Driving capacitive loads - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

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 9th March 2013, 11:13 AM   #1
diyAudio Member
 
Join Date: Sep 2009
Location: Stavanger (NORWAY)
Default Driving capacitive loads

Hi !

I have a question about preamps "driving ability"
I see that usually they are measured using pure resistive loads, even very low loads like 600 ohm, but never with capacitive loads
Looking at the specs of some amps I see that the input capacitance can be up to almost 1000 pF
and moreover there is a cable in between with its own capacitance
Driving inputs of this value could not effect the performance of the preamps ?
is it any power amp completely within the driving ability of any preamp ?
Thank you very much indeed for any kind advice
Kind regards,
gino

Last edited by ginetto61; 9th March 2013 at 01:17 PM.
  Reply With Quote
Old 9th March 2013, 12:30 PM   #2
willamp is offline willamp  United States
diyAudio Member
 
willamp's Avatar
 
Join Date: Dec 2011
Location: Austin, Texas
Interesting questions. Looking at specs for a few amps I don't see input capacitance listed except on phono stages. A quick ltspice sim does seem to show that input capacitance is at least as signifcant as source impedance which is the thing I usually concern myself with. Hopefully someone more knowledgable will chime in.

I'd like to know how to set up a test circuit to measure input capacitance of the equipment I have built.

First screen shot below is a source with 1300 ohm output impedence driving load of 100k and 100 to 2000pf.

Second screen shot is a source varying from 300 to 2000 ohm driving a load of 100k and 1000pf.
Attached Images
File Type: jpg capload.jpg (261.1 KB, 98 views)
File Type: jpg source_imp.jpg (264.0 KB, 98 views)
  Reply With Quote
Old 9th March 2013, 03:15 PM   #3
jcx is online now jcx  United States
diyAudio Member
 
Join Date: Feb 2003
Location: ..
few small signal amplifying devices in common amplifier input circuits will have more that a few 10s of pF effective input C

some amps will add a few 100s of pF to gnd as RF filter

cable can range from 10(rare, foamed dielectric)-50? pF per ft so it can be the largest C load

some feedback circuits can become unstable when loaded with C on the output - often a isolating series Z is recomended

usually this has to be > ~10 Ohms, its not too strange to see up to 100 Ohms in series with line level audio source/preamp outputs

some CD players used muting circuits that added up to kOhm series output R - less common today than earlier when noise at "digital black" level was a competive number in ads
  Reply With Quote
Old 18th March 2013, 10:40 AM   #4
diyAudio Member
 
Join Date: Sep 2009
Location: Stavanger (NORWAY)
Hello !
please excuse me for another question
Could a tube line stage have problems when asked to drive a capacitive load like 500-1000 pF ?
Which could be the sonic drawbacks ?
I ask this because we made a comparison between a CJ PV10 and a Bryston preamp
The Bryston had a much stronger low end and even the top end seemed cleaner.
Thanks,
gb
  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
good ESL amplifier that works with extreme capacitive loads thadman Solid State 2 31st January 2007 11:20 PM
Behringer DEQ ok driving multiple loads brucemck2 Subwoofers 0 18th January 2006 09:49 PM
Driving Low Impedance Loads weinstro Solid State 14 8th May 2005 09:53 PM
Gainclone driving inductive loads diyman Chip Amps 1 12th April 2004 09:53 AM
Zen driving high impedance loads supa-roo Pass Labs 2 18th April 2003 07:23 PM


New To Site? Need Help?

All times are GMT. The time now is 01:00 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