples topography with lots of active components. It is my least favourites except for instruments. The thing sound precise and impressive but is hard and mechanical-the so called pro sound. Nothing to do with fashion exfcept for its use in pro gear and Japanese products.
  Reply With Quote
Old 24th February 2003, 08:42 AM   #7
ijhill is offline ijhill  United Kingdom
diyAudio Member
 
Join Date: Feb 2003
Location: UK
My reason for asking is I am attempting to make some attenuating interconnects for my hi-fi system.

Using the following PI attenuator circuit

http://www.qsl.net/4f5aww/module5p.htm

I have using a reduction from my CD's 2V to 150mV giving a 11dB required reduction and the impedance of my Rotel RC-850 pre-amp of 18kOhms. I have established I require resitors of value R1=42K8 and R1=40K2 (nearest available).

This should give the required attenuator, but I have assumed that the required impedance is the impedance at the pre-amp and that the CD will be able to drive this (it should as it does normally)

Is this correct or should I look at a different method of attenuation.

Ian
  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
3C24 in a SE output stage - output transformer impedance recommendation !!! aldovan Tubes / Valves 15 6th September 2008 10:18 AM
Output impedance overdrajv Tubes / Valves 8 5th March 2008 05:54 PM
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
Output Impedance? ble0t Parts 4 19th January 2006 05:45 PM
Low output impedance pre miguel2 Tubes / Valves 13 23rd July 2003 09:51 AM


New To Site? Need Help?

All times are GMT. The time now is 09:07 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