Go Back   Home > Forums > Amplifiers > Chip Amps

Chip Amps Amplifiers based on integrated circuits

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 29th September 2004, 08:38 PM   #1
diyAudio Member
 
Join Date: Sep 2004
Location: iowa
Default buffer/preamp?

I am confused on exactly what buffers and preamps do. From my current understanding a pre-amp shows the source high impedance, letting it work easier. Then takes the low voltage source signal (1-2v?) and amplify it to (18-20v?). Why this helps I don't know. Also it the preamp shows the amp a low impedance, 100-200 Ohm. I think this helps the amp work easier. I'm I correct?

What is the difference between a buffer and preamp?

What does a typical gainclone like Brains kit want for voltage in and impedance?

I have a cheap apex dvd player, computer, and Ipod. How can I measure what they put out?

I found this out about the Ipod.
An output test on the Ipod
http://members.brabant.chello.nl/~m....surements.html

Data sheet for the Wolfson WM8731. The DAC/headphone amp used on the ipod
http://www.wolfsonmicro.com/uploads/...31_WM8731L.pdf

The output test shows about 90v out but from what I got from the data sheet it does about 1.3v. The output test shows an output impedance of 100 ohm from the Ipod. It also looks like the bass response is better when the Ipod sees a high impedance load.

Knowing this what can I expect if I connect an Ipod directly to a basic BrianGT kit with out pot? How would a pot help?

How would a preamp/buffer help? And how can I build a preamp/buffer to take what I got and make it into what I need?

Which of my three sources do you think would have the best sound? I'm thinking the Ipod, because it runs on batteries and probably has the best DAC.

Sorry for all the rambling. Any help would be appreciated. Iím reading a couple of electronic books, one on op-amps and another on general hi-audio equipment. But the reading is very slow.

Thanks,
Matt
  Reply With Quote
Old 2nd October 2004, 06:14 PM   #2
diyAudio Member
 
Join Date: Jul 2004
Location: Charlottesville VA
Default source compatibility

most solid state devices, such as Your IPOD and CD/DVD player will get along fine with the relitivly low input impedence of the GC. However if you want to run multiple boards per channel for a bridged or parallel set up (for more power) you may want to look into adding a buffer to increase the impedence that the source sees. also, some tube equiptment is designed with higher impedence in mind, so if using a tube preamp a buffer is in your best interest.
Now for the buffer vs. preamp issue. Basicly a preamp is variable in its output and a buffer is fixed, but a buffer can be made variable by simply putting a pot in line after the source and before the buffer. I also think it is kosher to put the pot after the buffer. I am running 2 amps per channel, without a buffer at the moment and a 100K pot as my volume control. because I dont need any more gain than I already have, I will probably go with a buffer to combat the low impedence.
Attached Images
File Type: jpg img-0710-edited.jpg (77.6 KB, 974 views)
  Reply With Quote
Old 3rd October 2004, 08:40 AM   #3
Nuuk is offline Nuuk  United Kingdom
diyAudio Member
 
Nuuk's Avatar
 
Join Date: Feb 2003
Location: Somerset, SW England
Buffers were originally used to isolate the input of the Inverted Gainclone from anything preceding it. This is because with the IGC, the electrical properties of items like pots, interconnects etc affected the working of the amp.

The original IGC circuit also has a fairly low 10K input impedance so a buffer with a higher input impedance often helps.

A preamp is really just a buffer (or gain stage if it is needed) with a means of selecting and/or controlling the level of the signal.

I have recently posted a design for a suitable preamp
here on my Gainclone pages.
__________________
The truth need not be veiled, for it veils itself from the eyes of the ignorant.
  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



New To Site? Need Help?

All times are GMT. The time now is 03:51 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